# Brake booster vacuum leak?



## Rod6er (Nov 20, 2006)

So I finished installing my new brakes and bled them twice to be sure, with a day in between. I'm going to try rebleeding again next week (not using the car right now) to make sure there's no air in the system.
I am running a new MC, new rear calipers, rebuilt front calipers, new brake lines (hard/soft) all around.
When the car is stopped, the brake pedal feels soft, goes down all the way even after pumping it repeatedly but doesn't feel "disconnected". Basically it's softer than it should be and the system doesnt feel like it's priming. Could this be a bad MC bench bleed? I did it myself until there was no air left but maybe I made a mistake somewhere.
When the car is started, the pedal goes down to the floor without much resistance...when hit repeatedly in a fast manner, the engine also starts to chug a little, oscillating maybe +-75RPMs max. I was think this is the brake booster leaking? I torqued the bolts holding the mc correctly but I am thinking I'm missing a gasket? The MC came with one but I didn't add any other.


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## Rod6er (Nov 20, 2006)

*Re: Brake booster vacuum leak? (Rod6er)*

Anyone? Could it all be because I didn't bench bleed the MC enough?


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## Eric D (Feb 16, 1999)

*Re: Brake booster vacuum leak? (Rod6er)*

You didn't bleed it on a bench, not much of a big deal, as you can do it on the car too. It is messy, so keep rags handy while an assistant pumps.
The rags are used to keep the fluid from shooting across the engine bay. You basically palm the rag in your hand around all 4 exits.
The rag will get soaked, so have a few handy. Once your done, remove the rags and attach your hard lines using the proper line wrench (flare nut wrench). 
Use brake parts cleaner to clean up any brake fluid and or cover the reservoir and clean the mess with water.
The idea is the keep the brake fluid from contacting painted surfaces or rubber hoses. You also don't want water near the reservoir, as brake fluid is hygroscopic, it absorbs moisture from the atmosphere. 
*
The vehicle must be supported by proper jack stands.*
*On models equipped with the load-sensing pressure regulator, the actuator lever must be held toward the axle beam (toward the rear of the car) when bleeding the rear brakes to allow maximum fluid flow.*
For the best possible results, bleeding should start at the wheel farthest from the master cylinder and end at the wheel closest to the master cylinder. Thus, the correct bleeding sequence is as follows:
1.	Right (passenger-side) rear
2.	Left rear
3.	Right front
4.	Left front


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## germancarnut51 (Mar 23, 2008)

*Re: Brake booster vacuum leak? (Rod6er)*

It takes a minimum of a quart of brake fluid to bleed the brakes. How much did you use, and did you use a power bleeder or a vacuum bleeder and do you have ABS brakes?
ABS brakes usually require a trip to the Dealer to be bled correctly (You need a tool to command the ABS pump to run and eliminate the air from the master cylinder and the ABS pump.
I hear that if you have the "good" VAGCOM, you can also control the ABS pump to bleed the brakes yourself.


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## Rod6er (Nov 20, 2006)

*Re: Brake booster vacuum leak? (germancarnut51)*

No ABS here, I bled about 2 quarts through the system, bench bled the brake master cylinder twice, the pedal firms up now but it is much too soft when I start the car, it needs almost no efftort to put it to the floor, the brakes work though, atleast the pads clamp on the rotors enough that I cant turn it..
didn't try w/ the car started up since last bleeding. I'll start the car tomorrow and see what gives.
I was wondering, I rebuilt the front calipers myself, being the first time, I couldv'e installed a seal incorrectly, I followed a DIY and it doesn't seem to be leaking from the piston seal, the caliper works as written earlier, maybe that could cause the squishy pedal? just throwing that out there


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## Rod6er (Nov 20, 2006)

*Re: Brake booster vacuum leak? (Rod6er)*

also I deleted the rear prop valve for now, I have one for disc brakes but the old one is stuck to the frame with stripped bolts, if it's critical I'll have it installed by my mechanic but as fa as I can tell if I watch out for my rear wheels locking I'll be ok.


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## germancarnut51 (Mar 23, 2008)

*Re: Brake booster vacuum leak? (Rod6er)*

It's pretty hard to screw up installing fresh seals in the calipers, as long as you don't damage the pistons when extracting them from the calipers, and use a good brake assembly lube when putting them back together.
BUT, you can screw up bleeding the brakes and leave tons of air in the system. Especially if you insist on using the two person pump the brake pedal method of bleeding the brakes OR you install the new pads before bleeding the brakes. Installing new pads make it very difficult to remove all of the air from the system because the fluid flow is so low with pistons fully pressed into the caliper bores by new brake pads. You can bleed all you want with new pads by pumping the brake pedal, and the odds are, you are still going to have air in there.


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## Rod6er (Nov 20, 2006)

*Re: Brake booster vacuum leak? (germancarnut51)*

well I use a motive brake bleeder. and the front dont have new pads, but the rears do, theyre completely new brakes as I converted drum to disc. I'm going to go see if the pedal feel is better today.


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## Rod6er (Nov 20, 2006)

*Re: Brake booster vacuum leak? (Rod6er)*

no change, pedal is softish and goes to floor when car is started. I'll try to remove the calipers when bleeding and let the piston out a little. how would I do that since i use a motive brake bleeder?
do I just remove caliper, place wood thinner than disc between the pads, press pedal to move piston outwards, bleed using motive pressurised at 15 psi, then close brake system, push piston back inside, replace caliper, move to next wheel? (going rr-rl-fr-fl)


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