Vacuum brakes holding boost?

[jerrad]

I've been searching and still can't find a good thread about holding boost at the line.
Please shed some light on this with your experience's.

I know putting in N and revving up while holding down the pedal helps but how much?
Thanks

 

[ttaowner]

from my experience vaccum brakes hold as well as the old pm setup.

 

[jpratt]

My vac brakes wont hold my car still at 0PSI 0vac. I installed a switch to hodl the fronts and now I can smoke the rears all day long. I have heard some one installed a line lock on the rears to hold at the line and build boost with out pushing. You could install 2 line lock, one for rear and one for front.

Lock the fronts for burnout then stage car and lock rear to build boost and unlock to launch. Or just get a tranbrake.

 

[jerrad]

Jpratt: Do you have the vacuum source at the tta vacuum port or did you go somewhere else?

Also, the line lock only holds the amount of pressure that is on the brakes, it doesn't multiply it. If you can hold with your foot on the pedal you won't be able to with a lock.

Thanks for the answers/votes.

 

[stagemonster]

on the vac i can hold about 8 pounds and on the pm 13 to 14

 

[jerrad]

stagemonster: do you have the tta block for the vacuum source?

 

[ttaowner]

when i go to the racetrack i usually have slicks on the back and skinnies on the front. i think the skinnies are my limiting factor because the car always wants to push through the lights with both the pm and the vaccum brakes.the most both have been able to hold were 10# but that was with the ebrake involved and it still want to push the car through the lights.apparently your rear brakes could get ripped off but i never had it happen yet but i hear i can happen. either way 10# was to most i could get out of it.

 

[87 WE2]

If you use the e-brake and the vacume brakes in tandem and practice leaving the line you can leave off 10-15lbs. Like so YouTube - Turbo malibu station wagon

 

[ttaowner]

i have practiced but i think it is the skinny tires not having enough footprint on the ground because the car pushes through the lights. i have pushed through with vaccum & pm brakes.i have not been able to hold more than10# with 3 diffrent cars gotta be the skinny front tires sliding through the lights

 

[87 WE2]

Are your brakes good? If your pads suck and calipers are beat its all a mute point.

 

[ttaowner]

3 diffrent cars all have newer brakes.no soft shoes or big wheel cylinders

 

[87 WE2]

Try a vacume reserve tank in line with the vacume brake booster. That helps a ton also.

 

[stagemonster]

stagemonster: do you have the tta block for the vacuum source?

Yes i have caspers billet block like the tta. Make sure that you have a good check valve at the booster sometimes they leak and you than get boost in the booster and loose brake pressure.

 

[ttaowner]

where do you get a check valve? i thought the thing that came in line from the factory in a NA CAR was a filter of some sort?

 

[stagemonster]

they sell them in the help section at the auto parts stores

 

[jpratt]

I tee off of the top the same as a TTA. If I have a few second I am alternately pump brake, lock switch, release brake, start to push brake and release switch, then start all over. I can feel the pedal get real hard and then it holds pretty good. If I stand on the brake as hard as I can and then build boost the car will roll

 

[turbofish38]

If you can't hold boost on the line it aint the front brakes that's the issue. It doesn't matter what compound you use for rear brake shoes. The drums have to be perfectly true as you need the entire shoe riding against the drums surface. That's why turned down drums, especially those used aluminum drums everybody thinks they need dont work too good. If you must use drums that have been turned down you need the shoes rearched to match. Not whole heck of a lot of companies doing that anymore. Try new drums with a fresh set of shoes to start with. The same philosophy works if you just installed S-10 wheel cylinders and your brakes have a nasty habit of locking up.

Think about it. Which end drives the car? The rear. Get the rear brakes to hold and when it starts pushing the locked up front skinnys through the beams than you can start blaming it on something else.

I have 11" drums on the back of my 86 GN. No problem holding 15-20 pounds with them but than anything past 12-13 pounds is useless with the stock D5 torque converter. I set the tune so I can spool effortlessly on the line. That's the key IMO. Idle up to the stage beam and than build your boost so it bumps you into the other beam and hold it until the right yellow comes on.

 

[turbofrank]

Are your brakes good? If your pads suck and calipers are beat its all a mute point.

start as stated above. I have never had a problem holding 10lbs or a little more at the line.