Fox Vibration After Gear Change

[Jim Wilson]

I just went from 3.08 to 3.73. Around 60mph I am getting a vibration when I let off the gas or push in the clutch and coast. I measured the backlash at .11 and had about 25 inch pounds on the pinion preload. I replaced everything in the rear bearings, seals, and races. Any ideas? Im going to try to turn my driveshaft as Im not 100% sure I got it back to the exact original location on the pinion flange.

 

[mikestang63]

Your driveshaft could be out of balance now and going to a lower gear will emphasize this. Try mounting it 180 degrees and see if that fixes the problem. If so, mark the driveshaft and rear end flanges so you will know which side goes where. Normally, There is a yellow dot that tells you which side goes where.

Couple of things if that doesn't work

what was the tooth pattern on the coast side of the gears
was the pinion gear depth set correctly.
The crush sleeves are a PITA - can you tighten the nut more with an impact
Pinion angle should be about 2 degrees
Check the weight on the rear end- is it there and tight
output bushing on the trans that support the driveshaft yolk- do you have a lot of play in the front yoke

 

[Jim Wilson]

I am gonna pull the driveshaft off this weekend and recheck the pinion. I will check the pinion angle. The coast side pattern was toward the center of the ring gear but not all the way to the center. The drive side was almost center. Where is the weight on the rear end? I will check that and the front yolk. I will update this weekend. Thank you mike

 

[Jim Wilson]

On the coat side. By center i mean the inside of the ring gear. The drive side was almost centered in the ring gear

 

[84Ttop]

was the pinion gear depth set correctly.

This is my guess. How did you check the pinion depth?
x2 on tightening the pinion flange with the impact

 

[7upstang91]

Agreed with Mike. Same thing happened to me after my gear change, only the shop that did the change didn't tighten the bolts on the driveshaft all the way. They ended up backing out causing the vibration.

 

[LX302]

My bet would be the backlash is fine. I agree with Mikestang63, check the driveshaft first. I had the same isssue when I went from 2:73's to 3:55's, installed an alum. driveshaft and smooth as glass.