Premature rear brake lockup?

2089 Views 11 Replies 8 Participants Last post by 22dodge, Jun 3, 2005

iTurbo

Discussion Starter · May 19, 2005

I recently had to get on the brakes pretty hard in my Shelby Lancer after a brief tango with a Camaro Z28. While braking, I noticed that the rear was locking up prematurely and getting really squirrely (slight fishtailing). Kinda freaked me out because I didn't think it would do this and it wasn't anticipated.

Why would this be happening? My SL has a complete 11" brake setup from a '91 Lebaron GTC. They are the same brakes that are on my Spirit R/T. I have the entire brake system from that car including the prop valve and 24mm master cylinder. It has fairly new Raybestos PG+ pads, and resurfaced rotors as well.

Perhaps the rear end of my car was a little too light? I had about 1/4 of gas and the car was pretty much empty including the trunk/hatch area. Could this problem be helped by swapping a different prop valve in or should I look elsewhere? I'd really like to retain control of the car if/when I need to use my brakes in an emergency situation..

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iTurbo

Discussion Starter · #2 · May 19, 2005

I just put the rear of my SL on jackstands and removed the wheels to have a look at things. The tires are good Kumho 711s that are Z rated and have plenty of tread left and are wearing evenly. The wheel bearings are fairly new and seem good. The brake pads and rotors are wearing evenly. Brake lines seem good too.

The only 'problem' I could find was with the rear rotors. They seem to be worn evenly but I think they might be out of spec (too thin). The rotors had what appeared to be some pitting too. Could this be the problem? If the rotors are unable to dissapate heat properly, will it cause premature lockup?

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Turbo Charger

· #3 · May 19, 2005

My 88 did that last year in a race.. I have the non-vented rotors and I feel fairly certian they were just overheating... which apparently causes brake fade.

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minimopar

· #4 · May 20, 2005

My 87 CSX has always behaved that way. Too much brake in the back. Using higher quality pads up front seems to help.

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Turbo Charger

· #5 · May 20, 2005

Interesting.. well I may find out soon. I've got some nice crossdrilled rotors on the way since FWDP had them on sale last week.

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lametec

· #6 · May 20, 2005

Same here on my Shelby Z. Last year I would "powerslide" it into work all the time, since I have to make a right hand turn into work, and the gravel right at the entrance combined with a little bit of brake would always cause the rear end to slide out. And this is at like 15 mph.

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overboostperformance

· #7 · May 20, 2005

brake fade and lock up are not one and the same. your fronts will overheat(fade) way before rears but you will lose pedal feel with the brake fade it will feel mushy to no exsistent. i had the rear lock up situation happen in my race prepped shadow(i.e gutted road car) i use adjustable prop valves to straighten that out. are you using the brake lines they way they are supposed to be? meaning cross diagonal braking. l/f and r/r brake together and r/f and l/r brake together?

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Turbo Charger

· #8 · Jun 3, 2005

Well.. I found out my problem. One of the front shoes was wore down to the rivets. Odd considering the other 3 front shoes had about 50% wear left. I think I'm gonna bleed them just to be sure both are working up to par. Pistons are fine.

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looneytuner

· #9 · Jun 3, 2005

dirt in lines

you could have dirt in line preventing the release of pressure. Make sure the pins are lubed too. I had the dirt problem on the rear on 96 Neon sport.

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d_snook6

· #10 · Jun 3, 2005

Turbo Charger said:
Well.. I found out my problem. One of the front shoes was wore down to the rivets. Odd considering the other 3 front shoes had about 50% wear left. I think I'm gonna bleed them just to be sure both are working up to par. Pistons are fine.

Shoes on a disc brake? Do you mean pads? And if they are wearing like that the caliper is sticking on the slider pins.

You guys need an adjustable proportioning valve for you rear brakes it would let you dail them in to meet your needs....

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Turbo Charger

· #11 · Jun 3, 2005

Pads sorry.

I actually jacked up my car and checked the tires after using the new brakes for a while. It was obvious nothing was sticking.

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22dodge

· #12 · Jun 3, 2005

if one pad is heavily worn vs' the rest, you have sticking parts (caliper slides, caliper piston, brake hose internal failure) are all classis causes for this problem.

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