1940 Buick 46S struggling to go faster than 60 MPR

[clipperfan]

Gentlemen

First of all, I want to thank all of your many contributors who helped me get the car started last Thanksgiving - it continues to start and run well around town - cool car and lots of fun!!.   

 

It drives at a comfortable 50 to 55 MPH and will hit 60 if the pedal is pushed to the metal.  It backfired slightly the first time I got it up to 60 so I retarded the timing slightly - seemed to fix that.  But these speeds are not comfortable - the engine is clearly straining to get there - and I don't want burnt valves or anything.

 

Since freeways are a fact of life in Southern California I want to get to a comfortable 65-70 MPH.  So I wanted to ask the community what options I might have. 

 

 

I was hoping maybe there was some sort of carburetor/intake manifold upgrades that might be possible - I did rebuild the existing 3 bolt mounted carburetor and it did seem to smooth out the ride but the upper speed limit remained.

 

Several folks mentioned while i was getting it started the possibility of a ring and pinion gear upgrade to a lower ratio (I'm assuming I have the stock 4.4 to 1 ratio) but my limited contacts have not found a source of these gears plus the torque tube drive shaft is a mystery to me - Is it full of oil from the tranny or rear or both?  I have replaced clutches/trannys  on cars with open drive shafts such as mid 60's ford, mercury and chevy cars so I'm not afraid to get greasy.

 

My goal is to be able to drive it along the freeways slow lane for about 120 miles before heading up Big Bear Mountain using Route 101 to 134 to 210 E to 38 N - going up the hill will mostly be a second gear ride.

 

So I would appreciate any leads you can send my way!

 

Best

Clipperfan

AACA #918917

BCA #52571

1940 Buick Special 46S

 

 

[Rusty_OToole]

If it was my car I would start by finding out if the engine stood a chance of surviving such speeds. Start by checking the oil pressure hot and cold and doing a compression test. If oil pressure is good when hot and the compression is good on all cylinders go on to do a complete major tuneup. Adjust valves, overhaul carburetor, do plugs points and condenser, check that the distributor is not worn and working right, cap and wires in good shape.

 

Finally a cheap way to raise gearing is to install oversize tires.

 

I leave it to the Buick experts if your  demands are reasonable for the model, and if there is a higher gear ratio available.

[Century Eight]

A suggestion would be to change from the probably stock 4.10 gear to the 3.36 or 3.9 gear.  I have driven both gears in different ‘40 specials and there is a big difference.  The 4.1 was good eighty years ago with slow hilly roads but if you are on flat interstates today, you worry about getting run over or straining the engine.  There should be a lot of lower gears out there to find, just stay on this site or check the Buick Bugle and you should come up with something, plus a lot of suggestions on how to do it.

[clipperfan]

Thanks

I will definitely check out the Buick Bugle for gear sources and disassembly and assembly info!

Rusty's suggestions will also be pursued - I have done some of it (points plugs and compression check ((ranged from 75 to 85)) but haven't adjusted valves yet.

 

[clipperfan]

I'll also give the 40-41 Buick Technical Expert a call - he's in Ohio so I'll remember the time zone delta

Thanks good suggestions 

[Matt Harwood]

5 minutes ago, clipperfan said:

I'll also give the 40-41 Buick Technical Expert a call - he's in Ohio so I'll remember the time zone delta

Thanks good suggestions 

 

Doug will tell you to change the gears or buy a large series Buick.

[Ben Bruce aka First Born]

Clipperfan, I am happy you are still with us.

 

  Every thing mentioned is good. I will go a little farther, maybe different.

   Backfiring :    Through the exhaust or carburetor?   I will comment based on my thinking it was through the carburetor.   Almost always due to lean condition. As in "not enough gas"  getting to the carburetor for the air the engine is sucking in.

  Just retarding the timing is not what I would do.  While it might have helped, it DID reduce the power.   Unless it was way high to begin. I doubt that being the case.  Use a timing light!  Set it by the marks on the flywheel.

 There is an old country saying where I come from about assuming.   Determine what gear you DO have. I am not certain about the 1940, but later years the ratio is stamped on the bottom of the rear-end housing . 

  There should be no oil in the torque tube.

