350C to non-lockup?

[b4black]

I tried this in the transmission section with no replies Maybe they are afraid of anything non-SFI.

My '82 GN came with 350C trans and 3.08 gears. I'm building it up for racing. The trans builder suggests doing away with the lockup. I am OK with that, since this will not be street driven much.

On most 350C's there are only two wires going to the TCC solenoid. On the the turbo V6, there are four. The other two are for 2nd and 3rd gear switches. If I do away with the lockup, will the ECM have issuses? Does it need to know what gear it's in? Will it turn on the check engine light?


From the service manual (two and four wire diagrams):

 

[dr_frankenstein]

thats a darn good question Rich...

I think your gonna have to be the test mule for this....

 

[Freddie's Buick]

Not sure about getting rid of lock-up even on a race car. The best bet is to get an older hydraulic controlled THM-350. Summit and Jegs and maybe a local shop can get you hooked up. Rich...been there. The ECM won't throw any codes. The ECM only controls the third gear, (that's all). It gets disengaged when you step on the brake, (you probably already know that). There are a few drawings out there which allows for manual control but you don't want to be worrying about that racing. If you're like me, (cheapskate), I choose to get B&M's lock-up control kit, (#70244). It allows you to dial in your speed for lock-up or shut it off right on the dash via a knob. Although it cost me $160.00 I justified that a replacement THM-350 transmission is way more. It's an easy DIY kit.

Now I've not installed it yet since my car is still without tags/insurance and can only be moved back and forth on my driveway and garage. I backdated everything on my car, (no ECM). That is why I bought the kit because I too have a THM-350C and I need something to deal with 3rd gear. My carb is from a 1980 turbo regal and so is the DIS.

 

[b4black]

The builder says he converts 350C to 350's all the time. Many more options on performance parts and torque converters hat way.

I'm keeping the ECM, so if I say with the lockup, controlling it is not an issue. I this were a 2-wire setup, then disconnecting it would be no problem (those two wires are just power and ground). It's disconnecting the 2nd and 3rd gear switches that I don't know the effect of. If they are just related to the lockup, then it's OK. If the ECM makes timing decisions or something else, then I could have a problem.

In the manual (image in first post), it shows the 4-wire setup as "TCC in all forward gears".

 

[Freddie's Buick]

....On most 350C's there are only two wires going to the TCC solenoid. On the the turbo V6, there are four. The other two are for 2nd and 3rd gear switches. If I do away with the lockup, will the ECM have issues? Does it need to know what gear it's in? Will it turn on the check engine light?

Rich, if you have a 350C the electrical male connector may have four wires going into it, but on the transmission's female connector only A & D are actually wired up, (A=red wire, D=white wire). That is of course if it's not a later MX-3 or MX-5. On mine, the ECM never threw a code when I was modifying the TCC system.

On Buick built MX-2 transmissions, lockup occurs only in third gear. Once it goes into third gear, based on load and the speed sensor, (25 mph), the ECM sends a signal switching on the third gear switch for TCC operation. Then another at 50-55 mph to unlock. That's it!

 

[b4black]

The transmission I have from the '82 3.8 Turbo car has 4 wires - 4 on the harness and 4 terminals in the transmission's connector.
I also have a 350C transmission from a '82 4.1 V6 GN - the transmission connector has 2 terminals and 2 blank spots.

Both transmission have "MX2" cast in the side. Only way to tell the differance is looking at the trans connector.

 

[b4black]

Did some more research...

This description for Car & Driver magazine:
"In addition, Buick has wired the Regal's on-board computer to the torque converter clutch in a new way. At 2500 rpm and wide-open throttle, the converter clutch locks up to transfer all the torque developed to the rear wheels. (In other GM applications, the converter clutch disengages during full throttle to allow low-speed troque multiplication.)"

And from another magazine:
"Another element of the improved turbo performance is the transmission, a THM350c lockup converter model that is shared with no other GM car. For turbo applications, the stall speed is raised from 1900 tp 2200 rpm for better off-line performance, and, for maximum acceleration, the Buick turbo transmission also locks up the converter in first gear under wide open throttle once the car speed hits 20 mph. In 2nd and 3rd it operates normally, locking up in cruise mode in high gear for better fuel economy, unlocking for part throttle acceleration."

