SILVERSIXX

Does the replacement converter need to be a lockup or can I just install a non-lockup?

Thanks.

7T1vette

I believe the early TH350's did not have lockup function, so you should have no problem finding one. If the converter doesn't have the passages there to receive L.U. oil pressure from the valve body, it will just "deadhead" and the tranny shouldn't know the difference. I'm not sure why you'd want to eliminate the L.U. function if you had it to begin with, but....to each his own.

sperkins

A non-lockup converter will not work in a TH350C. Ask my buddy 69camfrk how he knows.

45ACP

But if it will help, you can disable the lock-up function by simply unplugging the wiring harness on the tranny.

DO NOT do this on any tranny other than a THM350C, or you will burn that mother up.

bliehr

What year C3 had THM350's that lock up?
I thought all thm350 where non locking.

45ACP

'80 and '81.

All THM350's are non-locking.

THM350C's, on the other hand, have lock-up.

SILVERSIXX

Does any company make a converter for the TH350C with a high stall, say 3500?

Richard Cooper

Guys,
I have a 1981 and would like to disable my lock up because I am changing my motor to a non computer one. How can I tell if my tranny is a THM350 or a THM350C? Thanks.

KENS80V

If it is the original transmission than it will be a 350C. You can tell easily by looking for the electrical connector on the drivers side of the tranny. I don't believe the lockup function is controlled by the computer on the 1981 Corvettes.

bozzman3

Yes Hughes makes them.I purchased there 2500 stall for my 1980.They have one up from that as well.3500 and even 3000 can be a very high stall rate if you do a lot of city driving,but lots of fun at the track

guitarcrazy02

We need to get Sixfooter in on this. I think he knows...

R96IMP

STOP!!!!!
The converters are NOT-repeat NOT interchangable between TH350 and TH 350C.
The TH350C has a 3/4" pilot on the end of the input shaft where the converter slides on and requires a lock up converter design ONLY.
The option is to have the 350C converted to non lock up by changing the input shaft,which requires substantial trans disassembly.
There are hi stall lock up converters for the 350C available as stated in the previous posts.The non lock up converter will not fully engage the splines of a 350C shaft.All you will do si burn the trans up if the car will even move.
About 15 yrs ago my buddy Tim had that problem with a Grand Prix and a 355/350 combo.It drove for about 12 miles and then let go.Metal in the fluid,a loud BANG and the car stopped.Found that problem and the splines all stripped out.OUCH!!!

Richard Cooper

Kens80v,

I believe the 81 computer does control the lock up converter. I do have an electrical plug on the side of the tranny, does this mean that I have 350C? Thanks.

R96IMP

Yes,the blue plug on the trans is for the lock up interface withe the early style pcm.The lock up 350C trans also had ribs on the pan where the regular 350s had a smooth pan.I believe they are interchangable,so don't use that as your only guide to id the trans.

a1sensei

Let me save you from yourself. You WANT a lock up converter even if you could use one that does not (better fuel economy, no draw backs, why get rid of that?). The same could be said about the CCC, but I'll resist the temptation to hijack your thread. God bless, Sensei

P.S. Even without the computer, lock up wiring is child's play.

Richard Cooper

a1sensei,
can you explain (in detail) how to wire my lock up without the computer? It may be child's play to you and many others, but I su-k at electrical. I have done tons of stuff to my 81, replace body mounts, complete front end, new oil pump, rear main seal, remove and replace gas tank and much more but NO electrical. Thanks for any info. Take care and have a great week.

C3 4ME

I drove my 81 Z28 for about 15000 miles and the converter didn't lock up becuase the wire was disconnected. I never had a problem with it.

surfshark

I have a converter that my brother gave me brand new several years ago that the builder supposedly altered it so that it would fit/work on the 350C input shaft yet not have the lock-up function. I plan to install it on my 350C (1980) sometime this month. The odd thing is, the converter was built by an individual, not a known company, so I have to see if I can dig up his phone number. When I got this converter given to me, there were (and probably still are) very few converter options for the 350C. Mine is a 2300 stall. It seems the ones available at the time were either slightly warmer than stock or 3500. The lock-up never made that big a difference in RPMs and I needed more stall. I'll let you know how this works and I'll look for that number. It's worth a shot.

surfshark

I see Summit sells the GM20L (2000PM) and GM25L(2500 RPM). Not bad prices either. Thanks Bozzman.

One thing I'm not sure of, is that I've read that the 350C is not as "strong" as the standard non-lockup 350. Without hijacking this link, can anyone confirm/support this?

SILVERSIXX