  Gears through 1955 will inter change with your 1940.  I used a 3.36 from a 1955 Century for mine. I do use 2nd more in town and hills. Price one pays to get speed.

 

  Willie Pittman  [Old Tank} on this site has a  tutorial on changing the gears out. Not too complicated.

  A Buick shop manual is really needed.  If you can't find one, the forum  Team Buick  has them in the reference section.

 

  Stay with us. We will get you there.

 

  Ben

[clipperfan]

Hi Ben good to hear from you

 

I will definitely check the timing - still have to find the flywheel mark

I have a '40 shop manual - tattered but there.

I think the backfire was through the carb but I'm hearing challenged so that's a best guess.

My son told me there is a high-pitched squeal - I don't hear it but figure it's the throw out bearing so I picked up a clutch/pressure plate and bearing from Bob's Automobilia to eventually replace

It doesn't slip yet but I'm getting off topic...

Lots to do now !!

Thanks all!

Jim

 

 

[edinmass]

That Buick isn’t made to do more than 50. Buy a big car, or drive the back roads. You will scatter that engine if you push it for long periods of time. 

[61polara]

The 1940 Buick Special standard rear end ratio was 4.4:1 with an optional 3.9 ratio.  With either you are beating the bearings to death at anything over 55-60 mph.  Buick did not offer an overdrive.  There was an individual who installed overdrive in the torque tube but I believe he has passed or no longer doing the conversions.  Post in the Buick section of the forum below and you will get more answers.

[MCHinson]

To drive at freeway speeds for long distances, you need to either install an overdrive, change out the rear end to a 3.6 or 3.9 ratio, or else sell that car and buy a Century. You are attempting to go faster than a 1940 Buick Special was designed to run. It will not last long being pushed that hard. 

[Century Eight]

Cant go wrong with a ‘40 Century - you get a 320 engine, lots of power 

[Ben Bruce aka First Born]

10 hours ago, clipperfan said:

Hi Ben good to hear from you

 

I will definitely check the timing - still have to find the flywheel mark

I have a '40 shop manual - tattered but there.

I think the backfire was through the carb but I'm hearing challenged so that's a best guess.

My son told me there is a high-pitched squeal - I don't hear it but figure it's the throw out bearing so I picked up a clutch/pressure plate and bearing from Bob's Automobilia to eventually replace

It doesn't slip yet but I'm getting off topic...

Lots to do now !!

Thanks all!

Jim

 

 

 

 High pitched squeal could be a vacuum leak.   Can he hear it at idle or above?

 

  The timing mark is hard to find. I remove the bottom flywheel cover so the lower half of the flywheel is exposed.  Turn the engine using the flywheel .  You will find the marks.  One for top dead center and one for the stated advance.  Nail polish works to mark them after cleaning well.

 

  Ben

[clipperfan]

Hi All

 

I need to think about all of the great responses - buying a different car wasn't really on my agenda - at least not yet! 

 

I will get to the timing like Ben mentioned (Thanks Ben) and will try to check the vacuum and if low I'll look for leaks. 

 

I'll try to look for that gear change tutorial and see what's involved - seems like that may be my only real option.  If someone can point me to it that would be helpful - are you able to search specific topics or authors??  Still learning

 

The first response mentioned larger rear wheels - it looks like I could get 18" wheels in the back (16's there now) -snow tires with a high profile?  What speed benefit would that get me? I am only looking for 10MPH.

 

Super Bowl is my near-term focus - I'm a Philly boy born and raised until '89 or so anyway - Fly Eagles Fly.

 

Thanks for the input - much appreciated!!!

 

Clipperfan

Jim Gilmore

AACA #918917

BCA #52571

1940 Buick Special 46S

 

[61polara]

You can play around with this RPM calculator to see how the RPM will change by speed, tire size and rear end ratio.  You can find the tire dimensions from Coker Tire's website by looking up the tire size.

 

Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio (purperformance.com)

 

[DonMicheletti]

A Special should be capable of going well over 60mph. I am not saying that it good (my 1918 will actually do 60) but it should.. If at full throttle it wont make 60 there are a myriad of things that can contribute - many mentioned here.

One of the crazy things about these engines is that the flywheel can be put on wrong, if it was removed for some reason. If so, the timing mark will be in the wrong location and be worthless. This is not an uncommon problem. Even if it is in the right place it is a bear to see where that view port is.

