Rear wheel camber

[padgett]

Is the rear wheel camber adjustable - the '88 FSM talks about adjusting the toe-in but not the camber (though it gives a specification for it) & mine is quite a bit over spec.

[Guest]

The Reatta rear suspension is generally not adjustable. However, aftermarket suppliers can get a tapered shim that fits between the hub and support. Having four holes, this allows four different camber,toe in adjustments depending on rotation of the shim.<P>This was discussed in post six months or so ago.

[padgett]

Thanks for the pointer - a search on "rear camber" did provide a number of postings as well as a bunch of mythinformation.<P>First is that cars with a "live" rear axle, even FWD cars like my Bonneville do not have camber issues - are fixed at zero. (How to give a road racing Firebird negative camber at the rear wheels involves cutting & welding the axle tubes 8*).<P>The Reatta is an IRS car (Independant Rear Axle) which like many years of Corvettes (since 1963 model) uses a transverse leaf spring. This means that the rear wheels are not fixed to each other and can move independantly.<P>When travelling straight ahead, you want 0 camber. This maximises the contact patch of the tire.. In a hard corner though, the tire deforms laterally (rolls) which causes positive camber on the outside (highest loaded) tire, decreasing the contact patch. This means that when you demand more side force, you get less. This is increased by any roll of the car body but is usually offset by suspension movement under load. A really good design will use body roll to induce a negative camber change in a corner. This require precision location and size of the lower arm.<P>So on a race car you design in negative camber so that in a corner, the contact patch increases as the tire deforms which increases the cornering force. <P>The downside is that in a straight line you are riding on the inside edges of the tire. With a Corvette on a race track, you are almost never going straight ahead so it does not matter.<P>In a street car like the Reatta, negative camber does not help anything except the tire companies - you will need replacements often.<P>Sports cars with IRS often use long shafts to minimise. The Corvette uses a lower pivot point close to the center of the car for this reason. The Reatta has a relatively short arm.<P>Next, when the springs age and settle (giving that "low rider" look, the camber changes just as if the body were rolling. This causes negative static camber. <P>On my car, I suspect the factors of age and wider track (1") are teaming up to give 2 degrees negative camber.<P>Do not want to raise the car as I like the look so will look into the shim as it sounds like an easy way out - just want to get under 1 degree negative.<P>Note: While the shim is said to have four positions, I suspect that only straight up will decrease the negative camber and not effect the toe. <P>Also a google search brought up nothing useful under "shim-align" - anyone know the brand name or manufacturer of the shim ?

[padgett]

Went to NAPA today and picked up a box of 264-2843 rear camber shims (book showed specifically for Reatta). Things look like a giant but very thin E-clip & are designed to slide under the top two bolts on the Rrear hub.<P>Was getting a sceeetching sound from the right rear and not a fingernail's worth under the pad feeler so time for new pads as well (knew was going to need when purchased so had a set of AC-Delco 171-557 aka 18024908 waiting).<P>Boy howdy ht factory plays godzilla with those bolts and the caliper bracket bolts (takes an 18mm socket) seemed to be lockers- came out hard all the way and had some green stuff in the threads.<P>Am reasonably sure was the first in there since the rotors sill had the little clips on two lugs.<P>Hub bolts were more of the same and even had to use a 12" 3/8 rachet on the bleeder valve. <P>Bottom line, the shims must be "generic" GM because they did not fit. Had to grind clearance on the ears to fit around the bearing and ground down a washer for the top caliper bracket bolt (for the driver's side which will be done tomorrow because ran out of steam tonight will grind the shim.<P>Started out on the end of the scale (2 degrees) on my gauge but must have been a bit more since with five shims rated at 1/4 degree correction each I still have about 1.25 degrees negative. Expected .75-1 negative.<P>Going to leave it there though unless/until I can find something better.<P>Had really expected a tapered box fitting under the hub and not E-clips on the top which leave gaps where they are not. Imagine the bearing is sealing the ABS sensor cavity (wheel was covered with a white powder) but just feel these things are untidy.<P>Put washer under the top caliper bracket bolt to compensate for hub offset but is still not centered so will leave off of other side and see what happens.<P>BTW when changing the rear pads, you need to remove the parking brake bracket and back out the adjustment screw else you cannot push the caliper piston back to fit the new pads. Duuno how the factory does it with 12" slip joints, my pliers are *bigger* and I can't, have to use a C-clamp every time. Maybe just weak.<P>So shims are in one side which means must do same on other before driving even though it is not an "elegant" solution. Manana.

[cpu]

What is the wheel alignment measurement instrument you are using?

[Guest]

...be careful! The rear calipers have a cross-slot inside on the face of the piston. This is actually a big screw. There is a socket that you can purchase that turns it in. Don't "C" clamp the piston back down like your gto. And then to minimize rattle you might need to adj the thing with the hex head bolt in the back of the caliper. i think it comes out ...then you turn...then put the bolt back in....whatever.

