Increasing rear brake holding power - how?

[project89]

ok heres the deal my car is a turbo car and in order to spool the turbo on the line i have been using the footbrake along with the emergency brake to lock the rear tires. its worked great as u can see here http://www.youtube.com/watch?v=-Lf9nTNFRSk the problem is it isnt very consitant comming off the foot brake and droping the ebrake at the same time. and now that im slowly increasing boost im having a hard time with pushing threw the rear brakes on the line i typically come ot of the hole at 7 psi and 4200 ish rpms what can i do to increase the holding power of the rear brakes (drums btw) ideally making them strong enough to hold the car on the footbrake alone would be great but i dont think thats possible were talkign about locking the wheels with 300+ rwhp and that number is only increasing so im open to any ideas or anything that will help and yes i know a transbrake is ideal but i run the 700r4 so thats not an option and between a 600$ converter and 1,200 transmission that would be very hard to sell i just cant afford to goto a th350 and transbrake

[91interceptorZ]

have you thought about using an adjustalble brake controller...get them on line or out of summit racing, you can adjust the pressure front and rear. that might work good, got one on mine and increased rear brake power quite a bit.

[project89]

i have one(just not installed) but the more i thought about it the proportioning valve still limits the amount of pressure to the rear brakes.

so i asume i would have to plumb it in with a tee to the front brake line to get more presure? or do i eliminate the proportioning valve all together?

would this take away from the front brakes?

and i quess i would have to go with a lever adjustable unit inside the car so i wouldnt be locking up the rear tires trying to slow the car down after a run?

is there anything like bigger wheel cyls or bigger drums that can be bolted on that would help?

[Saigon_Bob]

Originally Posted by project89

i have one(just not installed) but the more i thought about it the proportioning valve still limits the amount of pressure to the rear brakes.

so i asume i would have to plumb it in with a tee to the front brake line to get more presure? or do i eliminate the proportioning valve all together?

would this take away from the front brakes?

and i quess i would have to go with a lever adjustable unit inside the car so i wouldnt be locking up the rear tires trying to slow the car down after a run?

is there anything like bigger wheel cyls or bigger drums that can be bolted on that would help?

you could run some sort of sick dual M/C set up.

[91interceptorZ]

no that I know of as far as bigger drums, don't go disc, they actually have less holding power. the adj. pressure regulator i believe it decreases front brake pressure, like a restrictor plate in the front lines, so then when you press the brake more, it increases to the rear. Another idea could be a line lock or two of them, I don't know, that's a hard one....the only thing else i can think is the transbrake.....that's a tuff one.

[project89]

yeah i know the disks have less holding power

i wonder about ditching the prop valve all together and just running an adjuster on each port a knob type on the front brakes so i can set them back to were they are now and then a lever type unit inside the car nexto the seat that i can flip to turn the rear presure back down after i luanch the car

anyone have experiance or can shed some light on a setup like this?

[Saigon_Bob]

Originally Posted by project89

yeah i know the disks have less holding power

i wonder about ditching the prop valve all together and just running an adjuster on each port a knob type on the front brakes so i can set them back to were they are now and then a lever type unit inside the car nexto the seat that i can flip to turn the rear presure back down after i luanch the car

anyone have experiance or can shed some light on a setup like this?

i think thats what they do in race apps... not sure...

not to go off topic but i got the MS running.... but its got some dumb issue where it will stall randomly, sometimes it runs great.. for three days then sometimes... bam stall as if it loses fuel or spark..

[project89]

take this to pms i had the same issue with my ms

[RacerX13]

Here's a few options-

A smaller diameter master cylinder will increase the pressure. It will also increase the pedal travel. You may be at the limit of what the brakes can do now regardless of pressure, but a different master cylinder would be a pretty easy way to find out.

A bigger rear drum setup. IIRC the drums on 3rd gens are the same as S10's and G-bodies. I don't know what's interchangeable but I would be looking to 77 and newer full size cars-many of them are 4-3/4" bolt pattern.

Eliminate the stock proportioning valve and put an adjustable one going to the rear brakes. When it's backed all the way off it will allow full pressure to the rears. Make sure and figure out where to set it for "normal" driving-cars that lock the rear brakes early are scary and dangerous.

Totally cool project BTW!

[87GTAj]

Originally Posted by 91interceptorZ

the adj. pressure regulator i believe it decreases front brake pressure, like a restrictor plate in the front lines, so then when you press the brake more, it increases to the rear.

