I should have built a 4x4 race truck!

[cbtoyz]

I'm having problems staging my truck. After I light the first bulb I build some boost, but I can't roll forward to light the second bulb without my rear tires breaking loose and hopping all over the place. I can only hold 10# of boost max but the pedal bleeds down. Things I have tried...
1) Adjusted the brakes.
2) Installed Gm 1 ton wheel cylinders
3) Replaced master cylinder with a new one.
4) Removed factory proportioning valve and ABS system.
5) Installed Wilwood proportioning valve for the rear brakes.
6) Installed line lock in front "Burnout"
Problem remained, so...
7) Removed factory drum brakes and replace with new disc brakes.
8) Switched the brake lines around (front feeding rear, and rear feeding front).
9) Replaces factory hose going from vacuum pump to booster.
10) Checked vacuum from pump..21"hg at idol.
11) Oh yeah, bled the brakes about 20 times!

The pedal feels hard when the truck is off. When I turn it on, it will bleed down. I noticed today that when I rev the truck up while holding the brake pedal, it drops even quicker.

I'm all out of Ideas. What are you 2wd racers doing to hold boost for a decent launch? I would love to be able to hold a 20# launch, I didn't think this was going to be such a problem.

 

[mattyboy72]

trans brake

 

[cbtoyz]

More like, trans break!

 

[SMOKIN93]

Add another caliper to the rear, I have seen it done for many years on turbo cars and now have seen some diesels doin it and it will get you your 20psi launch.

 

[Big Blue24]

Have you tried disconnecting and plugging all of the vacuum lines except for the main line going to the brake master cylinder?

I assume you are running slicks if you want a 20 psi launch, what other suspension/traction mods are on the truck? When I added a bunch of preload on my homemade traction bars, it seemed to help keep the rear planted, even when building boost at the line and I have no problem building/ holding back 15 psi with the stock turbo. My street tires couldn't take more than a 4 psi launch so i haven't tried 15 psi very many times but it will do it.

My new turbo obviously has spool up problems so I can't compare boost from a larger single vs boost from a stock turbo.

 

[Hurley]

The pedal feels hard when the truck is off. When I turn it on, it will bleed down. I noticed today that when I rev the truck up while holding the brake pedal, it drops even quicker.

Is this not due to more vacuum being present from the pump operating at a higher point with higher RPMS?

 

[bigorange]

you could try a pinion disk break, lots of off roads guys use them but depends on how you drive shaft hooks to your axle .

 

[UNBROKEN]

Dual rear calipers or a pinion brake....that's about all you can do.

Shoot a PM to Michael Watkins (MDW), he's running one on his 2wd Pro Street truck....I know he'll steer you in the right direction on setting up a pinion brake.

 

[White Knight]

Does no one else find it odd that nothing has resulted in no improvement in boost holding power? Not even bigger wheel cylinders and then rear disks? What makes everyone so sure more brakes are the answer?
op:

 

[Big Swole]

Add another caliper to the rear, I have seen it done for many years on turbo cars and now have seen some diesels doin it and it will get you your 20psi launch.

This is what Jeff Garmon did to his white truck... Holds awesome!!
He could be 40-60 psi if he wanted..

I don't think I have a pic of the setup handy...I'll see.

 

[stock600]

I have a trans brake and dual 4 piston rear calipers, doubling the rear brakes makes all the diff. I mostly run off the foot brake now since it's much easier on the driveline, but with 1 set on the rear, Id push around 8# with the dual it easily brought it to more like 20#, and when I pull it in manual second an easy 50-60# if I want it; it leaves about as good in second on the foot brake as Low on the trans brake. Not sure Id bother with a pinion brake

 

[cbtoyz]

Have you tried disconnecting and plugging all of the vacuum lines except for the main line going to the brake master cylinder?
Yeah I tried that today. I unplugged everything and ran one line from the vacuum pump to the booster, and checked the vacuum that the pump was making. Makes 21"hg at idol. Nothing changed. I am running slicks, they should hold a 20# launch.

Is this not due to more vacuum being present from the pump operating at a higher point with higher RPMS? It might be. Today was the first time I noticed it though. I might have just missed It before.

Thanks for the advice everybody. I think I can fabricate something to get another set of calipers on there. I'm going to head out to the track tomorrow. I'll see if I can get someone to shoot some video for you guys.

 

[rockjeep73]

looser converter?

 

[nrose07]

The Grand National guys used to ditch their rear discs for drum brakes, they also had spooling issues. The thinking was that discs were great for high speed, but the drum had more surface area and held against the motor better.

 

[Lower]

The Grand National guys used to ditch their rear discs for drum brakes, they also had spooling issues. The thinking was that discs were great for high speed, but the drum had more surface area and held against the motor better.

More area but less clamping power would be the issue with that.

 

[Big Blue24]

On my 95' it would almost push through the brakes at idle. I checked and it had almost zero vacuum at idle. I raised the idle a few hundred RPM which in theory should make it more difficult to hold the truck and my brakes worked 10 times better. When my truck would push, the brake pedal would get really hard. Now with the vacuum leaks fixed, the pedal is firm and predicable.

