Rebuilt 5spd Transmission Back on the Bench

[Zinmocean]

Hello All, looking for some advice on my transmission project.

Quick Background, 1978 280z, owned for 11 years, 200,000 on car, 100,000 by me. Thankfully a PO undercoated the car when new, so the underbody is perfect, car remains rustfree though body has some character. In the last few years: Engine rebuilt, currently at 20,000 miles. Lots of polished parts under the hood. Tokico blues, lowering springs, and poly bushings. F+R strut bars. Techno-Toy Tuning TC rods. D/S rotors, hawk pads. New stock interior. N42 Manifold, 60mm TB, 280zx Turbo Fuel rail (to eliminate CSI cleanly.) Fidanza Flywheel. 15x7 Konig Rewinds and 205/60 Goodyear GT's. 240 bumper swap, 3pc IMSA spoiler, BRE airdam...I could go on and on, but that's another post. 

 

Why I'm posting today is I purchased a 'rebuilt' Ebay 5spd trans last year, installed it, and discovered Reverse didn't work. Seller split the cost of a rebuild kit, which was fair, so I rebuilt the trans. (bearings synchros seals etc) Project went well. also replaced Reverse Idler Gear as it was shot.

Trans worked great for 1200 miles, and then 10 minutes into a weekend cruise it seized up. The original 4 speed went back in, and I've started dismantling.

I could tell two gears had engaged, and was hoping to find a shift fork pin had come loose or worst case a shift fork had broken...once I got the case opened I found 2nd gear and Reverse were engaged, but nothing else seemed to be wrong. I popped it back into neutral, shifted it through the pattern a few times and it seems fine.

Any thoughts in this? Not in a rush to reinstall and be stranded again. Thanks

 

 

[erichwaslike]

it seems you probably left one or more of the detent balls out when assembling the shift rails into the case. or maybe on of the springs associated with them. if all the roll pins are in the forks/rails and no broken rails the only way it could engage both is if the detents werent done right to allow 2 gears at once

[Zinmocean]

All the balls and springs are where they belong, just double-checked. Maybe the springs are weak and not holding the balls into the detents enough?

Its a weird one anyway, I really expected a roll pin to have come out, but everything is solid. The lock nuts are still tight and peened, no metal in the fluid, etc etc...

Thanks

[Zinmocean]

Spent a day going through it, and while all the interlock and check balls, springs, and plugs were present, in the proper places, I did notice some wear to the bottoms of the plugs where the springs ride. Kind of a crescent moon shaped wear pattern from the spring seating. Measuring the balls with a micrometer also revealed some wear. No measurements for spring height like valve spring specifications, but I can only guess they are worn and relaxed as well. No luck searching the usual sources for replacements, anyone have a source for these? I'd want new plugs, springs, and all 7 balls. My back-up plan is to put a washer between the spring and plug to take up any wear.

That's the only issue I could find, which really seems pretty minimal. I still don't see how two gears could be engaged at once. The striking lever is secure on the rod, and no amount of hard shifting and abuse on the bench could beat the pattern and leave two gears engaged.

I really liked the 5 spd transmission over the original 4, and want to put it back in. I was thinking about (after finding a suitable plug) cutting a hole in the tailshaft near the forks so if the thing seizes again I can at least get it back into neutral instead of being stranded. (Then it would be back home, and the 5 speed to the recycler where it belongs...)

Given the scarcity of these gear boxes and the parts to keep them alive I'm giving serious thought to the 240sx/z bellhousing swap I've stumbled across while troubleshooting this trans.

Thanks

[datzenmike]

Trans worked great for 1200 miles, and then 10 minutes into a weekend cruise it seized up. The original 4 speed went back in, and I've started dismantling.

 

Well it couldn't have jumped into gear while moving, so you must have stopped and just shifted a gear, maybe backing up? How were you in 2nd?

 

Are you sure that second wasn't selected as you twisted the tailstock to disengage the shifter to remove it? The last thing the striking lever is near, prior to removing the tailstock, is to pass through the 1st/2nd shift selector. It may have been in reverse when taken out of the car.

[Zinmocean]

You are absolutely correct about sitting still, I had come to a light and then couldn't go when the light went green.

On the second point the shaft was locked up before disassembly and after removing the front cover I could see where the top and bottom shift rails had moved. That was before the tail-piece was removed.

If I can decisively fix the issue I'd love to run the transmission again, but another tow truck ride isn't an option. This last one was the first since I bought the car in Dec 2001.

Any thoughts on where to get replacement parts?

Thanks for the replys.