928 man transmission question

[palaur]

Hi, i have a 5 speed transmission in my 928 78mod, it shift the gears upward just great but it grinds in all the gears when downshifting ( hard )..

If it is the transaks wouldn't it grind when in the gears upward also?
It is easy to put in reverse and first, i have adjusted the clutch..
Is it possible that it is the little plastic brake that is worn out?
would it do any god to change the sync rings perhaps?

Do anyone have advice please, oil, adjustment and so on ..

[palaur]

By the way do anyone have a vin decoder, the car is to old that i could use the vin decoder that i have found at the Ethernet, i am trying to determine if it got a LS diff?
Vin: 9288200677

[Landseer]

Can you get underneath and read the code on the bottom of the transaxle?
That's the place to start. I'll decode it for you, or somebody else here will by using the tech spec books. You probably want LSD for icy conditions in Norway? Makes a difference.

Its possible to check for LSD by lifting rear of car, turning a rear wheel, and looking for the directional behavior of the opposite wheel. If turn in same direction, LSD.

If you take the back cover off, it can be shown definitively.

Mine upshift well, but grind into the lower gears on downshift. Many of them behave this way on early cars. Theory is that poor clutch maintenance and inferior design of synchronizer arrangement work together to damage the parts. I have one rebuilt early box that is very smooth on downshift, so it is definitely possible to have good performance.

[palaur]

Thank you again, lifted the car and turned the wheel around, it turned the opposite wheel the same direction also, so i assume it is a lsd.. I called the prev owner and he could tell me that he used just plain motor oil in the diff( he never got to drive the car since the engine where broke so he just filled it with engine oil so he could preserve it)

So i did a little test run today, and the diff seams ok but i have to change the oil cause it locks when turning..

I have read in this forum about the Mobil 1 red line, but is this a ls oil?

[Danglerb]

Differential takes 75w90 gear oil, some do a mix with and without friction modifier, but I don't recall the details.

[Normy]

I really don't downshift my car, also a 5 speed.

This puts extra wear and tear on the clutch, which is expensive. The brakes are for stopping the car, and the pads are cheap and easy to replace. If your tranny is grinding, then the synchro's probably have a lot of wear and cannot match speeds properly any more. The 928 manual transmission is straight-forward, but like any major job, it is going to cost mucho dinero to rebuild and take a while to get done. Might be easier to try to buy a used one on eBay or from 928 International.

Good luck!

N

PS: One other thing to think about- Is your clutch completely disengaging when you push the pedal in? If it is dragging, then this makes it very difficult for the synchros to match speeds....

[Landseer]

Differential and gearbox on a 5 speed are connected and share fluid. Be sure to drain the front and rear of the unit to get all the old fluid out.

I'm using a Valvoline or a Mobil 1 LS 75W85 or 90. A little bottle of slip additive can be added but the LS has it in already.

My worn boxes shift better in summer and when they are warm. I've filled mine on an angle with almost a full extra quart. Seems to make it marginally better shifting when warm.

[924CarreraGTP]

Due to my recent rebuild of my shift coupling in my 911, It comes to mind that shift couplings on the 928 can wear out and cause problems too. They can also break completely and cause the car not to shift. I was going to buy another 928 for $800 once that I figured had this problem. It wouldn't shift out of gear and felt stuck. I also replaced some in a 944 once that made it shift much better.

[Landseer]

Clutch pivot, front shift link pivot and rear coupler should all be refreshed.

[palaur]

I'm going to take the gearbox out after this summer, and try rebuilding it with new sync rings anyhow that seam not so expensive compared to the aftermarket price of a transmission 1500usd - 2000usd and that is not with shipping cost.
Then the car would have a new drivline from front to the rear after i have rebuild the transmission hopefully,

I'm buying Mobile gear oil to use this summer then.

Thank you all for the help

[Danglerb]

Guys I know that rebuild say most average over $1k in parts. Deciding which parts need to be replaced is the hardest part as many don't show wear in very obvious, to me at least, ways.

Rennlist has a couple good threads on rebuilds with plenty of pictures, and step by step instructions.

[riber.bentsen]

I had good results with the Red Line synthetic 75w90 oil, made hard shifting when cold go away