1950s 1956 Delco Moraine booster problem

[56Fleetwood]

Any suggestions for the following problem after a rebuild?

- purchased a deluxe rebuild kit from Harmon's. Brake pedal was going to floor. Tear down indicated a bit of brake fluid leaked in, likely due to corrosion on m/c plunger rod.
- rebuilt by a knowledgeable retired mechanic who owns classics and does excellent work for other classic car owners here
- bench tested rebuilt booster assembly under vacuum, pushed in power brake push rod and it returned to position
- installed booster, bled m/c and all 4    wheels as per manual
- cleaned and checked all linkages, no binding
- adjusted power brake pedal to relay rod as per manual (groove in rod 7/8" from toe board)

- Problem 1: pedal return very slow. Needs a very slight push to return. Rebuilder notes that m/c plunger provided is made of stainless steel vs OEM part being hardened chrome. Chrome has a lot less friction than stainless. Double checked all linkages to confirm no binding. I rigged up a low tension carb return spring to the linkage and it worked in returning pedal.

Problem 2: Hard brake pedal. Checked for engine vacuum to booster and it is good. Tested vacuum canister and it holds vacuum perfectly.

Problem 3 (weird one): Have original stop light switch and now it does not make contact with the adjustable cam on the brake pedal. It's got a gap of about 1/2". Cam is tight and untouched from when I took the booster out. It's impossible for the brake pedal to have bent.

Sorry for being so wordy but wanted to get all details in. Would really appreciate any help!

Mike

[dn010]

Not sure about '56 (I know, totally different system/setup) but my '57 has a return spring that goes on the master cylinder arm to aid in the return, perhaps 56 has a spring somewhere along the line too? Otherwise, for problem 1 and 2, I'd look at the problem and correction list at the end of the brake section in your shop manual and see which ones are similar under hard pedal and brakes slow to release.

[Jeff Rosansky CLC #28373]

I had to tweak the brake switch on our 55. I just put a shim on 1 side so that it is canted a little while mounted.

[J. Gomez]

Mike,

- Problem 1: pedal return very slow. Needs a very slight push to return. Rebuilder notes that m/c plunger provided is made of stainless steel vs OEM part being hardened chrome. Chrome has a lot less friction than stainless. Double checked all linkages to confirm no binding. I rigged up a low tension carb return spring to the linkage and it worked in returning pedal.
 

It is common for the pedal to return very slow and stop short the only force to get it back is the large spring inside the power booster which could lose its effectiveness with age/usage or if the rod has any obstructions.
a-   You will have a dust felt seal at the firewall inside the cabin, the felt tends to get very hard causing the rod to drag, have you check it?
b-   Also the carpet (if it was ever replaced) could cause the rod to drag as well, have you check the area?

Problem 2: Hard brake pedal. Checked for engine vacuum to booster and it is good. Tested vacuum canister and it holds vacuum perfectly.
 

There should be a vacuum reservoir canister on the left side inner fender, this should hold vacuum and provide it as need it if there is low vacuum from the engine.

You can also test the function of the booster, with vacuum apply to the booster and the main rod to the relay disconnected pressing the rod slightly you should hear a faint hiss (vacuum valve open to the inside of the booster) allowing you to press the rod with ease this will push the plunger in the m/c. Once you built hydraulic pressure in the m/c it will be harder to keep pressing on the rod, just in case.
 
If you feel very hard to press the main rod initially something may be wrong with the booster as it is not providing the needed brake assistance, not hearing the hiss is an indication vacuum is not entering the booster for the brake assistance.
 

Problem 3 (weird one): Have original stop light switch and now it does not make contact with the adjustable cam on the brake pedal. It's got a gap of about 1/2". Cam is tight and untouched from when I took the booster out. It's impossible for the brake pedal to have bent.

You may have made the adjustment (you know the 7/8" between the firewall and the grove on the rod) with the brake pedal down. You will need to have the pedal all the way up (making sure the brake light switch is fully close) and them make the necessary adjustments to both rods (booster and the brake pedal at the relay) the pedal should not move from this position while doing the adjustments. There is also a round disc/cam at the pedal that presses the brake light switch which can be rotated slightly to make very minor corrections as well as the light switch or the mounting bracket.

Hope this will help..!

[56Fleetwood]

Thanks for these suggestions Jose. I'll try them out and report back.

The troubleshooting section in the manual suggests hard pedal can be due to faulty check valve. New one was installed but will look into that too.

Don't think I can do the 7/8" adjustment with the brake pedal all the way down; the brake pedal rod connects directly to the brake pedal so the 7/8" adjustment determine the brake pedal height. The in/out adjustment to the rod is done at the trunnion end at the relay. If I'm missing something please let me know. Thanks!

