We have been trying to track down a noise problem that being transmitted through the body and floorboards of our 1986 Trans am with a Moser 9" ford rear. We have Spohn torque arm and crossmember. When you start taking off in it, even at slow speed down a gravel road, you can here the noise start being transmitted through the car, it's hard to describe, but sounds similar to driving a big dump truck or something, that has alot of drive line noise. Another way to describe it is similar to a locked up fan clutch. It doesn't sound like a typical rearend gear howl, although you can detect a little slight howl when letting off the throttle at cruise. It is a Moser 3.062" Nodular case, US/Strange 3.50 gear set, and a Detroit TrueTrac carrier for 31 spline axles.

We checked the gear oil earlier today, and it has a bit of metallic in it, so we think maybe the noise that's being transmitted through the car, is indeed coming from the rearend. We went ahead took the third member back out awhile ago, and want to see what you think about how the gear pattern looks after being ran, it's only been driven just a few times, maybe 1/2 mile at a time, just down the road and back. The noise makes the car feel uncomfortable to drive, as it puts a "rough rumbly" feel through the floorboards/seats/transmission tunnel, it's not really a bad vibration like an unbalanced driveshaft or anything like that, just a doesn't make for a smooth driving car like it was factory. Makes it feel more like a drag car, not a street car. We built the rearend ourself, and used our T&D setup tool to setup the pinion at the right depth, we ended up with .046" shim to get it too 1.023" pinion depth, although the US/Strange gears said to set it st 1.025" + or - .002". 1.023" seemed to get the best gear pattern when we initially put it together, so thats what we left in it.

Another thing we thought of, is the Detroit TrueTrac may have something going wrong with it, but you cant see the internal gears in it to tell anything about it, but it still functions correctly

Although I can't remember for sure what brand of gear oil we ran, I do know it is a conventional 80w90 gear oil, probably Oreilly brand, but not 100% sure. I wanted to include a couple pictures of our ring gear after its been ran just very few miles, less than 10, to see what you thought about them and maybe see what y'all think is putting all the noise through the car. The first picture is the Drive Side, the 2nd picture is the Coast Side

Thanks!

 

Do you have any gear marking compound to put on it?

 

Looks like he used the white stuff, uee the yellow. From the looks of it, the pinion is too deep, the pattern is all down to the root of the gear.

 

I see very little marking compound, if any, but I don't see the pinion being too deep. I'd like to see it with marking compound on 3 of the ring gear teeth and rotated several times in both directions so that the pattern shows well.

 

Thanks guys, we took it to a local shop to us that builds them for a living, and he said it looked like it was setup real close already, and said there wouldn't be any reason to have him set it up again, it turns smooth as glass, can't tell anything is wrong with it at all, it did only have about .0085" backlash, so what we did was add .002" pinion shim and brought the pinion depth to a 1.025", from the previous 1.023", since that was what the pinion said to set it up at, and we rechecked backlash after doing that, and it had about .011-.011.5" backlash, that what we were shooting for, so we left it there, we already put it back in and filled it back up with Lucas 80w90.... we will see what happens when we drive it.... you could not ask it to turn any smoother, we put the wheels back on it, and we spun it using the wheels before we put the driveline back in it, sounds good, can't hear nothing out of the ordinary. We are starting to think it's something in the transmission, and the local guy I took the rearend too, also agreed, that the noise I described to him, he said it sounds more like a transmission problem than a rearend problem, maybe either too tight of end play somewhere, or a planetary or bearing going bad in there... that's the next step. I appreciate your help

Brian

 

Well..... I just wanted to give an update..... we drove the car after putting the third member back in it, and still had the noise like driving a "dump truck" , just alot of driveline noise....but the rearend is quiet, it sounds good, so we thought we would double check our driveline and pinion angles before taking the transmission back out, and we finally found the problem! We are not experienced at setting the pinion angle, but we thought we went step by step setting it back years ago, but found that it was totally wrong, pilot error Lol. What we did before was measured the angle of the output shaft on the trans, which was 3.5* on the left side of the 0, reading the gauge from the drivers side, and adjusted the pinion angle to the same 3.5*(equal but oppisite), and then adjusted the pinion back down 1.5* from there to get our negative, so that it would run straight under load. The only problem is, when we adjusted the pinion to 3.5*, it was on the opposite side(Right Side) of 0 reading it from the drivers side, instead of on the same side(Left Side) of 0 like we were suppose too!! And then when we put the extra 1.5* negative in it, it read 5*!! So if my calculations are correct, we had it adjusted -8.5* from 0 angle!!

I found a neat little app on my android Note 4 phone, it is available also for IPhone. It is called Tremec ToolBox, and it has a digital angle checker that tells you if your angles are within correct operating range or not, it takes the angle off the trans output shaft, the angle off the driveshaft, and the angle of the pinion and calculates them, and if any numbers come out red, something is wrong and has to be adjusted, if they all come out green, it is within correct range and will be fine. It's super easy to use, and requires no calculations at all, it does it all. I checked ours with that too, before we readjusted it, and sure enough, 2 of the 3 angles were in red. So we took our cheapo analog angle finder, and checked the transmission tailshift, it was 3.5* on the LEFT side of the zero from the drivers side, meaning the motor and trans are pointing down towards the floor 3.5*. I then took our analog angle finder and put it on the flat plate on the bottom of the torque arm, and adjust the pinion all the way back up until it went back to 2.5* on the LEFT side of the 0 reading it from the drivers side, that should give us -1* pinion angle from 0*. I double checked it with the Tremec app I mentioned earlier, and sure enough, all of our numbers came back green, so it showed it was now within the correct operating range!! The car is completely different again now, all of the driveline noise is now a thing of the past, we are histatic!! We've been trying to figure out this noise for years! Now, in saying that, this is a project car, so we don't get to work on it often, it doesn't get driven much yet. We can still feel some resonance through the floors and seats from the Aerochamber muffler, but we hope to fix that too, we ordered a new Magnaflow crossflow muffler to replace it with, I hope it cures that..... it crazy how much driveline noise a car can make when the driveline angles are incorrect!! We won't make this mistake again, that's for sure!

Thanks for the help

Brian