IRS Grinding ?

[gt40gordy]

I have searched the site looking for something similar to the problem I am having with my Unique FIA with a Jag IRS.

When the car rolls, you can hear and feel a large clunk coming from the rear end. CV's seemed okay when we checked them, but I may need to remove axles to get a really good look.

Also, when slowing down under braking, there is a loud grinding sound coming from under the car. again near the rear end. It is not consistent, but does seem to be doing it more and more lately. Can't find anything rubbing.

These two issues possibly related ?

The previous owner did mention that he had put in hard brake pads, and the car doesn't stop well until they are heated up, with a lot of pressure on the pedal.

Thanks for any ideas.

[RICK LAKE]

gt40gordy If you have a car lift, put the car on the lift and run it and listen for the noise. A long screwdriver in your ear works good too start. If you don't have a car lift to use, 4 good jack stand under each corner of the suspension. The front lower control arms and the rear ones as far out as possible without hitting the tires. This keeps the drive drive at a better angle to run. Run the car up through the gears until you hear the noise and locate. If you think it is the brake pads, this noise comes and goes when the brake pedal is pressed. If noise still there look for any looseness in the hubs for the wheels. Hub bearing may be going bad. If you heard or find no play, you are down to the final drive or the trans if the car is a GT-40. It sound like you have a broken rearend or teeth missing on the pinion or ring gear. Take a fluid sample from the rearend and look at the color. If it comes out with a silver or metal color, you found your problem. If not unhook outter shafts to wheel hubs and spin them and listen for noise. Put or leave tires on them for weight and load. Stop here. You might have to go to a garage or get a good mechanic to look at the car. Does any one live near you with a GT or Cobra?? Good luck Rick L.

[joyridin']

I would take a good look at both sides of the rotors first. It sounds like the pads are toast. If it is grinding, you will see one of the rotors torn up on the outside or inside. It may not be real noticeable at first if it is down near the center of the rotor.

I had a grinding sound a while back. It was the spider gears. They were in bits and pieces.

[gt40gordy]

The car is a Cobra FIA from Unique.

I have had the car at our former auto repair company already. When the car was on the hoist we checked the CV's, any loose bolts in the rear, the wheel bearings,and the condition of the rotors/pads for the rear brakes. All looked god.

I may not have described the problem as well as possible.

When we push the car, not running, there is a low clunking sound which you can also feel as resistance as it rolls coming from around the rear end.. Not really a dragging feel, more like resistance, then rolls free, then resistance again.

The thing I hear when slowing down under braking sounds like the driveshaft is grinding on the frame, the car actually shudders when it happens, and it's loud. Can't find anything in the rear hitting, but it sure sounds like it is. The real kicker is that it does not occur all the time, or under any particular situation except braking and not every time.

My tech said we need to pull the axles and check the CV's when they are free from load.

Sorry for being so long winded, and thanks for the ideas, keep them coming.

By the way, other than this, I LOVE the car.

[CHANMADD]

I replaced my rotors and pads on my Benz, and have similar sounds. I put premium rotors with ceramic pads and they squeek and grind ( no clunking though) enough for me to have twice taken off the wheels and put silicone behind the pads, which works for a while....hey the pads will last a long time......I would not use them again, and remembered that I have in the past tossed expensive ceramics and put back "cheaper" pads. This is one example of cheaper is better....for the street...

[joyridin']

What happens when you either jack the rear of the car off the ground or put it on a lift and rotate the rear wheels? Do you still feel or hear the sound? You mention a resistance when pushing the car. You should easily be able to feel this if the rear tires are off the ground.

[rjbh20]

I had what sounds like a similar situation in my M3. Turned out the differential fluid was replaced with the wrong type & the limited slip clutches didn't like it. It was particularly noticeable in low speed tight turns like in parking lots.

[RICK LAKE]

gt40gordy Gordy From what you have said, there are a couple of things that come to light.
If the car is hard to push or drags when turning It could be the alignment or the posi rearend in the car. I don't know what rear is in the car but a Jag rear has it's limits of about 450/450 HP and Torque. This is on street tires that are harder that say a 300 wear. Burnt out and hole shots do the most damage to the rearend with soft tires. The drag is not the problem, the clunk is. You say it frees up after the clunk. Jack the car up and pull the rear cover. If it's a Jag rearend and older, It's the same as a Jeep dana 44. The other way it to clean both surfaces well and use RTV and allow to setup for 24 hours. I think you will find the problem once you remove the cover. You are looking at the teeth on the pinion and ring gear. Also any metal flakes in the fluid when you drain it. This is easy to do. If you can get a couple of pictures of the inspection this will help us also. Rick L. Ps my concern is the locking up and breaking free. This happens most of the time when a gear tooth is broken or a stub shaft bearing is coming apart. This stub shaft bearing I know about first hand. Rebuilt Jag rearend and it went 3 miles and destroyed a bearing. Rearend locked up in parking lot. Spun car out was only going 20 mph. No damage to any thing. ON the street a different story cold happen. Rick. Just want you and the car safe and have many more years of cruising and fun.

[krausewich]

Hi Gordy.
Double check the diff mounts are all solid and healthy, driveshaft
and joints, etc. too.. ? Sway bar mounts/links/springs for the clunking ?

Good luck. Look forward to learning of the resolution.
Mike.

[gt40gordy]

So I finally got the car back to the shop and we tore into it to find the source of the strange rearend noise.

Opened the diff and everything looked good, added the recommended two tubes of GM additive and topped off with 80/90.

Disassembled the axles, all CV's good and then had a chance to check wheel bearings. A definite grinding sound was coming from the driver's side (hard to tell when running) , pass side okay. Bearing replaced and car reassembled.

First test drive seemed to confirm that the problems (fingers crossed) are solved. I am still not happy with the brakes, Wilwood front/Jag rear, as it seems like the current pads are mega hard and the car is not stopping as it should.

Unfortunately the pads are obsolete, according to Wilwood, as we were going to swap them out for something not quite so aggressive. May have to change out the calipers but at least it looks like the grinding issue is solved.

Thanks everyone for the suggestions and support.

[Naja289]

I'm not too up on rear ends...except her's (rim shot!!...but it looks to me like my right Rear Axle Hub Assembly is shot...broken right off...Jag IRS with Wilwood inboards...I can see 2 IDs on the Hub assembly but they don't seem to reference anything...Left side has 'P26698' and right side has 'PBM 8'...I need to get this up and back to running asap and have no idea where to source parts...please if you reply be as 'lay' as you can...thanks! ...'92 Unique 289 FIA