Old car, funky brakes

I have only recently started driving my ’49 Cadillac (about 100 miles total, longest trip was 12 miles one way) and have been experiencing some strange behavior by the brake system. All of this driving was done around 30-35 mph (dry rotted tires, have now been replaced) on surface streets, with many traffic light stops.

As I drive, the hydraulic pressure in the system increases – the pedal becomes increasingly firm and the brakes begin to drag. On two separate occasions, it has gotten to the point where the brake lights stay on (pressure switch on MC) and by the end of the 12 mile trip all four wheels were smoking. In that situation, I cooled them down with a garden hose and they caused no issue for the return trip. Since that experience, I have driven a maximum of about two miles per trip and have had no obvious issues.

Brake system specs:

• stock-type (non-power, single channel master cylinder w/ four wheel drums)
• entire system was completely redone (all new lines, hoses, wheel cylinders, shoes, springs) by the previous owner
• I’m unsure if he rebuilt the MC, but it appears to work perfectly
• System has been completely bled
• all four wheels turn freely when cold
• pedal feels nice when cold

This is my first experience with an older car with all drums, but have a pretty good understanding of hydraulics. I’m at a total loss to explain this phenomena and any help or direction would be most appreciated.

Okay if you think the master has been changed 1st place to look is the master it self. Pop the cap you should be able to see the bottom it will have two small holes look down in to the holes do they look open and clear? have a helper slowly push the pedal you should see a rubber cup go past the rear hole then past the front hole. if you don't see it pass both only the front hole the actuation rod is to long. Many are adjustable under the dash. The other likely problem can be a bad rubber line that has an internal tear that's turns in to a "Check Valve" and holds back some pressure when you let up but if all 4 brakes are getting hot it's most likely the rod depth.

Thinking about it more, the rod adjustment makes perfect sense. Unfortunately, the master cylinder location in this car is truly, unbelievably, stupid (on the frame rail under the steering column) and getting at it is a nightmare (which might explain why it wasn't adjusted correctly)

BTDT I feel your pain.

This may be the only forum on the planet where you could get that good an answer on that issue in one post. Best of luck with it!

ultraclyde wrote: This may be the only forum on the planet where you could get that good an answer on that issue in one post. Best of luck with it!

In 7 minutes.

About a 49 Cadillac.

I was going to talk about the lines acting as a check valve, but he not only covered that, but his other idea is way better.

There should be an access panel in the floorboard. My Belair has the same setup.

I had a great idea until I saw it was non-power brakes.

hrdlydangerous wrote: There should be an access panel in the floorboard. My Belair has the same setup.

I'll have to pull back the carpet and check that out!

I just had this same problem on my 1991 spirit r/t.

Took it out and drove it until brakes started sticking. Jumped out and unfolded the mastercylinder a little and it cleared right up. Come to think of it I need to go out and fix that properly.

This all by asking on the forum.

m/c under floor?

i would be concerned that PO who "redid everything" failed to reinstall or reinstalled the incorrect residual pressure valves or installed them the wrong way.

Pushrod length on the MC is the place to start, thats for sure. You can probably pull the boot back off the master and see whether the piston is up against the snap ring, and yes, there should be a hatch in the floor.

patgizz wrote: m/c under floor? i would be concerned that PO who "redid everything" failed to reinstall or reinstalled the incorrect residual pressure valves or installed them the wrong way.

This is another concern, don't drums take a much lower residual pressure than discs? Cheap imported master cylinder might have the wrong one built in. Has it been converted to dual circuit?

Kenny_McCormic wrote:

patgizz wrote: m/c under floor? i would be concerned that PO who "redid everything" failed to reinstall or reinstalled the incorrect residual pressure valves or installed them the wrong way.

This is another concern, don't drums take a much lower residual pressure than discs? Cheap imported master cylinder might have the wrong one built in. Has it been converted to dual circuit?

drums need a 10psi valve and the discs need a 2psi valve

Finally got around to checking it out (I forgot to mention before that I was in Mexico on business until yesterday).

There is an access panel (kind of), but you have to remove the brake pedal to get it all the way off. Also, I couldn't see down into the MC at all - even with a mirror. I tried to take a picture down into it with my phone, but it was either too dark w/o flash or the too washed out with the flash against the brake fluid. I think the only way to really see the ports in there would be with a colonoscopy type camera.

Anyway, there is a spec in the manual to adjust the rod until the pedal lever is 3/4" from the floor pan. Mine was at about 1/2", so I did adjust it to the spec (it only took about one revolution to do so).

One thing that's bothering me about this theory is that the pressure symptom would only occur during actual driving. It seems to me that just pumping the brakes in the driveway should accomplish the same thing if it is a blocked bypass line (either because of rod adjustment or debris).

I plan to take it for a drive later, we'll see if there is any difference.

Thanks everybody for the advice!

