Adding overdrive to a TH350?

[qu1cks1lver56]

I know I've seen bolt on overdrive units, but can't seem to find any on the net. Anyone have any ideas on how to add overdrive to a TH350 and not break the bank?

[71STPSDE]

The most popular is Gear Vendors. They aren't cheap. Around $2400. It would be cheapier to get a 700R4. Just a thought!

[Pyrotechnic]

Gear Vendors and US Gear are the two I know of.

A complete install of a GV (do it yourself) is about $3000 when all said and done, maybe more. The US gear unit is a little cheaper. Not sure what your budget is, but to me it's a waste of money. If you have a stock to mild engine, you're much better off getting a 700R4.

[qu1cks1lver56]

Gear vendors, that's the one I remember seeing. $3000, ouch. I think an 700R4 would be much better, anyone know the average cost of setting one up in an old truck like ours?

[68GMCCustom]

....or try getting a 200-4r (built up of course). The 200-4r is the same length as a turbo350, has a different ratio for 1st gear(and 2nd?) for a better 1-2 shift w/o the bog, and has a slightly lower (.67) overdrive. I think (not sure) that even the spline count is the same...meaning you can use your old driveshaft. I think the only real change other then the TV cable, is the tail mounting location, meaning slight changes to your tranny crossmember. I'm no expert so I could be off on some of these details.

[Conundrum]

Originally Posted by 68GMCCustom

....or try getting a 200-4r (built up of course). The 200-4r is the same length as a turbo350, has a different ratio for 1st gear(and 2nd?) for a better 1-2 shift w/o the bog, and has a slightly lower (.67) overdrive. I think (not sure) that even the spline count is the same...meaning you can use your old driveshaft. I think the only real change other then the TV cable, is the tail mounting location, meaning slight changes to your tranny crossmember. I'm no expert so I could be off on some of these details.

The trans mount is in the same place as a th400, so you would only have to move your trans crossmember back a little ways. I found this info....although i'm not to positive on the accuracy of it, I think the 2004Rs 1st gear is a 2.74. Although it came from TCIs site.

TH350_________TH400
Lo 2.52 2.75____2.48 2.75
2 1.52 1.52____1.48 1.57
3 1.00 1.00____1.00 1.00



200-4R__700R4/4L60E__4L80E/4L85E
Lo 2.78______3.06_________2.48
2 1.57______1.63_________1.48
3 1.00______1.00_________1.00
4 0.67______0.70_________0.75


http://www.tciauto.com/Products/Tech...ear_ratios.asp

[coater]

I have a TH350 in my '85 and having a motor machined as we speak,but was wanting overdrive also. Are there any computer hook ups for the 700r4? Can you just bolt it up to a mild motor and ride?

[qu1cks1lver56]

thanks for the info.

[68GMCCustom]

700-r4 and 200-4r only require a a TV (throttle value?) cable...but it has to be setup right or you can burn up the new tranny.

[coater]

what about just going with a 400 with a lock up converter?

[Conundrum]

Originally Posted by 68GMCCustom

700-r4 and 200-4r only require a a TV (throttle value?) cable...but it has to be setup right or you can burn up the new tranny.

You also need to control the lock up converter some how.

[qu1cks1lver56]

I've got a TH350C with a lockup converter, and I guess my highway RPM's aren't too bad compared to others, I just do alot of highway travel to and from school everyday and would like something lower than 2500 RPM's @ 70mph

[3r!c84]

Originally Posted by qu1cks1lver56

I've got a TH350C with a lockup converter, and I guess my highway RPM's aren't too bad compared to others, I just do alot of highway travel to and from school everyday and would like something lower than 2500 RPM's @ 70mph

all maters about gear ratio ,my th350 screams down the highway at 75mph @3000rpm thanks to the 3.42 gears

[68GMCCustom]

forgot about that. Is there a diagram somewhere for the 4 wire connector and how to rig up a switch for it? I'd like to be able to keep the lockout "locked out" unless I'm cruising 80 or something and need it.

[Conundrum]

Not sure about that, but I do know that B&M has a kit that will control your converter and it is adjustable from 30-90 mph and it doesn't appear that you have to remove the pan to install it. I remember reading a few years ago that you can change a few things in the 2004R and use a th400 kick down wire to control it, but I don't know of anyone that has done it.

[68GMCCustom]

My tranny builder provided a nice TV cable for me so I'm set there. I'll have to look into the B&M lockout options.

[joe231]

Originally Posted by 68GMCCustom

....or try getting a 200-4r (built up of course). The 200-4r is the same length as a turbo350, has a different ratio for 1st gear(and 2nd?) for a better 1-2 shift w/o the bog, and has a slightly lower (.67) overdrive. I think (not sure) that even the spline count is the same...meaning you can use your old driveshaft. I think the only real change other then the TV cable, is the tail mounting location, meaning slight changes to your tranny crossmember. I'm no expert so I could be off on some of these details.

depends on which length TH350 you have.....the 200-4R is very short.
there are 3 tail shaft lengths available on a TH350. 6", 9", and 12".
the 700 is very close to the same length as a mid length tail shaft equipped TH350. the 200 is very close to the same length as the short tail shaft equipped TH350

[qu1cks1lver56]

Originally Posted by 3r!c84

all maters about gear ratio ,my th350 screams down the highway at 75mph @3000rpm thanks to the 3.42 gears

haha 3.42's is what I've got. 75 is about 2700rpm for me. which is great for no overdrive, but I'd really like 3.73's and an overdrive.

Originally Posted by joe231

depends on which length TH350 you have.....the 200-4R is very short.
there are 3 tail shaft lengths available on a TH350. 6", 9", and 12".
the 700 is very close to the same length as a mid length tail shaft equipped TH350. the 200 is very close to the same length as the short tail shaft equipped TH350

didn't know this, I thought it was only long or short shaft TH350's.

[3r!c84]

[QUOTE=qu1cks1lver56;3893899]haha 3.42's is what I've got. 75 is about 2700rpm for me. which is great for no overdrive, but I'd really like 3.73's and an overdrive./QUOTE]

how can i test to see if my lockup converter is working ?

[qu1cks1lver56]

Originally Posted by 3r!c84

how can i test to see if my lockup converter is working ?

only way i know of, is to unhook the vacuum switch, and run down the highway and see if you have any higher rpm's than normal, then hook it back up and see if its any different.

[Conundrum]

Originally Posted by joe231

depends on which length TH350 you have.....the 200-4R is very short.
there are 3 tail shaft lengths available on a TH350. 6", 9", and 12".
the 700 is very close to the same length as a mid length tail shaft equipped TH350. the 200 is very close to the same length as the short tail shaft equipped TH350

Forgot all about the different tailshaft lengths.

[3r!c84]

how much will it cost to cut your drive shaft?