I have since plugged all vacuum lines except the main line to the master cylinder and now have excellent brakes.

If more RPM hurts your braking ability, I wonder if your vacuum pump is a little weak, or if possible the crank case is building pressure limiting the effectiveness of the vacuum pump.

All that said, to get the brake power you're after, it sounds like dual calipers is going to be your best bet.

 

[cbtoyz]

Well, I just got back from the track. Only made one run today. Well most of one run. Had a close call, and nearly met my maker. I pulled a Drake and blew my tranny cooler lines just before half track. Thankfully Brad Ponci was a car length ahead of me so I didn't collect him in my mess. I slid sideways through the 8th at 7.94-75.35 mph and fishtailed for a while before getting it pointed in the right direction. I'm just thankfull I was able to keep it out of the wall, and not roll it. I should have built a 4x4...:hehe: I was able to hold a 10# launch, spun a little and netted a 1.9 60'. Not real impressive, but it's a step in the right direction.

 

[COMP461]

The Grand National guys used to ditch their rear discs for drum brakes, they also had spooling issues. The thinking was that discs were great for high speed, but the drum had more surface area and held against the motor better.

Dead on , most stockers have drums for two reasons , first a drum’s are self energizing and hold at a dead stop far better than dish. Second drums have less drag once releases.


First find the right convertor, just loose enough to let you spool , but tight enough to not require lock up immediately ., let the convertor work.
Build a engine program that will spool on launch, and not require big boost braking.


I worked extensively to get Project X diesel, the results, netting a 1.67 60’ on street drag radials.

This was with the looser of the two NADP convertor and 66 turbo, single pump, small injectors, and single stage of Progressive NX nitrous.

The secret, leave at lower boost levels, and drive in to the launch. Leaving lower , and bringing on the power , will allow the rear suspension to work. If you load up the rear suspension to the max, when you launch, the suspension is bound and not able to hit the tire, and start weight transfer.


The suspension when bound up by extreme torque braking, has nothing left to give, or drive the tire in to the track .

This leaving with out setting the tire is flat, with extreme tire spin. You can put a top fuel tire on the rear, and it the tire doesn’t set on launch, it will spin.

With a 2 wheel drive, you need to make the rear suspension work. Working means to use the rear suspension to drive the tire in to the track, and start the transfer of weight.
The best way is to remove all of the spring leafs but two, just enough to hold up the truck. You can supplement with air bags off track. Use the long pivot Cal Tracs, use a good rear shock.

Once weight starts to rock back on the rear , the tires will remain stuck to the ground.
If you have al of this right , you will as the saying goes , “hooks hard and goes straight” if you fishtailing all over the place , it’s because you never initially set the tire .
This is basics of suspension.

I recommend you get the book by David Morgan


Here is project X, I have disk brakes , for land speed racing , and still had no problem holding

this pass , one of the most famous of Project X , was a 1.79 60 foot . notice We are both at the 60 foot clocks , and I'm ahead. This guy was shocked

here are some stock , and super stock elimanator trucks . these are the guys to look to , some use leaf suspension , some have gone to 4 link

this one has leaf springs , and small times , and at most 550 hp

 

[COMP461]

here is some of the passes with the smaller turbo . this was very little NX the 60 foot was 1.87. I was having problems with the shirfting , the best time that day was a 11.28 at 127 mph with a 1.71 60 foot . This was at 6280 lbs

YouTube - Project X diesel drag week 11.53


here is with a very tight convertor , and a 71 charger , it pushed the front tire, started the clocks and a super slow 60 foot dure to this , this was a easy 10 second pass it the brakes would have held.

it also brake the rear end , shortly in to this pass.

YouTube - Project X diesel at Hot Rod Drag Week 2008

 

[MDW]

I'm having problems staging my truck. After I light the first bulb I build some boost, but I can't roll forward to light the second bulb without my rear tires breaking loose and hopping all over the place. I can only hold 10# of boost max but the pedal bleeds down. Things I have tried...
1) Adjusted the brakes.
2) Installed Gm 1 ton wheel cylinders
3) Replaced master cylinder with a new one.
4) Removed factory proportioning valve and ABS system.
5) Installed Wilwood proportioning valve for the rear brakes.
6) Installed line lock in front "Burnout"
Problem remained, so...
7) Removed factory drum brakes and replace with new disc brakes.
8) Switched the brake lines around (front feeding rear, and rear feeding front).
9) Replaces factory hose going from vacuum pump to booster.
10) Checked vacuum from pump..21"hg at idol.
11) Oh yeah, bled the brakes about 20 times!

The pedal feels hard when the truck is off. When I turn it on, it will bleed down. I noticed today that when I rev the truck up while holding the brake pedal, it drops even quicker.

I'm all out of Ideas. What are you 2wd racers doing to hold boost for a decent launch? I would love to be able to hold a 20# launch, I didn't think this was going to be such a problem.

Change it too hydroboost to start