1958 Cadillac low vacuum question

Listen at the booster both inside and outside for a continuous hissing while the pedal is held down. That would indicate a leak in the booster. Then kill the engine and mash the pedal down firmly and hold it as you crank the engine back up. The pedal should drop noticeably when it comes up to idle, if not then the booster is not working. Your idle vacuum is somewhat low but mine is about the same on the 55 and it works fine. The 55 booster is different though.

Have you tee'd into the vacuum line to the booster to see what it does when you depress the brake pedal? If the vacuum drops below that and stays low as long as the pedal is depressed, that would also indicate a leak in the booster.

I would have a looksee at the distr vacuum pot, the bellows in it are likely old and maybe your vacuum leak. You could pull the line off the carb and plug it at the carb, start the engine and see if the motor runs stable and vacuum back to normal. I would test the vacuum pot on the distributor with a 'mighty-vac' and see if it holds vacuum. It has been too long since I worked on a '58ish Caddy and don't remember the vacuum line system. I remember best getting the radio to work, there is nothing sweeter in this world than listening to Patsy Cline in that radio.

@ TexasJoe55 and ojh:

Thank you for your good advice. Unfortunately, the booster does not hiss and the vacuum advance at the distributor is also tight. All hoses are ok as well.

Last Sunday, I started up the Cadillac again, connected the booster vacuum to the carb again but disconnected the vacuum line that goes from the front of the intake to the wiper and plugged the wiper up. Then I connected the vacuum gage directly there - with the same results: 13 to 14 inch at idle (450 rpm). When I rev the engine up to 1600 rpm, the vacuum increases to the desired 18 to 19 inch. Then later that day, after the engine had cooled off again (I know I should do this at operating temperature but with the spark plugs under the A/C compressor I did not feel like getting some burn blisters) I removed the spark plugs and measured compression. The first surprise were the plugs - they are black and covered in oil crust (oil fouled). I attached some pictures for your viewing pleasure.

The next surprise were the compression results. According to my Cadillac engine manual, the compression results should be 165 to 185 psi (again: with engine at operating temperature). However, a general engine overhauling book states that for engines with 10:1 compression ratio, the result should be 140+ psi. I measured the following:

right bank:

Cyl 1: 145 psi

Cyl 3: 140 psi

Cyl 5: 170 psi

Cyl 7: 150 psi

left bank:

Cyl 2: 145 psi

Cyl 4: 140 psi

Cyl 6: 150 psi

Cyl 8: 160 psi

Then I squirted the recommended 4 pulls of oil onto the piston (of cyl 1 and 3 - they are the easiest accessible) and the pressure increased to 155 psi (cyl 1) and 150 psi (cyl 3). This is a 7% increase - my general engine overhauling book says it's the rings if the pressure increased by 10% or more (again, they recommend the test at operating temperature). So the thing they recommend when the pressure stays low is to check the valve lash (solid lifters) or open the nut of the rocker (hydraulic lifters) by half a turn.

I am tempted to buy a leak down tester - but I am not sure that this would tell me more if it is the rings or the valves.

I can imagine that a leaking valve guide might have led to carbon build up on the valves and valve seats, preventing them from fully closing.

Can the valve stem seals be replaced without pulling the heads? I am thinking about bringing the piston to TDC and pressurize the cylinder through the spark plug. Then compress the spring (not sure how, yet), remove the valve locks and replace the valve stem seals. Has anyone done this already?

Thanks,

Chris

Chris,

Oh my! Haven't seen plugs like that in a looooong time! Do they all look like that? Time for a set of plugs and general tune up.

Does the engine blue smoke and show alot of blowby? Are the plugs the correct PN and heat range for that engine? They look too cold.

If the engine does not blue smoke and it does run smoothly, It needs a bottle of Marvel MysteryOil in the crankcase and then drive the sh t out of it. If it hasn't had an oil change in a while, do that first then add MMO. After running it awhile,several hundred miles if possible, drain oil and change again with new filter. It really looks like it just needs to be driven. I can't imagine the plugs looking like that if it is not blue smoking. Are they original? Ha Ha.

You didn't say if you watched the vac guage while depressing pedal and whether or not the vacuum dropped and stayed low with pedal down.

Also, does the pedal drop if held down and engine is started up?