The two satatements don't exactly agree. but they do explain that the turbo trans is different. The 2nd statement somewhat explains the need for the 2nd & 3rd gear switches. For sure it's locked in 1st gear @ WOT. Sounds like it's also locked in the 2nd and 3rd @ WOT, but normal at part throttle.

On one hand, it seems all fours wires are for the clutch and nothing else, so it should be OK to disconnect it. But on the other hand, now that I know how it works, I'm thinking I want to keep the lockup........."TCC in all forward gears" sound pretty cool.

 

[Freddie's Buick]

Rich, you may want to get this book:

http://www.amazon.com/Turbo-Hydra-Matic-350-Handbook-Sessions/dp/0895860511/ref=sr_1_1?s=books&ie=UTF8&qid=1369270943&sr=1-1&keywords=0895860511

The book states.....the MX-3 will lock on 2nd gear too. The MX-5 will lock up in first gear as well at WOT and speeds over 20mph, (all forward gears so that verifies the second statement). I also read somewhere that running a transmission without lock-up tends to overheat and beat the hell out of it.

That's why the older 350 transmissions were a compromise. I rebuilt my bare bones MX-2 with Kevlar clutches and the kitchen sink. Wouldn't trade her for a 200R-4 no matter what, (screw that fourth gear). THM-350's are practically indestructible, easy to find, cheap and reliable. Am I biased??

Wouldn't strike me unusual at all that the Turbo variant of the 350 would be beefier and somewhat different then the N/A one, (mine). It won't throw a code, but it would definitely mess up the transmission I assume if it locks up the way it's mentioned. Mine is a much simpler design.

BTW the image you posted the upper schematic of the THM350C is an MX-5. The lower one is a MX-2, (mine). I don't get why your transmission behaves like an MX-5 and has the same connectors but is stamped MX-2??

 

[b4black]

I will get that book, thanks!

The geneal internet consensus says just unhooking the TCC connector on a 200-4r is bad, but OK on a 350C. Different fluid paths. Early Monte SS owner's unhook 350C's all the time without problems.

I'm guessing that all 350C start out as MX2, and becomes an MX5 with just a couple of switches and wires. They wouldn't cast a separate case just for that. The important part is the ECM. The image up top labels the MX5 and MX2.

 

[Freddie's Buick]

...I'm guessing that all 350C start out as MX2, and becomes an MX5 with just a couple of switches and wires. The important part is the ECM.

Good assumption. I'd agree. The dark art would be in that ECM PROM. It has to be flashed with a different program in order to lock on all forward gears at predetermined loads. It must use TPS voltage and the speed sensor for parameters. I believe the 1982 Turbos shared the same ECM as the N/A. So it has to be the PROM.

 

[b4black]

Ok, I'm keeping the lockup and the four wire connection. Trans is at the rebuilder now. Interesting thing about this trans, it's a dual pattern - Chevy-BOP. The other two 350C's I have are BOP only. All three came out of '82 Regals and have MX2 on the case.

 

[Freddie's Buick]

......Trans is at the re-builder now.....

What you having done to it?

 

[b4black]

It needs a full rebuild. It's the reason the car was parked 19 years ago. Once he opens it up, we'll decide exactly what to do. Adding clutch packs, etc. Maybe a smaller diameter converter with about a 2400 stall. Aluminum pan. Nothing to fancy, just a little more durable than stock hopefully.

 

[Freddie's Buick]

Many years ago Eric Fisher gave me a beat destroyed 350C. I then bought an E-bay video, a GM 350C service manual and a high quality complete rebuild kit from:

MURPHYS AUTOMOTIVE LLC

http://stores.ebay.com/MURPHYS-AUTOMOTIVE-LLC?_rdc=1

I made just one special tool that was needed for assembly. The rest of the tools I used were standard tools. Most of the assembly was so simple I laughed. Total cost of upgrade rebuild: $150.00. Been kicking ass for 7 years since. Now you understand why I think the 350C is an awesome transmission?