wrd1972

iTrader: (12)

Cruising around 75-80 MPH on the interstate, if you just barely give gas or let off gas, around that spot where force applied to the drivetrain is near zero, I get a quick rumble strip sound and vibe that is very annoying. It is especially noticable on cruise control like when cresting small hills and the driveline becomes slack for a moment.

The rumble strip sound and vibe occurs for only a split second, again transitioning between accel and decell. The vibe is felt in the floorboard and in the seat.

Similar vibe occurs when at 80MPH and you simply hold the clutch to the floor.

All other driving conditions are vibe free and smooth as silk.

Thoughts.

SS RRR

iTrader: (2)

Could be a backlash issue between the ring and pinion gears. Mine does it as well. If you have an adjustable T/A then check the pinion angle as well as making sure it is not shifting under torque.

wrd1972

iTrader: (12)

If its backlash, guess im living with that however it feels normal by turning the yoke. I checked the driveline angle and even made a couple of adjustments, still there.

Seems like slop of some kind but ONLY when force applied is minimal. U-joints feel fine installed but I am going to pull the DS for closer inspection of them.

96LT1355Z28

iTrader: (2)

I took my DS to be looked at for a similar vibration. They "rebalanced" it and it didn't solve my problem. After spending ALOT of $ chasing the rest of the driveline and still not finding it, I took the DS to another shop. Thy checked it for straightness and again balanced it. That took care of it. I say take the DS to a reputable shop and have it checked for balance and straightness, and a new set of u joints can't hurt. My vibe came on about 70-75 and increased with mph, when the clutch was depressed it nearly doubled. Second shop charged me $95.

Kevin97ss

I seen something the other day that I never noticed before. There is a rubber bumper on the top of the trans that; on my ride at least, is in full contact with the trans tunnel. The MWC crossmember put the trans as high as it could go and has nearly fully compressed that bumper. Possible you may have the same situation and a vibe that may normally not have been felt or absorbed by the trans mount is being transmitted in to the tunnel.

You can see the bumper in this pic between the top plate and shifter.
http://www.5speedtransmissions.com/T56_97_Camaro.jpg

bowtienut

iTrader: (1)

I don't know how your 9" sets up, but your symptoms are classic of pinion shuck, the pinion moving fore and aft in the bearings when unloaded.
It's common on crush sleeve setups that are botched.

Kevin97ss

I think Eric sets up all his 9in builds with a solid spacer.

ShaggyLT1

A loose pinion nut will cause this problem. I had he same symptoms in the past. Disconnect the DS and check for play at your pinion.

bowtienut

iTrader: (1)

Anything that fails to keep the pinion bearings loaded can cause it - it doesn't have to be a crush sleeve setup.
As Shaggy alluded, any play in the stack can cause it.

wrd1972

iTrader: (12)

Hmm I will check that. Thanks.

MWC set these gears up and I was told that a solid spacer was installed. Pulling the pinion support out and checking preload is on the list.

I also found that the rear u-joint had a notches likel from not enough operating angle. I replaced it and really noticed no improvement. Front one felt perfectly fine.

Looking at the pinion preload is likely next on the list.

wrd1972

iTrader: (12)

Hey a question for you guys on driveshaft balance, just wanna rule it out.

80MPH, push and hold the clutch, get a vibe and rumblestrip sound.
80MPH, lightly transitioning between accel and decell, vibe and sound.
80MPH, any positive or negative load applied to driveline, silent and totally vibe free.

Does this indicate that the balance of the shaft is fine?

bowtienut

iTrader: (1)

That indicates the driveshaft is fine.
It still sounds like you have freeplay between the pinion bearings. Loaded either way, it's fine. Unloaded, it shucks. Common, classic case.

bowtienut

iTrader: (1)

Unfortunately, that's not the way to check it.
Pulling the ring gear out and checking the rotational torque on the installed pinion will give you the answer. You're looking for something on the order of 5 inch-lbs on a setup that has already been run. I've got a feeling you're going to see zero and may even be able to feel some play in the stackup.

Edit: Doh!! never mind.....I'm not thinking 9-inch

wrd1972

iTrader: (12)

LOL yeah its a 9" diff so pulling the pinion support for inspection aint too hard.

After getting the pinion support out, it seems obvious that the pinion preload is a little loose. It has some resistance when turning but my inch pound beam wrench says at best, its got 2-3 inch pounds of resistance and thats with the seal in place. Also after clamping the support in a vise, I can feel just a bit of wiggle when shaking the yoke, clearly not good but hopefully this is a smoking gun.

I guess I need to order a solid spacer kit for the 9" cause I doubt I can tighten the pinion preload without the shim assortment. I really hope that this is the problem.

96LT1355Z28

iTrader: (2)

A set of U joints is a cheap maintenance item that could also cause your symptoms.

wrd1972

iTrader: (12)

Done replaced them. No improvement.

Tbird232ci

iTrader: (4)

I had a similar set of symptoms with an 8.8 in a Thunderbird. In my case, the gear lube leaked out, and it caused my bearing to prematurely wear. I didn't catch it in time and the bearing let go. That sucked at 70mph.

Anyways, it is quite typical of slack in the pinion.

wrd1972

iTrader: (12)

Update,
I shimmed the pinion preload tighter and that fixed the original problem but now I have whine. Damnit. Previously, the setup was 95% quiet.

I ended up pulling .004" from the pinion preload shim pack and that tightened the preload to about 10" pounds. Of course this moved the pinion forward about .004" so I countered that by removing .004" of pinion support shim so the pinion would move towards the rear .004" and back into its original location with respect to tooth contact. Someone please confirm that this is correct.

Anyway now, I have whine all over the place at all speeds and if the tooth contact has been properly restored as illustrated above, I suspect the pinion bearings are shot (even though I saw no abnormal wear) and are simply not taking kindly to being tightened up. I can hear it on decal all the way down to 15MPH and it has a very loud spot on accel around 70MPH or so.

Well it looks like I am pulling the pinion support back off again.
Someone please confirm if my shim adjusting above is correct and if they thinks its only bearings.

Thanks.

fergymoto

iTrader: (129)

You should have left the pinion support shim in.

wrd1972

iTrader: (12)

Are you referring to the original thickness of pinion support shims? After thinking about that more, I think your right. I only drove about 10 miles on it so hopefully I did not waste the gears.