Also, if you pull the big hose to the booster, it should kill the engine immediately, if not, maybe it is not open or connected to manifold vacuum.

The compression results are not alarming, I wouldn't chase that right now. If it drinks oil you will be rebuilding it anyway.

Yes, stem seals can be changed by the method you're considering. I've done it that way. A very low tech method is stuffing a length of 1/4 inch rope into the cylinder with the piston part way down, then bringing the piston up by hand until the engine won't turn any more. This keeps the valves from dropping out of the guides. Crude, but effective!

Terry

Can the valve stem seals be replaced without pulling the heads? I am thinking about bringing the piston to TDC and pressurize the cylinder through the spark plug. Then compress the spring (not sure how, yet), remove the valve locks and replace the valve stem seals. Has anyone done this already?

There many tools to remove the valve springs without removing the head. Here is one a OTC 4573.

Those plugs are horrible.

I would be doing a complete tune up: pull the distr and get it onto a distr machine to get it to factory specs; new plugs and plugwires; pull the carburetor(s) and go thru them; while plugs are out go thru the the valvelash adjustment.

The plug(s) in the picture, are they typical or are they the worst?

As far as 'leakdown testing' if you have a good clean compressor you can modify a compression tester hose/disconnect etc to fill the cylinder and you can hear the escaping air - a leakdown tester only quantifies the leakage. There is a procedure to follow or you'll get false leakage when the piston is forced all the way down. Be certain your air compressor etc is perfectly clean, else it'll blow trash into the cylinder.

I wouldn't get overly concerned about the compression test or launch into the leakdown test, you need to do the tuneup first and drive it to clean it out as TexasJohn reccommended.

Its a logic problem - 'solve the knowns and the unknown will solve themselves' - we don't know about the low vacuum readings but we do know the plugs need replacement and continue from there.

This may come off as redundant but I think you have a vacuum leak. I would first examine or just replace EVERY vacuum line. There aren't many and they go bad and leak so Easily. They are cheap and remarkably effective at taking care of vacuum leaks. After that I agree with the distributor advance as a good place to check but without swapping out all the vacuum lines, you're looking at high dollar work for a few pennies problem. This would also help address the poor state of tune that is evidenced by the plugs.

Hello TexasJohn,

I read an article about non-foul adapters that are screwed in between the block and the spark plug. The guy had a 1948 Buick in need of a ring job, but did not have the time to get to it immediately - so he put those adapters in and kept driving. He wrote that the engine ran much better.

Do you think this could be a (temporary) alternative until I get to it? If so, can I use 8 of adapters (one for each cylinder)? The package says not to use on more than half the cylinders...

Chris

Forget the non-foul spark plug adapters.. Just take the car out and DRIVE it.. Spark plugs can look TERRIBLE just from the short drive distances so many older cars get. Engines need to get up to operating temperature and be operated at temperature for a minimum of 30 minutes. THEN take the plugs out, and look at them.

What is the history on the car? Fresh from sitting and not running for a decade or two?

As mentioned in an above message, change the oil. add MMO or similar snake oil, DRIVE IT.. and drain the mud and replace the oil. Then DRIVE it..

Engines do not like a short run cycle.. the trip from the garage to the neighbor's house half a mile away is the worst way to treat an engine.

GLong

Hello TexasJohn,

I read an article about non-foul adapters that are screwed in between the block and the spark plug. The guy had a 1948 Buick in need of a ring job, but did not have the time to get to it immediately - so he put those adapters in and kept driving. He wrote that the engine ran much better.

Do you think this could be a (temporary) alternative until I get to it? If so, can I use 8 of adapters (one for each cylinder)? The package says not to use on more than half the cylinders...

Chris

Chris,

The adapters do indeed work and I have used them. My assumption is that they shield the plugs from direct oil spray/splatter but allow ignition of the fuel charge. I do not know why it is not recommended to use them in all cylinders, I do not know what harm might be done, but the engine obviously already needs some repairs if they are being used. If the spark plug is not fouling and causing a misfire then it would not be needed in that cylinder. Any plug that frequently and repeatedly fouls and causes a miss would need the adapters.

As suggested earlier, change the oil, add MMO, change the plugs and set the timing first.. After as much running time as you can, change the oil and inspect the plugs. Make your decision after that. Things may improve.

You did not say if it blue smokes badly or if it is misfiring.

