Since I bought my IROC, the brakes have sucked. Bad. My pedal is inconsistant. Most of the time it grabs pretty far down. Sometimes it grabs even farther down, and sometimes it grabs up closer to the top. It's not a situation like when you've got air in the lines and need to pump the brakes. Pumping makes no difference. It may grab up high on the fist pump, then low on the next. I never know where they'll grab. It would appear that my rear brakes aren't doing much. There's surface rust on the rotors. I've had the calipers apart and they seem to operate properly and aren't siezed. I've got new pads and rotors on the back, I've got new pads & good rotors on the front. I've changed my master cyllinder 3 times and I've bled the brakes more times than I can count.

Before I change the rear calipers and the prop. valve, what else should I consider? What the hell am I missing here?

There were some guys on the GTA sourcepage that said they removed the valve thingie from their prop. valve and their braking is much improved. Should I give this a try?

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The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

Jim, arent you running a sick cam in your IROC? I would imagine if your Vacuum is varying, so would how effective your power brake booster is. If possible, see if you can get a vacuum gauge under the cowl hood, and measure the vacuum versus pedal at the booster source. If your pedal travel decreases with vacuum, there you go. It might be time for a vacuum canister. If the vacuum is inconsistent with pedal effort, time to look further in(proportioning valve, hoses, and possible caliper adjustment in back. Good luck. Mike

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"Experience life, Don't use it" Julie (petrick) Fink

 

My cam is fairly mild. 214/224 .442/.465 with a 112 LSA.

Without vacuum, is the pedal going to go to the floor or will it just require additional effort? I've always thought that when you lose vacuum, your pedal gets hard as hell to push because you get no power assist.

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The IROC Homepage
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View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

True; plus, you said your first pump has a high pedal, then your second has a low pedal. I'd think if it were a vacuum problem, the situation would be reversed.

Could the m/c be leaking internally?


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Try replacing the front and rear hoses. After time they start to bulge under pressure. Check the vacuum, you might have a leak for the booster.

As for calipers. The fronts are $10 + core, the rears (i assume you have rear disc) will be around $75. If you replace the front hoses, you might as well replace the calipers...especially for that price.

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• 89 Formula 305 WS6
  SFC's, LCA's, Air Foil
  Spohn Panhard Bar
  Flowmaster Cat Back, Tranny Cooler
  A/F Ratio Meter (not a mod but it sure spurs interest)
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  !cat
  CAI W/ K&N
  
  15.559 @ 88 MPH
  (Not good enough)

 

I really don't think it's the front calipers. If there was a problem with 1, the car would likely pull, but the car brakes perfectly straight, so unless both have a 100% identical problem and both randomly vary the same every time, I've got to rule out anything that's wheel-specific, which unfortunately seems to rule out the rear calipers too. I've changed my MC 3 times, so I'd really like to say that's ruled out too unless all 3 had the identical problem. The rear brake lines are all steel, so the only rubber parts are the front ones. I can imagine that they could fatigue and give a soft pedal, but not at random like this and not to the extremes that I'm seeing.

I'm totally lost here. I may try changing the prop. valve and maybe the booster this weekend if it's not some stupid high price.

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The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

I was told the prop valve for the 4-wheel-disc cars doesn't do much proportioning.. that it was more of a spot to hold the "BRAKE" warning switch. I don't see how yanking any valve out of it would help things; if you fix the problem and want to try pulling the valve later, then sure, but it might be better to leave it alone for now.

How are the bushings & slides & mtg bolts on the rear calipers? Did you ever have the recall parts put in? If the rear body-to-axle brake hose is old & clogged, that might explain the lack of rear brakes...

And actually, the rear brake lines aren't all steel. The passenger side has a hose running between the axle's hard line and the caliper. Hm; could there be a pinhole in a rubber brake line somewhere that's letting air in, but is too small to let fluid out?

Have you tried driving around (in a parking lot or somewhere else safe) with the vacuum line disconnected from the booster, and plugged up at the engine? That would certainly eliminate the vacuum possibility...


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Tom, you've got some good ideas there.

A bunch of guys on the GTA sourcepage praised the great brakes they got after removing that widget from the prop. valve, but they've got the newer style rear disks.

The bushings and slides on the rear calipers seem to be fine. When I got the car I pulled the calipers apart, cleaned and greased everything and reasembled with new gaskets/o-rings.

I forgot about the body to axle hose. I may throw this on my "to change" list.

I forgot about the hose on the passenger side too. I only visualized the driver side when thinking about the routing.

The parking lot thing sounds good too. I still think that a vacuum problem would result in the opposite of my problem, but it's sure easy enough to pull that line off and see what happens. Thanks for the tips.

------------------
The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

Well, I figured I'd give an update. I put new (remanufactured) rear calipers on the car and the world is good again. Hopefully the Chevy dealer will be able to cancel my proportuniting valve in time.

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The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
Custom Thirdgen Subwoofer Enclosures
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

hmm. My pedal still seems to exhibit the same inconsistancy, although thanks to the new rear calipers, it all happens with a LOT more pedal underneath me. It figures that I just cancelled the prop. valve yesterday.

------------------

The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
Custom Thirdgen Subwoofer Enclosures
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

have you changed the steel lines at all? i know they tend to get crusty through the years and may be partially clogged. thats just one more thing to think about. i seem to have the same problems on my Z, but i havent given it as much thought as you. bleeding the brakes doesnt seem to help, and i have yet to touch the rears (drum) aside from bleeding them in the 1 1/2 years of owning the car. while inspecting the vacuum thing (even though that doesnt seem to be the likely problem) you might want to replace the check valve in the booster, i'm sure motormite (help) makes it and it cant be more than $5.

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85 Z28- 350, Comp 262, Edelbrock Performer intake, Edelbrock 600 cfm carb and Edelbrock cat back, Summit headers and vette servo
-JVC, Eclipse, Pioneer, MTX, Phoenix Gold, Planet Audio

 

Try replacing the vaccuum booster. The Booster causes a lot of problems, because even though it may be worn out. People are still reluctant to change it.
If you have read any of my 1LE brake upgrade posts. A worn out booster, and a worn out master cyl can mask other brake problems.
Replacing the booster is cheap insurance!
Thanx,ANDYZ28

 

HOW MUCH IS A BOOSTER THO?

 

Actualy the mod was developed for earlyer model rear brakes but works on both equally well.

Personally I would start with hoses and rebuilding the calipers. You very well might have a leak that is water tight but not air tight. and it wouldn't hurt to replace your old hoses with stronger newer hoses.

 

Look between the rear rotors and the rear pads... if there's a gap, your new calipers don't have the GM recall parts installed. (Mine didn't either.) Pick up the recall kit from GM, and put it in the rear calipers... see how that does. https://www.thirdgen.org/techbb2/sho...threadid=78725