MTFCA Forum

Hi all,

Well I have constructed an engine stand so I can stand the whole assembly on end to check and set mag gaps, run out and 4th main alignment. I struggled for ages to get the transmission shaft to be better than 5 thou run out and then gave up and got it cleaned up in a lathe. Now I have less than two thou at shaft end. Then I found my driven plate was all over the place and it became obvious it is the bushing. My transmission is 8n fairly good shape, for example the triple gears were reasonable, but I had a bad 4th main so whereas the rest of the bushes feel okay and in good condition, the driven plate can be rocked back and forth by about 6-7 thou on a dial indicator and the clearance is probably more like 8-9 thou in the bush. I checked the shaft end and it is at 0.9325, so some wear I believe but otherwise good and uniform. The other mid point of the shaft where the brake drum bush sits is still at 0.998. My thought is to replace the driven plate bush T-3327-B. However reaming and such may be a pain so I am tempted to put a new bush in and then use timesaver to fit it. I would select best position for the driven plate on the brake drum and then keep it there and work it in with timesaver in place. This would/should keep it inline with the other bushes I think and be easier than trying to get a reamer and align it with the other bush.

What do you all think?

Using a reamer will follow the bushing making for an off center condition.
The output plate bushing needs to be bored in a lathe.
When doing so, you will likely see that the plate dosent quite run square to the shaft. Some clean up cutting on the drum mating surfaces will be required. If you turn the brake drum, you will find the plate mounting surfaces also in need of a little clean up cut.
Ideally or necessary you would also bore the brake drum bushings.

Everything you wanted to know about a T transmission but we’re afraid to ask.
https://www.mtfca.com/discus/messages/3 ... 1375578307

Thanks to Herm.

Thanks all for responses.

I bought the new bushes and they (unfitted) are just as loose as my current bush on the transmission shaft. I think my transmission shaft is good. The main bit is .998 or very very close to it. The driven plate bush runs on the thinner diameter bit of the shaft that I have measured at .933, but I do not know what that should be when unworn, would anyone know the correct diameter for that bit of the shaft?

I bought the new bushes as this driven plate just seems such a loose fit, but perhaps that is okay or normal?

BobUkPipedream wrote: ↑

Thu Feb 23, 2023 12:03 pm

Thanks all for responses.

I bought the new bushes and they (unfitted) are just as loose as my current bush on the transmission shaft. I think my transmission shaft is good. The main bit is .998 or very very close to it. The driven plate bush runs on the thinner diameter bit of the shaft that I have measured at .933, but I do not know what that should be when unworn, would anyone know the correct diameter for that bit of the shaft?

I bought the new bushes as this driven plate just seems such a loose fit, but perhaps that is okay or normal?

I'll start by saying I do not for a fact, know the original diameter of what you're now measuring at .933. However, most sizes, especially of that era, follow fractional dimensions. 15/16" would be .9375". Also, common practice back then was to subtract any desired clearance from the shaft, rather than add it to the inside diameter of the bearing. So, let's say that .004" was the intended bearing clearance. That would put the shaft at .9335" diameter. What really matters though is what the bushing ID is after it's installed. Hopefully it's at a good clearance or can be bored to a good clearance.

Jerry VanOoteghem wrote: ↑

Thu Feb 23, 2023 12:18 pm

BobUkPipedream wrote: ↑

Thu Feb 23, 2023 12:03 pm

Thanks all for responses.

I bought the new bushes and they (unfitted) are just as loose as my current bush on the transmission shaft. I think my transmission shaft is good. The main bit is .998 or very very close to it. The driven plate bush runs on the thinner diameter bit of the shaft that I have measured at .933, but I do not know what that should be when unworn, would anyone know the correct diameter for that bit of the shaft?

I bought the new bushes as this driven plate just seems such a loose fit, but perhaps that is okay or normal?

I'll start by saying I do not for a fact, know the original diameter of what you're now measuring at .933. However, most sizes, especially of that era, follow fractional dimensions. 15/16" would be .9375". Also, common practice back then was to subtract any desired clearance from the shaft, rather than add it to the inside diameter of the bearing. So, let's say that .004" was the intended bearing clearance. That would put the shaft at .9335" diameter. What really matters though is what the bushing ID is after it's installed. Hopefully it's at a good clearance or can be bored to a good clearance.

Right on.

The drive plate bushing is practically redundant with a good & proper fit of both brake drum bushings.
However, if off center it can put pressure on the assembly pushing away the lower bushing clearance causing an off output shaft.
You can feel some friction spinning the assembly on the center shaft.
The plate bushing is best lathe bored to perfectly center. A hand reamer following a pressed in bushing is typically not perfectly centered.
Even in boring said bushing, I typically find a 90% clean up. Some times a smaller I.D. bushing is needed for a full clean up & stay in tolerance.

Thanks for replies,

I have not removed my old bushing yet fr9m the driven plate. My brake drum has two bushes in it so was I suppose done at a time before that changed to one. It feels fine with no indication of any wear on the transmission shaft and it does not feel loose.

The amount of slop on the driven plate is very high, however the new bush feels the same when I slide it on the shaft. Maybe once pressed into the driven plate it would tighten up and need reaming, but as it is it feels loose. I have an old worn transmission shaft with the main part at 0.996 and the bush feels the same on there too.

I will try to measure the clearance from transmission shaft to driven plate shaft with a dial indicator. May be it is 4 or 5 thou and I am worrying about nothing.

BobUkPipedream wrote: ↑

Thu Feb 23, 2023 5:14 pm

Maybe once pressed into the driven plate it would tighten up and need reaming, but as it is it feels loose.

Right. How it fits before installation is kind of immaterial. Install it and see what you've got. If it's still not right, push it out again and get a bushing with a smaller ID, then install it and bore it to size.