You did not say if the vacuum drops low as long as the brake pedal is held down and if it recovers when brake pedal is released.??

Thanks everybody so far for your tips. Here is a brief update what I did so far:

- If the hose to the brake booster is pulled, the engine dies immediately.

- Vacuum does not change with the brake pedal depressed.

- Checked timing and found dead on.

- Disconnected and plugged all vacuum lines and ran engine - still only 13 to 15 in vacuum.

- Sprayed starter fluid around base of carb and around intake manifold flanges. Got slight rpm increase when spraying on back of carb.

- Replaced carburetor to intake manifold gaskets.

- Still low vacuum and noticed smoke coming out of oil filler tube. Suspect internal leak (blow by) due to sticking rings as a result of too much oil getting into cylinder.

- For peace of mind, I replaced the valve stem seals - found 2 that were damaged. Interestingly enough not at the worst looking cylinders.

- Added Marvel Mystery Oil in the crankcase oil.

- Squirted 10 cubic centimeter (small syringe) of Marvel Mystery Oil in each cylinder through spark plug opening, turned engine through several times and let soak for days. (Call it wishful thinking but it feels like the engine turns over more easily now - by hand).

- Found that butterfly valve (heat riser valve) in exhaust manifold will only open about 10° instead of 90° it should. It is not binding, but hitting something inside the pipe (valve sits close to welding bead - maybe a piece of wire from wire welding is stuck inside. Dosed the bolts with "RustBuster".

- Found articles about the damaging effects a stuck butterfly valve can have (overheated intake manifold, increased back pressure in one cylinder bank affecting combustion etc) and hoping that fixing this issue will solve my low vacuum eventually.

Next steps: Look at heat riser valve and make it fully operational, turn the engine over by hand several more times, then put spark plugs in and drive it. I might temporarily hook up an electrical auxilliary vacuum pump to support my brake efforts and check the vacuum again after I put several hundred mile on it.

Chis

Chris, if your car has a large vacuum storage tank for the booster with a check valve inline, the reservoir will hold maximum attained vacuum for the booster. If it hits 20" vacuum revved up or decel, the checkvalve will hold that in the reservoir for the next brake application. Soooo, 13" at idle is not critical for brake performance unless you have made more than 1 application at idle. That is assuming that the checkvalve and canister circuit AND the booster is not leaking. You could simply suck on the line to the brakes and see if it holds vacuum, it will be quite obvious if there is a leak in the system. You could also do this test with a hand vacuum pump to determine integrity of booster and reservoir.

We've had 2 '58 Cadillacs in the shop in the last year with brake problems after expensive rebuilds of their boosters. In both cases it was that check valve. One customer had his car in 2 other shops that couldn't figure it out. We fixed the problem and he now thinks we are geniuses but the truth is we found the issue purely by accident.

I checked my check valve "per mouth" and it was working ok. But for $6 I guess I could try to buy a new one and test your theory.

Thanks for the tip.

Are you planning on putting some miles on the Cadillac this weekend? I'm sure it will improve vastly with a few hundred miles on it. The brakes will work fine, when you are driving at say 30mph, and let off the throttle, the manifold vacuum will be well over 20". Your brake booster will work fine.

The low vacuum may well improve once the car has been driven some.

Oil in cylinders can come from just not running the engine enough to keep the rings free, and clean. Once the oil ring gets clogged, it will not control oil consumption. The engine needs to be driven, and frequent oil changes done.. This might clean up the engine enough to keep the spark plugs from fouling.

Drive it !!! Half or more of the problems will go away.

GLong

In my opinion, the only thing that the non foul spark plug adapters do is increase the heat range of the spark plug by moving it away from the head which is the heat sink to lower the temp of the spark plug and keep it from pre ignition and burning off the tip of the sparkplug.

You see this when the correct spark plug for the vehicle is used, but it is not properly torqued into the hole and is on the loose side. You can also get the proverbial melted hole in the piston from spark knock.

The easier way to help this with a more accurate result would be to move up one heat range from the correct spark plug and see how it runs. The moving up a heat range is an old temporary fix that has been around forever.

Just my opinion and experience.

Update...

With two little kids that want to be entertained when I am home, this is a slow process.

