Swapped to a SRA now have a VIBRATION

[MG01SVT]

As stated, swapped to a SRA. Yes, I tried searching.
Parts on the car: FMS diff, moser 31's, alum DS, Steeda LCA's and Stock UCA's.

Initially, after the swap, I would get a noticeable vibration around 80 mph. Was wheel speed related only. I had the DS rebalanced and that problem was corrected. Now, the vibration occurs at about 120 mph and when I push the clutch in the shifter vibrates really bad. Gonna try turning the DS, but suspect Backlash run-out. Just checking for any other ideas before I open the diff. Keep in mind I had no issues at all pre-swap.

Thanks very much for your assistance

Aaron

 

[mblgjr]

If you can clutch and the shifter still vibrates you have a few possibilities.

1) Clutch disc coming apart/slung friction material off.

2) Driveshaft is still out of balance (or lost a weight)

3) Recheck your pinion angle. If you've lowered the car 1.5" or greater you'll need adj. UCA's.

If it vibrates as bad as you say, reindexing the shaft prob. won't fix it.

 

[MG01SVT]

thanks for the suggestions. My car is lowered way below 1.5". Guess I'll try some adjustable UCA's.

Thanks again

A

 

[mblgjr]

Don't just buy parts and throw at it (though properly adjusted UCA's will prob. fix it).

Check your pinion angle first.

 

[MVD]

Did you index the driveshaft during the swap?

 

[mblgjr]

Did you index the driveshaft during the swap?

Because the rear pinion was either A) New or (B) swapped from the IRS to a solid utilizing a different pinion; it doesn't much matter whether it was or wasn't.

Had he been taking the shaft out/in on the same flanges; yeah you'd keep it indexed.

 

[MVD]

Because the rear pinion was either A) New or (B) swapped from the IRS to a solid utilizing a different pinion; it doesn't much matter whether it was or wasn't.

Had he been taking the shaft out/in on the same flanges; yeah you'd keep it indexed.

Apparently you are clueless.

A) New pinion flanges are indexed to the driveshaft also (even from the factory).
B) If he swapped the old flange to the new axle and it was indexed everything would be fine.

 

[P49Y-CY]

^ isn't the pinion flange index more of a result of the overall balance of the differential/gears?

or are you saying that the flange index is balanced to the driveshaft, and even a new axle would still be in balance to the driveshaft as long as the pinion flange is reinstalled the same way relavtive to the driveshaft?

i am curious about this as i am getting ready to put my irs back in, but while it was out i had the differential overhauled and a trutrac differential put in; i asked the drivetrain shop to mark the flange so i could reinstall it the same way it came off the car, but i was thinking it wouldn't matter because the entire center section was rebuilt. (although the ring and pinion gears were in good shape and reused) they didn't have too much to say about it, sort of like it wasn't going to affect the balance of the driveshaft

thx for any info

 

[mblgjr]

^ isn't the pinion flange index more of a result of the overall balance of the differential/gears?

Yes, but once it's been removed and retorqed onto another pinion I've seen them change. I suppose just tolerance stackup and being torqued down differently, etc. etc.

or are you saying that the flange index is balanced to the driveshaft, and even a new axle would still be in balance to the driveshaft as long as the pinion flange is reinstalled the same way relavtive to the driveshaft?

The pinion flange and DS do not get balanced together "as a part". Every DS assembly balances out different and has different runout, so if you pull one and reinstall another, they may want to be in different positions when installed on the same flange. I'm not quite sure what you were asking here because of the "axle" comment.

i am curious about this as i am getting ready to put my irs back in, but while it was out i had the differential overhauled and a trutrac differential put in; i asked the drivetrain shop to mark the flange so i could reinstall it the same way it came off the car, but i was thinking it wouldn't matter because the entire center section was rebuilt. (although the ring and pinion gears were in good shape and reused) they didn't have too much to say about it, sort of like it wasn't going to affect the balance of the driveshaft

It sure didn't hurt anything ;-)

thx for any info

:beer:

 

[mblgjr]

Apparently you are clueless.

A) New pinion flanges are indexed to the driveshaft also (even from the factory).
B) If he swapped the old flange to the new axle and it was indexed everything would be fine.

Why thank you. :lol:

Pinion flanges are not balanced with the driveshaft assembly at the factory. The entire rear axle assembly gets installed "complete" and as a unit as the car comes down the line. Engine/trans/driveshaft and rear axle all get lifted in together.

The shafts *DO* typically get paint-marked once assembled; thus 'creating' a starting index mark.

Would the guy have been better off keeping the index between axle assemblies? Yes. Is it the end of the world, no. Can the runout change once you've untorqued it from one pinon/axle assembly and moved it to another (which he did)...yes.