Transmission Rebuild.

[Halswell]

Soon I will begin rebuilding the Transmission for my 31 Coupe. I am advised by the experts over here that it is unwise to mix the repo gears with the old original gears and it is best to throw out all the old gears even if only one is worn and replace everything with new parts. I am wondering why? Surely if they are made to the correct form they should run together OK.
I note that the repo gears are made in a variety of places some in USA and some in Denmark etc. Which are the best? I know that the old original Ford parts were great but good condition originals are impossible to find. We Kiwis have used them up.
Any advice with this would be a help

[Mitch//pa]

i replaced the main shaft (input) with no adverse effects of operation or noise. i would not hesitate mixing new and repo on others.
i used the USA made

here is a link to Tom Endys transmission prudence if you have not seen it. it gives good info on what basics should be done on an overhaul

http://www.ocmafc.org/techarticles/T...20Prudence.pdf

[Roger V]

Your statement " Surely if they are made to the correct form they should run together OK." is the issue. Not much reproduced is exactly the same. Have heard what your experts have said for years. Besides different production processes, some said it was the conversion from inches to metric by some of the manufacturers. I found a mixture of gears in a A I bought and was noisy. I replaced the repros with used originals and it was then quiet.

[Tom Wesenberg]

I've only used original gears on the few transmissions I've rebuilt, but I wouldn't be afraid to mix new and old grears. From what others report MARK makes good gears. You want a snug sliding fit to the shaft. With the shaft held vertical, and oil on the shaft, the gear should slowly slide down the shaft. If it's a fast drop, then the gear is too loose on the shaft.

[700rpm]

I've mixed old and new without problems. The critical factors are how well they fit on the shafts and are the old teeth in good condition. Never throw anything original away. Find someone who wants it.

[Purdy Swoft]

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Here is how I do mine. I only use original gears. If the transmission doesn't jump out of gear, I just replace the bearings, cluster gear shaft and reverse idler shaft and gaskets. I have used original gears from other model A transmissions with no bad effects . On uinknown model A transmissions, I pay special attention to the fit of the second and high slider gear to the main drive gear. With some practice you learn the proper feel. The fit of the main drive to the pilot bearing is another thing to look out for. There is some good info in the mechanics manual by Less Andrews that I haven't seen elsewhere about fitting of the gears.

Don't expect the model A transmission to be as quiet or operate the same as a modern transmission. If you test drive with the floor boards and mats removed, expect some whine in the lower gears.

[Halswell]

A big thankyou to those who have resonded with information, advice and to Mitch//pa the link was most useful. Happy Motoring.

[RonC]

You are better off just buying all new Mark gears and shafts if you want a quiet smooth shifting transmission. The gears are A+

[CarlG]

"Back in the day" (late 50's) when you could still buy Model A parts at NAPA, I replaced one of the gears, don't even remember which one, but the "original" had teeth missing. Never had another problem with it, driving it all over Arizona as any teenager would.

[Kevin in NJ]

Send me the old bad gears!!!

Look at what you have.

First look at the teeth. The original unworn teeth were broached and will have machining lines across the face. If they are really mirror smooth then they are worn. They also need to be parallel across the two sides. If they taper then you are likely to get the gears to jump out.

There is also some non-sense about putting oil on the spline shaft and letting the gear slide down it. It should slide slowly. Problem is I took a gear that was measured to have just shy of .001" wear on the shaft with just shy of .001" wear and it slide fast but will work just fine. Learn how to measure with a good micrometer. A dial caliper is a nice tool to get estimates, but is not accurate enough to make decisions.

[Purdy Swoft]

Originally Posted by RonC

You are better off just buying all new Mark gears and shafts if you want a quiet smooth shifting transmission. The gears are A+

If money is no object and you have no feel for fitting gears then go for the new gears.. It will be very expensive. My transmissions shift just as smoothly as a non sycronized transmission can shift. My model A's are fun cars and not even a new old stock model A transmission will be as quiet or shift the same as a modern sycronized transmission. The original gears were made of high quality material. To me the choice of parts depends on ability and common sense.