Cupping of rear tires on the 85 Riviera

[Guest Straight eight]

Do you have cupping of the rear tires? Other than rotating front to rear every 4,000 miles or so, are there any other cures?

[Guest BJM]

The 85 Riviera has an independent rear suspension requiring a proper four wheel alignment. Be careful and take it to a trusted mechanic or else they will only adjust the front suspension angles.

Not 100% sure what you mean by cupping as that has several meanings but there are 2-3 adjustments that can be made on the back of the Riviera, toe, camber and maybe caster.

The suspension probably has adjusting bolts seized or hard to loosen and adjust. Therefore, lubricating every visible suspension fasterner back there well in advance of the alignment would be good for you.

Mechanics get paid about 1 hour for an "alignment" but this can mean many things. We were trained to "set the toe and collect the dough" meaning if we could "align" it in 15 minutes, we got paid for one hour.

Most of the cars I did required 4 wheel alignments. I took a different outlook and took my time in doing all four wheels and still made some money.

This sounds horrible but is not. Do you want a rookie doctor replacing your knee and it takes 4 hours or a do you want an experienced surgeon taking half that time?

On the other hand, this can create abuses. If the mechanic gets underneath there and sees rusted adjustment cams, they can fudge the front end numbers to bring the car inot alignment - long enough for you to leave.

You should tell the service advisor ahead of time you will want the print out of the alignment results. This should show an alignment correction to within tolerances.

The issue comes with the rusted / seized rear fasteners needed to be limber in order to do the alignment. A time limit places a burden on the mechanic and a suspect mechanic could cut corners. Since you specifically noted the rear tire as the issue, the adjustments need to made back there.

Make it clear to the service advisor that you want the issue fixed. You want proof of the fix and may even want to talk to the mechanic.

Edited October 18, 2009 by BJM (see edit history)

[RivNut]

In my experience, cupped rear tires on any FWD vehicle usually meant that the rear shocks were worn. Instead of putting the tire back on the ground and holding it there, the worn shocks will let the tire dribble down the road.

Is your leveling system still functioning or have you perhaps changed to some aftermarket non-air shocks?

Is the cupping uniform across the entire width of the tread or just on one edge? Is it the same for both tires?

Ed

[sosuzguy]

I have also noticed the rear wheels at an angle too because they were adjusted with a leaking ELC system. Basically adjusted with no air in the system, then you get in the car driving it and it's inflated and not aligned right.

[Guest Straight eight]

Thanks guys for the help. When I bought the car with 14,000 miles on it the previous owner warned me to be careful who aligned the wheels, as few techs understand the system. This had the effect of my just not getting an alignment. I'm at thirty thousand now with uneven, sort of cupping on the outer edge of the rear tires only. The tires have about 6,000 on them now.

[tim63riv]

Because of the rear suspension design of the 79 to 85 GM "E" body cars, they are very sensitive to rear wheel toe-in adjustments, and that is what is causing the cupping of the rear tires.

Most reputable alignment shops will only do a four wheel alignment on vehicles that have four wheel independant suspension like your Riviera. The trick can be to find those places! Most GM dealers would be able to handle the alignment as well as a good quality independant garage, but look for one of those that specializes in alignments if possible.

After the alignment, rotate the tires in an "H" pattern (front to back, back to front) every 2500 miles and you won't have any further issues with the tire cupping.

Good Luck!

Tim

[Guest Straight eight]

Has anybody got a copy of the shop manual suspension pages? It is the only section missing in my 85 Riviera manual. I would like to read how the air suspension works, and how often the pump should come on. Tests for proper operations would be helpful too. If someone has, and would like to email them, I sure would appreciate it.

Edited October 21, 2009 by Straight eight (see edit history)

[sosuzguy]

Straight Eight, I have the ELC section scanned already and will email to to you.

[sosuzguy]

Straight Eight, your email address isn't working.

[Guest Straight eight]

Thanks for the copy

Edited October 21, 2009 by Straight eight (see edit history)

[sosuzguy]

Back in Feb I finally found a company that was rebuilding the elc compressors for many GM and Ford cars. Suspension, Air Suspension, Parts, Conversion, Kits, Air Ride, Airbags, Shocks, Coils, Buick, Cadillac, Chevrolet, Chrysler, Ford, Hummer, Range Rover, Lexus, Lincoln, Mercury, Oldsmobile, Pontiac, Toyota - Suncore Industries. However they didn't rebuild the 79-85 systems, just the 95-99 and various other GM's from 86-current. After discussing with the Supervisor that the air dryer in these compressors for the Riv had a valving arrangement just for E-bodies that needed to maintain 15-20 psi at all times they agreed to rebuild it since, "they were all the same pretty much" according to the company. The valving arrangement is just a couple of springs and a rubber flap like a check valve that is inside the dryer on the system. I have finally got around to getting this rebuilt compressor on the car. I've also built myself an ELC tester very similar to the ones the service manual says to use (pictured) Now I've found that the rebuilt compressor is leaking down after about two hours. There were a few hicups during this rebuild process with the company Rep finally saying they were not going to rebuild these anymore for the 79-85 models!

