73/trans

[scompton]

The trans grinds when the fluid is cold on the down shifts 1st, 2nd and 3thd, shifts fine when is warms up. I have changed the trans fluid to a lighter weight 80/90. The problem is no better. Have any of you had luck with synthetic gear lube?
Thanks
Steve

[Wayne 962]

Hmmm, I doubt that switching to a new type of transmission fluid will help too much. Sounds like the grinding sounds may be caused by worn synchros. They work using friction to spin up the gears to the proper speed before engagement.

Here's what I think may be happening:

The synchros are worn on the gears. As the transmission heats up, the synchros expand due to this heat. The expansion of the synchros counter-acts the fact that the surface of the synchros are worn.

Sound reasonable? Anybody else?

For more info on synchros and how the transmission works, please see our tech article on repairing 1st gear on the 901 transmission. Also take a look at our 914 parts diagrams for exploded views of the synchros.

Hope this helps,

Wayne

[Tim Polzin]

I agree with Wayne. Just rebuilt a 73 transmission and replaced the syncro rings plus had to replace the syncro hubs for 1st and 2nd among other things. This is not a big job. I suggest you consider replacing the rings soon before you wear the hubs (read expensive) excessively.

[Wayne 962]

Tim is right. When the synchros get worn and fail, then you start grinding the expensive stuff like dog teeth (synchro hub) and sliders. A typical 1st Gear slider costs around $300, and a typical dog teeth synchro hub costs around $100.

Beware of 'rebuilt' transmission where only the synchros have been replaced. If the hubs and the sliders are destroyed, then you will not be able to get it into gear easily...

-Wayne