A "licence safe" highway cruising speed in the UK is about 80mph, at which the engine revs are approx 2850. I would really appreciate an overdrive that would drop the revs to say 2200, for both comfort and economy. However I wouldn't want to lose the dog leg gate, as the 2-3, 4-5 shift planes are ideal, nor would I want to lose the current gear ratios.

However I could do with a gearbox that wasn't so bloody slow. When I see people in other cars shift in a fraction of a second, and it seems to take forever to change in my car - although this is improved with fresh gearbox oil.

 

again, doesnt make a bit of sence unless it was designed to fix one of two problems the 928 5 speed transmission has for racing. we actually have close to the same gear spacing as the corvette 6 speed and the viper. its kind of like a blend of the 2.75 and 2.2 gears on a 928.

the second issue is feel . it would be nice to have a short throw, bullet proof type gear box like found on a GT3cup car, or BMW. our 5 speeds are a little clunky shift fast. you have to be very deliberate. (which is an aquired taste, and an art form ,actually)

the only way the 6 speed would make any sense is if they could stick a gear between our 2nd and 3rd. and one between our 3rd and 4th while making 4th taller (see GTS 5th gear) and loose the 5th 2.2.

viper vet speeds in gears
55,80,105,128,171,......300mph or somthing for 6th

928 speeds in gears
55,80,115,150,225

2.75 928:
50,70,104,138,183

 

What about the ability to at a reasonable cost setup a tranny with gear ratios matched to a given track?

I am a die hard stick fan, but if somebody wants to start swapping tranny's I would rather have the option of the slush box out of the Vette.

Has anybody ever considered just a total reworking of the 928 manual box, same basic dimensions, upgrade everything reasonable to upgrade inside with modern common parts?

As long as there are parts cars with decent drive trains to pull, not a lot of incentive to spend more.

 

IIRC, the three speed is supposed to handle north of 400HP. If yours doesn't, it's time for a rebuild?

I luv my three speed with the 2.75, and some cam advance. 1st-60, 2nd-90.

 

This is a good idea...or the AMG 5 speed would be nice too.....whatever they put in the 4K+ lbs 600hp+ 738ft-lb will easily handle whatever a 928 can throw at them....but I don't think they were designed as a transaxle? Bummer because it would be sweet! Of course rebuilding a stock 89+ 928 auto with AMG gears would give some great gear ratios too! and be far cheaper than a new MB unit!

Its well documented that the vette-viper 6 speed will not fit without serious mods.....but what about a 6 speed from the euro turbo 968? That should work...but would be pricey!

 

Doesn't seem the 6speed helps out for typical street driving. Don't see the ROI. $10K would get you a nice S/C upgrade or new suspension, which would help far more than the extra gear IMO.

 

Porken,

I am north of 600hp, my 3 speed can't keep up.

This is more of a "If you build it, they will come" thing...

If someone built it, I would buy it, but admittedly for much less than 10k.

--Adam

 

Could you be more specific about your problem?

You wrote that you have north of 600 hp but you did not explain your problem?

Some examples; the old US 2 speed boxes were best for 1/4 miles times because there was no time loss gear change.

Maybe you want more top speed? But that is more a question of final drive & engine revs rather than a 3 speed box?

With north of 600 hp you must have more than enough power to spin the rear wheels at most speeds so maybe you need wider wheels and stickier tires.

In my simple view of the world more engine power = less gear box speeds? So long as I have enough power to spin the wheels what does it matter what gear I am in?

But what exactly is your issue with the 3 speed?

Marton

 

This is my second transmission. The first was the original in the car with just under 100k on it. This second one was a rebuilt from 928 International (great people to deal with, excellent parts, just stupid me thinking that a stock rebuilt 3 speed would hold up). I don't even drive the card hard, but since this latest tranny, my car has pretty much lost 3rd gear. The things that I have noticed is that it wouldn't even go into third gear until driving for about 3 minutes, and now when it does reach 3rd gear, any attempt to accelerate (even mildly) results in slipping.

If anyone has any other ideas on what the problem may be, I a more than willing to try it.

But in a nutshell, that is why I am looking to do something else to transfer my power to the ground.

 

Ah ha, had a similar problem with my Mustang.

there are people who make so called "bullet proof" mustang auto transmissions using multiple clutches and kevlar brake bands.

The 928 auto is basically an MB box, there must be people who "race harden" MB auto boxes; did you investigate this approach?

Marton

 

Marton is right, MB shops ought to know how to harden that trans with AMG parts. Or, go to a 4-spd box and again look at AMG internals.

 

Ever considered a 928 4-speed auto? Todd's 6.1 @15-20 psi of boost with Micky Tompson drag slicks has yet to see a transmission problem. He has a stock 1987 4-speed with over 160,000 miles on it.

He does have a gear vendor overdrive unit (originall designed for the C5) in his car giving him 7 (or 8?) forward gears. Even before the gear vendor unit was installed he was not having any issues with this transmission.

 

The truth is I am sure I will end up with a 4 speed in the car, my father hasno problem with his (87 S4) and the price of a rebuild is around $1,995. Hopefully that fixes my problem, and I am sure that sooner or later, especially with the following that the Shark has, someone will build a better, viable replacement for the 928.

 

I like your optimism, I really do. Problem is, loyal following or not, we are very small in numbers. If we could get say, 10 people to commit the money to have something designed, who knows? Problem is, who is willing to shell out that kind of money for a project that has a 50/50 chance at best of actually happening.

We see a lot of started projects around here, most with very good intentions. Most never make it past the prototype stage or maybe 1-2 cars in the field.

There is already a solution to the Mercedes transmission – AMG rebuild. Not cheap, but neither is making a 600hp 928.

As for the 5-speeds, GTS transmissions are getting very rare. If anything, it would be cool to have someone like Todd take apart a GTS transmission, diagram everything to be reproduced and start making a few. He could do it, no problems there, but who is willing to pay that much for one?

 

Perhaps Steve Cattaneo who deals with 928 auto transmissions quite a bit? Steve Cattaneo posts here on ocassion. You can email him at 928euro@mastertechtrans.com