phoenix916

About a year ago I put in a 9 bolt rear with 96 TA discs and brakes. When I did I left the stock proportioning valve in because everyone on here said that 89-92 were the same regardless of drum or disc. When I slow down from a High speed or use my brakes alot my font brakes get hot and jump around and it is very scary in the 120+ plus range. I have slotteds on the back and I can hear them click when I hit the brakes but they are not doing enough, it feels like the front brakes are doing everything. I've bled them I don't know how many times and after a year there is no way there is air in there, should I switch the proportioning valve and put slotteds on the front?

Thanks
Brett

87DJP2001

I can only tell you what worked for myself and that was to use the Proportioning valve from 9-bolt rear disc set-up. No problem with my rear drum to Discs. Cure the problem first before changing rotors.

aklim

I'm assuming there is no water in the fluid whatsoever. Are you using Dot 3 or Dot 4? If you are using 3, try getting all the fluid out of the reservior and filling it with Dot 4 and flush the lines to get rid of the 3. BTW, how are your brake hoses?

90rocz

What does this mean?Does it pull, or shudder??

phoenix916

I use what ever brake fluid is recommended and there shouldn't be any water in there. When I slow down from a high speed it's like a hard shudder in the front. When I'm speeding through hills and turns they heat up real fast and when they shudder around turns its very hard to turn. My brake hoses should be fine I never had any problems with my brakes before and I replaced atleast one of the front ones and my car always passes state inspection.

Thanks for the replies
Brett

aklim

Hate to burst your bubble but I see several problems here:

1. You are bringing it down from 120 mph. Since when was your car supposed to be doing that? You are not a Formula 1 race car, no matter what you think. Therefore, if you want to pull such stunts, the recommended stuff will not work. The recommended stuff is Dot 3. You would need to upgrade to DOT 4 or maybe even DOT 5.

2. State inspection doesn't mean a hill of beans. If you think carefully, you will notice that they don't do 120 - 0 stops either. Just like brake calipers or rotors. YOU NEVER REPLACE JUST ONE. . You do them at least in pairs of Front or Back. When I did my leaky hose, I changed the ALL to Earl's Hyperfirm kit which is 5 pieces. One for each wheel and one to the splitter in the rear and it made a difference. Perhaps one of your hoses is better than the others and it doesn't balloon out as much and that might be the cause of the problem. I can tell you that it raised my pedal up quite a bit and made it firmer when I mashed the pedals and I, like you, never had a problem with the hoses till one leaked.

trackbird

When rotors get hot, they can change shape. This is due to the internal stresses in cast iron and some castings are better than others. Also, the front brakes on these cars are terribly undersized for the weight and speed potential of the vehicle. The problems get worse as speeds increase. The faster you go, the more energy there is for the brakes to dissipate. Small brakes don't have much mass to absorb heat and are pretty small heatsinks (not much surface area) to radiate that heat. So, when making a panic stop from 120 mph, you will generate extreme temperatures in the braking system. This can allow the rotor to bend, following it's natural stresses (think of tossing an ice cube in water, the cracks are "stress" from freezing. Cast iron is a liquid that "freezes" when it becomes solid, it is a very similar occurence). I suspect that is where you warp is coming from (I've seen this on my 2002 when trying to melt the brakes to make sure the dealer could find my warped rotor, it got hot and the braking was quite violent. Once it cooled, the warp was gone. I guess I stress relieved it and the dealer didn't find a problem....go figure). That much heat can boil brake fluid which can cause a real mess when the fluid boils and the brakes just "quit". So, dot 4 is a minimum. Upgraded rotors (not drilled and slotted, but good quality like Brembo OEM) will help and better pads (Hawk HPS, or similar) will improve things as well.

There is some tech info on my website under the technical section that may help you out.

And, as Aklim said, with what you are trying to do with your car, "good enough" and recommended no longer are enough.

My thoughts.

phoenix916

Ok guys I see your points and thanks for your replies. But, I had no problems slowing down from 120 berfore the rear end swap. I can follow my friends 97 TA and do everything he does only my brakes get hot and his don't. He's got dot 3 and the same brakes atleast on the back and an 80 pound heavier curb weight.

Is it worth it for me to try changing my proportioning valve, Or should I just change the fluid first?

trackbird

The brakes that were stock on the 3rd gen (and the 4th gen LT1 cars) were not nearly enough to really stop those cars from 90 mph much less 120+. They will stop....eventually. Even the LS1 cars don't like to make panic stops from that speed with stock pads (pad fade is a serious issue in many cases, even with the larger brakes). But a pad upgrade helps a whole lot. You may have too little braking being done by the rear wheels and that would cause the fronts to do nearly all of the work (they usually do about 70% of it anyway) which would explain the difference in performance. However, an external proportioning valve will only reduce pressure and it sounds like you have too little as it is. I would try to find out if the proportioning valve in the master cylinder changed between years (not so much the valve, but the spring that is uses for tension, I know there were at least 2 different springs, one for drum one for disk rears). That is where I'd start.

Be safe!

aklim

I'd say you need to do the hoses and fluid at the same time. I messed up a "good" hose when I took the calipers off the axel to change the brake pads.

90rocz

Sounds like warped rotors, and most likely is being caused by your calipers sticking, not fully releasing, hence the heat, then the warping...I have had this problem cause by the MasterCylinder once, the fluid return valve stuck and didn't let the pressure off of the calipers fully,,,since it's the cheapest to replace, I'd start there...
Shuddering is usually in the front brakes, which is why you feel it on hard turns..
Since brakes are very important coming down from 100mph+, just replace the calipers and rotors and pads,,,ALL,,, thoroughly bleed out all of the air and you should be fine..

aklim

If the rotors are warped from that, you can easily tell. There should be bluish spots on the rotor from the heat. Take it to a machine shop and they can run it on a lathe and tell you the runout.