How do you buy a used transmission

[Jeff Berk]

If you've been following my thread on a FS5W71B with a slipping 3rd/4th, I've disassembled and found numerous worn parts that cannot be replaced. To quote zKars "Holy crap, those teeth are in bad shape. ..You are out of luck as to finding a replacement. Time to look for a new transmission I think. "

I found a used transmission on Facebook/market 3 hours away:

https://www.facebook.com/marketplace/item/428839345022192/?referralSurface=messenger_lightspeed_banner&referralCode=messenger_banner

Is there anything I can do to check it out before I pay for it? 

[Zed Head]

You can remove the drain and fill plugs and maybe some of the switches and look inside at some of the synchros and gears.  But I found that even a transmission that was extremely damaged, with broken shift forks and synchros and bearings, would still shift through the gears and the shafts would turn.  Kind of like you found with the one you're replacing.  It's difficult to tell until you get it apart.

You have to use your ability to judge character I think, and the various internet tools.  I don't know how the FB marketplace works.  Does the seller have a visible profile?  A way to see opinions of them and past sales?

I bought a whole non-running 1978 280Z in the past, just for the transmission.  Probably the best buy I ever made.  The engine was good and it ended up in my car too, along with other parts.

[Zed Head]

Another thought - you could take a portable drill and a piece of hose and use it to spin the input shaft at high speed.  Listen for noises and look for wobbles.  After I bought a mystery 5 speed I hooked it up to a spare engine I had that I had running on a stand (Harbor Freight dolly).  I put some used fluid in that I had kept and ran it through the gears on the running engine.  It sounded like a blender and the fluid came out looking like silver metal flake paint.  A drill motor and a piece of tube might get similar results.  With no drivetrain load on the output shaft you can shift gears without worry.  Even with no fluid you can still get an idea of the quality of the parts, if the seller will let you do it.

[EuroDat]

Unless you can crack it open and visually inspect it, it will be a gamble.

Maybe the owner will let you do that. I paid a guy €25 once to let me open it first. Then I could inspect the synchros and gears. If I didn't buy it, I would bolt it back together afterwards and he could keep the €25. I'd rather spend €25 than end up spending €300 on a dud transmission.

Zed head has already given you some good tips to try.

The problem is such a test could identify a shot centre bearing and put you off buying it, but a centre bearing is readily available and easy to replace. The rotation test will not find a worn synchro ring or selector. There is simply not enough force on the gears for it to jump out of gear or create noise.

Edited January 20, 2021 by EuroDat

[Jeff Berk]

Thanks for the pointers. I like the idea of using a drill to spin the transmission. That and checking for metal flake in the fluid seems like a good plan. 

[Jeff Berk]

Well that transmission had an issue. I couldn't get the shaft to spin by hand let alone a drill. I decided to buy it anyway after the seller agreed to accept $200 for it figuring once I tear it down, I can figure out what the problem is and hopefully fix it. The seller insisted that it was working fine when he pulled it out of the donner car last month. He also will switch it out with another one he has if this one doesn't work.

Unfortunately, I cannot pull the tail piece off more than an inch or so and for now the front section is stuck to the adaptor plate. 

UPDATE: I GOT THE TAIL OFF! 

UPDATE 2: I GOT THE FRONT OFF

The main shaft bearings are a little loose so I'll get to use the rebuilding kit.

Edited January 21, 2021 by Jeff Berk

[Zed Head]

Did you find out what was binding the shafts?  

Since you have one that is worth little you can experiment on it to figure out how to remove parts without damaging them.  Kind of like being in the wrecking yard.

[Dave WM]

if you have some V blocks it would be a good idea once you strip it down to check the main shaft for straightness. just support the two ends, get a dial indicator on the middle and give it a spin. Its def something I would do now knowing what I have learned from doing a rebuild. IF you have an issue there is a place somewhere in the mid west that corrects this, I don't know if it would be a DIY thing as I presume it would take some experience to know exactly how and where to press if its bent. You maybe able to detect with it intact by spinning the main shaft and just looking for obvious run out of the synchro hubs. All that being said, these are really not that complex, just keep up with the order of disassembly, the small ball bearings used to located some of the parts on the shaft, the orientation of the parts as they come off (like thrust washer on 1st gear). After you have done it, you will be "wow that was not so bad".

[Jeff Berk]

Some of the apprehension is gone since I've mostly torn my first one down so I know what to expect. I just picked up an inexpensive parts washer (Performance Tool W54043 ) because this one has lots of dried oil on it.

I have to find a GOOD pair of snap ring pliers. Maybe a pair that locks would work.

[Dave WM]

yes the good pair of snap rings is essential, the idler will get the best of you with out them.

[Patcon]

I bought a set from northern tool. They have worked really well

[Jeff Berk]

I ended up purchasing a CHANNELLOCK 929 because it has a lock on it. My old Craftsman won't hold the rings open far or secure enough, OEM #25014 won't hold the interchangeable tips securely, and the OEM #25356 interchangeable tip holder broke off.  The 929's are 3-4 times expensive so I have my fingers crossed.