I would start with establishing proper timing.

 

Edited February 7, 2023 by DonMicheletti (see edit history)

[Ben Bruce aka First Born]

Jim, as can be seen,  I do not agree with everybody else.  For goodness sake,  Buick made a car in 1940 that was meant to run only 50 mph?   I don't think so!

   BUT, to help, specific things are needed.   What rpm is the engine running at 60 mph?. Maximum horse power is somewhere around 3600 rpm.  Has the fuel delivery system been taken care of since we helped last year? With the "pedal to the metal" are the throttle plates all the way open.

 A little trick for timing the ignition.  Hook up a vacuum gauge and adjust timing for MAXIMUM vacuum. 

 

  I do envy you the car.  Coupes were seldom seen as far back as when I had my 1940 in 1953-1954.

 

 Ben

 

[Grimy]

Clogged exhaust can be a cause, as well.  Here's a quick, easy, non-invasive, and CHEAP (how often do we get all of those?) way of checking for exhaust clogs:

 

Fit a vacuum gauge to the windshield wiper vacuum port on a well-warmed up engine.  Have an assistant sit in the driver's seat while you monitor the vacuum gauge.   Have your assistant run the engine up to about 1,500-1,800 rpm and hold that same rpm consistently for TWO full minutes.  The vacuum gauge will stabilize in 15-20 seconds, and you note the reading when it first stabilizes.  If the vacuum drops over the rest of the two minutes, that's an indication, indeed a very strong possibility. of a clogged muffler or other exhaust components providing back pressure or resistance to exhaust leaving the system.

 

That said, I agree with all the comments about fitting taller diff gears or adding an overdrive to this car, which I believe came with 4.44 gears.  As @61polara commented, calculate what your rpm is at desired cruising speed.  My own Rule of Thumb for pre-war cars is to limit *cruising* speed to 70% of the rpm advertised for max horsepower for your car--which is 3,400 rpm for a 1940 248.  70% of 3,400 is 2,380, but 2,400 is close enough.  I would apply a higher percentage to engines designed for fast spinning, but I don't consider a Buick straight 8 one of them.

Edited February 7, 2023 by Grimy
added 2 words to clarify (see edit history)

[EmTee]

Check the throttle linkage.  Is the throttle plate fully open with the gas pedal floored?  Mine wasn't.  Adjusting it to open properly made a BIG difference! 

 

I would definitely check vaccum at idle, dwell setting and timing in that order.

[Rusty_OToole]

I believe your Buick is supposed to have 6.50X16 tires. Going to 7.00X16 will increase diameter by 3.33% and 7.50X16, another 3.33%. This is the easiest way to raise the gearing but, your speedo will no longer be accurate.

[Ben Bruce aka First Born]

18 hours ago, 61polara said:

The 1940 Buick Special standard rear end ratio was 4.4:1 with an optional 3.9 ratio.  With either you are beating the bearings to death at anything over 55-60 mph.  Buick did not offer an overdrive.  There was an individual who installed overdrive in the torque tube but I believe he has passed or no longer doing the conversions.  Post in the Buick section of the forum below and you will get more answers.

 

 Have you owned a straight eight Buick?

 

  Ben

[DFeeney]

You have a very nice car and as others have mentioned you are asking it to do something it was not meant to do.   You can make it go faster for time and money.  I would not want to get in a accident or panic stop  at freeway speeds particularly  with your family in the car.  Buy a 70's Buick and keep your 40 intact.   " Just Sayin"

[charlespetty]

1940 Buick Special develops 107 hp at 3400rpm.  With stock 6.50x16 tires the engine is spinning at 3300rpm at 65mph.  Right in the power band.  I drove my 1940 Buick Special sedan 55-60mph all the time and never had an issue.  I put over 10,000 miles on it during my ownership and it ran just as well when I sold it as when I bought it with great oil pressure.  Never had an issue getting up to 60-65mph and it had more pedal left.

Edited February 8, 2023 by charlespetty (see edit history)

[61polara]

3 hours ago, Ben Bruce aka First Born said:

 

 Have you owned a straight eight Buick?

 

  Ben

Yes, a 1947 Roadmaster.

