42 Cadillac very hard to start after driven and engine hot.

[42cady]

I have a 1942 Cadillac 61 series 4 door sedan. I am now retired and would like to use this car on tours plus I do drive it to local car shows when everything is normal. This car will never be a car that I would show at a National show for class judging so if minor modifications needs to be made to make this car reliable is ok with me. If taken to a National show it would be a DPC. It is a 6 volt system positive ground. The problem I have is that it starts great cold but if I drive it to an event the engine has to cool completely at times before it will restart. I would like to use it more just like this past Saturday where our Region toured to a Retirement home   for a drive-by for the residents. We made a stop at our club house to have an outdoor meeting and when ready to go would not start and almost getting dark so I had to call AAA. Has anyone had experience of using a 8 volt battery or convert the starting system to 12 volt? I have heard that either may make it more reliable to start when I need it to if done correctly. Does anyone know of a shop that would be good to use near North Carolina to help with this problem? Thanks for any help you can offer.

 

[JFranklin]

First off , if the battery turns the engine over and you have the correct cables with clean good connections you don't need a higher voltage one. Do you use non-ethanol gasoline? if not try a tank full next fill and I would bet your trouble will be solved.

[hidden_hunter]

Harding starting after running doesn’t sound like anything electrical so changing out the battery might nit achieve anything.

[Graham Man]

I agree if you are using alcohol fuel it most likely it is boiling/evaporating off when hot.  Non alcohol fuel should fix it.  Do you have a carb spacer?  This one has some insolation material over the fuel line. 

 

Edited November 15, 2020 by Graham Man (see edit history)

[Grimy]

IF THE STARTER TURNS VERY SLOWLY WHEN HOT:  Flathead Cad starters are (in)famous for worn starter bushings causing drag during hot starting.  Look for marks on the field coils from the armature hitting it while a bit cockeyed.  I'd "start" with that.  Also, the contact disc in the solenoid may be scarred up.  That can be turned over to a fresh surface (remove horseshoe clip, flip, reinstall) if that hasn't been done before; if it has been done before, have the contact disc machined. .  Finally, check the Cad Club to find a source for high-torque field coils.  If the starter is being opened up, replace all brushes as well.

[Oldtech]

Forget the 8 volts. my experience is that they do not last , and to use properly charging rates need adjusting, etc. You didn't say if the starter was slooow or if it spun normally and wouldn't fire. Grimy has the right advice if it's the starter.  If just no fire it may be flooding  ( hold pedal to floor, ) or sometimes a coil will not work when hot. 

You say it's positive ground. ( I thought GM was always Negative but I don't own a Cadillac). If it is, be sure the coil is connected with the  negative to power and the Pos. to the points. The coil will have a bit more zap if connected correctly.  

[Matt Harwood]

Bigger battery cables, clean grounds, an additional ground cable  between ground on the frame directly to the starter, and an electric fuel pump should greatly alleviate the problem.

 

However, flathead Cadillacs are notorious slow starters. Every one I've ever owned, right about the time you think it won't start is when it finally fires.

[Marty Roth]

As noted above, be sure you have excellent battery cables, preferably 00 or even 000, and with soldered ends, and be sure to clean contact areas down to bare metal for great contact.

I use a pair of 6-Volt Optima batteries in parallel (not Series). 

No reason to consider 8, or 12 volt conversion - just more problems trying to mask the real issue(s).

Yes, check out the starter as suggested if it is turning even slower than when cold.

 

Add an electric 6-Volt Fuel Pump in-line as far back, and as low as possible, maybe on the inside of the driver-side frame rail, and wire it with a toggle switch. Use it to provide additional fuel to reduce the problems of vapor lock and poor quality gas. Then turn it off when you don't need it. Also helpful in hiot weather.

The rotary vane type pump is far better than the cheaper pulse (bullet) type, and will last many years longer.