[J. Gomez]

Mike,

The troubleshooting section in the manual suggests hard pedal can be due to faulty check valve. New one was installed but will look into that too.
 

Yes, that is possible this is a one-way valve so when vacuum from the engine is apply it will fill both the booster and the reservoir once vacuum is off the valve will close (engine side) and the reservoir will supply vacuum back to the booster.

Don't think I can do the 7/8" adjustment with the brake pedal all the way down; the brake pedal rod connects directly to the brake pedal so the 7/8" adjustment determine the brake pedal height. The in/out adjustment to the rod is done at the trunnion end at the relay. If I'm missing something please let me know. Thanks!

Sorry one small correction, what I meant is the pedal would need to be "up" making contact with the brake light switch until it stops and held at this position. You will notice the position of the brake pedal on Fig. 7-9 which is up (away from the carpet/firewall) and as you noted the adjustment is made relay trunnion screw.

I can share a video file of one of the rebuilds I did for another Cadillac owner back in 2014 unfortunately the file is too large to be posted here, that will show the testing of the booster as per my comments above.

[JungleCadd]

Following.

I just yarded out my bendix and shipped it out for the same problem.
No pedal return. Mine looked to be already freshened up but still crusted iver from sitting. Ive gone through the linkage and reset the toe board offset. Dont know what else to do. Will have to wait for m/c to get rebuilt. One thing yiu can check isbthe pedal bushing to the pedal frame... the pivot. Bushings are polymer and might be roached. Theres a guy on facebook who has taken it upon himself to maxhine them out of brass. Let me know and ill shoot you his contact.
Cheers,
E

[56Fleetwood]

Following.

I just yarded out my bendix and shipped it out for the same problem.
No pedal return. Mine looked to be already freshened up but still crusted iver from sitting. Ive gone through the linkage and reset the toe board offset. Dont know what else to do. Will have to wait for m/c to get rebuilt. One thing yiu can check isbthe pedal bushing to the pedal frame... the pivot. Bushings are polymer and might be roached. Theres a guy on facebook who has taken it upon himself to maxhine them out of brass. Let me know and ill shoot you his contact.
Cheers,
E

Great - Please let me know how it goes

[Warren Rauch #4286]

 Cadillac Serviceman Supplement #3  August 1956

BRAKE PEDAL STICKING

RECENT REPORTS FROM THE FIELD INDICATE THAT SOME CASES OF SLUGGISH BRAKE PEDAL RETURN ARE BEING ENCOUNTERED.

An investigation has disclosed that lubricant used in the power brake vacuum cylinder evaporates with use.

This condition can be corrected by injecting one ounce of Delco shock absorber fluid into the power brake vacuum cylinder. Remove the air cleaner cover,mounted on top of the vacuum cylinder,and pour the fluid into one of the two atmosphere ports under the cover.

Note: This should be performed as a regular maintenance operation every six months.


I bet you guys haven't been doing it. I never did on my 56.

Warren

[56Fleetwood]

This is great info; I have not been doing that. Thanks!

[tluke]

my '57 has a return spring that goes on the master cylinder arm to aid in the return

'54 had a return spring but the '55 shop manual supplement said it was eliminated for the M/C. It says "Use of a softer master cylinder boot and pedal shaft seal at the toe-board has eliminated the necessity for a brake pedal retracting spring on cars with Power Brakes" Interesting that just a rubber change made such a difference in how the pedal retracts. You might want to check those rubber parts on your '56.
Terry

[56Fleetwood]

Thought I'd post the solutions to the problems I was having (Brakes work perfectly now!)

Problem 1: pedal return very slow. Rebuilder notes that m/c plunger provided with kit is made of stainless steel vs OEM part being hardened chrome. Stainless has a lot more friction than the OEM hardened chrome which likely caused extra drag. There were no detectable binding issues otherwise. I rigged up a low tension carb return spring to the linkage and it worked in returning pedal.
Solution: Kept return spring in place.

Problem 2: Hard brake pedal after rebuild. Went through all diagnostics with no success.
Solution: Spoke with rebuild kit provider who suggested removing the diaphragm retainer plate, saying that the properties of repro rubber parts can differ from OEM thereby affecting operation of the power piston. They likened it to removing a spacer washer. We did remove it and to our surprise the hard pedal problem was resolved.

Problem 3 (weird one): Have original stop light switch and now it does not make contact with the adjustable cam on the brake pedal. It's got a gap of about 1/2". Cam is tight and untouched from when I took the booster out. It's impossible for the brake pedal to have bent.
Solution: Dissapointed that I couldn't find the cause of this anomaly; solution was to use a replacement generic switch with a longer plunger.

Thanks to everyone who chimed in with good suggestions and special thanks to Jose Gomez for taking extra time with me to go through detailed diagnostics.

Nice to be able to properly stop again!