8 3/4 Help

[rowdymopar]

8 3/4 from 67' GTX recently rebuilt new bearing clutches & went from 323 gears to 355 now haveing slight growling sound & vibration comming from Diff area at around 75- 80 MPH any suggestions & or comments on what it could be, ??

 

[1badgtx]

Is the new gears in a 742 case?I would recheck the torque on the pinon nut first..You can also block the wheels and put the car in neutral ,shake the driveline next to the third member to check for anything loose that way..Could be the pattern for the ring gear is not correct..
Petty Blue 67 gTx

 

[blackblazer717]

Also, some ring and pinions are naturally loud by design. Depending on where you got the gears frkm. Or your pinion depth isnt correct, and/or the nut has backed off. This is common when using a
"Crush proof" crush sleve thats for bearing preload.

 

[Cranky]

If pinion depth isn't correct, you will generally have noise on acceleration or coast depending if the pinion is too shallow or too deep. If your back lash is way off, that could be your problem. If the pinion nut is tight, check to see how much rotation the yoke has in relation to when the wheels move. If you have more than about 20* rotation, it's too much.

 

[rowdymopar]

it is a 742 case I barrowed a good snap on torque wrench from a mechanic at work & started at 100 ft.lbs. on the pinion nut , it was way loose . worked my way up & tighted it to 240 ft. lbs as stated in FSM test drove on a country road upto 80-90 MPH & it seems alot better no noticeable sounds at speed but did notice as cranky said a noise at coast. need to take it onto a smooth patch of interstate tomarow & see what I hear & feel but initial response was posative. About 1 year ago i installed the 355 gears , bearings & clutches,ect. had it nearly perfect but could'nt get the tooth pattern 100% perfect , so I took it to a local mechanic weekend racer dropped it off 2 hours later he calls me to pick it up , he said my pattern was fine ( if he even checked it ) & charged me $50.00 I looked down in the box I had brung with it had extra shims & pinion seal,ect. I had ended up with 2 seals somehow ?? also had the actual pinion beraing because I spent the extra bucks for a set up bearing . I noticed both seals still in the box & asked if he installed one he had laying around he trys to blow me off & says yea yea yea I asked him again & said the seals were still in the Box. ? Oh OH ?? the genious forgot to put it in & then installed it & just slapped the pinion on with his impact & said it would be fine ( He's built 100's of Ford 9 in. race car Diff's before ) ( I beat he his cars havent won many races ) then got too looking i noticed he left the set up bearing in the Diff . he said it's fine he does it all the time ( now the set up bearing still had to be pressed on & off with a Shop press so it was'nt like it just slid on & off by hand ) but still had me conserned, this guy was & is a real winner . No wonder I end up just doing things myself .