Help with transission

[SER240Z]

I have a 80 zx, the five speed was/is making a kind of grinding/metal to metal noise when you get on or let off the gas in all gears. Just yesteday it started having this awful vibration in all gears above 1500rpms. All noises and vibrations go away when in neutral or if I have the clutch in.

Any suggestions as to what the problem is? I assume it's time for a new tranny, but wanted to make sure. Anybody have any ideas for a good shop, or parts source? Never torn one down, any help with rebuild tips would also be good.

Thanks,

Scott

[Arne]

Sounds like mainshaft bearings to me.

A typical manual transmission of this vintage has three shafts, all supported by various bearings. You can generally determine which bearings are bad by the times that the noise is heard, and how the tone changes in different gears.

The three shafts are the input shaft, the mainshaft and the countershaft (or layshaft if you're in the UK).

The input shaft is the one in the bell housing that the clutch disk slides onto. It is a short shaft supported by a big bearing at the front, and a needle bearing at the back where it mates with the mainshaft. This shaft spins at engine speed whenever the clutch is disengaged, even in neutral.

The mainshaft is the one the driveshaft attaches to at the back end. It will have one or two caged roller bearings in addition to the needle bearing at the front where it meets the input shaft. This shaft spins whenever the car is moving regardless of gear, it's speed is constant with road speed.

The countershaft is the connecting shaft in all gears other than 1:1 (fourth in both 4 and 5 speeds). It is directly driven by the input shaft and spins at the same times and speeds as that one. But it is only under load in reverse, first, second, third and (if applicable) fifth gears.

So from this description - noise when you get on or let off the gas in all gears. Just yesteday it started having this awful vibration in all gears above 1500rpms. All noises and vibrations go away when in neutral or if I have the clutch in. - it can't be the input shaft because it doesn't do it in neutral. If it were the countershaft, it would be quiet in fourth gear, so that's out as well. So only the mainshaft bearings are likely to make noise at the times you noted.

As for rebuilding it yourself, that is not a job for your average home mechanic. There are many parts, springs detent balls, etc. It's very hard to find good service manuals for transmissions, let alone the necessary parts.

[bigoak]

Your transission needs an "m".

Glad I could help...

[e_racer1999]

thanks for that arne! now i know what bearings to replace

is that in an FAQ or sticky somewhere? that would be good information for easy access....

[Victor Laury]

Scott - Arne gives good advice - Main shaft! Thats what went bad on my roadster 5, and the symptoms were exactly how you described. Ask Les for a recomendation on a shop.

[jmortensen]

If you download the 280ZX FSM from www.carfiche.com it has the complete rebuild instructions. I've done 2 manual transmission rebuilds, and they're not that hard. I had a Nissan master tech buddy who did the 5 speeds all the time for the local Datsun freaks. I think he charged 5 hours labor for the job if they brought the trans to him. I think the book time for a headgasket replacement is longer...

[Arne]

My experience is with 3-synchro MGB gearboxes, both with and without overdrive. I would not hesitate to tear into a Datsun 'box as long as I can get good instructions.

[=Enigma=]

As Arne said, unless you know exactly what you're doing, this task is best left to professionals. That said, if you want to do it yourself, here's a place to order the parts you need.

http://www.drivetrain.com/nissian4_5sprwd.html

[Ron Carter]

Les's guy builds all my race transmissions and I have had excellent luck with the transmissions that I have had Les go through. I am pretty mechanically inclined and am not interested in taking on a rebuild of a transmission.

This IS best left to the guys that know these transmissions otherwise you will be pulling your tranny out on a regular basis to "fix" it...

[SER240Z]

Thanks for all the info guys, (especially you Bigoak). This car is my commuter, I recently picked it up for 300 bucks. I'm not sure if I want to put any money into, or turn it into a learning project. I might even just get rid of it as I am running out of room for Datsuns right now.

Thanks again, if I decide to tear into it for the experience, I'll let you guys know. I'll probably have a bunch more questions if I decide to go this route.

Scott

[JimmyZ]

It will be cheaper to get a Junkyard tranny for $100-175 than to replace the bearings. If you buy bearings at a local bearing house rather than Nissan You might get away with spending 100-125. You are really better off getting nother unit though.

Should you decide to take this challenge...

I've replaced bearings and synchros in my Z tranny(s) over the years. It's a fun thing to do because of the sense of accomplishment once it's back together. The bearings sitting in the lower part of the tranny seem to go earlier because of what runs through them.

Making a plate out of wood to hold the bearing carrier and getting the detent balls/springs back in proper order is as difficult as it gets. You will need to take the input shaft to someone to press off/on it's bearing otherwise the rest is "in house". Get a really GOOD set of snap ring pliers otherwise you'll cuss your way through the whole thing.

I used an unfolded pizza box to arrange parts as they came off. The Haynes manual was my best freind for helping get the detent balls back in right.

2c

Jim

[bigoak]

Ser,

Sorry...just being cheeky. I hope you stick with the Z. I'd go the route of a used tranny if I were in your shoes. The downside to Z's is rapidly disintegrating bodies (particularly up here in Canada, not so bad where you are...). The upside is a typically bullet proof drive train as long as the car isn't beat up. The abundance of orphaned drive train components due to rust, rot and wrecks means that costs are pretty low (hence why a number of us make this a hobby/passion/obsession).

Good luck and let us know how you do...

Cheers,