TheSamba.com :: View topic - Installed bigger booster - now brakes drag

Sat Oct 18, 2014 4:45 pm

Install bigger booster, rebuilt from autozone
adjusted clevis to 4 3/8 per bently
front wheel spins fine on jack with engine off
turn engine on and brakes drag a lot
turn engine off, brakes drag
remove vacuum hose and release vacuum, brakes are free

Please help, thanks.

Sat Oct 18, 2014 5:14 pm

Try adjusting your clevis for pedal travel. It sounds like you need to back it off.

Sat Oct 18, 2014 5:58 pm

this, you should measure the length of the pin sticking out of the stock booster, and set the new booster to the same, if you have done the BMW conversion you will need to cut around 8mm off the end of the threaded bar on the booster, i have just done the same conversion for a customer today :)

while you were at it, did you look at your clutch pedal, the clevis pin behind there, usually never see's grease, and they wear oval, sometimes to a slot because of it, you'll need to weld the hole closed and re drill a new hole.
again i had to do that for today's job also, to find it had been done, bust not greased, so it had started to wear again.

boof1306 wrote: Try adjusting your clevis for pedal travel. It sounds like you need to back it off.

Sat Oct 18, 2014 7:11 pm

Sorry I just assumed you were following Hermans Blog. If not here ya go.
http://vanagonsyncroproject-herman.blogspot.com.au/

Sat Oct 18, 2014 7:31 pm

he might have been, i have found that they are not all adjusted the same.

boof1306 wrote: Sorry I just assumed you were following Hermans Blog. If not here ya go.
http://vanagonsyncroproject-herman.blogspot.com.au/

Sun Oct 19, 2014 8:42 am

I have been following the directions to a t

It seems to be a problem with the booster when it is in a vacuum, the brakes drag

release vacuum, brakes are free

Sun Oct 19, 2014 11:16 am

any chance the bmw booster has a weaker spring and can't overcome the booster spring in vacuum at idle, thus causing the brakes to drag?

Sun Oct 19, 2014 5:34 pm

i doubt it, none of the ones i have ever fitted have caused the symptoms you are having.
have you got the non return valve the wrong way around, making pressure instead of a vacuum

Mon Oct 20, 2014 7:43 am

Check valve is installed correctly

I have stock brakes all the way round.

Mon Oct 20, 2014 8:09 am

You need more pedal freeplay or the booster is bad. I would back off the pedal freeplay completely and then apply vacuum to see if the brakes drag. If they do, then the booster is bad. If not then your adjustment is bad.

Mon Oct 20, 2014 10:26 am

Why would someone install a larger booster? The thought of doing so just never occurred to me.

Mon Dec 01, 2014 7:47 am

I replaced the first booster from auto zone with another and the same symptom as before, the front brakes drag. Any ideas?

Mon Dec 01, 2014 8:54 am

The proportioning valve tripped, is stuck?
It's the only thing that would cause this phenomina.
The booster by itself wouldn't make the front brakes stick or drag.

If the booster was causing the problem the back brakes would be dragging too.

So, by changing the booster alone would not create this issue, it's there to make the brake pedal application easier--that's all.
It's there to give you a mechanical advantage when applying the hydraulic brakes--

Perhaps the master cylinder is messed up.
Something else is causing the problem in my opinion, and you've just shown that by swapping out two new booster's and still have the same problem.

Are you 100% positive that the rod is the correct length from the master to the booster?

I'm out of practical idea's to this problem--what did you do other than swap out to a different booster?