My choice is the Carter P4259 - $78.11 & FREE Shipping at Amazon.com

I use this model on my

1930 Packard,

1937 Buick Roadmaster,

and 1941 Cadillac

https://www.amazon.com/Carter-P4259-Line-Electric-Fuel/dp/B000CIS4IU/ref=sr_1_4?dchild=1&gclid=Cj0KCQiAwMP9BRCzARIsAPWTJ_EVycjP6Y_TX2aDAx_qM6aEgNOYBimwB3t4kdE0jYQzVTnHNCcqun8aAkX4EALw_wcB&hvadid=177570362789&hvdev=c&hvlocphy=9025155&hvnetw=g&hvqmt=e&hvrand=7371372844440783517&hvtargid=kwd-3628355007&hydadcr=5739_9590425&keywords=6+volt+electric+fuel+pump&qid=1605486563&sr=8-4&tag=googhydr-20

[MCHinson]

Since I see other posts while typing this one, it is probably repetitive but here you go anyway...

 

My experience is with Buicks of the era, but basically making sure the starter is working correctly, an appropriate thermal insulating material under the carburetor, an electric pump to refill the carburetor after the fuel boils off from engine heat soak will probably resolve it. I would remove the starter and have a competent shop check it out. While it is off, I would make sure that the flywheel housing where the starter bolts up is cleaned up to remove any excess paint where the starter bolts up. Clean any paint off of the starter where it bolts up to the flywheel housing to insure a good ground. Make sure the battery cables are all properly sized and all connections are clean and tight. An additional ground wire from the starter to the chassis would be a good idea. A thick carburetor mounting pad to thermally insulate the carburetor from the engine is a great idea. Non-ethanol fuel is much less affected by heat soak than fuels containing ethanol but even non-ethanol modern fuels are more volatile than fuels of the era, so they tend to boil off more easily than fuel used to.  An fuel pump mounted near the fuel tank will enable you to refill the carburetor to prevent having to crank the car long periods of time to refill the carburetor so you can more easily and quickly get the car started when warm.  If you still have a problem with hot starting after dealing with fuel issues, I would suggest a new coil and/or a known good condensor. Sometimes those can fail when hot while working when cold. This is a possibility, but the fuel supply is more likely to cause the problems as described. 

Edited November 16, 2020 by MCHinson (see edit history)

[Grimy]

1 hour ago, Oldtech said:

You say it's positive ground. ( I thought GM was always Negative but I don't own a Cadillac)

Cads were positive ground through 1942, including this car, but changed to negative ground when production resumed in 1946.

 

@Graham ManYour photo is worth TEN thousand words!  Especially with ethanol fuels, these days it's essential to insulate that tubing between fuel pump and carburetor, the line being unfortunately placed above and generally parallel to the left exhaust manifold.

 

@42cady To clarify, my initial comments were directed to the starter turning much more slowly when hot than when cold.  All the ideas presented are worthwhile, IMHO.

[Stude Light]

Agree with Matt Harwood, Marty Roth and Matt Hinson.  This is a very common problem with the Cadillac 346 flathead. My 1939 LaSalle had the same issue and the fixes mentioned solved that problem.  I kept a 6 volt system, used heavy cables, rebuilt starter, ensured a good ground path, carb insulating block and it has an electric fuel pump along the frame rail towards the rear of the car.  Even after a hot soak, it starts every time. Up to a 5 second crank occasionally but always fires off. I really don't think the insulation on the fuel line to the carb does anything.  That little bit of insulation isn't going to stop the 250 degree underhood temperatures from heating that fuel after a 15+ minute soak. I found no difference with or without having that line insulated.

Scott

[Jubilee]

Have you tried pulling the coil wire when it’s hot to see if starter spins it faster? Timing to far advanced or something holding timing advanced when hot?

[edinmass]

I agree with all of the above.......it's hot soak and modern fuel issues. Learning how to start the car hot is also important. Every car is different, and with modern fuel, most often holding open the throttle wide open will clear the puddle in the manifolds. I have been considering a "new normal fix" for this situation. I have been considering installing an electric fuel shut off valve. It would solve the hot soak problem. Just shut the fuel off five hundred feet from your stop, and let the carb run dry and the motor quits. Use the boost pump when ready to leave before cranking, and it should eliminate the problem. Gas isn't going to get any better, and with the "Green New Deal Idiots" coming into power, you can bet there will be more junk getting added to the fuels in the future. Anyone like the idea of the fuel cut off? I know they valve were being made a few years ago for Ford guys with leaking carburetors.  

