Brake Booster Problems

[Canadian1968CoronetR/T]

Just would like to know if anyone out there has had a brake booster problem.
I stopped yesterday to have our local mopar muscle mech check my low brake pedal it was really hard to stop the car, no matter how hard you pressed, now when I got the car the owner said he had changed the front brake to disc and replaced the booster which he had to reorder because he forgot to tell the store it had a high rise manifold. At first we thought it may be low vacuum , he checked that and said the car did not have a serious cam. So he thinks the booster is not working and he would send it out for rebuild. Now I am not a very lucky guy so I asked what if that did not fix the problem, he said it would or we would send it out for a warrant rebuild. He said it is common to get bad brake booster, I never had to replace one in my 60 years? The only other way to fix my problem would be to loose the booster and go to standard brakes, but I want my wife to be able to drive it as well so good brakes are a must. Lets hear your brake stories.

 

[ChargerRTguy]

Just a thought, could be a proportioning valve ? I know that has to be changed, when going from power drums to front disks.

 

[cr8crshr]

Most likely it is because your present booster is too small. I would recommend upgrading to a dual diaphragm type. Also make sure you are using a disc brake master cylinder verses a drum brake master cylinder. Very easy to get them mixed up but it will effect your braking....

 

['68 383 Charger]

I agree on the master cylinder. There are differences between drum and disc master cylinders

 

[67 coronet]

has the car always been like this,or is it a new problem?

 

[ws27]

OK, opinions are going to vary drastically. I completely agree with possibly needing a dual diaphragm booster. But I don't agree on the master cylinder difference. Sorry guys no offense meant. The difference between masters is a bleed valve and larger reservoir for the fronts. Neither will affect stopping power, cylinder size will, and there are a couple of different sizes. You say the pedal is low and it's hard to stop? First it shouldn't be too low. Someone really needs to rip into the whole system carefully. Is the booster push rod adjusment correct? Are all the pistons at the wheels moving? Pads/shoes glazed over? Sometimes the newer metallic shoes don't work well and you need to go back to organic. Rear shoes correct? Rear adjusted correctly. Can you pump the pedal up? Just food for thought.

 

[Propwash]

OK, opinions are going to vary drastically. I completely agree with possibly needing a dual diaphragm booster. But I don't agree on the master cylinder difference. Sorry guys no offense meant. The difference between masters is a bleed valve and larger reservoir for the fronts. Neither will affect stopping power, cylinder size will, and there are a couple of different sizes. You say the pedal is low and it's hard to stop? First it shouldn't be too low. Someone really needs to rip into the whole system carefully. Is the booster push rod adjusment correct? Are all the pistons at the wheels moving? Pads/shoes glazed over? Sometimes the newer metallic shoes don't work well and you need to go back to organic. Rear shoes correct? Rear adjusted correctly. Can you pump the pedal up? Just food for thought.

I agree.......The residual valve (usually found in the seal port of the master) for drum brakes is meant to keep a constant pressure in the lines, primarily to reduce a long pedal swing and keep pressure to the cup seals on the wheel cylinders. If your Disc's circuit were indeed plumbed through a drum type residual valve, without a doubt your disc brakes would be dragging. I would also go along with investigating why your pedal swing is so short. With all the Hocus Pocus GM based slap on Disc brake converstion kits out there, it's pretty easy to run into a braking system that is assembled incorrectly. Also, patching together odds and ends OEM stuff can lead to the same issues. Was the Vacuum from the engine verified recently to ensure you have proper Hg? Even if the cam that went in doesn't have radical curves, there are cams out there (like Thumper for instance) that dump the vacuum out of the motor like crazy. Has the check valve for the booster and the line to the manifold been checked? For what it's worth, a great majority of boosters with power disc back then where all dual diaphragm. I agree, could be the issue as well...but check the more obvious stuff first. Your '68 would have had a Dual Diaphragm Bendix Booster if disc up front were factory. PST and other sites sell that style booster, firewall plate, master and linkage rod if it ever gets to that point. Good luck!

 

[Canadian1968CoronetR/T]

has the car always been like this,or is it a new problem?

Since I got it last October, don't know about before me.

- - - Updated - - -

OK, opinions are going to vary drastically. I completely agree with possibly needing a dual diaphragm booster. But I don't agree on the master cylinder difference. Sorry guys no offense meant. The difference between masters is a bleed valve and larger reservoir for the fronts. Neither will affect stopping power, cylinder size will, and there are a couple of different sizes. You say the pedal is low and it's hard to stop? First it shouldn't be too low. Someone really needs to rip into the whole system carefully. Is the booster push rod adjusment correct? Are all the pistons at the wheels moving? Pads/shoes glazed over? Sometimes the newer metallic shoes don't work well and you need to go back to organic. Rear shoes correct? Rear adjusted correctly. Can you pump the pedal up? Just food for thought.

Pumping make no difference, unless you give it more revs in neutral when stopping you get one good press, you get more by revving up motor

- - - Updated - - -

I agree.......The residual valve (usually found in the seal port of the master) for drum brakes is meant to keep a constant pressure in the lines, primarily to reduce a long pedal swing and keep pressure to the cup seals on the wheel cylinders. If your Disc's circuit were indeed plumbed through a drum type residual valve, without a doubt your disc brakes would be dragging. I would also go along with investigating why your pedal swing is so short. With all the Hocus Pocus GM based slap on Disc brake converstion kits out there, it's pretty easy to run into a braking system that is assembled incorrectly. Also, patching together odds and ends OEM stuff can lead to the same issues. Was the Vacuum from the engine verified recently to ensure you have proper Hg? Even if the cam that went in doesn't have radical curves, there are cams out there (like Thumper for instance) that dump the vacuum out of the motor like crazy. Has the check valve for the booster and the line to the manifold been checked? For what it's worth, a great majority of boosters with power disc back then where all dual diaphragm. I agree, could be the issue as well...but check the more obvious stuff first. Your '68 would have had a Dual Diaphragm Bendix Booster if disc up front were factory. PST and other sites sell that style booster, firewall plate, master and linkage rod if it ever gets to that point. Good luck!

Disc were added 11" drums were all the way around, now I don't know if had power brakes from day one, I was guessing they were.
The fellow I am taking it to has been racing and driving mopar for many years, I will ask him all your questions, I will ask him to check all this out.

 

[Canadian1968CoronetR/T]

The mechanic took off brake booster to send for rebuild, when he took off booster he said the insides fell apart, when I bought car I was told front brakes were changed to disc and booster replaced or added. I don't know what happened?

 

[BeastlyBirdie]

If it fell apart, it is unlikely that it was a new unit. They have a tendency to deteriorate over time. And, if the rear of the master cylinder went south, it can happily push fluid into the diaphragm. I pulled one off my 1 ton, must have had over a quart in it. But, from what you previously stated, should just be the booster, especially since it only changed when revving the engine to create more vacuum.

 

[Smartpatrol]

Do you have a radical cam? You may just need more vacuum.

 

[Canadian1968CoronetR/T]

No the cam is not that bad, not lumppy at all