[Guest Greg Ross]

I recently had rear calipers replaced and still have left side rattles, thes are GMX (GM rebuilts-not aftermarket)A year ago the Caliper mounting brackets and fasteners were renewed (major slop on the sliders)<BR>As my '88 is set up, The right side caliper is mounted forward of the Axle (same as the front calipers) but the left corner has the caliper trailing behind the axle. Is this correct, it seems to me with the rotation of this rotor any shock induced is going to be lifting the caliper/ pads and contributing to my rattle woes?<BR>Can someone set me straight.<BR>Barney had suggested an adhesive spray for application to the pads to reduce rattle, I haven't had the opportunity to try this yet.<BR>I recall someone mentioning in a post some time ago that the adjuster works with application of the Park Brake while backing up???<BR>I'm confused!<P>

[Guest Greg Ross]

Padgett-when you first installed the new rims you made an observation about concern for torque-steer-how does she handle now. Regarding Camber, I recall at the last alignment the Tech. mentioning the 2 deg negative you are in the process of correcting. I've accumulated mega miles and with routine tire rotation no signifigant inside edge wear has occurred. The only problem I've had that may be associated with this condition is short life span on rear wheel bearings. Aftermarket replacements are lifetime warranty and I've done them three times now-we adjusted one of them once but it didn't last long, the damage I guess was already done.

[padgett]

Now you tell me about not using the C-clamp. FSM says to use big pliers (fig 5B7-8 in '88). Did discover that nothing happens until you back out the screw on the back. Also found that unless you apply pressure to the piston while backing out the screw, it just sinks into the housing.<P>Handling is fine, have not noticed any adverse reactions. Ride seems smoother and NO lock under hard braking in rain just like my other cars with Michelin X-1s (X-Plus from SAM's has very minor tread pattern difference but appears the same otherwise.<P>Am not terribly happy with shims but was going in for rear brake pads anyway. If I find something better will replace.<P>You meantioned replacing bearings several times. Is that available separate from the hub/ABS teethed assembly ?<p>[ 09-09-2001: Message edited by: padgett ]

[Guest kennyw]

PADGETT,<BR>shame on you for not knowing that the pistion screws back into the em. brake setup. That [is] where it goes. They make a tool but any thing to turn it back is o.k. Then you don't have to mess with the adj. on the em. brake arm........... Let me know when you finally get the tires back flat on the ground..............ken

[Guest]

.....sorry Paggett i see you are aware of the adj screw on the rear of the caliper. To prevent rear wheel rattle i'd suggest that you jack the car up.....remove the retaining nut(i previously called it a bolt) on the back of the caliper and move the stamped sheet metal parking break lever out of the way and with a deep socket, adj until the lever seats on the stop(check by putting the lever back on). Or with the caliper and pads removed use the special socket to screw until the lever lifts from the stop....then turn back the other way until it just rests on the stop. Test the wheel by turning by hand to make sure the adj isn't too tight....then repeat this proceedure two months from now after the brake pads have seated. This in conjunction with bending the little pad retaining clips and silicone seal(brake grease) and parking brake cable adj.<BR>i did have to replace my right front wheel bearing and right rear caliper. The caliper was siezed and the bearing had too much slop. It was a sealed unit hub that could not be serviced. i don't know if the toothed sensor ring was part of the unit.<BR>i think the big pliers trick only works if no one had ever adj the hex nut in the back of the caliper and just replaced the pads instead. Otherwise it looks like the caliper and pads are offset or someone switched calipers while you weren't looking and it won't go back on. <BR> As far as tapered shims....you really want to talk to Tom Walsh as he is familiar with the correct brand......>>>>>>>>>>>>

[padgett]

Both sides now done with five 1/4 degree shims in each side. This now has both sides at 1.25 degrees negative which is high but acceptable. Do not want to put any more in because of side loading on the bearing.<P>Still trying to figure out what the white powder coating on the passenger side ABS surface was. None on driver's side. In fact it was bright and shiny new with the NDH (New Departure-Hyatt) logo clear. Would have wondered if a replacement except the two clips on the lug nuts to hold the rotors in place were still there - never have seen a service man put those back.<P>With five shims (1.25 degrees) you *must* put a washer under the top caliper bracket bolt else the rotor rubs on the guard when tightened. One washer (think it was a 5/16") is just right with rotor nearly centered on both sides.<P>Need to have pressure on the piston when loosening the adjustment else the screw is liable to sink into the housing - I wound up using a woodworkers clamp which fits most calipers nicely and has a screw tightener. Just kept it tight.<P>Once caliper is mounted, the parking brake needs to be adjusted - tighten the screw until it gets solid (should turn easily before that) and then install arm so that it has ideally 20-30 degrees movement from the stop to tight. Do not try to install arm tight against stop or brake will drag.<P>My brakes did not rattle but saw two things that could:<BR>1) spring has a "insert" - looks like black paper but suspect rubber. Goes inside spring and cable goes through it.<BR>2) spring does not push agaist back of lever but insead fits over the extrusion on the front of the arm - had to use a brake spring tool to put it there so if installed by hand, it probably isn't.<p>[ 09-09-2001: Message edited by: padgett ]

[padgett]

Just had a call back from Michelin concerning X-1/X-Plus wear question. They felt that 2 degrees negative was too much but that 1 degree would be OK.<P>On reflection, the normal cause of negative camber on a car with IRS is age sag. However given the space in the wheelwells ( <A HREF="http://www2.gdi.net/~ldkp/enkb.jpg" TARGET=_blank>http://www2.gdi.net/~ldkp/enkb.jpg</A> ) I just find it hard to believe that is the cause. <P>Of those who have had an alignment checked, were there any that were in spec ?<p>[ 09-10-2001: Message edited by: padgett ]