RyanPerrella

Jim good point

Ideally yes you need to have a car that finishes a race first and foremost. I guess that puts things into perspective when it comes to racing 928's If your going to have a DNF, i guess its better that the entire transaxle explodes then something minor break. If your going to go, go big right!

BC

GO BIG OR GO HOME.

mark kibort

The hard truth is that most of my competitors do try and go big, and usually go home, while i log 91 consecutive race days with all stock stuff.

Hey, i hear your point, but there is some logic in having the clutch not be too strong as to inject even higher forces in the gear box, but i do like the fact that the much lighter clutch assembly will make down shifts a little easier and faster.
However, i do think some of the inherent issues with our gear boxes, is more in the area of how sloppy the linkage is. If you ever drive a BMW race car, you will know what i mean. they are like driving / shifting motorcycles.

mk

John Veninger

Hopefully my gears and lay shaft are just a bit stronger since they were chilled. Jury is out on that, but sure didn't hurt.
Funny how I had a transmission failure and was still able to win at Sebring.

As Jim pointed out, towing from NJ down to Florida is expensive in both time and money. Did I like that the trans broke? No. But I sure wouldn't have been much more unhappy if I had to go home from a clutch failure.

RyanPerrella

well the clutch failure would have been cheaper. That was my point.

Are you talking cryo treatment? They arent just frozen are they? Ive read a few years back about the repeated heating and freezing of components thats changes the crystaline structure to make it stronger and wear longer. I dont know how many times you need to do this to get this effect. I am sure the procedures are different for different allows or differing grades of steel, but I think the only way to know for sure is to analyze it with a microscope or something to that effect. Ive heard that wear goes up 200-300% and strentgh goes up in the double digits percentage's.

John Veninger

Yes, cryo treated. Including hose weak little spider gear shafts in the diff.!!

RyanPerrella

What did that run by the way? I was always curious how they price that stuff, ive heard its per pound? What does it cost to have the entire lot of transmission internals done? What would you say a crank costs?

mark kibort

Yes, it is funny how both of your competitors broke a little earlier. you were the sole survivor. actually even more funny was that both of them were 928s!! (actually there was a pesky '79 911 4 seconds a lap slower in 2nd)

mk

Stan.Shaw@Excell.Net

hmm, three 928s broke in one race. Now who is it that is always saying how reliable they are ? .....

John Veninger

Was able to keep the other competitor behind me taking several laps "broken".

mark kibort

You had a great time rolling. nice to know your work to run hard and gap that "other " competitor for the last few laps was worth it. i wonder if he was smelling blood? It looked like you were a 4 second faster car.

did you just loose a gear? i forgot what happened to your transmission.

In our enduro with Chuck's Euro, we only had 4th gear. funny, it cost us, no more than 3 seconds a lap!

Are you ready for Sebring this year? when is you first race.

mark kibort

Only if amzoil is used.
I dont know what David's failure was, but you are right. wasnt a very good showing for the 928s!!
Then, both Joeseph and Mark BOTH brake in the Laguna Grand finale race. (joseph, some timing belt tensioner issue i think, and Mark stripped 3rd gear)

I have a strange suspicion, that the 928 drivetrains, need to be kept near stock!

Mk

John Veninger

Well a bit of feedback after installing the tilton clutch.
I love it! I can now shift the car into reverse while running! The old clutch use to go out of adjustment very quickly. Think it was a combo of a high rate pressure plate and a slightly worn intermediate plate.

The clutch is "grabby" at first, but then I got use to it. Makes loading onto the trailer an adventure.

On the track it worked fine. The lighter flywheel made rev matching a bit easier.

Vilhuer

There was local straight teeth gearset project going on for early 928transmission, G28/05 IIRR. At cost of custom made gears one could have bought one or maybe even two GTS gearboxes. Project is dead now I think as racer who ordered it isn't around anymore. Making non syncro straight teeth gears would get more strenght in them but it wouldn't do anything to real problem of pinion and layshafts geting away from each other due to lack of support on pinion shafts front end.

Nothing much can be done to 928 trannys weak link as easiest fix would be to make casing where there is no bolt on top cover. Next big thing to fix would be to add 3rd bearing row to support front end of pinion shaft. Factory tried to do what they could within staying in original gearbox layout by increasing diameter of input shaft bearing in '85 MY and diameter of pinion shaft front end in '92 MY. Two bearings between input and pinion shaft are clearly larger in GTS box than in previous versions.

Probably easiest way to make these boxes stronger would be to extend input shaft forward and add extra bearing to it further forward outside gearbox. This would require shorter torque tube, center shaft and custom made bearing housing in which extra bearing could be properly aligned and supported. Extending pinion shaft forward inside input shaft and adding third bearing inside it could be done too and also layshaft could be made longer with third support at front. Problem with these kind of ideas is that cost gets quickly to custom race tranny territory.