Edited November 16, 2020 by edinmass (see edit history)

[Matt Harwood]

1 hour ago, edinmass said:

I agree with all of the above.......it's hot soak and modern fuel issues. Learning how to start the car hot is also important. Every car is different, and with modern fuel, most often holding open the throttle wide open will clear the puddle in the manifolds. I have been considering a "new normal fix" for this situation. I have been considering installing an electric fuel shut off valve. It would solve the hot soak problem. Just shut the fuel off five hundred feet from your stop, and let the carb run dry and the motor quits. Use the boost pump when ready to leave before cranking, and it should eliminate the problem. Gas isn't going to get any better, and with the "Green New Deal Idiots" coming into power, you can bet there will be more junk getting added to the fuels in the future. Anyone like the idea of the fuel cut off? I know they valve were being made a few years ago for Ford guys with leaking carburetors.  

 

I don't know if a fuel shut-off would solve this type of problem. Either you're running the electric pump to refill a dry carb or you're running it to refill a carb where the fuel has boiled and evaporated. The process is still going to be the same: prime then start. Maybe a shot of cooler fuel would cool things off if the carb is dry, but the process of evaporation cools things off even better and you don't run the risk of spraying cool fuel into a hot carburetor and cracking an irreplaceable casting. Let it evaporate to cool itself and eventually it'll reach a stasis temperature and fresh fuel won't be as much of a shock.

 

Also, an electric fuel valve just sounds like another thing that can break and another set of fittings that can leak. For me, simple is always better with old cars.

[Grimy]

9 hours ago, Jubilee said:

Have you tried pulling the coil wire when it’s hot to see if starter spins it faster? Timing to far advanced or something holding timing advanced when hot?

Thank you, @Jubilee you reminded me of another issue that affects starting, especially hot starting, on flathead Cad V8s:  The distributor plate moves (advances and retards) on three ball bearings which fit into a snap-in channel on the inside of the distributor body.  Over time and miles, the ball bearings develop flat spots, and the channels themselves develop depressions.  Both these wear issues tend to prevent the plate from rotating.  What is experienced most frequently (in my experience--I owned and drove--a lot--a 1939 Cad 75 for 42 years but no longer own it), is that the plate no longer returns to the no-advance position when the engine is shut down hot while heat expansion is at its greatest.  Therefore the engine is cranking with too much advance, and may crank more slowly than when cold.  The aftermarket offered replacement snap-in channels (one brand was "Spark-O-Liner" or something similar), and I MAY still have one left.  If you go into the distributor, check for wear in the channels and the three ball bearings.  Mic the ball bearings and if you find flat spots, replace the ball bearings.  I believe this system and its problems affected other GM 8-cylinder cars of the period.

 

The aftermarket also offered "Dyna-Flite" brand replacement plates, some with single sets of points as originally equipped, some with dual points (I recommend avoiding these), which had MANY ball bearings.  All those I've seen, even decades ago, had very hardened old grease from long shelf life.  Such NORS plates would need to have the hardened grease removed and new grease applied before installation.

 

@42cady, we need clarification from you on your issue:  Is your hot start problem that of very slow cranking, compared to cold cranking?  Or is it that much more cranking is necessary before the engine will start?  All of these issues are fixable, and your Cadillac will be a reliable, wonderful tour car!

[edinmass]

3 hours ago, Matt Harwood said:

 

I don't know if a fuel shut-off would solve this type of problem. Either you're running the electric pump to refill a dry carb or you're running it to refill a carb where the fuel has boiled and evaporated. The process is still going to be the same: prime then start. Maybe a shot of cooler fuel would cool things off if the carb is dry, but the process of evaporation cools things off even better and you don't run the risk of spraying cool fuel into a hot carburetor and cracking an irreplaceable casting. Let it evaporate to cool itself and eventually it'll reach a stasis temperature and fresh fuel won't be as much of a shock.

 

Also, an electric fuel valve just sounds like another thing that can break and another set of fittings that can leak. For me, simple is always better with old cars.

