[grivera]

So here’s the issue - the 64 Lemans has a vibration dependent on RPM - 2100 rpm and above. Doesn’t matter what gear it’s in but more noticeable at cruising speeds as that is when I spend more time at that rpm. It has low mileage (~1K miles) TKO600, new bell housing dialed in with off-set dowels, new clutch/pressure plate/TO bearing. Tires recently balanced, new 3.5” driveshaft too.

Is this likely caused by an out of balance rotating assembly (see below)? What testing can I do to isolate the issue and determine next steps?

Background - When the prior owner (Steve) acquired the car back in 2018, it already had the 400/461, JBP balanced rotating assembly, 4.25" crank, h-beam rods and Ross “dished pistons for 9.5 compression w/72cc heads” according to the invoice from 2010 (Piston part # TSR-CR0690-35). Because an examination of the engine revealed damaged ring lands, Steve opted to have it rebuilt with new pistons/rings, all new bearings, HR cam all purchased through JBP. The new Ross pistons have a -29cc dish as the engine retained the 72cc #16 heads. When I do the math with current set up, I come up with about 9.36 compression.

The fella who assembled the engine did NOT have the assembly balanced. I’ve sent both the original invoice from two owners ago and the most recent invoice for the -29cc pistons to Butler as the only thing that changed in the assembly were the pistons/rings. Based on info provided, tech support said the dish on the original pistons would have been -30.5 to achieve 9.5 compression vs the new pistons at -29cc and the balance shouldn’t be far off. Wallace Racing calculates the old pistons would have to be -27 cc for 9.5 compression but I may be missing a variable.

[steve25]

And out of gear with the car stationary does the motor vibrate above 2100?

[grivera]

Originally Posted by steve25

And out of gear with the car stationary does the motor vibrate above 2100?

I have yet to do a good job with that particular test but will do so this upcoming weekend. I did try that with clutch depressed/RPMs up while at speed and it wasn't helpful in feeling the vibration.

[ponjohn]

Was the bellhousing indexed?

[Scarebird]

I would bet your driveline angles are off - TKO's don't fit too well in A bodies.

I chased this issue for a couple years, finally chopped the floor and raised the rear of the trans - it made it better.

A driveshaft with a CV joint in front may solve this.

[grivera]

Originally Posted by ponjohn

Was the bellhousing indexed?

Yes - using off set dowels

[grivera]

Originally Posted by Scarebird

I would bet your driveline angles are off - TKO's don't fit too well in A bodies.

I chased this issue for a couple years, finally chopped the floor and raised the rear of the trans - it made it better.

A driveshaft with a CV joint in front may solve this.

Wouldn't a driveline angle issue be dependent on MPH vs RPM?

If I'm calculating correctly, my angles are in check based on my digital angle finder but I'd be ecstatic if its as simple as driveline angle...

[Greg Reid]

Originally Posted by steve25

And out of gear with the car stationary does the motor vibrate above 2100?

This is the first thing I wondered. Seems to me if vibration is internal to the engine you should be able to feel it sitting in your garage in 'Park' by revving the engine up to that RPM.

[grivera]

Don't want to get ahead of myself but assuming there is vibration during static revving of the engine, what other external components would be suspect? Clutch cover? Flywheel?

[Gach]

Originally Posted by grivera

So here’s the issue - the 64 Lemans has a vibration dependent on RPM - 2100 rpm and above. Doesn’t matter what gear it’s in but more noticeable at cruising speeds as that is when I spend more time at that rpm. It has low mileage (~1K miles) TKO600, new bell housing dialed in with off-set dowels, new clutch/pressure plate/TO bearing. Tires recently balanced, new 3.5” driveshaft too.

Is this likely caused by an out of balance rotating assembly (see below)? What testing can I do to isolate the issue and determine next steps?

Background - When the prior owner (Steve) acquired the car back in 2018, it already had the 400/461, JBP balanced rotating assembly, 4.25" crank, h-beam rods and Ross “dished pistons for 9.5 compression w/72cc heads” according to the invoice from 2010 (Piston part # TSR-CR0690-35). Because an examination of the engine revealed damaged ring lands, Steve opted to have it rebuilt with new pistons/rings, all new bearings, HR cam all purchased through JBP. The new Ross pistons have a -29cc dish as the engine retained the 72cc #16 heads. When I do the math with current set up, I come up with about 9.36 compression.

The fella who assembled the engine did NOT have the assembly balanced. I’ve sent both the original invoice from two owners ago and the most recent invoice for the -29cc pistons to Butler as the only thing that changed in the assembly were the pistons/rings. Based on info provided, tech support said the dish on the original pistons would have been -30.5 to achieve 9.5 compression vs the new pistons at -29cc and the balance shouldn’t be far off. Wallace Racing calculates the old pistons would have to be -27 cc for 9.5 compression but I may be missing a variable.

It’s possible and out of balanced or bent drive shaft. One thing that might help, Jack it up disconnect the driveshaft. And see if there’s vibration. Had that same issue with my buddies 64, turn out to out of balance driveshafts. could also tell you with it discounted if its in the motor or trans

[grivera]

The driveshaft is completely new - bought it cause I thought the vibration was coming from the original driveshaft. The vibration is RPM dependent, not speed dependent which should rule out the driveshaft.

[Gach]

Gotcha

[sdbob]

I had a vibration in my 65 Lemans yrs ago. Drove me crazy. It was a bent axle housing tube. The axle was tight coming out.

[62posbonny]

Do you possibly have a stock balance flywheel on a neutral balanced rotating assembly?

[grivera]

I’m not sure about the flywheel but will look into that possibility.

Edit- here are screenshots from Modern Driveline - invoice- first page indicates crank zero balance and second page is the part number for flywheel and basic description. Not sure if it’s the correct application but I can contact MDL tomorrow.

[Murf]

When you do your “stationary testing” try it with & without the belts on. It’s worth a shot.

Good Luck!
Murf

[OCMDGTO]

How about something simple like bolts backing out of fan to water pump or pulley to balancer? I've been there

[grivera]

Originally Posted by 62posbonny

Do you possibly have a stock balance flywheel on a neutral balanced rotating assembly? The one on the engine is stock type.

Does the harmonic balancer play a role in this equation? This is the link to the flywheel and no indication if it’s for internally balanced:

https://www.moderndriveline.com/shop...wheel-326-455/

Originally Posted by Murf

When you do your “stationary testing” try it with & without the belts on. It’s worth a shot.

Good Luck!
Murf

will do

Originally Posted by OCMDGTO

How about something simple like bolts backing out of fan to water pump or pulley to balancer? I've been there

Good points

[PDC]

Originally Posted by 62posbonny

Do you possibly have a stock balance flywheel on a neutral balanced rotating assembly?

I would definitely check this. I ran into this doing a TKO swap (shipped with a neutral balanced flywheel) into a factory auto trans car with an externally balanced flex plate. A machine shop matched the flywheel from the TKO kit to the external balance of the factory flex plate and all was well.

[JLMounce]

Often overlooked is the combination of engine and trans mounts. What does the car have in it? If it's got a poly trans mount with rubber engine mounts, this combination can cause vibration. Recommend either replacing the engine mounts with a poly setup if this is high performance, or if there isn't a real issue with needing more solid engine and trans mounting, put a factory rubber mount under the transmission.

I recently had this come up with my 4l80e swap. Changing the trans mount made a huge difference.