desperately need to improve braking modulation/control...

[formula]

first: just the facts, ma'am.

--stock sub
--front: air ride LCA's, SPC UCA's, Air ride double adjustables.
--rear: air ride 4 link, air ride double adjustables.
--tires: 255/35/19 front, 325/30/19 rear
--brakes: 13.2"/ 6 piston front, 12.2" 4 piston rear, hydroboost, wilwood tandem master (can't recall bore--1.125"?)
--air ride front swaybar, no rear swaybar

I'm having what I believe to be just too darn much weight transfer under heavy braking--all four wheels lock at any sort of serious pedal pressure, and the back feels like a pickup truck in the rain. This may be aggravated by the hydroboost, but it seems to be proportioned correctly in controlled tests and I'm not sure, beyond that and without getting into swapping parts, what I can do to make things more progressive. Front shocks are two clicks from max on compression, rear shocks are four clicks from max on rebound. Front springs are at 90 psi +-2psi.

Anybody got any ideas? Maybe it's just terribly hard, sh*tty tires? Is there any way to back the hydroboost down without getting into new parts? I'm tempted to just rip everything hydraulic on the car out and start from scratch, as the clutch and brakes are both on-off-switches as of now. Either that, or rip the bags out and put coils in instead. Hell, maybe both?

Summary: if anybody has any idea of things I can do short of:
--better tires
--smaller bore master/switch to full-manual brakes
--cranking the shocks/springs up even higher

I will buy you multiple beers at RTTH or the next time you're in south carolina.

Edit: looking on wilwood's website, I have to track that master size down--if it's really 1 1/8", that's obviously problem #1 and switching down to something other than THE BIGGEST DAMN BORE THEY LIST ON THEIR WEBSITE will probably help quite a bit.

[ArtosDracon]

IMHO, with the highly linear pressure of a hydroboost, the 1.125" master is almost definitley problem #1. However, you can modulate your braking by changing the throw on the pedal as well. Assuming you have a pedal set up for power brakes, you might look at moving the master cylinder mount on the pedal further down, or moving the fulcrum point up. Neither of which is a hugely easy task, but a small change will make a huge difference in pedal feel. Not only will it mean you have to push the pedal further, which will reduce sensitivity, it will make the pedal a little stiffer, which will help keep you from mashing it as hard.

[pitts64]

I read that cars with Hydroboost use the 3:1 manual brake ratio..

I'll check my Chevy 3500 truck out.

I know this much, I would want Hydroboost on my car..

[formula]

I'm rethinking--line pressure is effectively boosted pedal pressure divided by bore--so a larger master should be helping things, not harming.

I'm diggin the idea of just reducing the pedal ratio a little. I'm gonna do some brake bias work as well--testing today is showing that the backs are locking first, which May be why things are going squirrely.

[Apogee]

Rears locking first could certainly explain the squirreliness. More rear proportioning and/or less aggressive rear pads could help you out there. Less aggressive pads in general might reduce your effective brake torque at the wheels and give you back some modulation. We typically go one or two steps less aggressive with the pad compounds when setting up a car with hydro so they don't feel so much like a light switch. The stickier your front tires are, the more weight you'll transfer under braking and the less rear brake you'll be able to tolerate, so I don't think stickier tires at this point would be a good move until you get things settled down with the ones you have.

Tobin
KORE3

[ArtosDracon]

Pads are a great idea, once you get the front to back sorted out. For street I really like the BP-10 or Polymatrix E.

[formula]

Great call on the pads-I feel like this may be more of a brake thread than a suspension thread after all. If a mod sees this, feel free to relocate.

[monteboy84]

Do you have an adjustable proportioning valve for the rears? If you simply dialed some rear brake out of it you'd cure the issue of them locking up first, until you get the different pads as Tobin suggested.

-matt

[MonzaRacer]

OK first of all under hard stop high pressure then MAYBE you need to drop boost pressure, actually a smaller master cylinder will up the pedal to pressure issue, IF its already 1 1/8th then you may have to go to something more drastic.
In all honesty it sounds like either pedal ratio or over boost is your issue, and a lot of learning.
If you can control it under dry conditions and modulated stopping, I also can agree you MAY have an issue with wet tire traction.
I took a car with Goodyear F1s and we put a Bridgestone on with the AQII wet traction technology tires(Id have to look up the actual model of tire again its been 4 yrs) and the wet stopping was PHENOMENAL. So looking at the actual ratings on the tires through several sources as your tires MAY NOT have good wet ratings but be awesome on track. Or if they are over 3 yrs old.
Most tires from new to 3 yrs are ok but wet traction depends on volatiles and silica content, after 3 yrs to about 5 or 6 the tire maybe fine for driving but tracking and wet work may be too aged.

[formula]

Do you have an adjustable proportioning valve for the rears? If you simply dialed some rear brake out of it you'd cure the issue of them locking up first, until you get the different pads as Tobin suggested.

