Brake problem is driving me nuts! Help!

roger c

Well Known Member
#1
Hello,
Problem: My brake pedal does not return to the correct height after driving a few miles.

It lacks about 1" returning to the rest position. I can turn off the motor & then pump the pedal 3 or 4 times & it gradually returns to the rest position, however with the engine running & vacuum to it, it will not return to the rest position.

While driving the car I can pull the pedal up with my foot, but as soon as I apply the brake, the pedal is 1" low again. If while driving I do not pull the pedal back up, I will loose all power assist to the brakes eventually. This has happened several times. I have driven the car with the vacuum hose disconnected & the brakes are hard to push but they work better than they do when they go out because of the low pedal with the hose connected.

There is no bind in the pedal linkage.

I replaced the booster & still the same problem.

Vacuum hose has been replaced with a non collapsible hose.

All brake lines hard & rubber have been replaced with new ones.

3 different new master cylinders have been tried.

2 new 7" dual diaphragm boosters have been tried.

I have adjusted the booster pin several times with no change in the problem, even used 1/16" shims this morning with no change.

Has a brand new proportional valve.

Discs on front & drums in rear.

It seems like the vacuum is causing it not to return. When I pull the pedal up to the rest position by hand, I can feel a slight resistance.

This is in a 56 Chevy with a stock OEM swing pedal. It does have the return spring on the pedal & the assembly works smooth & is free of any binds. If I disconnect the adjusting rod from the brake pedal, it returns to the rest position every time easily.

It seems to me that something is not right with the booster & not letting the vacuum equalize on each side of the diaphragm when the brakes are released.

I have been a mechanic for over 45 years & have never had or seen this problem before,

Is there any kind of adjustment to the rod that comes out of the booster on the firewall side? I did notice that it turns, but I didn't think it was adjustable. I used the rod that attaches to the pedal to adjust pedal height inside the car.

Any help would be appreciated.

Thanks,
Roger
 

1958 delivery

Well Known Member
Supporting Member 2
#3
Bad booster, you can not adjust it to work correctly. This has been going on for a few years now. I get about a 10% return for this problem.
 

roger c

Well Known Member
#4
Bad booster, you can not adjust it to work correctly. This has been going on for a few years now. I get about a 10% return for this problem.
Should I buy a more expensive booster to get away from the bad ones? Is it just a certain size, cause mine have been the 7" dual diaphragm type bought off the dealers on ebay?
 

1958 delivery

Well Known Member
Supporting Member 2
#5
It's a crapshoot. All these booster essentially come from the same Chinese source, I don't care where or from whom you buy. When I get a call from a customer that says "my pedal stays down" I just send them another booster, that usually takes care of it so not every one is bad. One of the problems is the big boys that import direct and have large inventories won't weed out their stock, they just continue to sell despite the problem. It was the same thing a few years ago with the chrome alum masters, the piston will get stuck after the master warms up, no one would throw out their bad inventory. I stopped selling those POS chrome alum masters.
 

1958 delivery

Well Known Member
Supporting Member 2
#9
Check all you want, it's a bad booster that needs to be replaced. I sell hundreds per year and over the last 4 years or so this has been an ongoing problem. You're right, when vacuum is applied the rod is pulled in slightly preventing the pedal from returning. Me, I give my customers a replacement, others deny any problem.
 

roger c

Well Known Member
#10
Hey there 1958 delivery,
I'm sure you are right on this. Everything logical says to me it is the booster, something wrong with the poppet valve assembly. Just my luck to get 2 bad ones in a row!
I am changing it out right now, just came inside for lunch. I have a new single diaphragm that I had bought for a 34 Ford I was building. Putting it on right after lunch.
Thanks 1958 delivery for your help,
Roger
 

1958 delivery

Well Known Member
Supporting Member 2
#11
2 bad ones, ouch:bang

One of the reasons I don't care to sell boosters. I will say the last batch I bought does seem to be a little better, no returns, yet.
 

roger c

Well Known Member
#12
Well that fixed, the old car works just fine now. Hard to believe them chinese don't have better quality control. Now I'm going to ask the feller I bought the last one from if his warranty is any good. Probably not, but I'll ask anyway.

Thanks you 1958 delivery, I kinda thought it had to be the booster but didn't want to try another one because I thought surely one of the two I tried would be good, but after you said there was about a 10% return on them, I changed it today & works great.
Roger
 

61BUBBLE348

Well Known Member
Supporting Member 9
#13
Mike, surely someone rebuilds boosters, or is it just not competitive. :dunno

Here in Adelaide we have a couple of brake joints that rebuild, new diaphragms and seals etc. I use an in line booster on my 38, I have had that thing for 30 years and had it rebuilt twice. :coffee

On the 32 I built I used no booster at all , just used a long brake pedal, got a lot better feel when hammering it through the hills.

Thanks for the the insight though, all goes towards the knowledge bank.

cheers
 

1958 delivery

Well Known Member
Supporting Member 2
#14
Most rebuilders don't have parts available for the Chinese imports plus the cost of a new one is less then what it would cost to rebuild.
 

roger c

Well Known Member
#15
I did contact the seller I bought the booster from. He said he would gladly replace it. I sent the bad one back to him yesterday. This is the old car I was working on.

 

roger c

Well Known Member
#17
Thank you, the 58 is my favorite. The blue 56 is our 'Grocery Getter' and I will be building a 32 Ford 2dr sedan starting in March, not sure what color on it yet. I would love to have a 409 to put in it!
 
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