Once again, I'm waffling and thinking about keeping the C4. If I do, the tranny definitely needs repair. I was considering tossing the 700R4 in favor of something I won't break every time I step on the gas. I no longer care about the OD, so a TH350 or TH400 are both viable considerations, but I wouldn't know what was required for such a swap.

I was also thinking of possibly going insane on the thing and ditching the injected 408 in favor of a 350 with a roots type setup. :D

I can't make up my mind right now. Basically, it doesn't cost me a dime to have the car collecting dust in my shop. If I sold it or parted it out, I could finish the renovations on my house much faster, but I'm not overly concerned about that either.

Thoughts? Suggestions?

 

Mojo,
replace the 700r4 with a 4L60E. If your PCM won't work with it you can get a stand alone ECM for it from TCI and other makers. Or maybe even a 4L80E (on big honkin' tranny) it will fit in a C-3, so it would probably fit in your C-4.
Another idea is to get a TH-400 and a GearVendors overdrive unit for it. If ould effectively give you 6 gears, since each gear has an overdrive associated with it. Gearvendors overdrive is about $2000-2300, just depending on where you get it. It bolts right on the end of a TH-400, or TH-350. And is good for something like 1500 hp.
Then there are some guys that can build you a 700-r4 that is as strong as a TH-400. George Kull, (GKULL) has an Art Carr 700r4 with switched lockup 3000-stall 9.5 -inch 3-clutch converter, he is running a ton of HP out of his 383.

 

I don't really need the OD anymore, I'm not taking it on any long distance cruises. Gear Vendors units are great, but they're prohibitively priced. I'd be happy with a simple Th350/400 swap. Someone here recently did a 4L80E swap, but I think it was a *lot* of work!!! Many people claim to be able to build bulletproof 700r4's, but for every person that makes that claim, there are 5 people that broke that indestructible tranny.

 

Well if you want strong then the TH400 is the way to go. They are inexpensive and fairly strong right out of the box. With a few touches they will handle just about anything thrown at them. It shouldn't be a very hard conversion. Good Luck!
PS. George Kull has broken more than a few 700r-4s, check his website at http://www.corvetteforum.net/c3/gkull

 

I put a 4L80E in my C3 Vette back in January. Despite it's size it fit like it belonged there. Other than accomodating for it's extra length by relocating the crossmembers mounting pad and shortening the driveshaft, the only other concern is controlling it. Without going with a full-manual valvebody, you will need an electronic transmission controller - basically an ECM for the tranny. If your car had a 4L60E, you should be able to rework the ECM, otherwise you'll need a stand-alone transmission controller like the TCI/FAST T-Com or one of several others. I chose the T-COM because it is very similar to the FAST/SpeedPro SEFI and I can use the same laptop to control rpm, shift speed, shift firmness, torque convertor lockup, etc.

Besides being bullet-proof when built properly, there are also kits available that will enable the 4L80E to have 6 forward gears by engaging the overdrive and different gears. This gives you benefits similar to running the Gear Vendors unit without having to modify your tranny tunnel, while costing and weighing less.

 

Mojo,
It kind if makes one wonder, sometimes. Do they not read what you've said? Do they not care about what YOU want? Why would someone suggest an expensive Gear Vendor overdrive, or a similarly expensive 4L80E, after you've said that you don't care about the OVERDRIVE? Personally, I believe that there are 700R4's that would suit your needs, but you have expressed no faith in them. Just because I don't happen to agree, why would I try to promote one to you?

Between your two logical choices, I lean towards the TH400. Partially because of my greater experience with them. The TH400 DOES soak up more horsepower than the TH350, so that IS a consideration. The TH350 will use the same slip yoke as your 700R4. Either trans will require driveshaft work, mount adaptation, and either a kick-down cable (TH350) or a kick-down switch (TH400). Both will also require a vacuum line for the modulater. As a minor consideration the TH350 has a 2.52:1 first gear. The TH400 has a 2.48:1 first gear. While there isn't MUCH difference between these two, remember that you're taking out a 3.06:1 first gear. The loss of first gear ratio will make you want to consider torque converters and rear axle gears a little differently than you have in the past. Just a couple of things to consider. I'm sure others will present other angles, too.

 

Just an FYI... after much research, on my brothers project car (71 w/454 expecting 600+hp at flywheel) we are going with a level 3 from http://www.700r4.com/trans/levels.htm

They know the kind of power we will have. They know it will be raced. They are still willing to give a 1 year warrenty. Does that mean we won't break it? No. But they have to have some confidense to give the warrenty. At least talk to them before you swap to a different tranny.

 

Dude, don't bother-yea they say bla bla bla.........I told 'em I was building a 406 so put "every upgrade in there." Less than a year and its gone; then the excuses started- blaming my driving up and down the hill for "overheating it." And thats with a Be Cool rad. with their 7 plate truck trans cooler plus a B&M trans cooler in front of the rad. They did rebuild it the one time and then said- "that's it, no more warranty." They do talk a good show until there's problems; then you'll get their attitude! Oh yea- I also had to take it back several times for leaks etc. and every time they'd screw up something that I'd have to fix-like torn wires to the tc, pulled apart the shift linkage.....

 

Has anybody done a TH400 swap in recent memory? Any info would be appreciated!

 

Are you looking for something specific that I didn't cover above?

 

I was specifically interested in how to mount the C beam.

 

Hmmm, I wonder if a Lenco would fit? Not known for breakage, shifts quicker than any auto. I guess I was thinking out loud also. :yesnod:

KM

 

Someone on the Forum posted a picture of an adaptor the he made up that bolts to the TH400 and accepts the "C" beam. It is made of steel and bolted to the trans with the tailshaft mounting bolts. I think it also tied into the trans rear mount. It looked like a beautiful solution. It was probably in the C4 tech section. Good luck.

 

Your car probly makes such an a s s load of torque that 3 gears would be plenty. :cheers: