Car won't hold boost at launch!

F

Fitman

Member
Joined
Jul 14, 2014
Hello everyone.
I'm writing this thread after reading a ton of info on this particular subject but unfortunately am confused as hell.
I'm running a vacuum brake set up that will only hold maybe 1psi at a launch while power braking but then the wheels start moving thru the beams. From my understanding due to the turbo building boost it changes the vacuum to positive pressure thus weakening my brakes.... Am considering an electric vacuum pump with a canister while at the track and going back to straight vacuum for everyday driving..
Does this make sense to anyone? I'm so close to buying a hydroboost but have read/heard so much negative feedback. At the same time I read about cars that have my same setup and are launching at 10-12 psi?!?!
One mechanic told me today to really fine tweak my rear drums and that'll make a big difference...
And yes i'm pumping the heck out of them before I do my launch.
Any help would be greatly appreciated!
 
I pull 1.5's with vacuum brakes.

1-Line Lock
2-The 3 flex lines replaced with SS lines
3-S-10 rear wheel cylinders
4-All long rear brake pads
5-Rear brake pads tightened as much as possible
 
1. Buy a brake psi ga, and find out what the system is really doing.
2. Not sure where you are getting the info on "I'm so close to buying a hydroboost but have read/heard so much negative feedback".
 
What Scoob said.......also make sure your master cylinder is bled properly. That was my issue, now I can hold 15-20 psi if I want (Husek converter helps)
Oh ya, also adjust the rears with wheels on through the window using a brake tool.
 
I forgot to mention I do have the S-10 cylinders & longer pads & a line lock.
I'll try adjusting the drums a little more.
Thanks everyone for all your help. Please send more helpful ideas whenever possible.
 
Fitman said:
I forgot to mention I do have the S-10 cylinders & longer pads & a line lock.
I'll try adjusting the drums a little more.
Thanks everyone for all your help. Please send more helpful ideas whenever possible.
Click to expand...

I had the same issue. The issue was cured when I installed a two step. What converter are you using?


Sent from my iPhone using Tapatalk
 
PTC 2400
I was considering a 2-step also.
Please tell me more about it.
Thanks for any help
 
Fitman said:
PTC 2400
I was considering a 2-step also.
Please tell me more about it.
Thanks for any help
Click to expand...

Mine is a ProTorque 3000 stall 9.5". I hold the 2 step button. Hold the brakes. Mash the gas. Go on last yellow. Hang on. [emoji51]what turbo?


Sent from my iPhone using Tapatalk
 
I don't know how common it is anymore but I put a jumper valve on mine so all the brake pressure should be sent to the rear. Completely stock back brakes and I can hold 10 psi or maybe a little more on the line. I think I have a 3200 stall with a te45a.

Sent from my SPH-L720 using Tapatalk
 
Fitman said:
I forgot to mention I do have the S-10 cylinders & longer pads & a line lock.
I'll try adjusting the drums a little more.
Thanks everyone for all your help. Please send more helpful ideas whenever possible.
Click to expand...

I had crappy line holding, turned out the drums were indeed not adjusted properly.
 
Turbo6inKY - any tips on the adjustments please? I've been instructed to engage parking brake very tight between adjustments.
Thanks for everyone's help!
 
Fitman said:
Turbo6inKY - any tips on the adjustments please? I've been instructed to engage parking brake very tight between adjustments.
Thanks for everyone's help!
Click to expand...

Sadly, no. For all the things I've dug into, drum brakes have never been my friend. I had a shop fix mine after I couldn't get a new master cylinder to "bleed" right. Turned out the drums were misadjusted, causing a soft pedal with too much travel. Since they adjusted them properly, I've been able to hold enough boost at the line that I can blow the tires off the car when I lift off the brake if I want to be hamfisted about it.

And that's with 275mm Rival-S tires.

There's no one thing. You have to check the system front to back, and don't be shy about another set of eyes.
 
Do you have a check valve in your vacuum line going to the booster? Whoever did your conversion may have skipped this important piece. If there is one, remove it and make sure its working. Lastly, try to get your hands on a pressure bleeder to make sure all the air is out of your lines, i couldnt get a good pedal no matter what i tried until i used one of these. I'm pretty confident i could crack the drums if i stepped hard enough on my brakes now, i have ss hoses, hydroboost, s-10 cylinders, 4 long shoes etc etc
 
Follow the vacuum hose from the booster back to the motor, itll look like a plastic fitting in line a little bit larger diameter than a quarter and about an inch long. If its missing youll be applying pressure to the booster instead of vacuum and youll lose your power assist as the boost comes up.
 
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