Hmmm...I always thought that the adjustable valve simply controlled the rear pressure. If you run the fronts straight off of the M/C, and tap into the rear line with the adjustable valve, you have a couple of choices: either a) both fronts and rears see equal and total pressure (valve fully open)[bad idea], b) fronts see all of their intended pressure, rears see none (valve fully closed)[good for burnouts], or c) some combination in between (valve open)[compromise]. Your front brakes should always be receiving their full pressure if you do it this way:
http://www.thirdgen.org/propvalve
Robb Millet did a very nice write up on it. If you follow his write up, by removing the stock prop valve, the fluid runs directly into the front lines (no restriction). All you're controlling is the amount (if any) of pressure going to the rear. This is my plan in the near future. Hope this clarifies the issue for some. Sorry for the long post.

[Lonnie P]

One of the safest methods may be to convert to disc brakes, with a setup for normal driving proportioning, and then adding a second caliper to each rear rotor. This way you have normal brakes, plus additional calipers for staging. I'm sure you could fabricate some sort of solenoid to apply the additional calipers during staging, but not under normal use.

Lonnie

[mesterz2889]

do what monster trucks do and put a disc on the diff ??? thats all i got

[project89]

Originally Posted by mesterz2889

do what monster trucks do and put a disc on the diff ??? thats all i got

i thought about this if u look in the hotrod mags they have the driveshaft/diff mounted ebrake kits.basically one caliper with a disk.i was told this setup would not hold though

im actually converting to 2nd gen rear end housing ends(shorten the rear 1/2 inch per side while im at it) so i can install my c-clip eliminators so im gonna see if i can find any larger drums to fit the rear with those housing ends

[midwest]

Get hydroboost
you should have it anyways, cause vacum boost dont work so well under positive pressure.

[project89]

that wouldnt make any diff unless i was pumping the brakes under boost.
on the line im in vacum when i step on the pedal and boost comes in after,the brakes are already applied.

now if i steped off the brakes and hit them again it would be like no brakes

and other then that on the street if ur hitting the brakes ur out of the throttle and in vacum anyway

[Gumby]

Hook up a booster on just the rear lines. You saw them all the time in the 80s is tow trucks. Little black box with a light and a slider that moved as you applied the brakes. Let you use brakes like normal without standing on it. Could also push the slider with your finger to apply the brakes. Hit up a junk yard.

[project89]

only thing i can think of liek that would be trailer brakes.

got a picture of what ur talking about?

[Gumby]

no pics

way similar could be the same deal, but ones I seen it on were big trucks pulling a trailer with no brakes. All it did was boost rear brake pressure.

[Jeffrey Fontaine]

The GN (and Monte Carlo) guys are using rear wheel cylinders out of a manual brake S10, which are 7/8 instead of the normal 3/4" for their cars. Assuming the F-body uses the same type as the G-body, it should be a bolt in.

Good luck.

[project89]

thnx man i was told by a friend with a tgn the same thing and they do infact bolt in,

on my todo list is new wheel cyls ,remove stock proportining valve and install a lever type adjustable unit inside the car nexto the ds seat,so i can apply full preasure to the rears on staging the car and then set it back to normal after launch

[racing geek]

You could do what the 4x4 guys do and attach a small rotor and single piston caliper to the driveshaft. It will hold better there than two brakes at the wheels because the torque generated from the engine hasn't been multiplied by the rear end gears yet, therefor making it easier to stop. If you go this route, the question becomes... how the heck will there be room for this on these cars?

Mike

[mesterz2889]

i already said that

[Jeffrey Fontaine]

FYI, not sure if you still have this problem, but i am wrapping up installing the 7/8" rear WC to match C5 front setup. Only issue is you need to cut/reflare the rear lines b/c the 7/8" WC from an 85 S10 (2wd, manual brake) is a 45* inverted double flare instead of the stock metric bubble flare. There may be a direct bolt in w/ the bubble flare if you sit at the parts store for an hour or two w/ a catalog. I should know by the weekend how it works as far as braking capability...

EDIT: Praise Dyno makes some wonderful drum advancements, including ceramic shoes that have a higher cf, just not sure if they need to be hot to work well, which might not fit your app.

[91interceptorZ]

Originally Posted by 87GTAj

Hmmm...I always thought that the adjustable valve simply controlled the rear pressure. If you run the fronts straight off of the M/C, and tap into the rear line with the adjustable valve, you have a couple of choices: either a) both fronts and rears see equal and total pressure (valve fully open)[bad idea], b) fronts see all of their intended pressure, rears see none (valve fully closed)[good for burnouts], or c) some combination in between (valve open)[compromise]. Your front brakes should always be receiving their full pressure if you do it this way:
http://www.thirdgen.org/propvalve
Robb Millet did a very nice write up on it. If you follow his write up, by removing the stock prop valve, the fluid runs directly into the front lines (no restriction). All you're controlling is the amount (if any) of pressure going to the rear. This is my plan in the near future. Hope this clarifies the issue for some. Sorry for the long post.

your right......my mistake..I was reading up on it....yeah the adj. valve only controls rear....which might be a fix for having weak rear brakes...I plan to do this as well...