[DonMicheletti]

Clipperfan,

Changing the rear end ratio or adding an overdrive are not trivial nor inexpensive jobs, even if you can find a set of lower ratio gears.

Get the low hanging fruit first. Something basic is wrong with the engine.

[FLYER15015]

To run a '40 Buick Special 60 - 70 MPH you only need 3 things.

350 crate motor, 5 speed gearbox, Ford 9" rear end.

Oh, and adapters for the stock rear rims.

I guess that's 4.

 

Mike in Colorado

[Ben Bruce aka First Born]

1 hour ago, FLYER15015 said:

To run a '40 Buick Special 60 - 70 MPH you only need 3 things.

350 crate motor, 5 speed gearbox, Ford 9" rear end.

Oh, and adapters for the stock rear rims.

I guess that's 4.

 

Mike in Colorado

 

 Shame on you!  

 

  Ben

[DonMicheletti]

I agree with Ben

[FLYER15015]

350 crate motor?

I guess I should have said 425 nailhead.

At least it would still be a Buick.

My bad...............

 

Mike in Colorado

Edited February 8, 2023 by FLYER15015 (see edit history)

[MCHinson]

On 2/6/2023 at 5:32 PM, clipperfan said:

 

Since freeways are a fact of life in Southern California I want to get to a comfortable 65-70 MPH

Your initial post sounded like you were expecting the car to do more than it was designed to do. Subsequent posts, make it sound like the car is difficult to get to 50 or 55 mph. While I still don't think your car should be expected to drive for long distances on freeways, which I intrepret as being roadways with speeds of 70 or more expected for extended periods of time, your car should perform better than what you seem to be experiencing. It sounds like you need to do some troubleshooting with a factory service manual and appropriate diagnostice tools, or else hire an experienced antique car mechanic to check out the car and resolve the performance issues so that the car will perform as it did when it was new. 

Edited February 9, 2023 by MCHinson (see edit history)

[clipperfan]

Hi Guys

I advanced the timing without the help of the flywheel mark - can't find the flywheel mark no matter what I do even with a timing light, flash light or trouble light and sneaking up on it with a starter switch - I haven't dropped the flywheel lower housing as Ben suggested yet - still on the agenda - but the advance did seem to me give a little more power around town -- I'll probably try the freeway again tomorrow  or this afternoon before rush hour. 

 

Swapping in an updated drive line is a last resort possibility - I did exactly what FLYER15015 suggested with my son's '66 Mustang about 15 years ago but everything was ford related pretty much bolted in including the 9" posi rear and the tremac 5Sped (was a C-4)- we did have to shorten the driveshaft - the torque tube is still a mental hangup of mine and mating a new driveline to the '40 Buick is an issue - I don't want to be welding fabricated motor mounts, trans mounts etc - but hey not everyone has a straight 8 and I'm not willing to lose that!  Would the bigger Century straight 8 bolt in?

 

I will see if the carb is actually fully opened when the petal is floored - I'll do that today with the help of my son and report back.

 

Even the owner's manual says 70 MPH is doable but with lower MPH expectations of 13 MPH (see page 23) - I can live with that as I'm getting ~ 9MPH now based on fill ups - gas gage stuck on either 1/4 tank or empty - so I do fill ups @ ~100 miles.  But suspect if I can cruise at 60 I should up the MPH a little.

 

Best

 

Clipperfan

AACA #918917

BCA #52571

1940 Buick Special 46S

Edited March 14, 2023 by clipperfan (see edit history)

[MCHinson]

There is not enough room between the front end sheet metal and the firewall for a 320 straight 8 engine. Fix what is wrong with your car and you will probably be happy with it in its stock configuration... just don't expect to drive it 70+ miles per hour for an extended time. It was not designed for that. 

[Jolly_John]

Clipperfan, Have you determined which rear end ratio your car has? I know this has already been suggested above. But, knowing that would save a lot of hoping and wishing about performance. 