 

 

Matt......I totally disagree..........I run our collection and EVERY car that has a shut off is closed manually EVERY time it's driven........so our V-16's and our PI's and PII's all have the fuel shut off and ran dry on EVERY shutdown, even though they are updraft. I also only run VP fuel in all of our cars....which is ten times better than pump gas, and I still find it worthwhile to shut fuel off. My cars start.........hot or cold. But certain cars are much more prone to hot soak and flooding at start up when hot. I won't stand this in ANY car, and the good fuel prevents much of it from happening. Pierce and Packard V-12 still load up excessively. The Auburn SC acts up more than I like also. Having great wiring, good batteries, welled tuned cars, and understand how to start each car hot are all important........but it pisses me off that my V-12's crank and have to clear floods before they fire off when restarting hot. I have experimented and usually you need about 15 minute before hot sake really kicks in.......and from 15 minute to an hour after shutdown its just a pain in the axx. I drove the PII today, and shut the fuel off in front of the door, drove it in, and it died in place just as I set the parking brake. Works like a charm. On the 16's, I shut off the passenger side tank first, and drive in on just 8, and run it empty in place. I think it's time to do a cut off on a local Packard....the three at the show yesterday were asked to move after sitting for a half hour.....all three started hard, and one needed an 88 year old guy to tell a guy in his 60's on how to clear the flood. In the end, the 88 year old jumped in the car and did it.....successfully I might add. 

Edited November 16, 2020 by edinmass (see edit history)

[Matt Harwood]

I agree 100% that shutting off the fuel if you're going to have a vehicle parked for any lengthy period of time is a good idea. Whenever possible, I do the same. I'm just not positive that it's a cure for hot start issues any more than simply using an electric pump to prime it and opening the carburetor to clear the fuel. I don't trust old float valves to stay sealed over time. Model As are notorious and I ALWAYS shut off the fuel as I'm parking it to let the carburetor run dry--not to help with hot starting later but just to keep it from leaking gas all over the place while it's parked.

 

You do make a good point in that all cars are different. Even two otherwise identical cars may have very unique preferences for starting, hot or cold. There's no consistency beyond the fact that today's gas is pretty much the opposite of what they were using decades ago and the combination of low H_vap and old carburetors designed to run hot is a bad one. Hot soak flooding can be a problem that acts just like boiling/evaporation in short-term cases and I've experienced it myself. That would certainly be a case where shutting off the fuel could help.

Either way, the solution is to get fresh, cool gas into the carburetor by using an electric pump to put it under slight pressure to help eliminate vapor pockets. Clearing the intake tract with your foot on the floor is probably the smartest way to attempt a hot start under most circumstances.

[Grimy]

Another point, a complication if you will, is that in 1943 (yes, 1943, during the war), Cadillac specified the inverted-bowl fuel pump as a replacement part for the no-bowl pump previously used.  Cadillac's short tech manual (perhaps 30 pages) dated 1945, now reproduced, mentioned that the reason for the change was poor performance of non-bowl pumps on wartime fuels.

[Steve Rinaldo]

I work a lot on the issue with the Tech editor of the Cadillac Lasalle club. There are alot of options to solve this. It is easier for to talk to on the phone. Dend me your phone number in an e-mail and I'll call you this is big problem the Flatty Caddy. 

s.b.rinaldo@att.net

[edinmass]

A hard starting Caddy hot can only be two problems......lousy starter set up, and hot soak. Removing hot soak will improve the driving experience three hundred percent.

Edited November 17, 2020 by edinmass (see edit history)

[Grimy]

@Steve Rinaldo and @42cady will you please let us know how this turns out?  Wishing you the easiest thorough resolution....

[WPVT]

I assisted a friend with a 50's vehicle whose carburetor fuel bowl would often dry up after stopping the engine for a few hours or a day or two. The engine wouldn't start after that.  As it turned out, the mechanical fuel pump worked well enough to pump sufficient fuel at engine speed, but couldn't refill the bowl at starter speed. Rebuilding the mechanical fuel pump solved the problem. With the newly rebuilt fuel pump, a few cranks of the engine would refill the empty fuel bowl and start the engine. 

