Manual torque converter lock-up on THM-350C.....

[Freddie's Buick]

Does anyone know and have instuctions for wiring-up a THM-350C to lock up when I want it to? I want to set it up to lock at 25 MPH and unlock at 55 MPH and bypass the ECM control.

Any ideas guys?

 

[WE4]

It is not hard... I will be back around Tuesday at shop.. call then

 

[crazygn]

thm 350c , what trans is this.

 

[Freddie's Buick]

Your post reads like you're fairly knowledgable about Buicks.
THM-350C stands for Turbo Hydro-matic 350-Computer controlled.

Or is their supposed to be something funny I don't understand about your post?

 

[WE4]

the 350 c .... The C designation......

It does not stand for computer control as they are not computer controlled. Clutch is the designation. What they are is powered all the time and when gov pressure in third gear circuit, trips a pressure switch, ground is made which in turn thru oil exhausting, locks the converter. Speed at which lock up occurs is determined strictly by trans being in third gear and what level of pressure switch you are using. It can be done with a toggle easily.


Bruce
WE4

 

[crazygn]

No nothing funny i run a th 350 from a 76 trans am and iam looking to get any thing i can from it, thats why i asked i was not sure about the c at the end.

 

[Freddie's Buick]

crazyGN,

I guess this is were us folks learn something knew all th time about these cars. The THM-350 is pretty much a standard 3-speed automatic most Buicks came with from what I've heard. (Most of the earlier GN's came with one).

Hey WE4,

I read that off of my Buick manuel I think, (about the 'C' designation). But it's probably dated. Anyway, I'm still waiting on those instructions for the TCC. I'll check back Tuesday. Thanks guys!

 

[Freddie's Buick]

Hey WE4,

So let's see if I'm understanding this. The torque converter is always locked? Something trips the pressure switch by grounding it? Which intern unlocks it. (I'm assuming the brake switch and ECM are the trippers). Please school me here...thanks!


By the way, anything on those instructions yet?

 

[MeanBuicks]

No, it's not locked up all the time.

What Bruce means is that the solenoid is fed a constant, key-on 12 V source. The solenoid still will not activate until it is grounded.

The ground to complete the circuit is controlled by the third gear pressure switch and a governor pressure switch. It'll only lock-up at a certain speed while in third gear when wired this way.

 

[WE4]

Yep Greg is right, but also...

The converter is locked until you fire motor. Just like in our cars with 2004r's or 700r4's. . Technically, lock up does not apply, it exhausts. The clutch is always on and line pressure feed from tcc valve kicks the clutch off. When the solenoid is energized, it allows the fluid to exhaust from front cover applying clutch. Yes, I know this sounds whacked and hard to comprehend, but that is how it works.

Bruce
WE4

 

[Freddie's Buick]

Thanks Bruce, Greg...

Anything on those instructions yet? (......the weekend is coming and I'm ready to dirty myself a bit again).

 

[MeanBuicks]

Re: Yep Greg is right, but also...

Originally posted by WE4
The converter is locked until you fire motor...Technically, lock up does not apply, it exhausts. The clutch is always on and line pressure feed from tcc valve kicks the clutch off.

Splitting hairs now but until you fire the motor, the hydraulic pressure required to actually lock the clutch (by pushing the piston from the backside) isn't present in the converter either. In other words, both sides of the TCC are exhausted. For that reason, I wouldn't consider the converter locked until the motor is fired.

 

[WE4]

You will need to drop pan. Give me a fax number and I will draw it for you.


Bruce
WE4

 

[Freddie's Buick]

Bruce,

You're out in california, 3-hours differance. I'm out in east coast Miami.....(you know...the Banana Republic). I'll e-mail you a fax number that anywhere from 6:00 A.M. - 12:00 P.M. P.S.T. you can send to.

Thanks!

 

[crazygn]

Ok so are you guys talking about a nomal turbo 350 trans, will it work on a 76 th 350 that i run, and will it help in the 1/4 some.


maybe iam just crazy

 

[WE4]

Hey Freddie....

The FAX number you gave me connects to a pissed off Latin lady!!
LOLOLOLOLOLOL

Whoever she is , she is pee oed at me boy!
twice it got her.

Give me a good number....

Bruce
WE4

I am still laughing......... LOLOL

And I got the email first before I saw the thread reply..... I put the name and the screen name together and sent it. Then I saw the board.... OOPS!!!! LOL

OOOOOOOOOO Now I see... you operate on the normal AM/PM time of day.... See, I only know that weeks go bye these days. No am/pm, just a week seems to be noticed these days.

Tell her I am sorrry whoever she was.........At this time (yawning) I dont read so good....

 

[Freddie's Buick]

Oops!

That's wifey dearest living in the 'unknown zone'....ha ha ha!
(Now I'm laughing). It's o.k.

Yep, try at those times I wrote on the thread. Nobody's home then. Just the fax man....just the fax.

 

[WE4]

sent 8:00 am 10/3

Bruce
WE4

 

[Freddie's Buick]

Thanks! I got it.......I won't get around to it this weekend though! I almost forgot.......my son's birthday.

I looked at the fax and I'll probably have more questions in the future. I'll stay in touch....thanks again!

 

[Freddie's Buick]

Alright,

From the fax picture, I gather that the gov switch you drew is the 3rd gear switch. And the seloniod is the pressure switch.

So I'll ground the wire that's going to the 3rd gear switch since it's being eliminated. I'll keep the brake toggle switch and I'll insert an additional toggle switch in the circuit.

Now with this set up, if I maintain the toggle switch on the 'on' position, will the converter lock-up at 25 mph and unlock at 55 mph automatically? Or will I have to toggle it myself?