Last year I decided to "upgrade" my th350 to a BowTie OverDrive 700r4 level 3.Spent a pile of money making the nessesary mods to put it in,took it easy the first week on the road,and blew it the first time I nailed the throttle.Cash flow being what it was,I parked the Vette and waited till now to fix it.

Over the past year I've poked around a few transmission shops and every one I tell I have 500hp/500lbs tq. in the 406 either decline to do the job,or insist I replace it with something else.I've also noticed in searching the web,there are a limited few "builders" that sell a beast of a 700r4,but in all cases the deal is you buy it and install it yourself. This way when the transmission fails they can put the blame on you know who.Not going down that road again.So the last guy I talked to is a local builder that does quite a few race transmissions,and he wants to put in a beefed up th350,for a good price,and will give a 6000 mile warranty even knowing about the 500hp.

The commute I run is 40 miles my house to the parking lot,mostly country back roads where I can't even use the overdrive.The only stretch of highway I hit is only for about 9 miles.The other interesting fact is I got 15.5 mpg running the th350 before the swap,and now I barely get 14 mpg running the exact same commute.

Shall I keep looking for a 700r4 builder,or ditch it?I know some here that have ditched,and some that are happy with them.This MUST survive. :mad

 

One of the forum members (can't remember who) often recommends the 4L80e for situations like yours... :yesnod:

 

I'd stick with an overdrive, in the hands of a good transmission man the 700 R-4 can be built to handle that power, I've also read alot of good things about the 200 R-4's out of the Buick Grand Nationals with internal mods being able to take massive HP, the 4L80e should handle your HP and you might even be able to find a shop to install it as it is a stock trans (not for your application though).

What are you breaking? Heat is the main destroyer of AT's. A good cooler, and properly adjusting your TV cable (with a pressure gauge through the entire operational range, not just at idle) is required in setting up a OD trans. correctly. If your breaking internal parts most of the ones that are prone to do this can be replaced with stronger ones from most hp trans dealers, e.i TCI

I doubt a stock 700 R-4 can handle the power you are throwing at it, but setup correctly it should last for more than one pull. The tires should give before the trans.

I'm no expert but I have been doing research as my new motor will require some mods to my 700 R-4 to be reliable. Anyway good luck

 

What are rear end gears? OD trannys with 500/500 need lower gears so the motor can run in it's efficiency range. The best gear choice for 200/700R4's has to be 3.90 if you live in an area where typical highway/freeway speeds are @80+ mph If your doing lots of goofing around 4.11 like mine are a logical choice.

The parts strength in a TH350 is simular to a stock 700R4. They both blow up. I couldn't get a TH350 to last even the hot rodded version. As I've said before I don't even worry about my 700r4 and it's got 20,000 some thousand bad miles on it since the rebuild.

 

700r4 trannies are a pretty weak device, even late model ones.....best thing is a 4L80e with that kind of power/torque.....
trannies are rated at torque input, not HP input.....anyway....

I tore up my 700r4 in about 4 years daily driven, with a ~400 hp 355 engine...

GENE

 

The rear gears are 3.70 and with the 10" wide 295 50's I can roast the tires for 30 feet from a 25mph roll,bang second and catch another 6 feet.(This I did just once.)
I just made three more calls to different local shops and all three said the 700r4 would no way handle the power,and all three recommended a th350 or th400 to replace it.I'm still not completely convinced the 700r4 can't handle it,but with no one around here that will work on it,my options are rather limited.
As for what broke in the transmission,I have not pulled it to see yet,but it slips in drive if I give it too much gas.All gears still work,as I've been babying the POS since last summer,but the original symtom was running 6500 rpms shifting into drive and expecting a huge rush of torque and feeling my stomach sink as the tach swung to 7000 rpms and the car started slowing down like I'd shifted into neutral. :banghead:

 

Your trans is probably toast now, but burning clutches is usually related to improper TV cable setup. Why not just order a high performace trans from TCI and get a local trans shop to install it and set up the TV cable for you?

 

Originally i wanted to put the 4l80E in Size weight, and amount of hp it burned convinced me that the 700R4 was a better choice. Even the modified art carr TH200's are doing 9 second passes.

I never really even worry about my tranny anymore. I worry about blowing out U-Joints or posi units. I'm actually tired of auto trannys and really want a TKO or a non OD 5 speed and install a 2.73 rearend.

One of out corvette forum drag racers uses 4.30 or 4.36 gearing in his drag vette

scott@artcarr.com

 

If it still operates through all gears and is slipping under a heavy right foot,
then it sounds like the clutches are slipping. Assuming it was all new and built properly,
maybe you got some bad material that let go under the strain.

It's not that bad to fix an auto tranny, if you're mechanically inclined.
Go get the Haynes book on GM auto trannys and check it out. It'll be cheap
to fix, and you will know what's in there.

:seeya

 

I've never had a transmission apart further than a B&M shift kit before,and all my freinds know more about computers and networking than I will ever care to learn.(Just don't ask them which way to turn the wrench to loosen a bolt.)
So I'm afraid I'm going to have to pay an expert for this job.

 

what broke??? it could only need the harded pump shaft????
correct about operating range just use 1-2-3 on back roads.