So, I fixed the sticking heat riser valve - it moves freely now. Then I decided since everything was already apart to also check the intake manifold gaskets. To my surprise, when I took the intake manifold off, there was no RTV used, just the stamped aluminum gaskets. Even though the manual says to lay "a small bead of gasket paste on both sides of the gasket". Well, the new ones will be definitely installed with RTV. Not sure if I like how the old gaskets look - decide for yourself.

I also replaced the old (original) booster check valve with a new one. I realized that when I tested the old one it worked ok 8 out of 10 times, but failed to close in two instances.

With all the changes I made at the same time, I will never what fixed the problem - IF (big IF that is) the issue IS fixed.

Chris

Some years ago, the Fell-Pro kit for the intake had a small tube of sealing paste/liquid which was sufficient if the manifold is not dancing on the heads. I'm not sure, but your gaskets may still have some residue from that blue product. I would never put RTV (as a matter of fact, I hate that kind of product) on those gaskets, it will be burnt at the cross-over port.

Why are your gaskets black at the cross-over ports?

Those gaskets do not appear to have been leaking.

I would suspect that the crossovers are dark because of exhaust heat.

Hello Roger,

First of all let me tell you how much I admire your thread about the Continental - you are a true artist!

The gaskets are black at the cross over ports because my heat riser valve was stuck in the closed position for who knows how long.

Chris

Update:

So after all that work (replaced valve stem seals, valve cover gaskets, carburetor to manifold gaskets, intake manifold gaskets, booster check valve) which required the dismantling of the A/C unit (compressor needs to be lifted out of the way, including condenser unit), the generator and the power steering pump, I am back where I started: 15 in vacuum. At least the needle sits still now.

Only one thing to do now (besides taking the whole engine apart): install the auxilliary vacuum pump for the brakes and drive the #$@%& out of it. I am so frustrated....

Chris

I drive a car of about similar weight (56 Packard Caribbean convertible) equipped with Bendix TreadleVac power brakes. With the dual 4-bbl carbs I only get about 15" of manifold vacuum at idle and have no issues with the brakes or the amount of power boost. Typically when decelerating from speed, the vacuum is much higher than it is at idle.

Well, looking at these two websites, they say that at idle you should have 17 to 21 inches. So 15 inches is not real bad. Another website said that 15 inches was OK. Also what is your altitude? If you are above 2000 feet, you need to subtract one inch for every 1000 feet higher. These websites give some troubleshoot procedures using the vacuum gauge.

http://www.gregsengine.com/using-a-vacuum-gauge.html

http://www.international-auto.com/fiat-lancia-tips-on-reading-gauges/tips-on-reading-gauges-vacuum-gauges.cfm

This site says 15 inches is OK.

http://www.secondchancegarage.com/public/186.cfm

Thank you Chris for looking at my Continental thread!

Regarding vacuum and brakes: I had a break-down with my '56 Biarritz; (overheating/vapor lock or whatever due to stop and go traffic for about 20 minutes); I had to be towed by an SUV (an Escalade!). We were not driving very fast, about 35 MPH; when we were out of the danger zone, the driver slowed down very gradually and I began to push the brakes as I was "connected" to the Escalade with a rope. To stop the car, I had to push the brake pedal with both feet!

Once cooled down, I could continue the trip.

Your problem is with the brake booster, not with your engine vacuum.

Hello Commodore,

Thank you for the useful links!

Here is another update: since I could only get 15in of vacuum, I (tempoarily) hooked up an auxilliary vacuum pump (sold for big block engines or radical race engines that do not produce enough vacuum to operate a brake booster). Direct connection with pump connected to booster check valve. I checked the pump and it generates 23in of vacuum before it shuts off and turns back on at 20in. Outlet at carburetor blocked off. The pump comes on, generates vacuum and shuts off - so my lines and the reservoir tank are ok. So far so good.

And guess what - the brakes still don't work properly. When I applied the brake, the pump comes on immediately and keeps running until I wiggle on the shaft to the master cylinder. I guess it is time to call the rebuilder and have a talk with him....

Chris

I'm not sure, but your full pump may be the same as on my '57 Olds, which is actualy a dual pump with the bottom portion being the fuel pump and the top portion being a vacuum boost pump. A ruptured diaphram in the top portion would cause a loss of manifold vacuum and also sooty spark plugs because manifold vacuum would suck engine oil from the front cover/timing chain area through the ruptured diaphram to be burned in the engine. Remove the screws from the top portion to examine the diaphram. Replacements should be readily available. PM me with your results.