-matt

Sure do and sure did--good call though, matt.



OK first of all under hard stop high pressure then MAYBE you need to drop boost pressure, actually a smaller master cylinder will up the pedal to pressure issue, IF its already 1 1/8th then you may have to go to something more drastic.
In all honesty it sounds like either pedal ratio or over boost is your issue, and a lot of learning.
If you can control it under dry conditions and modulated stopping, I also can agree you MAY have an issue with wet tire traction.
I took a car with Goodyear F1s and we put a Bridgestone on with the AQII wet traction technology tires(Id have to look up the actual model of tire again its been 4 yrs) and the wet stopping was PHENOMENAL. So looking at the actual ratings on the tires through several sources as your tires MAY NOT have good wet ratings but be awesome on track. Or if they are over 3 yrs old.
Most tires from new to 3 yrs are ok but wet traction depends on volatiles and silica content, after 3 yrs to about 5 or 6 the tire maybe fine for driving but tracking and wet work may be too aged.

Alright I'll break this one down:

--it is 1 1/8, confirmed.

--I'll agree that I have a lot of learning to do, but Steve Chryssos had the same problem when driving my car (Sorry again, Steve) so it can't be entirely the nut behind the steering wheel.

--The problem I've been describing is all on dry pavement. No modulation, nothing but lock and slide.

--Tires are 1 year old General Exclaim UHPs. I'll admit it, I cheaped out and probably shouldn't have. I should still be able to slow from 50-60mph without locking everything down, though.

[MonzaRacer]

I would either drop pedal ratio as a first try to get pedal effort up and application leverage down, this meaning your movement may be more before hitting the lock threshold. Ie longer to stroke the master.
This should give you more modulation ability, then maybe see about dropping the boost pressure. Heck you may have a setup that doenst need boost.
Try one change, drive for a while, then make another. Good Luck.
Also do you have access to brake pressure gauges? If not PM me, I can rent out a set(very expensive units) if needed.

[MonzaRacer]

I would either drop pedal ratio as a first try to get pedal effort up and application leverage down, this meaning your movement may be more before hitting the lock threshold. Ie longer to stroke the master.
This should give you more modulation ability, then maybe see about dropping the boost pressure. Heck you may have a setup that doenst need boost.
Try one change, drive for a while, then make another. Good Luck.
Also do you have access to brake pressure gauges? If not PM me, I can rent out a set(very expensive units) if needed.

[ArtosDracon]

I agree with Lee, need to get to work on the pedal, attempting to drop boost in a hydro is going to be a lot more difficult.

[ProdigyCustoms]

It is the hydrobost, exactly why I am not a fan of those in performance driven (autocrossed) cars. You have killer brakes and the hydroboost is over kill.

That is a 1 1/8" bore master, biggest you can get.

Pads are standard issue pads for that kit, nothing real aggressive.

Wilwood make have a even less aggresive pad, but those are not exacly soer soft pads by any means.

I do no think there is anyroom to move the pedal rod dowm the pedal, but if there is you could redrill and mount it lower and decrease the pedal ratio.

But at the end of the day you are crutching the hyper aggressive Hydroboost unit and trying to autocross where it is deficult to push the gas pedal through the floor one second and lay your toe on the brake pedal the next.

[John Wright]

Is there a way to dial out some fluid pressure only at the hydroboost, so that it isn't full steam at the booster but doesn't effect the steering box pressure?

Will that help make it less sensitive?

[a67]

There is additional information in this thread:

http://www.turbobuick.com/forums/brakes-suspensions-tires-wheels/314291-brake-drag-s-10-brakes.html

Note the 1-1/4" '95 Astrovan M/C. Apparently GM also thought the line pressures were getting too high.

And from the problems Lee (original poster) has been having, I'm still not a fan of hydroboost from a van or truck on a sports car.

Bob.

[cheapthrillz]

It is the hydrobost, exactly why I am not a fan of those in performance driven (autocrossed) cars. You have killer brakes and the hydroboost is over kill.

Yep..... Dude, I agree with Frank.

I think your car is light enough that you could run manual brakes and have a killer set-up for track and street alike.

IF you want my opinion, then keep reading lol.

1. Ditch the hydraboost and sell it (face it, the valving is the problem, and we can't figure out how to fix it with out a hell of a trial and error run.)

2. Upgrade your pads a few notches.

3. Change the pedal ratio to mate with manual brakes.

4. Sell 1 1/8 and buy 7/8 or so...... or possibly run a balance bar if you like the way mine turns out.....


Benefits: Better brake control and feel. Should be able to make some money off of selling the booster. Less stress on your PS pump. Wouldn't be too expensive (like changing to coils... or whatever lol).

Downside: Might be a little downtime (I'm sure you're used to this by now... remember the blown up tranny?). Increased pedal effort (not a problem for you hefty ass lol). Having to sell parts.