New transmission locks up. Only spins free in neutral. Thoughts?

[Terry,OH]

Can you show the three blocks of the 81A syncro all three should be identical.

[Ideucev8]

A while back I rebuilt a trans & the new syncro rings the owner supplied did not have the slots machined deep enough & I had to file them deeper to give the rings clearance to operate correctly. Phil

[Tim Ayers]

Originally Posted by Terry,OH

Can you show the three blocks of the 81A syncro all three should be identical.

Yes, had that hub apart three times. (I'm now an expert on putting the balls back in- LOL).

Here are some pictures. The hub in there now is identical to the old one I had. Here is picture of an older synchro I had that was identical to the NOS I used to replace it with.

The pict of the input shaft is when I pulled it way from the hub slightly. When I do this, the trans works as it should.

[Tim Ayers]

Originally Posted by Ideucev8

A while back I rebuilt a trans & the new syncro rings the owner supplied did not have the slots machined deep enough & I had to file them deeper to give the rings clearance to operate correctly. Phil

Phil:

Interesting. I'll compare the new ones in there to the old ones I have.

[Mart]

Are the rings turning freely on the cones on the input shaft and 2nd gear? Or are they "wrung" on?

Mart.

[Tim Ayers]

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Originally Posted by Mart

Are the rings turning freely on the cones on the input shaft and 2nd gear? Or are they "wrung" on?

Mart.

Wrung on, Mart. I noticed that too. Out the trans, I can spin them freely. Once together in the trans, they mate to the cone and don't spin.

[alanwoodieman]

new syncro rings will stick to the tapered steel part of the input shaft and also to second gear, make sure they are free--also a good syncro brass ring should have clearance between the ring and the land on the input shaft and second gear- 1/16 plus gap

[Mart]

You need to look at axial clearances. The hub shouldn't be pushing the rings onto the cones until you want to select the gear. Even then, it should be the angled teeth on the outer sleeve that do the pushing.
Mart.

[rotorwrench]

Some of the late reproduction brass blocker rings do not have the correct dimensions. Mac VP has a clearance figure for the gap between the synchro hub teeth and the blocker ring. The taper on the blocker might not be correct as well as the slot windows. There are some junk replacement parts out there.

There are several types of main output shaft and each has to have the correct 2nd gear & bushing parts to work together. One has a spring pin and the other doesn't. The bearing that fits in the main input could also be suspect. Do you have Mac VP's book? It is an excellent guide to working with these old cog boxes.

Ford first used the synchro with the stainless steel plates and the spring rings first in 1939 then they changed to the one with the ball bearings. They eventually changed back for the transmissions after 1948 or so. My 51 Mercury cars have the plate & spring ring set up and they shift smoother I think but that's just my opinion.

[Charlie ny]

Tim,
Your problem is , as mentioned, the depth of the 3 slots in one or both rings are shallow. From the the back face of the ring to the bottom of the slots must be .295-
.302 max. I have to mill every new ring to get the depth. Upon occasion the female taper is out of spec just to make things extra challenging.
Charlie ny

[philipswanson]

Originally Posted by Mart

The synchro hub and synchro rings need to be able to turn freely, as a unit, relative to the cones on the input and second gears. The synchro rings should be able to rattle around a little bit, while still be held in the right relationship to the synchro hub.

Is it all bound up?

I suspect this too. Same thing happened to me when I put all new gears in my 51 transmission. Free up the syncros and the problem goes away. I used valve lapping compound between the brass syncros and the part of the gear edge they ride on when assembled. Spin them to get a nice drag free fit.

[Tim Ayers]

Problem solved!!!!. Replaced synchros with some older unused ones I had in my stash. Replaced both and works like a charm. Difference was .030” on each. Amazing that little difference can lock the trans up solid like that.

Thanks for everyone’s help. I was loosing my mind. Look out Mac, I may go into the trans business after tearing this thing apart five times in 48 hours.

[Tim Ayers]

Double post. Deleted

[Mart]

Glad you were able to home in on the culprits Tim.

It's amazing the number of incorrect replacement parts there are out there. Wheel cylinders are another example that spring to mind.

[svm99]

Tim, bolt a u-joint to the back, sometimes the rear shaft tends to be to far into the trans, the ujoint will pull it back against the rear bearing. Paul J.

[Talkwrench]

Yes it does pay to attach the Uni just to check, and when bolted up make sure the baffle is not distorted and has a small gap.

[svm99]

Originally Posted by Talkwrench

Yes it does pay to attach the Uni just to check, and when bolted up make sure the baffle is not distorted and has a small gap.

Yes, prefitting the bearing, slinger and ujoint to the shaft saves time later.

[Bored&Stroked]

Another repop part that I won't use are the "new" cluster shafts - two problems with all that I've seen:

1) The material and finish is nowhere near what Ford made. Also, they tend to be soft.

2) They are about .001 undersize - which is a major issue for me. This not only causes the bearings to be a bit loose, but contributes to case leaks both front and rear.

[Charlie ny]

Guys,
I'm pretty sure VanPelt is addressing the cluster shaft issue.

The pre ground and semi hard material being used is a joke which is made worse by roller skate caged roller bearings offered by too many vendors. Each roller
should measure .1875 but usually are .185- .186.
Charlie

[philipswanson]

Originally Posted by Tim Ayers

Problem solved!!!!. Replaced synchros with some older unused ones I had in my stash. Replaced both and works like a charm. Difference was .030” on each. Amazing that little difference can lock the trans up solid like that.

Don't you mean .003?