Author Topic: 87 suburban brake problems  (Read 6752 times)

Offline 87suburban

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87 suburban brake problems
« on: December 12, 2010, 08:11:44 PM »
i bought an 1987 Chevy suburban 3/4t 4x4 with the tbi 350, and of course i knew i was getting a basket case before i bought it. Anyway, I'm having problems with my brakes on the truck. In the beginning i couldn't get the brakes to fully pump up like they should, so i ended up bypassing the rear height sensing proportioning valve an that didn't help the problem. Then i found out the master cylinder apparently was bad, so i bought a new one and bench bleed it before i put it on the truck in which it didn't solve the problem. Then i ended up replacing both front calipers, and changed the front brake proportioning valve oh probably 3 times. After i put the third valve on it, i got the brakes to pump up a little better than what they were previously. then about 2 or 3 weeks ago, i went an re-ran the rear brake line but still kept the height sensing valve bypassed but only bled the rear brakes. then i went an bleed the front brakes an now when I'm moving it around the house, the rear brakes lock up when i barely press on the brake pedal. at this point I'm getting fed up with dealing with the brakes on it, I'm still pointing fingers at the front proportioning valve as the culprit considering i got it from a junk yard. however, now I'm beginning to wounder if the problem lies with the fact that the height sensing valve isn't hooked up.

Can anyone tell me if that height sensing valve needs to be hooked up for my brakes to work correctly, or is there a way that i can "cheat" and get my brakes to work like they should without that valve? At this point, i found an aftermarket company that sells the front proportioning valve and I'm half tempted to order a new one in hopes it solves the problem. Any help would be appreciated

Offline topp

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Re: 87 suburban brake problems
« Reply #1 on: December 12, 2010, 08:48:10 PM »
After you replaced the master Cylinder, did you bleed all the lines?
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Offline 87suburban

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Re: 87 suburban brake problems
« Reply #2 on: December 12, 2010, 09:02:25 PM »
yep, i bleed all four wheels numerous times. right now i was able to get them to pump up a little better, but the rear brakes lock up as soon as you put a little pressure on the brake pedal

Online Da67goatman

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Re: 87 suburban brake problems
« Reply #3 on: December 12, 2010, 09:12:56 PM »
I had that same problem and I just backed off the rear adjusters till they all lock at the same time on gravel. 
<Pitcrew>
1989 R2500 Suburban mild 350 TBI 700r4 10.5" 14bolt 4.10 w/ 33s
1992 fullsize Blazer  HIDs, Hella driving lights, Tj Flares, huge bumpers
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Offline 87suburban

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Re: 87 suburban brake problems
« Reply #4 on: December 12, 2010, 09:19:32 PM »
oh, so your saying that it could be an adjustment problem on the rear brakes?

Online Da67goatman

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Re: 87 suburban brake problems
« Reply #5 on: December 12, 2010, 09:33:47 PM »
I bypassed my height proportioner in order to get my rears to do ANYTHING. but my rear brakes were adjusted wrong one side locked instantly the other side did nothing, so I corrected my problem with the adjusters, It could solve yours.
<Pitcrew>
1989 R2500 Suburban mild 350 TBI 700r4 10.5" 14bolt 4.10 w/ 33s
1992 fullsize Blazer  HIDs, Hella driving lights, Tj Flares, huge bumpers
2005 Mazda RX8 Coilovers, Re Audio, Custom All black interior, AEm CAI, Fiberglass Front Splitter, GTO Wing

Offline Dr_Snooz

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Re: 87 suburban brake problems
« Reply #6 on: December 12, 2010, 09:37:24 PM »
Definitely check the adjustment. Also, what condition are your brake hoses in? If the parking brake cables rust shut, it will be very hard to adjust the rears properly so much sure the cables are working and are adjusted properly. I wouldn't think that a prop valve would cause this much trouble. If you change that part and nothing happens, then look elsewhere for the problem.
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Offline 87suburban

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Re: 87 suburban brake problems
« Reply #7 on: December 12, 2010, 09:53:31 PM »
To:Da67goatman

hmm, never really thought of checking the adjustment on my rear brakes. when you bypassed your height sensing valve, an adjusted your rear brakes did that cause your brake pedal to feel soft or did it have no effect on the brakes?

To:Dr_Snooz
ok, the hoses look to have plenty of miles left on them.

Offline arkoza63

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Re: 87 suburban brake problems
« Reply #8 on: December 13, 2010, 12:17:59 AM »
my bet would be on the rubber brake lines
gone crazy, be back soon

Offline 87suburban

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Re: 87 suburban brake problems
« Reply #9 on: December 13, 2010, 08:05:14 AM »
maybe one of them is blocked? cause when i bled the brakes i got fluid coming from all four wheels, but i can get a lot more fluid from the front brakes than the rear. although that maybe do to the calipers requiring more fluid than the wheel cylinders though.

Offline 87suburban

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Re: 87 suburban brake problems
« Reply #10 on: December 14, 2010, 06:33:31 PM »
ok, ive been doin some thinkin on the problem with my brakes. could the problem lie with the proportioning valve causing the problem? are the proportioning valves designed to work with the height sensing proportioning valve? and would a proportioning valve off a car be any different from one for a 3/4 ton 4x4 suburban?

Offline Captkaos

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Re: 87 suburban brake problems
« Reply #11 on: December 14, 2010, 11:23:40 PM »
If you put the correct combo valve on the truck it should be fine.  If you have all the air out it should be ok.  Bypassing the rear load prop valve isn't a problem.  Most of them didn't work that well.
Is you pedal mushy or smooth?  Power vacuum or Hydroboost?
If the rears are locking I would pull the drums off and check everything and readjust it.  The bleed it again.

Offline 1979C20

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Re: 87 suburban brake problems
« Reply #12 on: December 15, 2010, 02:06:39 AM »
When you replaced the master cylinder, did you bleed the 2 lines at the cylinder as well? I would definitely say check the adjustments. My friends 76 c20 locked up just the right rear wheel, I opened up the adjuster and then they all worked about equally. When I did my brakes, when I got the truck the rears didn't work at all, and the reservoir would empty over night just sitting. I replaced the wheel cylinders and bled and adjusted my brakes and then it worked fine. The rear brakes would lock up at the top of the pedal, barely touching it. So, I was just super gentle with them, and they've worn to where I have to push the pedal in inch and a half or so until they catch. I'd say the adjustments
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Offline 87suburban

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Re: 87 suburban brake problems
« Reply #13 on: December 15, 2010, 08:21:02 AM »
Captkaos :

the proportioning valves that i put on it my truck, when i got them from the junk yard i made sure they came off of trucks. because i don't know if the valves off of a older "land yacht" would be different than a valve for a truck. so i take it when those height sensing valves went bad, i take it that people would bypass them? cause i went to a local GM dealer an they said that bypassing that valve would cause the rears to lock, now if they were just saying that or if it was a fact i honestly dont know. the pedal before would straight to the floor before the brakes would stop it, but now it doesnt go all the to the floor but its close to it. but they feel like they can pump up alot better than what they are now, even though they're a little bit better than what they were when i started workin with the brakes.

1979C20:

yep. well i never messed with the adjustment on it, an considering what i've seen on it so far i'm beginning to wonder about that. although im still kinda pointin fingers at the proportioning valve, because my trans am did the same thing after replacing almost all of the brake parts an then bought a new valve for it an that solved the problem.

Offline Captkaos

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Re: 87 suburban brake problems
« Reply #14 on: December 15, 2010, 05:20:55 PM »
Sounds like you still have air in the lines.

 


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