Rebuild of 915....recommended upgrades

[gavinc69]

Winters nearly here and its time for another project...gearbox!

The box has never been particularly great and is now slowly getting worse.
I've added a few small uprades along the way including Fidanza lightweight flywheel, Wevo PSJ, new shifter bush's and Wevo engine + trans mounts.

For a short while now I have been able to feel a slight vibration with clutch up or down and just recently if I give it full throttle as I pass around 80mph there is a vibration through the car. But its fine if I ease passed 80 on part throttle.
I would say it was possibly drive shafts and will check them out also but a few people have said possibly a clutch issue.

Its a 1980 SC and the engine has been turbocharged, so its maybe around 280 to 300hp at present. I don't envisage going much further with HP so as I've read over the years the 915 should be OK as long as I don't drag race from the lights, which is fine by me.
The box maybe getting worse now due to it being tired anyway plus its now got more HP/torque to handle.

Right...so if the gearbox is rebuilt.

What upgrades would be recommend whilst its being done?
I have seen the Wevo bearing retainer plate and transmission side covers, they seem to help strengthen things up a bit.
Also what clutch would be recommended and lightweight flywheel?
I went for Fidanza mainly due to low cost but being Ally I wonder if now its a turbo it has warped or something causing the vibration!!

Thanks

[JohnJL]

You don't mention your LSD or not. That's the single most $ and meaningful upgrade decision.

[gavinc69]

Are....no idea if it has LSD.
I'll check this weekend. Don't you raise the rear and spin one wheel and see what happens with the opposite side wheel or something?

[Matt Monson]

Originally Posted by gavinc69

Are....no idea if it has LSD.
I'll check this weekend. Don't you raise the rear and spin one wheel and see what happens with the opposite side wheel or something?

Doesn't matter if it is worn out. When they wear out and no longer have any preload left, they spin opposite directions, just like an open differential.

Look at the type number on the gearbox. If there is a 12 between the type number and the serial number, it was originally equipped with an LSD. Thought that doesn't guarantee it wasn't snatched along the way.

Gearbox rebuilds really cannot be predicted in advance. It's one of those things where it has to be apart on the bench and inspected before you can have a full and accurate quote of what it will cost.

Might be a $2500 job. Might be a $5000 job. Add an LSD and you are in for another $2500.

Need a good builder over there? Talk to Mike Bainbridge and MBE. Or Autofarm. Or Francis Tuthill. Or Kevin at Historika. There's a pile of good vintage builders.

The upgrade formula is always the same. 1 piece bearing plate. 930 sized bearing billet side cover. Here in the States, myself, Wevo and CMS all make our own versions. I wouldn't doubt that there would also be local UK workshops making the same parts. Tuthill buys a ton of gears from me and bearing plates (aka teddy bears), but they've never purchased a side cover. Maybe they have a local source.

Pick up an issue of 911&Porsche World's newer Classic Porsche magazine. Good source of vintage suppliers who continue to service the 915 and the air cooled cars.

Regards,

Matt Monson
Guard Transmission LLC

[gavinc69]

Managed to drain the gearbox oil today and was interested to see what metal bits maybe stuck to the drain plug!!!

Only the one tooth.......No idea when the oil was last changed as the box was second hand when I got it. I know I should of changed it earlier.
The oil that came out was black and stinky, so with any luck some fresh oil should help things a bit.





Also got the type number off the bottom :

[JFairman]

I've never seen black oil come out of a manual transmission from a car. Motorcycles with wet multiplate clutches where the engine and transmission share the same oil yes, but never a car.
Anyway.. with those broken selector teeth and black oil your transaxle needs a rebuild. It's just a matter of time before it gets a lot worse if you keep driving it.

[gavinc69]

Its was just the one tooth that I found, posted two pics of same tooth.

Left the trans oil to drain overnight and then poured it into an empty oil container to measure it as it seemed a minimal amount of oil :



I thought it should have aprox 3.5 litres in there! Maybe another reason why its not working 100%

When I finally manage to get the filler plug out, it's being a beeeeyatch to get out, I'll measure the amount of oil that goes in to compare.