Two Chevy overdrive transmissions are available for older cars and trucks: 700R4 and 200-4R. The 200-4R is nearly a drop in replacement for a TH350. Same bolt locations and length and it can use the same drive shaft as a TH350. The 700R4 is bigger, heavier, requires a new cross-member and a shortened drive shaft. The 200-4R seems to be an underrated trans because the early versions had a weak 4th gear and input drum. Many of the performance re-builders have solved these issues. A 200-4R from TCI or Bow Tie Overdrives is capable of handling 450-500 horsepower.
Lockup or not?
Perusing Jeg's and Summit's web site for transmissions I saw there are lockup and non-lockup versions of the 700R4 and the 200-4R. The advice I found on the Chevy High Performance website was:
"If this is a street car, run a lockup converter. The lockup mechanism is a simple device used to physically lock the crankshaft to the transmission's output shaft in Fourth gear. By doing so, you improve economy and extend the life of the transmission."
TCI and Bow Tie Overdrives sell kits with the relays and wiring required to enable lockup.
The mysterious 'TV Cable'
The Throttle Valve (TV) Cable controls line pressures, shift points, part throttle downshifts and detent downshifts. This cable tells the transmission what it should do based on the position of the throttle and it has to be precisely set in conjunction with the throttle cable. If it isn't set correctly it can cause the trans to fry itself and die a smokey death in just a few miles. Some people seem to think the TV cable requires voodoo magic to set it properly but the reading I have done says there is one specific procedure for setting the cable and it shouldn't be 'adjusted' or 'tuned' to make the transmission shift differently. The TV cable also requires a mounting bracket that is specific to the type of cable and the carburetor or EFI system you are using. Bow Tie Overdrives has their custom 'TV Made Ez system' systems.
Final thoughts
I'm still trying to decide on whether to go with a simple (and cheaper) TH350 or spend a bit more money and add some complexity to get the overdrive. I think the overdrive will make the truck more pleasant to drive on the freeway. The truck would be turning less RPM's at freeway speeds and probably get better gas mileage. My biggest concern with the overdrive trans is the TV cable but there seems to be a lot of detailed information available on the internet on how to setup it up.
Related links
Overdrive trans info on Chevy High Performance
Performance transmission builders
www.bowtieoverdrives.com
www.tciauto.com
TV Cable instructions and info
TCI TV cable instructions
Bow Tie Overdrives TV info
No comments:
Post a Comment