Hi,

Wow, it has been a LONG time since I've had the time to post here.

When I finish grad school (in just a few months) I want to build a 4.0L Buick-Olds-Ponitac-Rover with a six speed auto and stick it in my 87 Fiero GT. My car is very clean, but far from numbers matching otherwise I wouldn't do it. Anyway, in order to understand what I'm asking I think I need to include the background of my though process:

Basically, my question is regarding the 6T70/75 six speed auto. This transmission has been manufactured since 2008 jointly by both GM and Ford. So despite it being new, there should be a lot out there, and I'm sure there are some wrecked G6's or a host of other vehicles I could pull one out of. The transmission should package well in the Fiero, considering it is about the same size as the G6 6 speed manual some guys are using in their Fieros now.

In a nutshell I've always liked the idea of a fast squentially shifting clutchless transmission, but if you've ever researched automated manuals and dual clutch transmission, you would find that most are made specifically for racing purposes and are VERY expensive. My idea is to rig a reverse manual valve body to a 6T75 transmission with a rachet shifter (drag racers might be familar with this setup). Essentially, it allows you to bump the shifter foward once for a quick downshift and back for a quick upshift and it will then rachet back to a nominal position. Its really slick and essentially a cheap and reliable way to make a clutchless squential manual. Shifts are as instantous as possible because you're not taking time to go through "N". A good driver with an H-pattern cannot shift faster than .35sec. It sounds like a small difference but it adds up and can actually make a significant difference in both effeciency and acceleration. Furthermore, it gets it right evertime, no grinding of gears, etc. The powertrain profs at my school tell me that theoritically, this is a great idea. However, I think I need to turn to some of you experts to apply it to real life.

Theoretically, the setup would be very simple considering there will be no transmission control module needed, because I would be simply pulling the gear selector arm on the transmission with a cable...thats it. No wiring. YAY!! Its different (better) than those stupid factory paddle shifters too. They are not directly connected to the transmission so when you say shift it thinks 'hmmm, well I suppose...if you like...maybe..." and then goes.

This setup apparently exists for the stouter 6L80/90 Corvette transmissions, probably because longitudinal transmissions are more commonly used for high performance applications, and apparently there are a bunch of truck owners drag racing with their 6 speed autos...but what about us Fiero people???

So that leads me to my questions:

1) Is there anyone anywhere who makes a manual valve body for the 6T70/75??? I cannot seem to find any but perhaps some of you might know.

2) If not, how much do you think is involved trying to make your own.

3) If either questions 1 or 2 are possible, the 6T75 is rated by GM at 315hp and 300lbft. I plan on making 400hp when I finally get to start this project, but I'm not a drag racer so no stationary launches for me. Do you think I'll be ok? If not, what kinds of things can I do to make it more robust?

4) Assuming I've made it this far, there are two types of manual valve bodies: those that engine brake when downshifting and those that don't. If I was ever interested in trying out a little road-racing at an SCCA event or something similar, which do you think would be better.

I apologize for such a long explanation, but it seems very difficult to desicribe much of this without being able to show you. I am a pretty serious car guy, and I know a lot about the engine I want to build, but the one major component I have yet to figure out is the transmission. Therefore, I'm hoping some of the transmission folks on here might know what I'm talking about, and be able to tell me what they think.

Thank you for your time and knowledge!

J

[This message has been edited by Yellow87FieroGT (edited 03-16-2010).]

Any ideas?

I think you're gonna be the "trailblazer" on this one...

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3.4L Supercharged 87 GT and Super Duty 4 Indy #163

Thanks for the reply!

Hmmm....I was just hoping someone had heard of a manual valvebody for transverse transaxles...I know they are available for the older 3 and 4 speeds on the older muscle cars and the newer 6L80/90. Just can't seem to find any for the 6T70/75.

Anyways, thanks!

There are also aftermarket valve bodies for the 4L80 but nothing for the 4T80. We just don't have the same racing support that those type of cars do.

Does a clutch-to-clutch shifted fully electronic transmission *HAVE* a gear selector arm?

No a dual clutch doesn't....and there are nice dual clutch setups for transverse applications - mostly expensive and from Germany though. Like the new Golf GTI 30,000E car I think has one. Those are really nice, but I figured I could get most of the benifits (like a fast positive shift) without the expense by modifying a 6T75 transmission with a manual valve body. That transmission is a true automatic, and yes it does have a little gear selector armature right off the transmission housing.

Basically, the idea is nothing new - drag racers have know the benefits of manually equipped autos for years. However those guys all use a typical longitudinally mounted transmission.

What I meant was: "Does it have a selector arm that can be used to select individual gears".

"Clutch-to-clutch" is the buzzword for the way the new generation of automatics operates. Traditional automatics only change one hydraulic component at a time when shifting. Modern electronic transmissions can engage one clutch while disengaging the previous clutch.

I haven't driven the transverse automatics, but the 6 speed in the new CTS has a "sequential style" shift option using the shift lever for operating the transmission manually. It generally sucks. I don't know if the operating principal for the shift lever option is electronic or mechanical.

quote Originally posted by Will: I don't know if the operating principal for the shift lever option is electronic or mechanical.

It's a Caddy... I'm betting it's electronic and difficult to deal with.

I'm sorry Will, I just misunderstood you there.

The Caddy is different, and not the same transmission, but to answer your question Will, the 6T70/75 series has a true selector like an older transmission - at least the ones I've seen do.

The reason why nearly all of them are so sloppy from the factory is that they are being shifted electronically when in "M" mode - I bet even on the Caddy (though I'm not familiar with that setup). They do this for a variety of reasons, but mostly to idiot proof the powertrain. So basically the TCM (transmission control module) and other things like the ECM etc get to together and take a vote when you go to shift. They argue, compare tables, preferences, etc and then decide to shift. I HATE that - an SRX I drove had that, a G6, etc they were all very sluggish.

If you get rid of all that, and use the mechanical setup like they used to do, you don't need all those computers and electronics because it will never shift itself - it will always respond when you want it to - but only with a properly designing manual valve body, of course. On the plus side, it will still act like an auto in first gear, refusing to stall. So you can idle at a light with no problems.

Anyway, this should all work in theory but it hinges on the availability of a manual valve body. I hope I'm explaining this right, it is a little difficult without being able to show someone...

All of that should only take a millisecond to decide. Slow shifts are not the result of the electronics trying to make a decision.

I'm not sure if the sluggish manual mode shifting that automatics have trouble with is purely hydraulic (IE, it takes time to fill/pressurize the clutch apply cylinders) or if it's a result of the shift timing/firmness specifications using a less than 100% duty cycle on the pressure control solenoid, and thus not applying high enough pressure for a fast shift.

IOW, it *can* be done, but most OEM's won't do it because they think that most people want smooth easy shifts.

Toyota modified their 8 speed automatic in the Lexus ISF for faster shifts. They supposedly relocated the solenoids to reduce the hydraulic delay between the solenoid opening and the gear changing. They also lock the TCC under all conditions except low speed in 1st gear.

quote Originally posted by Will: They also lock the TCC under all conditions except low speed in 1st gear.

Now that I would love to have. I hate the vague feeling of the TCC unlocking for acceleration... always feels like a slipping clutch.

The mechanical side of it isn't as difficult for me as long as the parts are available, which is why I'm asking. That's all I meant.