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

[Tim Ayers]

OK, I got the transmission assembled, double check tooth count, back lash, etc. Everything fits perfectly, but the trans locks up in forward and reverse. Only free spins when the lower/reverse slider is located in neutral (first pict on the far left).

I've read Mac VP's and Max Navarro's books. I still can't figure out the problem.

The sychro hub/sleeve is very hard to move back or forward. I've placed the top on it to move the synchro fore and aft and it still locks up the trans.

Any help or tips would be appreciate. Thanks.

Tim

[Brian]

1st picture shows transmission in neutral, 2nd picture, it's in 1st gear, third picture it's in reverse gear

[kjvma131]

Not sure if this will help. Do you have the front bearing retainer on yet? If so, pop it off and see if it spins. I had that happen on a t87 3 speed before. I must have tightened it up cockeyed and it locked up the front bearing. The bearing retainer also has an oil groove that has to line up. Good luck, hope you figure it out.

Sent from my SM-G960U using Tapatalk

[Tim Ayers]

Originally Posted by Brian

1st picture shows transmission in neutral, 2nd picture, it's in 1st gear, third picture it's in reverse gear

Correct. When in "gear", the trans just locks up tight. You are unable to spin it when you grab the input shaft by hand.

[Brian]

OK, so, in neutral, if you hold the tail end of the mainshaft to prevent it spinning, can you freely turn the input shaft?

[Tim Ayers]

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Originally Posted by Brian

OK, so, in neutral, if you hold the tail end of the mainshaft to prevent it spinning, can you freely turn the input shaft?

No, I can not. The input and the all the parts attached to the main shaft seem locked together.

Let me take a picture of the synchros. I'm getting a hunch that may be it.

[Brian]

Yes, somewhere in synchro hub, end of input shaft, or front of mainshaft, you have a problem. If you loosen the front bearing retainer, can you get true neutral?

[Tim Ayers]

Originally Posted by Brian

Yes, somewhere in synchro hub, end of input shaft, or front of mainshaft, you have a problem. If you loosen the front bearing retainer, can you get true neutral?

I don't have either front or rear retainers on. I have bolts with washers so I can look at the bearings.

I replaced the worn synchro with one that looks a little different. It fit the same , but now I wonder.

The original one had a sloped or tapered "collar". The replacement one has a block "collar". I'll swap them to see if that does it.

[Brian]

What part no's are your input shaft and 2 gears?

[Tim Ayers]

Originally Posted by Brian

What part no's are your input shaft and 2 gears?

I'm not sure. Would they stamped on them? I've had this set for years.

I have a complete used set that I kept together from a good known trans. I'm leaning towards cleaning up those gears, replacing the wear items and see if that works.

When in neutral, aside from not allowing the input or main shafts to spins independently, the gears will spin and coast so I believe they are right. I did the gear tooth math and it worked out.

It's this snychro. If I pull it out from the synchro hub, the trans works, goes into gear and main and input shaft spin free of one another in neutral.

[Tim Ayers]

New twist. If I take out the cluster gear shaft and let the cluster drop to the bottom of the case, the trans works as it should. Hmmmm

Cluster is a NOS 28 tooth part #51A-7113A (that was in the box).

[alanwoodieman]

different gear pitch, correct tooth count but wrong pitch which causes the lock up. 51A is from a later trans

[Tim Ayers]

OK, thanks. According to Mac VP, it can be used. It was a later replacement for earlier gear sets.

I think I found a few issues. The brass washer between the synchro hub and second gear was too tight. I changed it for an old one I had. New one didn't leave enough slack. I have .006" now (.008" is max).

Also, the sychro hub was NOS and stiff as heck. I've been working it back and forth, it has loosened up a lot. I also put the old springs in the blocks. Seems to have helped.

Too late to put it back together tonight.

[Tim Ayers]

Now I'm completely stumped. I swapped the 28 tooth cluster out for another 28 tooth cluster that came from a 40's car.

Still locked up in all gears, but neutral and the the input and main shafts will not spin independently when in neutral. It is either the synchro hub or the synchros themselves.

When the input shaft synchro is pulled away from the synchro hub, it works as it should. When mated in the hub like it should, locks up.

[Brian]

Tim How wide is the tapered synchro face at back of input shaft?

[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?

[Tim Ayers]

Originally Posted by Brian

Tim How wide is the tapered synchro face at back of input shaft?

They are on there now, so I don’t know. I did compare it to known good use it was the same. It really believe it is a synchro issue. Just don’t know what.

[Tim Ayers]

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?

Yes. The front synchro on the input shaft seems to be locking the rear synchro with the main shaft. The “notches” in the synchro rings are mating with the blocks in the synchro hub. I don't get it for I followed both Mac's and Max's book to the letter.

What the heck is going on?

Taking a closer look at the synchro ring (in a pict above) and the "blocks" from the old synchro assembly I had (side shift box), the blocks of had a slanted end on one side. I'm assuming this was to let the synchro spin. Not sure, just thinking out loud.

All the parts I have the ones mentioned in Mac's book. I'm stepping away from it today and will come back to it on Monday,

[Terry,OH]

Your first two pictures of the blocker rings show a ring that is bad. It is badly worn from something rubbing against it on it's OD. The second two photos show the blocker ring as it should be, both the front and rear rings should be identical. How about a photo or two of rest of the syncro. What hub are you using 81A, 91A or 01A?? There are different blocker rings for the different syncros. as well as different outer sleeves.

[Tim Ayers]

Originally Posted by Terry,OH

Your first two pictures of the blocker rings show a ring that is bad. It is badly worn from something rubbing against it. The second two photos show the blocker ring as it should be. How about a photo or two of rest of the syncro. What hub are you using 81A, 91A or 01A??

Yes, the worn one was an old one I took off of the other gear set I had. Let me confirm the hub part number. It's the one for the 3" fork set with the larger ring size and the "groove" towards the back. The blocks use the balls with springs.

[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?