 

Your report of getting 9 MPG was a red light for me. Either you have a very low (high number) rear end or there are timing and possibly mechanical issues with your engine. My 1939 BUICK 40 series car with the 3.90 rear end ratio consistently produced slightly better than 15 MPG on the highway. I would frequently tour with a buddy who had the same year and series BUICK, but with the 4.10 rear end. He was getting around 12 MPG. He always got mad, when we'd fill up on a tour, and my '39 would need less gas! John

[edinmass]

Pushing that engine that hard when new, was a very bad idea. An old tired engine will especially not like it. You bought a nice Buick, to go that fast, you should have bought a different car. The brakes, suspension, steering, none of it was designed to go 70 or even 60 for sustained distances. Think of the car as a 50 mph car……..it that doesn’t suit your needs, sell it and buy something bigger or newer. Going in the fast lane safely in the pre war era can be expensive. Pre 1937 it’s very expensive. 

[clipperfan]

Hi again

Well, as seems to be the case the more you look the more you find...In this case my son and I tried to confirm that the pedal fully opened the carb before taking it for a spin - and found the pivot screw for the accelerator pump was missing and threads in the top section of the carb were stripped.

luckily, I found the screw on the garage floor but the stripped threads will prevent me from reusing it anyway and the thread style was a little strange too -- so looking for the right tap and tube/sleeve to use to replace it - will probably go with 1/4 X 20 screw.

Project on hold for the time being - will head to the hardware store and get back on it.

 

Thanks - all good input

 

clipperfan

[clipperfan]

Hi

The thread was a left hand (counter-clockwise) thread not the normal right hand thread - and good thing I found the screw - it went back in - need to find some threadlocker and a little lube and will be back in business - whew!  I did not want to cut threads into an aluminum casting!

clipperfan

[Century Eight]

The most important thing about driving an old car that fast as you are talking about is being able to stop it.  I had tried to refrain from suggesting that you buy another car because your car looks so nice.  But a Century with a 320 engine also gives you bigger brakes. You sound pretty able, and that being said, you could put in a 263 from a fifties car and also a disk brake kit, because they are more available.  

 

There is a big difference between my 40 Century and my 40 special.  I don't know what to say about a Limited, but you could ask Matt.  It has that big engine but a lot more weight.  You should also run everything by Doug, the technical advisor.  He has done it all.  My 40 Century does very well on the highway and my 50 Super almost acts like a new car.  

There is a guy in my local AACA club that tours all over the east with a 41 Super, that would have the 248 and the dual carb setup.  If you get it sorted out, you can have that old car experience all day long without stuffing a 350 into it.

[pfloro]

3 hours ago, edinmass said:

The brakes, suspension, steering, none of it was designed to go 70 or even 60 for sustained distances.

I'm glad that Ed mentioned the above.  I have been thinking about a car such as this being driven on any freeway in any lane at 60+ MPH (for more than short distances).  Things might be fine until someone around you does something dumb.  That 1940 Special could quickly lose control. There is a lot of kinetic energy in that machine at these speeds... 

 

The elephant in the room...

 

Paul

Edited February 9, 2023 by pfloro (see edit history)

[Ben Bruce aka First Born]

4 hours ago, edinmass said:

Pushing that engine that hard when new, was a very bad idea. An old tired engine will especially not like it. You bought a nice Buick, to go that fast, you should have bought a different car. The brakes, suspension, steering, none of it was designed to go 70 or even 60 for sustained distances. Think of the car as a 50 mph car……..it that doesn’t suit your needs, sell it and buy something bigger or newer. Going in the fast lane safely in the pre war era can be expensive. Pre 1937 it’s very expensive. 

  Unless he has an extremally low speed rear end,  I say BS.  He has the same brakes as my 1950!  The total weight is , I believe, about 100 lb LESS.  The only difference in the 1940 engine and the 1950 248 is Babbitt versus insert rod bearings.

  With the compression readings shown earlier, the engine may well be worn so much it will not perform as well as it is capable of. And I agree with Jolly John.  Fuel milage is suspicious.

[Ben Bruce aka First Born]

5 hours ago, MCHinson said:

There is not enough room between the front end sheet metal and the firewall for a 320 straight 8 engine. Fix what is wrong with your car and you will probably be happy with it in its stock configuration... just don't expect to drive it 70+ miles per hour for an extended time. It was not designed for that. 

 Matthew, I have always, and do, respect your knowledge. PLEASE let us know where your information of "it was not designed for that" is available. I have found nothing in Buick literature that indicates such.

 

  Thanks

 

  Ben