Does anyone have any suggestions on how to get these compressors rebuilt where they don't leak down? I'm suprised more people aren't having trouble with these.

Is there any other company out there that maybe I don't know about that would consider rebuilding these? Since our 79-85's are getting some collector attention I'm sure the need for these will be more in demand, not to mention it's the same compressors used for Eldo and Toro of this vintage.

Sorry but manually adding air to the system is not something I'm interested in doing. Pictured is the tester I made for these systems. Mine is permantely mounted for the time being.

[tim63riv]

Jayson,

Why not install an in-line check valve if the compressor is leaking down? Just a thought!

Tim

[sosuzguy]

Because also in the compressor is the exhaust solenoid. If any air needs to be released it won't be able to get back to the solenoid to be released. Good try though. Thanks

Edited October 26, 2009 by sosuzguy (see edit history)

[sosuzguy]

If anyone is unsure of how all your suspension componets are intended to work with your ELC system there is an article on Hemmings outlining where it originally came from, Cadillac.

Hemmings Motor News: Suspending Disbelief

[Guest Straight eight]

Had alignment on all four wheels aligned. Right side needed attention

[NTX5467]

In some cases, certain tread designs are more sensitive to toe-in settings than other tread designs. When many "knobby"-treaded "all season" tires were used on GM vehicles in the middle 1980s, GM had to change the toe-in settings (at least on the front) to basically "zero" (whether measured in inches or degrees) AND also started recommending 6000 mile tire rotations to help combat the irregular tire wear of these particular tread design tires. In later years, the tire tread designs have been refined and are not quite so critical, but the toe-in settings have not changed from "zero" toe-in.

With every modern electronic alignment set-up, there are wheel sensors that are attached to EACH wheel, not just the front. There are too many cars which now have 4-wheel independent suspension for alignment shops to not be set up to check them! The computers will also provide a print-out of the initial and "adjusted" alignment measurement values, both for technician/shop documentation and also for the customer to have (if desired). In other words, you end up with a "four wheel alignment" whether you might need one or not.

It would seem that if the rear springs have "worn" or sagged enough that, with the engine not running, the rear of the car "droops" compared to when the engine is running, it should be a simple action to request that the alignment tech to the work with the engine running. This would ensure that correct "ride height" was maintained during the alignment proceedings! Usually, though, alignment values do not change very much within about an inch deviation from factory ride height specs, by observation.

ALSO, remember that all of the rear suspension pivot points are rubber-isolated with bushings just as the front suspension control arms are. With time, even with very low miles, the rubber will dry out and deteriorate, which can cause more issues with wheel alignment than a minor deviation of rear suspension ride height. Therefore, checking any of the rubber bushings in the rear suspension on components which might affect "rolling toe-in" settings should be advantageous to request. Just to be sure, you might firmly apply the parking brake and then lightly throttle into the engine, putting stress on the rear wheels with the locked brakes (NOT all four as it would be if you used the foot brake) and then look to see where any wheel/suspension deflections might be taking place--taking care to maintain observer, operator, and vehicle safety during such a scenario. Do such a check in "forward" and "reverse". If the bushings are allowing "too much give", it should be obvious, I suspect.

Typically, toe-in is a critical adjustment on an independent rear suspension vehicle, moreso than camber as radial tires are more critical of toe-in than camber being out of whack. Bias-ply style tires are critical of BOTH camber and toe-in.

In some cases, suspension designs have a built-in negative camber built into them. The Cadillac Catera is one such vehicle. They ALL exhibited negative camber on the rear suspension, even when new. The only adjustment was for toe-in, on the rear suspension. Checking the Holden forums and other similar sources revealed no "fix" for this negative camber situation, so it could be suspected to not be a real issue for rear tire wear on those vehicles.

So, make sure the rear control arm bushings are in good condition, the rear wheel toe-in is set to specs (even on a solid rear axle vehicle, there is a small amount of toe-in in the basic design of the rear axle housing, for a little stabilizing effect on the vehicle, independent of the front tires' toe-in setting), the rear shocks are still in good condition (no fluid leaks, air leaks of the air shock section, good damping action), and the rear tires are inflated to something akin to factory specs. If you need to purchase new tires, choosing a tread design that is more "ribbed" than "knobby" might be a help, too. Of course, tire rotation every second oil change can help.

Regards,

NTX5467

[Guest Straight eight]

Thank you all for all the information. It sure makes things a little easier when you know why and how to correct problems.