TH 350 overdrive and Lockup converter? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

383drvr · 10-11-2003, 10:09 PM

Hey guys,
Did they install overdrive TH350 transmissions in the 80's, (1983)? Mine had a cruise control harness going to the trans, and I took it, and the rest of the cruise control system out. (I think I regret it now). So does this mean I have a lockup converter and an overdrive transmission?
I'm getting ready to replace the trans, that would suck if I have to replace the expensive lockup converter to keep my (existent?) overdrive.

I do think I feel a difference in the rpms I'm driving at at highway speeds since I removed the cruise control. Do I need the cruise control harness and computer to make it shift into overdrive, or is that operation concealed in the transmission itself?

Thanks in advance

Tom · 10-11-2003, 10:16 PM

No overdrive th350's, only 700R4's and 2004R's.

You should have a lockup th350.

gchemist · 10-11-2003, 10:22 PM

????
The TH350C is considered the poormans overdrive. The true overdrive is the 700R4. First ID your transmission. A square pan is a 700R4 and a spuare pan with a corner cut off is a TH350. Another way to tell is by your shift indicator if the tranny is original. P-R-N-D-3-2-1 came with a 700R3. P-R-N-D-2-1 came with TH 350 and TH400.
The converter lock up does not need a computer. It is tied to the brake switch and a vacuum switch under the hood. I removed the original cruise harness in my 83. I still have a 700R4 and a lockup torque converter. The difference in RPMs is about ~200-300. At highway speeds you really can't tell unless you have a tach.

*1FaastC10* · 10-11-2003, 10:53 PM

Quote:

Originally posted by gchemist
Another way to tell is by your shift indicator if the tranny is original. P-R-N-D-3-2-1 came with a 700R3. P-R-N-D-2-1 came with TH 350 and TH400.

700R3? is this something new like the TH250, TH275, and TH375 that i havent heard about yet?

383drvr · 10-12-2003, 12:05 AM

I know mine is a TH350. So I have a TH350 with just a lockup converter? What will happen if I replace the lockup converter with a standard converter with a stall of around 1800? How much of an rpm difference shall I expect?

Thanks for everyones help

Mike76251 · 10-12-2003, 08:44 AM

My '81 Z/28 has a overdrive TH350 from the factory.

**swervin ervin** · 10-12-2003, 10:24 AM

No such thing as an overdrive TH350. There are TH350's with lockup converters which are called a TH350C. But you are badly mistaken saying GM ever made an overdrive TH350.

Mike76251 · 10-12-2003, 12:10 PM

Quote:

Originally posted by swervin ervin
No such thing as an overdrive TH350. There are TH350's with lockup converters which are called a TH350C. But you are badly mistaken saying GM ever made an overdrive TH350.

Semantics.................pure and simple.

My TH350 has "another gear?"...............shifts into something else after third?..............has a big RPM drop after third?

I just try to make it simple to understand there Mike.

houston6 · 10-12-2003, 12:18 PM

My TH350 has "another gear?"...............shifts into something else after third?..............has a big RPM drop after third?

I just try to make it simple to understand there Mike. [/QUOTE]

Am I missing something here?Are you saying that your th350 in your camaro has four gears from the Factory? are you positive its not a 700r4 ?Im not saying youre wrong Ive never seen a 4speed 350 before thats all

**swervin ervin** · 10-12-2003, 01:12 PM

Mike,

the only thing that is happening is the converter is locking. You have around a 200 to 300 rpm drop. The reason for the drop is the converter is no longer slipping. To check it, after you feel it lock, lay your foot on the brake pedal. You will feel or see if you have a tach, the rpm raise back up.

How's that for simple?

Mike76251 · 10-12-2003, 11:07 PM

Quote:

Originally posted by swervin ervin
Mike,

the only thing that is happening is the converter is locking. You have around a 200 to 300 rpm drop. The reason for the drop is the converter is no longer slipping. To check it, after you feel it lock, lay your foot on the brake pedal. You will feel or see if you have a tach, the rpm raise back up.

How's that for simple?

I know it works that way but I don't care what one calls it..........it feels and works just like another gear.

If it looks like a duck,
Quacks like a duck,
You get it.

Mike76251 · 10-12-2003, 11:14 PM

Quote:

Originally posted by houston6

My TH350 has "another gear?"...............shifts into something else after third?..............has a big RPM drop after third?

I just try to make it simple to understand there Mike.