 

 

 

 

[Pete O]

I had similar issues with my '51 Buick.  It was a combination of things.  First, the fuel in the bowl would percolate if the engine was hot, flooding it.  So opening the throttle wide on hot start up (which btw, is in the Buick instruction manual for the car) cures that.  Turns out the water jackets were clogged, and cleaning them made the engine run much cooler.  Second, I found that when hot, the start motor would bind up.  I had a spare starter that turned much more freely by hand, so I replaced the starter and now it turns over much faster.   Third, I had good thick cables on the battery,  but I suspect the battery wasn't completely healthy all along. It would quickly loose much of it's charge if I had to crank it more than say 10 seconds.   It was one of those that you bought dry, and had to add the acid and charge it.  When I eventually had to replace the battery, I got a gel battery, and boy did that make a difference in cranking power.  I can crank it for 10 seconds and it doesn't slow down at all.  Now, it starts like a champ even when hot.

[42cady]

Thanks for all of the information. I guess I should have included more information to start with.  I had the starter rebuilt about 2 years ago by a repair shop most of the antique car folks use in the area. I have a large about 1 1/2 inch wide bradded ground cable and have made sure the connection to the frame is good. The cable to the starter is a 2/0 heavy duty welding cable 600v that the place that rebuilt my starter made for me. I only use gas without ethanol. I had the engine and transmission gone thru by George McNeal restoration in North Wilkesboro N.C. before he passed away and at that time he said he repaired what was needed in the distributor. He installed a electric fuel pump on it that I turn on when starting but cut it off after the engine starts. I did not notice if the starter housing had any paint on it before it was reinstalled. Since this starter was reinstalled it seems that when cold it turns over much slower than before but always starts and when on a hot soak will not turn over very good at all. Do you think that the starter need to be looked at again? I had to have it towed home last weekend.  I have heard about a carb spacer helping. Where can this be purchased and is there any other modifications that have to be made when installed? Thanks so much for all of the assistance and hope I can get this resolved  before the tours start in 2021.

[42cady]

On 11/15/2020 at 7:37 PM, Marty Roth said:

As noted above, be sure you have excellent battery cables, preferably 00 or even 000, and with soldered ends, and be sure to clean contact areas down to bare metal for great contact.

I use a pair of 6-Volt Optima batteries in parallel (not Series). 

No reason to consider 8, or 12 volt conversion - just more problems trying to mask the real issue(s).

Yes, check out the starter as suggested if it is turning even slower than when cold.

 

Add an electric 6-Volt Fuel Pump in-line as far back, and as low as possible, maybe on the inside of the driver-side frame rail, and wire it with a toggle switch. Use it to provide additional fuel to reduce the problems of vapor lock and poor quality gas. Then turn it off when you don't need it. Also helpful in hiot weather.

The rotary vane type pump is far better than the cheaper pulse (bullet) type, and will last many years longer.

My choice is the Carter P4259 - $78.11 & FREE Shipping at Amazon.com

I use this model on my

1930 Packard,

1937 Buick Roadmaster,

and 1941 Cadillac

https://www.amazon.com/Carter-P4259-Line-Electric-Fuel/dp/B000CIS4IU/ref=sr_1_4?dchild=1&gclid=Cj0KCQiAwMP9BRCzARIsAPWTJ_EVycjP6Y_TX2aDAx_qM6aEgNOYBimwB3t4kdE0jYQzVTnHNCcqun8aAkX4EALw_wcB&hvadid=177570362789&hvdev=c&hvlocphy=9025155&hvnetw=g&hvqmt=e&hvrand=7371372844440783517&hvtargid=kwd-3628355007&hydadcr=5739_9590425&keywords=6+volt+electric+fuel+pump&qid=1605486563&sr=8-4&tag=googhydr-20

How do you wire the batteries in parallel? What cables do you use?

[Matt Harwood]

11 minutes ago, 42cady said:

How do you wire the batteries in parallel? What cables do you use?

 

Negative to negative to ground, positive to positive to starter solenoid (reverse that if it's positive ground). The setup below cranked over my 414 cubic inch 1935 Lincoln V12 without any effort, hot or cold. With 1600 cold cranking amps, the thing can't NOT start. I probably could have driven it home using the starter with that much amperage on tap.

 

 

 

You still need to use big, heavy cables, clean your grounds properly, and it doesn't hurt to add extra grounds between a starter mounting bolt and the battery's ground point on the frame and between the engine block and the frame. Dirt, paint, grease, and other crud have built up between all those joints in the car and inhibit the current's path. Big, new cables attached to bright, shiny metal with extra grounds and a healthy battery should cure slow cranking issues in any car under any circumstances unless your starter is tired (easy enough to have it rebuilt and not terribly expensive).