Chris, what is your vacuum reading when pedal is depressed? The booster can be sealing at rest but leak like crazy when depressed or vice versa, depends on the failure.

Still sounds like booster failure.

being that the hydraulic plunger moves in and out of both the vacuum booster and the master cylinder, i suspect that it is worn enough to cause a vacuum leak from the booster past the seal and goes out the pressure relief passage. i used to have the problem with my 1953-1954 pontiac treadle vac that if i push hard enough on the pedal, the booster/hydraulic seals would fail and the booster would suck brake fluid out of the master cylinder, then the brake fluid would make it's way to the intake manifold, the brake fluid would burn during combustion, and a huge white cloud would come out the tailpipe. charles coker, 1953 pontiac tech advisor.

being that the hydraulic plunger moves in and out of both the vacuum booster and the master cylinder, i suspect that it is worn enough to cause a vacuum leak from the booster past the seal and goes out the pressure relief passage. i used to have the problem with my 1953-1954 pontiac treadle vac that if i push hard enough on the pedal, the booster/hydraulic seals would fail and the booster would suck brake fluid out of the master cylinder, then the brake fluid would make it's way to the intake manifold, the brake fluid would burn during combustion, and a huge white cloud would come out the tailpipe. charles coker, 1953 pontiac tech advisor.

Charles, I am not sure of the 58 design but on the 55 Delco booster, that was true, however they had a weephole in the flange of the MC with a small bent nail or wire dangling from it to keep the hole open to drain the brake fluid and prevent the booster from sucking it up. At least that was the theory.

I'm not sure, but your full pump may be the same as on my '57 Olds, which is actualy a dual pump with the bottom portion being the fuel pump and the top portion being a vacuum boost pump.

'58 to '62 fuel pump on Cadillacs are from the same type: just a fuel pump...The vacuum for the wipers on '54 to '58 Cad is provided by the intake manifold and a vacuum pump located under the oil pump.

The vacuum for the brake booster is pure intake manifold vacuum.

Send your booster to POWER BRAKE EXCHANGE in Pittsburgh. Will cost you about $500 for a complete rebuild but it will be right. They have done quite a few boosters for us including 2 1958 Cadillacs, a '57 Biarritz as well as a '58 Brougham and several Skylarks. Two times we have sent them units that were aledgedly "rebuilt" by others.

OK-- I see PLENTY of the guys tell you to take it out and DRIVE IT- But no mention that you DID what they say: DRIVE IT------- Also see you mention putting RTV on the intake gaskets--- DONT DO THAT-- NEVER use RTV on the intake gaskets-- YES you can use a sealant, but NOT RTV-- I use a spray like Hylomar for intakes and head gaskets. But You NEED to drive that thing and not baby it.

Hello RodsoftheValley,

I started this thread initially because I had brake problems that I accredited to low vacuum. This is how the vacuum chase started. After my last attempt to solve the vacuum issue failed (see post from 5/21) I decided to just drive the car and hope the vacuum will improve. However, I still have my brake problems and driving a 4,700 lbs car with spotty brakes is just not the thrill that I am seeking.

So I did more testing today: I checked the wheel cylinders and they work ok - none of the wheel cylinders is "frozen". With the electrical vacuum pump (sold through eg. Summit racing for big block or race engines that do not produce enough vacuum to support the booster) in place I checked the vacuum tank (canister) alone and the vacuum holds steady. When I plug up the connection to the vacuum tank and just connect the booster, I struggles to make the 21in before the pump shuts automatically off. It comes back on after only a second as the vacuum drops - which leads me to believe the master/booster was not rebuild properly and still has a vacuum leak.

To TexasJohn: Without the vacuum tank connected, the vacuum drops to 0 when the brake pedal is depressed and quickly returns to 15in with keeping the pedal depressed, but not higher. A slight movement on the pedal will cause it to drop down to zero again.

With the vacuum tank connected, the pressure drops instantly from 21 to 15in when the pedal is depressed, and will not recover (even with the vacuum pump going) as long as the pedal is depressed. Once I let the pedal go, the pressure will increase to 21in again but will not hold without the pump coming back on.

As I said earlier, I will have a conversation with my rebuilder, especially since I just had the booster/master overhauled.

Chris