Slight driveline vibration after trans. swap.

[GTS Dean]

I had a bad synchro or blocker ring in 3rd gear, so I swapped in a known good transmission, put some new u-joint straps on and went for a spin. There's now a minor shifter vibration under accel/decel above 3k engine rpm. No vibe when declutched. Prop shaft was indexed to the diff yoke pre/post. I tried loosening the rear mount and sliding the trans to the side a touch but no improvement. There is a little more room. I'm running IPSCO shifter, trans x-member, Engergy trans bushing. Throw-out bearing and pilot bushing are in good shape, as is the clutch. Motor mounts are reasonably new OEM and I don't wheel hop the car at all.

I picked up a couple of worm hose clamps to try an external shaft balance, but that would seem unnecessary given that it wasn't vibrating at all before.

Any ideas? I have a race next Fri/Sat and need to sort out this weekend.

 

[daveg]

Get vibration in every gear above 3k?
Just trans and no clutch / Flywheel work?
Do you feel the vibration in your ass (seat)?

 

[Old School]

Since the new thing is the transmission, maybe it's a loose tail housing bushing. Is the driveshaft yoke loose in the trans?

 

[GTS Dean]

Dave, just a straight-up transmission swap. I went thru all those other parts about 4500 miles/3.5 years ago. Most of the driving has been street/highway with 4 events at COTA, 1 at Road America.

Mike, it felt perfect going in but I am considering that. I think I'll start with 1 clamp on the transmission side to see if it helps or hurts because it's the easiest thing to try. Belly pan is already off and I have a 4 post.

 

[daveg]

.... maybe it's a loose tail housing bushing. Is the driveshaft yoke loose in the trans?

Thats was going to be my next thought if it was just Trans. Grab the front yoke and see if it moves up / down, left / right.
Also make sure the rear driveshaft is seated in the rear-end yoke.

 

[GTS Dean]

No play at all in the yoke. I put one hose clamp on, drove it 4 times with it indexed 4×90 aligned with the u-joint ears. The #2 was maybe a tad better, but not significant. Seems to synch with rear tires in 4th gear a bit, and they need balancing.

 

[daveg]

So next step is to Balance Tires?

 

[Old School]

Got another set of tires to try?

 

[GTS Dean]

I went out this morning and scrubbed the marbles off the A7 rears, then drove by Discount and made a will-call appointment to have them balanced. I don't recall the vibration with my street tires, but didn't drive very many miles on them since the trans swap before mounting the Hoosiers.

 

[randyzimmer]

Vibrations will be caused by misalignment of the two shafts at either end of the driveshaft. The the engine/trans and diff need to be parallel on both planes. Maybe the rear trans mount is too high or too low or the tail is too far left or right. Good luck with this, vibrations can get maddening to find and fix.

 

[Tom and Vipers]

Since the new thing is the transmission, maybe it's a loose tail housing bushing. Is the driveshaft yoke loose in the trans?

I had to replace my 96 GTS bushing around 80k miles. But I never experience any vibration.

 

[GTS Dean]

There's no more tire-induced vibration, but the shifter still has some harmonics in it. Time's up and I'm going to run it as-is.

 

[GTS Dean]

Back from Hastings with no change in the vibrations. Have only just started post-event inspection and nothing out of sorts. I will try loosening the motor and trans mounts, get the floor jack under the oil pan and lift gently to resettle - same with the trans, then re-torque all 3 fasteners and give it a run.

 

[KyViper]

When I was working on Aircraft, chasing vibrations was a bundle of fun. We did have a very useful tool (Chadwick) that was primarily made to balance props. Part of this unit was a sensor that would pick up the Vibration and give it a frequency (RPM). Then you could take the unit and dial in a given RPM and see if that was the origination of the Vibe. Of course, this was a lot more exacting when you knew the rpms of the suspected cause. On Aircraft engines with accessory gearboxes that could have several rotating components we could get the manufacturer specs and match the accessory speed to the engine RPM and Bingo. This was very successful.
If you really want to nail this Vibe, then maybe researching local area to see if anyone has this equipment and put Her on a Dyno to hunt down the Frequency you could marry that up to the source.
I know this is a lot, but Vibes can drive some people crazy. (especially Pilots).
Ky

 

[Dan Cragin]

Are you running an aftermarket trans mount?

 

[GTS Dean]

Yes Dan - Energy. No vibration issues with 2 previous T-56 boxes. I've had this bushing in the car for 25 years with a near-stock driveline. No damage to it.

Original (Trans #1) got the Ipsco shifter about 4500 miles ago. Had tunnel interference troubles until I bought the Ipsco rear x-member. Went 2.5 years and broke a Gear 4 synchro, so swapped in an unknown take-out (Trans #2) and used the stock shifter with same bushing. For a year, it had Gear 3 issues, so I swapped in the 20k (Trans #3) straight from my '98 parts car and installed the Ipsco shifter and x-member. Had to jack the motor around along with the trans jack to get it to slide into the FW bushing. Was not in a bind to install/tighten the bolts to bellhousing. Shifts perfectly, but has a small accel/decel shifter vibration. I have not yet loosened and retorqued all isolators yet.

 

[Dan Cragin]

Ok,
I experienced some engine vibration with these aftermarket trans mounts
on the Gen 2's, more so with the metal plate installed under the mount.
Solid or high durometer engine mounts make it worse.

Do you feel the vibration in neutral with rpm?

 

[GTS Dean]

No, only under load. It does NOT have the preload plate installed.

 

[Dan Cragin]

It could just be the nature of that used trans, in a different car.
You just never know with used parts.

You might want to have the driveshaft sent out and checked for balance.
I had a couple on racecars that bent the shaft , causing a vibration.

 

[GTS Dean]

If necessary, I can try the other one since it's laying within 4' of my car.

 

[Old School]

Have you checked the U-joint angles? Moving the tail housing up/down will change them. The angle of the u-joint in the front needs to be the opposite of the one in the rear.

 

[GTS Dean]

It's the same as it was.