Fun with overdrive gearboxes

I have a quick question for those of you with overdrive gearboxes in your TR6s. My gearbox in direct third starts to whine a little. When I shift into fourth it doesn’t change much. Then as I increase in speed, it starts to get a pretty loud whine. Then, when I drop the overdrive in, the gearbox goes silent. Any thoughts as to why this might be happening? The gearbox has new front, center, and countershaft bearings and synchros, bushings etc... The overdrive has had nothing done to it. The gearbox seemed all to spec when I put it together. There has been no change in this behavior in some time. I have flushed it a couple of times to no avail. I have tried running gl4 90 wt gear oil, and redline as well. It seems to be something on the output side as it is speed related…..

Did you change any of the gears or syncros? It seems to me that if you put gears with anykind of wear on new shafts with new bearings and bushings they mesh somewhat differently than they did before the rebuild.

As to the box getting quiet with overdrive engaged - It can't be many things - Either the RPMs drop enough with overdrive engaged that the box doesn't make noise, or
Something in the Overdrive unit may be the culprit and you're interpreting the noise as coming from the gear box.

To be really honest I'm just using deductive reasoning and there are many more expert guys on this forum, some of which have probably run into your exact ailment before - They'll be along shortly.

Welcome aboard mate!

Bob M.

I had my gearbox rebuilt in my 71 TR6, and it did have a whine at highway speeds. However once I drove the car a good 500 miles or so the new parts were "Broken In" and the whining noise dissapeared.
Maybe you just have to drive it a while to get all the new parts accustomed to the remaining old parts.
I also had an automatic trans rebuilt in my work truck and that had the same story......it was fine after about 500 miles of driving.

Unfortunetly, the whine has not gone away after many more than 500 miles. It did this before I rebuilt it as well. It must be something in the overdrive....