TC rearend - "grinding" noise

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TC rearend - "grinding" noise

August 27, 2009, 02:19:04 AM

I also need to pick your guys' brains over a grinding noise I am hearing from the rear after going 8.8/rear discs. The sing (low-medium pitched) sound appears around 15mph and doesn't sound like it changes frequency up to 30 mph. The sound is similar to if I were to leave the parking brake slightly engaged. The rear brakes themselves are great though and we ran the car with the rear up on stands - no noise at idle or revved to 2k.

Would anything in the rearend have a similar sound? I'm thinking it is either brake or ujoint related (will be checking the latter tomorrow). Any opinions?

TC rearend - "grinding" noise

Reply #1 – August 27, 2009, 10:43:25 AM

Could be the dust shield for the rear discs. Maybe you bent them when putting the car back on the ground.

TC rearend - "grinding" noise

Reply #2 – August 27, 2009, 12:33:22 PM

They clear - we rebent/straightened and coated them long ago. There is no contact there from looking under the car. That is what it sounds like though. I don't know of what else could sound like this than brakes.

TC rearend - "grinding" noise

Reply #3 – August 27, 2009, 01:44:42 PM

Are the lers contacting the driveshaft? (Just stabbing in the dark)

TC rearend - "grinding" noise

Reply #4 – August 27, 2009, 02:27:39 PM

Wheel bearings? Did you put enough fluid and friction modifier in the diff.?

TC rearend - "grinding" noise

Reply #5 – August 27, 2009, 02:44:51 PM

The exhaust hasn't moved from before the swap. The driveshaft isn't hitting anything, including the parking brake cables. The cables do not rub the tires. The rear wheels spin freely without contacting the brakes.

I drove it up the street to get the differential topped off and ujoints greased - still there. It sounds like road noise but a little louder and coming from the rear end area. It's possible it IS road noise going through the Bilstein shocks but I doubt it as it sounds like it comes from lower than the trunk. It seems most prominent in the "10-20mph" range (stock speedo gear, now 3.55 gears) where it quiets up a little higher (more rapid?). I can hear slight rearend noise at 40mph (real) but much quieter than the 7.5" rear I took out that whined since the early 90's.

I need to get myself a new speedometer gear here really soon...it's way off as one would expect.

TC rearend - "grinding" noise

Reply #6 – August 27, 2009, 05:23:03 PM

If you slightly step on the brakes at the speed you here it, does it still make noise?

TC rearend - "grinding" noise

Reply #7 – August 28, 2009, 07:26:28 AM

I have bigger problems to worry about now - I'm getting a rapid thump thump (or whatever) sound that speeds up with speed increases and is gone with more throttle. I can hear this with the window down and sticking my head out also - it sounds like it's drivers side rear but could be anything. On the highway (had to get back home), it sounds like I'm driving over the lane separator strips/bumps. What could be causing this? We replaced the axle bearings/seals earlier today and the inside of the differential looked great. Nothing ishiznitting anything with the car up in the air and idling in drive, or on the ground and looking under the car. The u-joints seem as tight as the day they went in (less than 10,000 miles ago, it sat much of a 9 month stretch last year) and they were fine prior to the rear/disc swap.

The sound appears around 15mph and occurs all the time with little load and perhaps 20% of the time with no load. I have yet to test this on hills versus dips. It really sounds like something hitting driveshaft/wheel but nothing is close! I can "feel" it in the seat but I'm feeling everything with the new suspension now...

TC rearend - "grinding" noise

Reply #8 – August 28, 2009, 05:27:39 PM

I took it to All Ford Performance - they cannot find anything wrong with the suspension/brakes and say the rearend itself would never make a noise like this. Their best guess is a brake pad moving around or the caliper somehow compressing from heat (rapidly though?). It does sound drivers side though. Is it possible that the internals of a shock make a repeated thumping/tapping noise? Besides swapping the shocks out for cheap part stores ones or replacing the calipers, I don't see what else to try. The brake pads are right in the calipers though and they don't drag - both sides work great and were in great shape when taken apart and rebuilt.

It sounds/feels like the rear going over a near flush railroad line. It has a "thump"/pop/whatever noise that speeds up with speed. 30mph seems to be as rapid as 50mph which is about as rapid as 70mph. Idling around at 5mph makes it thump about 2-3 times a second. It's a continuous popping noise at the above speeds. It can be felt through the floor pan. Occasionally it feels weird when the transmission shifts up/down (I have the pressure set higher than stock and it jolts the car a little when it shifts).

Help? No one can seem to help me. Everything was nice and tight when we put it up on the lift. Nothing was moving or rubbing. It also was fine jacked on the rear end and using a creeper.

TC rearend - "grinding" noise

Reply #9 – August 28, 2009, 07:19:21 PM

Is anything contacting the drive shaft?

TC rearend - "grinding" noise

Reply #10 – August 28, 2009, 11:40:02 PM

Nope, not the exhaust, not the parking brake cable, not the floor pan. It has clearance all around, as do the wheels. The sound comes from the drivers side as it sounds like both in the car and with someone standing outside and listening to me drive by at 5mph. This is what led to us lifting the car up from the rearend and on a lift but we still could not find anything contacting. This guy I did this with works on dozens of Mustang a month, ranging from all kinds of installs of everything. He was clueless as to where it was coming from.

The driveshaft "harmonic balancer" thing did have one loose bolt but it wasn't the problem. I also don't have a center bumpstop on the car. My car does have two rubber ones on the sides where the axle housings would hit. Driving on smooth ground at 5mph it doesn't move though and it wasn't close to contacting when we had it up in the air.

TC rearend - "grinding" noise

Reply #11 – August 30, 2009, 09:59:53 PM

This is a dumb question... I don't know what rims you run, but could there be something inside your center cap rolling around? I once had a grease cap fall off and roll around inside my 10-hole rim's center-cap-area. Made a wierd noise like that.

TC rearend - "grinding" noise

Reply #12 – August 31, 2009, 01:48:09 AM

Snowflakes and this is the rear - the only thing back there are lugnuts and the center cap. We've been doing the rear end swap/suspension/rear disc brakes so we've had the entire thing apart a few times and know what's there.

It only starts after driving around for about 5 minutes. 10 minutes and it's there whenever I'm going 5mph also. I'm out of ideas.

TC rearend - "grinding" noise

Reply #13 – August 31, 2009, 02:23:57 AM

I'm sure you checked this, but, are your lug nuts all tight? The wheel could be popping back and forth...

TC rearend - "grinding" noise

Reply #14 – August 31, 2009, 09:03:50 AM

Yes they are. This has happened both before and after pulling the wheels off many times. Know of any shops that have something like an in-air dyno that this could be detected on?