Just pumping the brakes while stationary doesn't create heat like actually slowing a car does. Heat = expansion, which means the brakes start to apply as the excess fluid cannot return to the reservoir.

Yup, I've had the exact same thing happen on my Locost on the track. Which is like a 1949 Cadillac in no other way. But if you have those return ports covered up, the hot fluid expands the only way it knows how, by pushing out those pistons at the wheel end. Adjusting the pushrod is the correct solution.

Run_Away wrote: Just pumping the brakes while stationary doesn't create heat like actually slowing a car does. Heat = expansion, which means the brakes start to apply as the excess fluid cannot return to the reservoir.

I'll buy that.

Same problem :(

Check those residual pressure valves, perhaps. It would be educational to remove the brake lines from the master when the car is experiencing the problem to see if it goes away. With the car stationary, of course. If yes, it's in the master. If no, it's downstream.

I found old Cadillacs to be poorly supported. Either find an old coot or talk to the guy in Canada - classiccaddy.ca, maybe?

Everything was feeling fine, I even did a couple of pretty firm stops to test. Then, I ended up having to do a full-on panic stop when the car in front of me decided to stop for a yellow light - after that the pedal became increasingly firm and I started to smell that distinctive aroma.

The pedal is not just firm, it's totally solid. There was no way to pull it back, the lever was against the floorboard.

I ended up pulling over and waiting for it to cool down (it is Friday night on Woodward avenue, might as well take in the sights). After 45 minutes, the pedal was still solid and the brake lights were still on. After that, I crawled under the LF and was able to open that bleeder to relieve the pressure. Driving home after that went fine, but I was very careful.

I'll adjust it out some more tomorrow, if that is still no good I'll dig deeper.

Thanks again.

That_Renault_Guy wrote: After 45 minutes, the pedal was still solid and the brake lights were still on. After that, I crawled under the LF and was able to open that bleeder to relieve the pressure. Driving home after that went fine, but I was very careful.

OK, witht that information i would look for rust or crud buildup inside the MC bore that is not allowing the piston to return to the non-applied position.

and if only one corner of the car does this, i'd look at the wheel cylinder and the adjustment mechanism (if there is such a thing) on that corner.

it just dawned on me that you posted about Woodward. I'm in Canton, and can probably come out to your place one evening this week to help troubleshoot the brakes. it's what i do. :-)

email angry_corvair_at_gmail_dot_com without the _'s

Update:

I have now adjusted the M/C rod as short as it can go, which moved the pedal lever to about 2" from the back side of the floorboard. I decided to make an extreme move, since simply moving it to the 3/4" spec did not fix it last time and I was still quite far from bottoming out the pedal (even while bleeding). I did not get a chance to test it in this configuration, because it was raining (not crazy about the idea of trying to stop quickly in the rain, plus the additional cooling affect of the water could potentially influence outcome).

Some other items that I noticed while poking around:

• there is a long length of steel brake line that runs under the radiator, directly where the overflow tube dumps out. The car has reached about 220-225 water temp when my brake problems start, is this line being bathed in boiling coolant? If so, could that be a contributing factor (I seriously doubt it's the whole problem, but it probably doesn't help).Regardless, I've been meaning to put in some sort of overflow/recovery tank anyway.

• The left-front seems to have something a little goofy going on, but I'm not 100% sure yet if it is cause or effect. Although all four wheels appear to spin freely when cool, the LF has a slight drag to it (really only perceivable if you turn the bare drum, without the extra leverage of the 235/75/15 tires).

• When I took the LF drum off, the "primary" and "secondary" shoes appeared to be installed vice-versa. Although it doesn't ever show it clearly in the manual, I would assume that the primary (forward location) should be the shoe with more lining area. The secondary shoe that was installed rearward had a ton of material build-up on it.

• Also on the LF, the wheel cylinder would not completely retract unless I relieved some pressure. I tested this several times after putting the drum back on. It would spin totally freely until I pressed hard on the pedal, after that there would be a very slight drag until I either opened the bleeder valve or cracked the hose connection (I did that to test the internal cut hose check-valve theory).

So, although I have not had opportunity to fully inspect all four wheels while "hot", I am positive that they are all dragging. What I can't say for sure, is whether the LF starts the party or not. It also seems conceivable to me that an MC problem might still affect the LF first, since it's the shortest distance away.

Anyway, I have ordered a new wheel cylinder for the LF and an MC rebuild kit and plan to progress in the following order:

1) test drive it as-is, with the super short M/C rod.

2) Install rad overflow reservoir

3) replace LF wheel cylinder

4) remove master cylinder to inspect for blocked bypass port and rebuild (if I have to take it off anyway, might as well throw a new piston, etc. in it)

Ken, thanks for you offer but I think I'm good for now - if I'm still struggling after the above listed steps I'll either take you up on it or there will be a cheap classic Caddy for sale

-Jim