Looking at buying an 85gs with a 12a. About 13k on a factory reman. New OEM clutch/PP. 113k on the trans. How hard can I lean on the OEM trans/clutch power wise?

Looking into a simple blow-thru setup. I figure around 200-250whp. Can the factory gear handle it? Won't be launched hard or raced. Just a daily driver/toy.

Thanks.

 

the stock clutch will live a short life, i'd suggest a stiffer pressure plate, and organic disc.

the trans should be ok, although its a little borderline. i'd have no trouble with it

diff should be totally fine.

 

Trans will be borderline for sure, but gentle use and a sprung clutch will help life tremendously.

The only problem with heavier duty pressure plates is that clutch forks crack up the middle or punch the pivot out, and the pivots themselves break. I reinforce them both, and I've even bent a reinforced arm and broken a reinforced pivot. Friggin' ACT clutches



This is the reinforced pivot that broke. You can see how I weld up the undercut section inline with the arm. I'd weld the whole thing up but then the retainer spring would have nothing to grab.

I wonder how well a standard pressure plate and a sprung 6-puck would hold torque-wise. Even if it did slip, it won't burn up/shred itself like a fiber disk.

 

i don't like the ACT extreme pressure plate, it breaks stuff. they have like a mondo one or something that isn't as stiff, and its a good upgrade.

the iron cross clutch disc works, but it sucks to drive on the street

 

The black car came with an ACT 6-puck unsprung disk and a pressure plate that had a ridiculous amount of travel to it, probably to counter pedal stiffness. After fighting having to crush carpet just to disengage the clutch, I ditched the pressure plate and installed a regular generic replacement unit, still with the 6-puck. Light pedal, decent engagement envelope, and you could still slip it fairly easily after about five minutes of practice.

One of my core engines came with a SR aluminum flywheel and an ACT pressure plate/sprung fiber disk that had a more realistic motion ratio. That's the one that I'm still using.

I don't know what models they are or anything, I didn't buy them new.

 

Southbend claims they can get away with a light PP (still 2200) and their full face carbon kevlar disc is good for 500ft lb. So I'd assume a full face kevlar clutch (maybe 6 puck) would hold my power goals. Also i'm told the kevalr won't glaze over. If you overheat it with excessive slippage you can re-break in the clutch and it will hold as good as new. Think I'd like to go with the kevlar over the bronze/ceramic.

What is a good pressure plate rate in your opinions for 300ftlb or so with a kevlar full face disc? How bad are the 6 puck clutches for street driving? Good friend had a 3 puck bronze disc and it was ridiculous for daily driving.

Also I had always liked the unsprung solid disc's. The lighter clutch seemed to be easier on the syncros going into gear at high rpm. Is this not the case on the FB trans? Like I said I won't be launching this car at the track or anything.

Thanks for all the info...

 

you want the sprung hub, that little cushion will keep the transmission intact

 

The sprung hub may help somewhat, but not for the reason most people think:

The rate of the springs in the hub is low enough that they completely compress with any reasonable amount of torque. Their purpose is to absorb the power pulses that happen with the firing of each cylinder (rotor face) under light load / cruise. The crankshaft (eccentric shaft) is accelerating and decelerating with each pulse, while the flywheel has enough inertia that it wants to maintain a constant speed. The difference in speeds causes chucking within the trans that is commonly called gear rattle. The sprung hub will absorb those slight differences in RPM and reduce gear rattle (and wear on transmission components).

All this stuff was really designed for piston engines. I don't know if the power pulses in a rotary are as distinct. I run a solid hub 6-puck ACT disc, and I can't discern any gear rattle in my T2 trans.

 

I broke several transmissions in succession with the unsprung disk. Went back to getting 10-20k out of a trans when I went back to sprung disks.

It's critical. Even if it was an electric motor, you'd want some form of cushioning between the engine and the rest of the drivetrain, or the gears will bear the brunt of it. And the transmission gears are far weaker and less well-supported than the gears in the rearend.

 

What was the failure mode on the broken transmissions?

 

I use an ACT 6-puck spring hub disc with a factory replacement PP for street use. Went overkill after destroying the factory replacement disc in 4 months. It's more abrupt but not undriveable.

 

so does it just Stutter a bit on start and stop driving? do you know about how much Wheel Horse Power you are making now? also does anyone happen to know the pressure rating on the Oem pressure plate?

 

so does it just Stutter a bit on start and stop driving? do you know about how much Wheel Horse Power you are making now? also does anyone happen to know the pressure rating on the Oem pressure plate?

 

Something was coming apart and allowing the mainshaft to "rack" forward and backwards. Changing load would move the shifter back and forth, proof that the shaft and gears were walking around. One got so bad that it would pop itself out of 2nd gear while on course. I'd generally take them out before I got to towtruck mode.

One of them DID go kaboom, due to one of the bearing retainer bolts coming out and getting stuck in the gears... So that may be a clue as to what was allowing the racking.

Never a problem with racking after going back to sprung centers.

 

Admin can delete this post

 

For what it is worth I have a factory clutch and pressure plate in my EV conversion 85 GSL and with 1000Amps to the motor it produces 277 ft-lbs of torque. I don't see any signs of slip. But I never have to slip it to start and I dont run it up and drop the clutch either. Static friction is almost always more than dynamic friction so my data point probably does not mean much.

 

Don't want to thread jack . . . but do you have more info on this conversion? Did you start a separate thread? I looked through your recent posts and didn't see anything.

 

The pisser, now that I remember that particular day, is that my times improved when I had to tone back my driving because I had to keep my right hand on the shifter, so I could only apply about a quarter-lock of steering.

 

Going faster by going slower. It really does work. What final drive gear do you run?

 

No idea what I was using at the time, I was indiscriminately going back and forth between 12A and GSL-SE ratios, which are so close as to make no meaningful difference.

 

Just wondering if lower rear gear would affect the strain on the transmission. Like on a bicycle lower gears are much gentler on my bad knees.

 

Thanks for the info all. Going to check out this "Gem" sunday morning. Been looking for a white FB in good shape for a while now.

135k with 13k on a mazda dealer overhauled 12A. At the time of the engine removal a new OEM clutch and PP and all new Ac components were installed. Original one owner car.

All original and bone stock.

It's the twin to the race toy... That will teach them to turn me down at the tag office...

 

That's a mighty nice pair.