Brake Booster help

[kampala]

Hello.  Today I took my 250sl out and the brakes felt really hard ... like non-assisted brakes but even harder ... scary.   The brakes felt pretty decent last time I drove it, not excellent, but decent ... this change is sudden.   I assume it's not the master cylinder as it didn't feel spongy.  I searched and have read quite a bit on this forum about failed Boosters and the common test seems to be that I should see a RPM increase when I press on the brake pedal and this is not happening ... no change in RPM.

I did the test of pressing the pedal a few times, than holding down the pedal and starting the car and the pedal is supposed to push down farther once started ... it did not.

I'm looking for help on how to confirm it's the booster.  Could it go bad suddenly, without much warning?  The RPM when cold seems normal and after warm up drops to normal. 

I have a later 250sl ... and would appreciate any advise on some tests to confirm the fault.  At the moment I happen to be in Southern California and if it turns out to be the booster I can take it to Power Brake Booster (Bell Gardens, California).

Would appreciate any advice.

Thanks

Oz

[Larry & Norma]

Check the hose from the manifold to the booster has not become blocked.

[w113dude]

Hello Oz,

I had the same issue with a 250 recently, the punctured diaphragm that is inside booster starts very small at the beginning you don't see the idle change that much, in my case it started effecting the idle after a few days that is when I knew 100% it was the booster. the best test is if you can hear a very low whooshing sound as you press the brake pedal (engine running) that is a sure sign your booster is gone, in my case I was lucky enough to find a used one on ebay for less than a $100.00, the brake booster on later 250s are quite common and you should be able to find one without much trouble If a new one too expensive.

[kampala]

Thanks Larry and Shaun ... appreciated.

I took apart the valve that is in the vacuum line and it does what it should ... allows flow in the correct direction only.  The line was also clear.   I once again carefully watched the idle upon pressing on the brake and it clearly DOES increase.  I missed it the first time as it is not an instant rise but goes up very gradually.   Tried this several times and the RPM goes up slowly and settles about 200 higher.  I also disconnected the line at the manifold and plugged the manifold end ... and upon pressing the brake, clearly no rise in the RPM. 

I believe I have a booster going bad ... 

Oz

[George Des]

Have this exact same issue and will send mine out to Power Exchange for a rebuild after the Holidays. Have read where people have had success with that.

[kampala]

George,

One other thing to check, if you have not removed the booster from the car, is the seal between the Master and the Booster.  According to Power Brake Exchange, this is what goes many times and causes a leak in the system and all symptoms are same as a bad booster and may be just that seal.

Best,

Oz

[George Des]

Yeah I will need to ck that out too when I get back to work on it. Thx.

George

[kampala]

Thought I would report back.  I had the Booster rebuilt at Power Brake Exchange.  Since I was in Southern California at this time, I took the booster to their Bell Gardens location.  The guys who work there are very helpful and Charlie, the owner of this facility is a vintage car enthusiast and is very interested in keeping vintage cars on the road.   They rebuilt the booster and powder coated it ... took a couple of days.  I also decided to replace the master cylinder and Charlie got me a new unit and cleaned and fitted my reservoir to it.

I installed the units and I have brakes again.  Hope it lasts ...   

A shot of the booster after the rebuild.


Oz

[w113dude]

Hi OZ,

It looks great.
Could you tell us the cost? I have a spare one that needs to be restored too.

Thanks.

[George Des]

OZ,

Looks good. I'll be going this route as soon as I get back down to Florida and pull my unit off the car. Have done all the tests and I'm certain it is the diaphragm that is gone on mine.

George

[kampala]

Cost for Booster rebuild including Powder Coat was about 200 US$.  They offered no paint, flat black paint, silver or black powder coat.

Oz

[1405Stby]

Would you please post the phone # and address of the Power Brake Exchange.  I am having the same problem with my 1969 280 SL.  Thanks for your help.

Brady

[kampala]

Here's the info --  they have two locations:


http://pwrbrake.com

http://pwrbrake.com/Locations.html

                          
Power Brake Exchange, Inc. - North
260 Phelan Ave.
San Jose, Ca. 95112-6109
PH. (408) 292-1305


Power Brake Exchange, Inc. - South
6853 Suva St.
Bell Gardens, Ca. 90201-1937
PH. (562) 806-6661
      

best,

Oz