 

 

[42cady]

Thanks so much.

 

[MCHinson]

3 hours ago, 42cady said:

Thanks for all of the information. I guess I should have included more information to start with.  I had the starter rebuilt about 2 years ago by a repair shop most of the antique car folks use in the area. I have a large about 1 1/2 inch wide bradded ground cable and have made sure the connection to the frame is good. The cable to the starter is a 2/0 heavy duty welding cable 600v that the place that rebuilt my starter made for me. I only use gas without ethanol. I had the engine and transmission gone thru by George McNeal restoration in North Wilkesboro N.C. before he passed away and at that time he said he repaired what was needed in the distributor. He installed a electric fuel pump on it that I turn on when starting but cut it off after the engine starts. I did not notice if the starter housing had any paint on it before it was reinstalled. Since this starter was reinstalled it seems that when cold it turns over much slower than before but always starts and when on a hot soak will not turn over very good at all. Do you think that the starter need to be looked at again? I had to have it towed home last weekend.  I have heard about a carb spacer helping. Where can this be purchased and is there any other modifications that have to be made when installed? Thanks so much for all of the assistance and hope I can get this resolved  before the tours start in 2021.

You can build your carb insulator by stacking a number of carburetor gaskets, if your suppliers don't offer a specific insulator. You may need longer studs to mount the carburetor. 

 

I would encourage you to pull the starter and sand or grind off any paint on the mounting area of the starter and the mating area of the flywheel housing. While you are there, remove, clean up, and reinstall all of the wire connections. You will be surprised how much corrosion you may have built up over time which interferes with the current flow to the starter. Just because a connection looks good on the outside does not mean that it is making good contact.  

[42cady]

3 hours ago, MCHinson said:

You can build your carb insulator by stacking a number of carburetor gaskets, if your suppliers don't offer a specific insulator. You may need longer studs to mount the carburetor. 

 

I would encourage you to pull the starter and sand or grind off any paint on the mounting area of the starter and the mating area of the flywheel housing. While you are there, remove, clean up, and reinstall all of the wire connections. You will be surprised how much corrosion you may have built up over time which interferes with the current flow to the starter. Just because a connection looks good on the outside does not mean that it is making good contact.  

Thanks for the info.

[Pfeil]

On 11/15/2020 at 2:23 PM, 42cady said:

I have a 1942 Cadillac 61 series 4 door sedan. I am now retired and would like to use this car on tours plus I do drive it to local car shows when everything is normal. This car will never be a car that I would show at a National show for class judging so if minor modifications needs to be made to make this car reliable is ok with me. If taken to a National show it would be a DPC. It is a 6 volt system positive ground. The problem I have is that it starts great cold but if I drive it to an event the engine has to cool completely at times before it will restart. I would like to use it more just like this past Saturday where our Region toured to a Retirement home   for a drive-by for the residents. We made a stop at our club house to have an outdoor meeting and when ready to go would not start and almost getting dark so I had to call AAA. Has anyone had experience of using a 8 volt battery or convert the starting system to 12 volt? I have heard that either may make it more reliable to start when I need it to if done correctly. Does anyone know of a shop that would be good to use near North Carolina to help with this problem? Thanks for any help you can offer.

 

I have a friend that has a 37 Ford with the small 60hp flathead V-8. The car started and ran great, but after it was warmed up there was no way the engine would turn over. Six Twelve Batteries, starters you name it. We lived on a hill so one day when it wouldn't start we pushed the car to the end of the street and turned down the street down the hill and popped the clutch, that car skidded all the way down the hill and stopped. So we put it in neutral and pushed it into a parking space, a couple of hours later we went back down and it started up fine.

 Couple of months go by and he drives the thing to my house says he's had it. I disassembled the engine to find the last Flathead expert installed Forged aluminum pistons, but clearanced the engine for the stock alloy steel pistons. It didn't take a metallurgist to figure out what had happened. A re-bore and new pistons. Still going strong after 40 years now.

[Marty Roth]

On 11/18/2020 at 4:39 PM, MCHinson said:

You can build your carb insulator by stacking a number of carburetor gaskets, if your suppliers don't offer a specific insulator. You may need longer studs to mount the carburetor. 

