mspiegle

I'm looking for some experiences on 5spd transmissions. High-torque cars that have had positive or negative experiences with their transmissions are what i'm after.

Specifically for Lag, how is your transmission taking the 513rwhp? Have you ever tried launching hard from a stop? Do you ever fear your transmission having issues?

I recently borrowed Andy's BFG comp t/a drag radials for "testing". I noticed that I could launch the car from 5K rpms with NO tire slippage whatsoever. I want to try for 6K, but as it is - i'm scared @ 4-5K because of the transmission-breaking factor.

I've noticed that redline sells a type of fluid for the 5spd that may lessen the damage of shock. Specifically, it provides some sort of cusion on the gear teeth to stop them from snapping. Has anyone ever had any experience with this?

Also, has anyone ever heard of cryogenically treating the 928 transmission gears?

And finally, I know its been mentioned before, but i'm looking for an updated answer. How much torque can a stock 5spd 928 transmission handle?

Thanks for reading!

Lagavulin

The tranny is doing fine, thankfully. I am running Royal Purple 75-90W gear lube and have no idea whether it 'helps' or not.

In general, I always have fears regarding the drivetrain's health. Mainly because of lack of traction, all of my street racing from a dead stop has been from 1500 RPM and rolling the throttle on; I have never dumped the clutch. However, if you have traction as you do, dumping the clutch at a higher RPM will be quicker off the line; obviously, it's going to be much tougher on the drivetrain too. Wheelspin is drivetrain-friendly, but it's not the quickest from point a to b.

The choice of blowers will have an impact too. Centrifugals are much easier on drivetrains due to their 'softer' power delivery versus a positive displacement blower or a stroker.

For roadracers, I'd venture a guess and say that a large percentage of failed transmissions is excessive heat and not managing it correctly. For example, without a tranny cooler, the Z06 guys can only go 15 minutes at top speed before their tranny overheats (..280+ degrees).

Dragging a car with sticky tires is an altogether different story while attempting to move 3500+ lbs from a dead stop; that's a lot of stress coming off the line. But it sure is fun though, isn't it?

At the very least, I would consider installing a sender and gauge and take it from there; if it consistently hits 240+ degrees, it's time for a cooler.

shaaark89

i agree with lag.
my car has an '87 lsd 5 speed in it and has not given me any trouble in race/de conditions.
again, i am not one to beat the h*ll out of it on launch, so that may be a separate issue, but as far as being able to handle the power and torque (i'm in the 500/500 range) it's not been an issue. very soon i will have substantially more power so we'll see if it still holds.
interestingly i was reading in one of the car mags of a company in russia that is making high end, high horsepower/torque (700ish) custom cars and the transmission they chose as the only one they felt could handle the torque was a 928 gt box.

Gretch

FWIW, I have found in a couple of instances that the clutch in Gretch cannot clamp down the horse power if I drop it at higher rpms.......Car launches pretty good, but the clutch slipped.....

Alternatively, if (like Lag suggests) I get a rolling start, or have full clutch engagement at 1,500 to 2,000 rpms, and then put my foot in it, She will break the tires loose and spin them to the rev limiter, in both first and secong gear. Now, If I had those big gummies that Andy uses, I suspect I would get launched like a Saturn B5.

So what I am saying is ; tires, technique, and road conditions all contribute to how fast you can launch a car, perhaps more so than just raw HP. Gretch use to have not quite enough horse power to attain maximum launch acceleration with the tires she wears, Now she has WAAAAAAAAY TO MUCH hp to apply it indiscriminately and expect optimum launch results.

One other thing, and perhaps more on the topic at question. The drivetrain is a "system". strengthing one aspect of it just nominates another to become the "weakest link". IE, you can ALWAYS break something. In high impact load conditions, I am betting the clutch and torque tube fail before the gear box does.

Old & New

Good point, Gretch, re/ clutch being softer than gearbox. With my double plate clutch, I suspiciously eye the CV joints as the weakest link.

It does suck to spin wheels through second gear, though. We need just enough tire to hook up sufficiently through second without the ultimate gummyness that will endanger the drive system (and wear out in 2000 miles).

Anyone out there in the 500 club happy with a particular set of tires?

goliver

What about CV joints? Any of you high HP animals had any problems?

Regards,

Gretch

So far the only thing I have put any significant wear on is my tires. everything else seems bullit proof. Course I am not doing hole shots (at least not on a regular basis). My unsociable behavior is limited to tire smoking in the first two gears, blinding fast runs up the interstate on-ramps to a buck and a quarter, and third to fourth gear *** stompins' of willing victims I find on the interstate.....

Other wise Gretch is a well mannered "brefiss wagon"

I am still looking for the 18 x 10 Cup 2 wheels, so I can put wider sneekers on the old girl.......Wish Andy would break down and buy a new set of wheels so I could buy his old ones......

goliver

Sounds like you use the tires as an alternate clutch. Sounds like a ton of fun.

Gretch

So much fun it should be illegal................come to think of it, most of it IS illegal...... oops.....



does sayin' "sorry" help? nah, I s'pose not.....

shaaark89

i have a double disc clutch as well. no driveline problems as of yet. tires definitely get used up though.

Mark Anderson

The weekest link in the 5sp box seems to be 3rd gear. I have broken 2 and Don Hanson has broke one that I know of. Since World Challenge does a standing start I do launch the car with some big sticky tires (335 rear) and never a problem. The CV's seem to be bullet proof. I think it is because the 928 has very good axel angularity.

Gretch

Well the meats you were running at Infineon looked like they were on steroids...How many positions did you make up at the start?

Mark Anderson

"How many positions did you make up at the start?"
I think I made up 5 by turn 2.

Gretch

great video man.........thanks.

Old & New

Mark.

Could third seem weak because it gets so much use? Perhaps if most track time is spent in 2-3-4, then third gets the most use and fatigue.