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Old 03-28-2007, 08:02 PM   #1
bigriv1990
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Question 1990 Riviera Rear Brakes - I'm Vexxed!

Hello all! I'm Matt. I'm a Florida teen about to graduate high school and head off to aviation school in New York, where i plan on living. I regret the lack of introduction but I'm busy and in need of help.

I drive a 1990 Buick Riviera and I love this car... most days.
I've been working on cars since I was little and I would rate myself as an above-average mechanic. I have the occasional absent-mindedness bug that gets me into mechanical binds every now and then, but I'm generally able to think my way out of any situation and keep my old tank of a car on the road.

Anyway, my issue is with the rear brakes. This car was equipped with GM's earlier rear disc brake setups. Normally, they're lovely. But to work on their a pain. I feel that it's a rather awkward setup with the inbuilt parking brake and all. Drums for parking and discs for service braking is a much more intelligent setup.

I'm having trouble getting a good, solid adjustment on these brakes. I replaced these rear calipers forever ago. Unfortuantely, Cardone saw fit to NOT include the special adjusting instructions (and warning of the the fairly catastrophic consequences of improper adjustment) and never having dealt with this kind of rear braking system before I was unaware that they needed to be specially adjusted.

Now they're giving me trouble in the form of extra pedal travel. I managed to get one brake adjusted so that the parking brake level is only about 1/8th inch from the stop when the pads are tight. But the other is much worse. The lever rotates over half an inch from the stop before the brakes get tight. But the nut that the lever attaches to is only a hexagon nut, and the next position back is too far back and the lever won't even reach the stop. Cardone's ProTech bulletin had some information, but I think it was written by a drunk, it suggested using a screwdriver between the pad and the rotor to pry the piston back into the bore and then rotate the screw so that the lever adjusts correctly. But it said rotate it backwards... which tends to result in brake fluid leak if not careful... not liking this method. Meanwhile, carquest had a fairly well written bulletin that stated the brakes will correctly adjust if I pull the lever forward and then allow it to snap back a few times.

I'm going to continue repairs tomorrow as I have to work tonight. I'm really not so crazy about shoving a screwdriver between my pads and rotor as I prefer my pads and rotors "gouge free" So what about the Carquest method. Will it work? Is there another method?

Any and all input is appreciated!

-Matt

Last edited by bigriv1990 : 03-29-2007 at 04:44 AM.
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Old 03-28-2007, 09:11 PM   #2
Cliffy
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So are you saying that the parking brake works via the disc/pad setup, like most cars these days? I agree that GMs usual setup is better, and more effective, I guess it's just due to service issues and the ease of having a 'one system works all' setup installed. This setup is often inferior to the other, too. Assuming this is the case, the brakes should adjust themselves when you press the brake pedal, ideally. Obviously this isn't the case with your car. I have never known for braking systems to require a particular adjustment setup, especially for a rear disc brake setup.

Can you explain the system in more detail, as in what the brakes look like etc. This might be an obvious problem to other Americans here at CF, so if one of them wants to jump in and call me stoooopid, feel free, lol. I'm from the UK by the way, so your car isn't sold here......

What I will say though is, don't worry about things like the brake fluid leaking, as you described in your post, as this will be normal given that you are squeezing the pistons back (it should, if the level's at maximum, push the fluid up through the resevoir filler....just don't sqeaze too hard, lol). Also, I'm assuming that from your description that the rear calliper's are of the twist/pushy piston type? (normal for rear brakes)
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Last edited by Cliffy : 03-28-2007 at 09:15 PM.
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Old 03-29-2007, 04:16 AM   #3
bigriv1990
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Okay so here's the deal.
First off, they don't twist. They actually just push straight out of the bore as any other disc brake does.
Secondly, the parking brake is actuated by a lever, which is mounted to a hex-shaped shaft and secured by a nut. Apparently the shaft leads to a "jackscrew" within the caliper itself. As I understand it, this screw rotates with the lever and turns inward, and physically drives the piston out of the bore, compressing it against the pads and the pads against the rotor.
Unlike normal disc brake calipers which constantly adjust for wear, this model requires operation of the parking brake to adjust it. Simmilar to some old drum brake systems. As I understand it, the jackscrew automatically adjusts itself. So I get the feeling that the jackscrew is somehow attached to the piston, preventing the piston from pushing itself out of the bore without the parking brake keeping up (which would render the parking brake useless). So in order to keep the pads tight, this brake must be adjusted correctly. Unfortunately, it's not as simple as cranking down on the parking brake cable adjuster. The lever has to be mounted on the hex at the correct spot. It has to be adjusted so that it takes no more than 1/4" of movement of the lever, measured from its stop, to lock the rotor.

I've managed to get the left on correctly. But the right... not so good. The only position I can get the lever on has a good 1/2"+ of lever travel before the brakes are tight. That's over twice as much as is acceptable. The next position I can get it on is too far back so the lever doesn't fit on. There's a proceedure for getting it right but it's insanely... not understandable... it was written poorly. I'm formulating my own ideas and I think I might have it but I was hoping someone might know something having done this already theirselves. It'd be reassuring to actually know what I'm doing. Right now I'm trying to apply knowledge of a totally different style of brakes to this situation and work my way out of it. But I'm finally learning that these brakes don't follow the normal rules of disc brakes. They're rebels.

Anyone who has information, I'm listening.
Thanks!

-Matt
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Old 03-30-2007, 11:38 AM   #4
dodger65
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they sound an awful lot like w-body rear calipers, where you just assemble it, pump it up, and set the parking brake 10 or so times once a month...
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Old 07-20-2007, 07:11 PM   #5
gwynn156
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Rear Brake Adjust

I have the exact same vehicle. Just did a complete brake job (lines and all)I had the same troubles. After asking around, it is just as the other gentelman said....Pump the parking brake..release...Pump the parking brake...release...etc etc It will finally come up to a decent pedal. I would do this at stop lights, when waiting in the drive, whenever. I can not remeber how long it took..but it was longer than I ever expected!
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