Drive Train Experts, T-3550 vs T-5


Founding Member
May 10, 2002
Hey guys – been a while since I’ve posted anything.
Got a confession to make, I’ve accepted defeat trying to complete the restoration of my Mustang myself. So it’s in a shop having the drive train installed.
It’s ’65 coupe with a 302 V8 and a Tremec 3550 5 speed. It’s suffered with vibration problems all the time I’ve owned the car, at pull away from a standing start. I’ve replaced the early motor mounts with the later ones, replaced the motor sport clutch with a ‘softer’ one and shortened the driveshaft. This has dramatically improved things. However the shop has told me that to correctly install a Tremec 3550 in a ’65 coupe the transmission tunnel needs to be reworked. If this is not done then the T-3550 angle will be wrong possibly leading to vibration issues. Mine has not been reworked. The T-3550 is touching the top of the tunnel. The shop has suggesting replacing the T-3550 with a World Class T5 which will fit in the existing tunnel. Thoughts anyone….
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well I can only speak for my experience, but I have a 3550 in my '65 and I did not modify the trans tunnel and I have no vibration issues. And the only reason I did not modify it was because of the same experiences other members have had deeming it not necessary.

What kind of vibration is it? when does it do it; certain rpms? certain speed? certain gear? on the gas? off the gas? in neutral?
Sounds like a clutch problem to me; nothing related to drivetrain. Does the vibration still happen when your foot is off the clutch? Does the vibration happen when you ease away versus punching the throttle and dropping the clutch?

If the problem only occurs with a heavy throttle, your leaf springs could be winding up and causing an issue. It also could be related to worn out or soft spring bushings or damaged spring mounts.

If it were related to driveline angles I would expect more vibration at higher speed or with sticky tires if you punch it.
Things are a lot better than they were.
Problem occurs when pulling away from a standing start.
I basically have to keep the revs down and ease away gently.
There's no way I can give it gas and dump the clutch. I basically can't spin the rear tires as the drivetrain would vibrate.
There are no vibration problems at speed.

Is the consensus that it is not necessay to modify the trans tunnel to fit the 3550?
no need to modify the trans tunnel. your problem is with clutch chatter. a bad mount, binding linkage, a bad clutch disc, a bad pilot bushing combined with a loose input shaft bearing, a poor flywheel or pressure plate friction surface, bad springs in the pressure plate, all conspire to create clutch chatter.
rbohm has some good ideas of things that need to be checked. Also check the driveline angles and make sure they are withing spec. I have a TKO 600 and had to modify my tunnel to get the correct angles, but I also have a MII setup.
I have did a lot of research and decided to go with a T5z just to avoid fit issues. I spoke with Bruce at Modern Driveline. he confirmed that anything but a T5 will give you some fitment issues in a 65-66. Not that it can't be done but the fit and drive line angle is so much easier to maintain with the T5. That being said, it sounds to meand i agree with the others that your main issue is somewhere else. I had this issue years ago from loose U bolts holding the rear end housing. Check them, then check the linkage for a worn or loose joint in the Z bar. The bushings are known for wear at the block and the fame. If you have any slack in them the whole Z bar will shake and cause a vibration simular to what you are discribing.
I'm going to stick with my T-3550, and making minimal transmission hump mods. I've made a note of the other suggested vibration causes and will address them as part of the rebuild.
Thanks guys.
If you have ANY metal to metal contact between vibrating parts (engine, transmission, rear end, exhauset, etc) and non-vibrating parts (basically the rest of the car) then you will have horrible vibrations that will make the car feel like it is going to come apart.

The first thing to do when diagnosing vibration problems is to make damn sure that nothing on the engine, transmission, or rear end makes contact with the body without first going through a rubberized mount. I'd make sure there was at least 1/4 inch clearance everywhere.

I had a similar problem (vibration from a stop between 2400-3200rpm) and it came from a very small amount of contact between the metal portion of the tranny mount and the crossmember - 10 minutes with the grinding wheel and the problem was gone.

Good luck...