power brake booster rebuild

[Charles 230SL]

over the weekend I noticed my engine idle rising 300 -500 rpm when I pushed the brake pedal and the pedal seemed a little stiffer than normal when braking...traditional signs of a booster going bad. I checked the seal between the master cylinder and booster and it isn't leaking.

This really surprised me since Bud's replaced the booster ($550.00!) when they restored my car 4 yrs ago and it's only got 10,000 miles use on it.  Based on comments from this forum I'll be sending it to Power Brake Exchange for a rebuild. 

Has anyone in this group had a booster go bad so soon? The booster only lasted 4 years/10,000 miles, so Bud's may have installed a rebuilt booster - but isn't it reasonable to expect it to last longer?. This is an ATE T51 booster.

[Tyler S]

Be sure your master cylinder isnt leaking brake fluid back into the booster. It degrades the rubber inside. Just somthing to check before you install a rebuilt booster.

[Charles 230SL]

yes,will do. I'll check the end of the master cylinder when I pull it.  A new master cylinder was installed with the brake booster - it too is only 4 yrs old.

[Tyler S]

You may also want to pull the brake booster vacuum line and have a sniff on the booster side of the check valve. If the car has had repeated short drives then it is possible that fuel vapors have migrated into the booster. This also degrades the rubber. Esp this ethanol blend.

[Charles 230SL]

yes, I'll check that as well ,,gotta love that ethanol.

BTW, I notice (2) locations for Power Brake Exchange; one in San Jose and one in Bell Gardens. Any advice from the Group as to whether one of these is preferred over the other? ie,, for better service and faster turnaround? thanks all

 

[rgafitanu@gmail.com]

To my surprise NAPA rebuilt my old booster for about $100 over 2 years ago and it's working very well.

[alchemist]

Brake booster live for a long time as long as 40 years. I have several Mercedes as old as 1967, all have the original boosters.

[Charles 230SL]

..so I had my T51 brake booster rebuilt and I installed it over the weekend. I took the car for a short drive and noticed the brakes were slow to release - after repeated braking, the brakes really began to drag. The ‘eccentric’ bolt is set as it should be and I’ve got a reasonable amount of pedal travel. The lower pivot is not binding and the vacuum line is air-tight.

In short, once they've warmed up, the brake shoes & pads won’t fully release unless I pull the vacuum hose off the booster.

After pondering a while I've concluded that the push rod inside the booster is simply too long and when a vacuum is applied, the rod continually applies pressure to the master cylinder.  So,,,looks like I'll be removing my M/C and brake booster (yet again). Anyone know whether the pushrod on a T51 booster is adjustable?

[Tyler S]

No the rod is not adjustable, However it may have not been seated in the center of the cone/piston during installation and may have cocked over to one side. This will cause the piston to be partially applied. Applying the brakes will make it worse as the master cylinder will have no way to bleed off.
Either way, as you stated, you are going to have to take it back apart to see whats going on.

[Charles 230SL]

I removed the master cylinder and confirmed that the pushrod was indeed seated correctly in the center of the M/C cone.  I re-bled the rear cylinders and front calipers, and took the car for a drive - the brakes are still far too slow to release and will hang-up for a bit after coming to a complete stop.
   
Its as though the booster pushrod is a tad too long. Is it possible the diaphragms in the booster are too tight and need to be 'exercised' to loosen them up? I know that sounds ridiculous but I've never encountered such as this before.   I'll keep at it and let the group know what I come up with...

[Shvegel]

Charles,
I have not Actually used my booster yet but on advice of others here I sent mine to Power Brake Exchange in San Jose.   Charles Pitts is the owner.  I did read somewhere that the plastic projection on the brake pedal side of the booster is no longer available so protect it well if you ship it out again.

[Charles 230SL]

Yes, thanks Shvegel; duly noted - will do.