Am I missing something here?Are you saying that your th350 in your camaro has four gears from the Factory? are you positive its not a 700r4 ?Im not saying youre wrong Ive never seen a 4speed 350 before thats all [/QUOTE]

You are not missing anything.........it is a TH350C lock-up trans.
"Pretty sure" it is not a 700R4 as I rebuilt the thing many years ago myself.

BTW: I wish it was a 4-speed TH350! It would be unique and those unique Z/28s are quite priceless.

I do have a 4-speed auto called a Hydramatic laying about.
Anybody want to debate that one? One hint: 1960

*1FaastC10* · 10-12-2003, 11:17 PM

Quote:

Originally posted by Mike76251
I do have a 4-speed auto called a Hydramatic laying about.
Anybody want to debate that one? One hint: 1960

i have 3 hydramatic 4 speeds laying around right now, and one in my 91 K1500, they're called 700R4s or 4L60s.

Mike76251 · 10-13-2003, 12:09 AM

Nope Jeremy...
No dice!
You have a Turbo-Hydramatic and not a Hydramatic.
Two very different transmissions there.

Notice the hint...........1960
That is when this trans. was made.

10-11-2003, 10:09 PM	#1
383drvr Registered User Join Date: Oct 2003 Location: Dallas, Tx. Posts: 308	TH 350 overdrive and Lockup converter? Hey guys, Did they install overdrive TH350 transmissions in the 80's, (1983)? Mine had a cruise control harness going to the trans, and I took it, and the rest of the cruise control system out. (I think I regret it now). So does this mean I have a lockup converter and an overdrive transmission? I'm getting ready to replace the trans, that would suck if I have to replace the expensive lockup converter to keep my (existent?) overdrive. I do think I feel a difference in the rpms I'm driving at at highway speeds since I removed the cruise control. Do I need the cruise control harness and computer to make it shift into overdrive, or is that operation concealed in the transmission itself? Thanks in advance

10-11-2003, 10:16 PM	#2
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	No overdrive th350's, only 700R4's and 2004R's. You should have a lockup th350. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

10-11-2003, 10:22 PM	#3
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	???? The TH350C is considered the poormans overdrive. The true overdrive is the 700R4. First ID your transmission. A square pan is a 700R4 and a spuare pan with a corner cut off is a TH350. Another way to tell is by your shift indicator if the tranny is original. P-R-N-D-3-2-1 came with a 700R3. P-R-N-D-2-1 came with TH 350 and TH400. The converter lock up does not need a computer. It is tied to the brake switch and a vacuum switch under the hood. I removed the original cruise harness in my 83. I still have a 700R4 and a lockup torque converter. The difference in RPMs is about ~200-300. At highway speeds you really can't tell unless you have a tach. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

10-12-2003, 10:24 AM	#7
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	No such thing as an overdrive TH350. There are TH350's with lockup converters which are called a TH350C. But you are badly mistaken saying GM ever made an overdrive TH350. __________________ Mike 1985 Chevy C-10

10-12-2003, 12:18 PM	#9
houston6 Registered User Join Date: May 2003 Location: north wilkesboro nc Posts: 221	My TH350 has "another gear?"...............shifts into something else after third?..............has a big RPM drop after third? I just try to make it simple to understand there Mike. [/QUOTE] Am I missing something here?Are you saying that your th350 in your camaro has four gears from the Factory? are you positive its not a 700r4 ?Im not saying youre wrong Ive never seen a 4speed 350 before thats all __________________ Scott

10-12-2003, 12:05 AM	#5
383drvr Registered User Join Date: Oct 2003 Location: Dallas, Tx. Posts: 308	I know mine is a TH350. So I have a TH350 with just a lockup converter? What will happen if I replace the lockup converter with a standard converter with a stall of around 1800? How much of an rpm difference shall I expect? Thanks for everyones help

10-12-2003, 08:44 AM	#6
Mike76251 Senior Member Join Date: Mar 2003 Posts: 2,499	My '81 Z/28 has a overdrive TH350 from the factory.

10-12-2003, 01:12 PM	#10
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Mike, the only thing that is happening is the converter is locking. You have around a 200 to 300 rpm drop. The reason for the drop is the converter is no longer slipping. To check it, after you feel it lock, lay your foot on the brake pedal. You will feel or see if you have a tach, the rpm raise back up. How's that for simple? __________________ Mike 1985 Chevy C-10

10-13-2003, 12:09 AM	#14
Mike76251 Senior Member Join Date: Mar 2003 Posts: 2,499	Nope Jeremy... No dice! You have a Turbo-Hydramatic and not a Hydramatic. Two very different transmissions there. Notice the hint...........1960 That is when this trans. was made.



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