 

I would encourage you to pull the starter and sand or grind off any paint on the mounting area of the starter and the mating area of the flywheel housing. While you are there, remove, clean up, and reinstall all of the wire connections. You will be surprised how much corrosion you may have built up over time which interferes with the current flow to the starter. Just because a connection looks good on the outside does not mean that it is making good contact.  

 

Connecting the pair of 6 Volt Optima batteries in PARALLEL, and using a minimum of 2/0 (Double Aught) cables, I have bought terminal/cable connectors from NAPA which make it easy to link the pairs. They are a heavy duty cable with a clamp over the battery post, and also include another post built on it for connection to the starter (and a similar one for the other battery post - in other words, designed one for positive and one for negative. I believe these may also be available for motorhome-RV battery trays where multiple battery connections are used. Of course you could just use cable with soldered ends which attach to the bolt on the cable clamp.

[edinmass]

I would recommend diagnosing the car instead of guessing. Everything is “gone through” but it turns slower now than it did before it was rebuilt?????? Turns slowly cold, and even slower hot? That simply is not correct. You should use an inductive amp probe and check starter draw hot and cold. If it’s drawing more than 300 amps cold you have a junk starter.......brushes, field, armature, or ground issue. If amperage is acceptable cold, rpm during cranking should be checked to factory specifications. None of this is rocket science. If your starter is good, your power source is good, and the cables and ground are adequate the car should start easily. I have seen people call a battery “good” because it’s ten months old.......CHECK EVERYTHING. It’s not going to be hard to find. Hot soak is a flooded engine from a carb dumping fuel after shut down.......if your car is slow to turn over when it’s hot, you need to solve that problem first. 

Edited November 21, 2020 by edinmass (see edit history)

[Grimy]

Here's what Marty Roth was talking about for dual Optimas:  (I use them for more reserve capacity for night driving rather than for cranking speed, which is a side benefit.)

 

And I agree with Ed's post immediately above.  Diagnose, rather than throw parts at it.  Sadly, it's difficult to get good work done these days.  That is, just because something was rebuilt doesn't necessarily mean it was done correctly.  If the starter is slow and draws too much current, see above posts on what might be wrong.

[edinmass]

George is correct.......rebuilt doesn’t mean it was done correctly. Remember, Cadillac was the TOP American car in 1942........no rich guy would tolerate as hard starting car when new........never.

[42cady]

Thanks for all of the information. Looks like I have my work cut out for me.

 

[Buick35]

My 35 Buick turned over very slowly when hot until I added another ground cable from the starter to the frame.I still need to install an electric fuel pump because it takes awhile to start after sitting a few days.

[Paul Dobbin]

I've used most of these tricks on flathead Fords too.  All good information here.

[John_Mereness]

I drove my 1941 for roughly 80K miles via AACA and CCCA (rebuilt everything 2 x times too).  

 

I ran a single optima batter for last 10 years of ownership.  

 

Secrets:

 

6 or 7 blade fan (I ran a V-16 fan for a good long time and then ran a 54 Pontiac or something like that for years too).

 

Replace the fuel line over rear axle hump with neoprene tubing (fender skirts keep in hot air).

 

I never ran an electric fuel pump, but you must run a really well quality rebuilt fuel pump at all times

 

CLEAN GROUNDS  NEEDED

 

Clean Wiring Connections also critical

 

Ground needed from battery to frame and also ground needed from frame to engine

 

Good grounds on Distributor and Coil too.

 

I ran the original batter cable - I would say it was a 0 gauge (I have installed 00 welding cable on many cars, but O works).

 

You need to be exceptionally careful when rebuilding starter - you need metal to metal contact throughout starter and also at bell housing (too much or really any paint is a killer - we painted everything fully assembled and then had end plate taped and ....).

 

NOT A CAR WHERE OK IS GOOD ENOUGH - EVERYTHING NEEDS TO BE ON ITS "A" GAME

 

 

 

 

[John_Mereness]

Sidenote:  My Stromberg carburetor sat on a 1/4 thick gasket  - I assume it was correct as car had 17K miles on it when purchased in 1979, from original owner, and car had 1956 license plates on it (by the way - it started right up with a battery, some starting fluid, and a full tank of gas from 1956 (drove it across town on emergency brake).