I just want to run this by some folks to make sure I'm not imaginng things. I recently replaced my brake master cylinder and bled the brakes (twice to make sure). When I went out to try out the brakes, they required a lot of pressue to get stopped and it was like I had no power brakes.

So I went over the brakes again and no leaks, no air ( the pedal is firm ). Drove it again and checked the brakes all around, they all appeared to have been engaged and working. They all seemed about the same temperature. Mechanically the brakes look good.

So I'm thinking its a bad booster, after all its 27 years old and did have a leaky MC on it for a while. While iding in the drive way I pumped the brakes. Each time I did this the idle would stumble. So I'm thinking the booster is bad and when I engage it, its a vacuum leak.

Any opinions or thoughts welcome.

 

did you put in a check valve or removed it by any chance? I had a problem similar, I ended up adjusting the master cylinder brake rod.

 

No, the check valve is in there and it works correctly I disconnected it and tested it to make sure.

I didn't adjust the rod any for the new master. Thats something to verify.

Thanks.

 

Did you happen to REVERSE the Tube with the Check valve in it?.That would make your Brakes feel Like you are Hitting a wall.The brakes will work,but feel like you Have to Really Get on them,Like grab the steering wheel and Force your body down sort of thing.They won't make the Car Screech to a Halt but will Stop the car...just something to check anyways...oh are you bleeding the brakes with TWO people?..(buddy is always helpfull to Pump,pump ,pump,,,,,,And HOLD..while you crack each bleeder!)..Left rear,right rear,left front,right front.

 

[QUOTE=misterstyx69;7230273]Did you happen to REVERSE the Tube with the Check valve in it?.That would make your Brakes feel Like you are Hitting a wall.The brakes will work,but feel like you Have to Really Get on them,Like grab the steering wheel and Force your body down sort of thing.They won't make the Car Screech to a Halt but will Stop the car...just something to check anyways...oh are you bleeding the brakes with TWO people?..(buddy is always helpfull to Pump,pump ,pump,,,,,,And HOLD..while you crack each bleeder!)..right rear.left rear.right front,left front.

 

No, the check valve is in correctly with the arrow pointing the right way. And yes I know how to bleed brakes. I make my wife sit in there and do the work of pumping the brakes as I work my way around from the right rear to the right front to the left front. Been there, done that.

I've just never had a booster go out on me on any vehicle and wanted to make sure thats the problem before I drop dollars getting one.

Thanks for the replies though and keep them coming. Maybe this will prove useful to someone else in the future.

 

Another test I found for the booster is to pump the brakes with the car off a few times and then stand on the brakes and start the car. If the booster is working the pedal should drop slightly, if it doesn't then its bad.

Anyone ever hear of a test like that?

 

Any other ideas for verifying the brake booster functionality ? I'm all ears.

 

Sounds to me like you're on the right track... And yes, I've heard of that procedure, and it should work, but I've never tried it myself. Good luck with it...

 

Thanks, I just wish I didn't have to remove the MC and disturb the brake lines again and have to rebleed the system. Should have replaced the booster when I saw it had brake fluid draining onto it in the first place.

Oh well lessson learned I guess.

 

So I did two tests now that make me think the booster is functioning at least partly.

One test is to run the engine and just use the brakes and then turn off the car. At which point you reach over to the brake booster and pull the engine side of the check valve. Next now remove the check valve, as you do so listen for a hiss as the vacuum being held in the booster sucks the air in. This tells me that the booster is holding vacuum and the popit valve is probably good.

Next I pumped the brakes with the engine off and held the pedal down. Then i started the engine. If the booster is functionaing you should feel the brake pedal dip or go down slightly. It did.

So before I run off and buy another booster, I'm going to check the clearance from the booster pushrod and the master cylinder, Its supposed to be .0004. Maybe I messed with the rod while I was putting the new master in or the new master needs this rod adjusted by tunring out. Either way I'll report back once I figure this out for good.

 

So I ended up replacing the booster with a new one and the brake issue is fixed and no more huge stumble on the idl when I press the brake pedal. There was a leak in the booster, I think when it was engaged.

 

dates, time ,year, may be out of date but info does not go stale -12/12/09 -I've just refurb my brake servo on FB RX7 1985- a blow thru on hose and it was stuck-no come ...no go... so a squirt of the penetrating fluid (Wd40)to get the little ball rolling in the valve and Voila ! she rolls sweetly and I have my vacuum ! no big expense -I am happy! and the brakes is good ! Oh Happy Day !

 

you can see if it holds vacuum. i had the one in Mr peepers rebuilt, it didnt hold vacuum if you had to move the pedal.

i think these are simple to do, but the FSM shows the BIG spring thats in there

 

the booster housing is not easy to take apart without a special tool and yes, inside, its just diapgram, sprgins and stuff.

hard pedal, drop in temp and noise when you step on the brake pedal are the usual indications of bad booster.

 

11-01-07, 10:05 am

 

I didnt even looked at the date and replies

 

:d