wolverine8490

Just had a few questions about the rear diff on my 96 GT. I have had a light vibration coming from the year of the car for about a year now. Also, I have this squeal/moan coming from what I believe is the rear of the car when I make low speed turns. The other day, I jacked the back wheels up off the ground and spun the tires. THey both spunt he same way as each other, so if I turned the one like I was going forward, the other spun forward as well. The only reason I thought this was weird is because my buddys 98 cobra spins opposite of each other. Just wondering if all of these noises and symptoms are related.

max427

the fact they spin the same way is normal, it does this because its not an open diff, when power is sent thru the pinion to the ring gear power is distributed (in a perfect world) evenly to each tire. in an open diff power is pretty much sent to the wheel with less traction. read up on how a differential works it should clear things up a bit. i would think a 98 cobra should do the same thing tho. anyway, as far as vibration/noise on turns. lay underneath and spin the driveshaft a few times checking for dents or knicks in the shaft, thats a very common cause of driveline vibration. otherwise the vibration could be improper pinion depth causing improper mesh of the ring/pinion, more wear on diff components and could even cause your moan noise.

max427

btw- if the driveshaft appears to be fine you can have you differential rebuilt and throw some lower gears in it too! say 4.10's ?
* check wheel balance and tires first and foremost!!

wolverine8490

Yeah, I had 3:73's installed about 8 months ago. I am wondering more and more if the install was not 100% on. My buddy installed him, and he is really good with chevys as well as he is a master ASE cert, but I wonder if something has gone wrong.

I have a driveshaft out of my buddys car that I want to put in to see if that changes anything, but when I jacked the wheels off the ground last night and turned them, there was one spot that made a noise when the wheels turned. That is why I think something inside the differential is the issue.

Strangest thing is when I parked it for the winter, I did not have a big issue. I did hear the moan noise, and a slight vibrtion from the rear, but nothing this bad.

max427

wait spinning the tires by hand u hear a noise? i would guess a rotor/brake issue, not something internal. if u can hear something clearly inside the diff at 1mph spinning diff unloaded, then by 20mph loaded the noise would be unbearable. on common thing ive seen is pinion bearings get trashed. put the rear on jackstands and run it at like 40 and listen underneath (safely, of course) or after a drive feel around the pinion or at the axle tubes where the side gears would be, if any one spot seems abnormally hot, theres you problem.

max427

i guess i should add that with a limited slip diff both drive wheels technically want to be at the same speed, so on turns the outside wheel speeds up greatly while the inside wheel slows down, cause a big diff in speeds between the two and the differential (<-- get it, DIFFERential) has to make up that difference. some noise while turning is normal, but it should be tire noise.. like a tire skipping, squealing.
maybe your diff has a locker in it. have u owned it since new?

wolverine8490

Yeah, I have a known good spare driveshaft that I am going to throw in to see if that helps.


This is what I think my issue is. I really hope not, but for some reason, I think it sounds like the noise is coming from the pumpkin.

No it was used when I got it. My buddy and I have been in it and it looked to be all stock components. When I eliminate the driveshaft, and anything else on the outside of the pumpkin, I am going to pull the cover off, and see if I see any metal shavings. I am just hoping it does not come to that.

Thanks for all the help and the explaintion of how it works! I never really did understand differentials.

max427

no prob, a rebuild wouldnt be too expensive, and besides that you could grab an 8.8 out of like anything in the junkyard lol. exploders, E/F-150s, stangs, town cars, crown vics. some probably with shorter gears too.

ezking

What brand gears did you have installed? Motives have had some feedback on making noise. I got frpp 4.10s and haven't had any of those problems although you can't hear much in my car. Check for shavings asap, or maybe the clutches in ur traction lock have gone out.

If you decide to rebiuld, 99+ stangs have a slightly wider housing with slightly longer axles that might b pretty desirable.

But if ur gonna do all that u might as well grab a locker and go 36 spline over the stock 28. Anyone driven a car with one of those elockers? I wanna feel one in action.

max427

it really does depend on the locker you choose, but you do sacrifice a lot around corners and daily driveability. i would compare it to driving a 4x4 on dry pavement, a lot of wheel hop and imo, unpredictability in corners.