Converter Lockup problem ?

[22229stingray81]

I had my mechanic tell me that the lockup doesnt have a pre-set rpm or speed for when it to go on, but a whole bunch of factors coming together.... so maybe not a problem to have it on at 20mph or so as long as it comes off easy? Just trying to contribute...

-Tatortot

 

[GerryLP]

Tatortot,

How far have you gotten with the lock up problem? I only ask because I feel that Stingray6974 may be up to something when he assured you that your problem had to be the solenoid.

Last night, I disconnected the tranny harness, and now the tranny does not seem to throw the gears as unpredictable as it was. Someone had described the problem as (and I am paraphrasing!) "it seems that it locks up the converter and then it throws the third gear" or something to that effect. :eek I couldn't believe how accurate that description was.

The car now shifts the gears better with the harness disconnected, and when it shifts I don't see the RPM gauge snap to 2,000 RPM in a flash (almost as if I could feel the converter locking right when the tach snapped). I think that my tranny is suffering from a bad solenoid also. The torque converter could cause this problem, but I feel that it is more unlikely, for in my situation I had replaced mine, and the L81 has good low end torque, but it won't brake a converter. The pin in it for the lock up is not as strong as high torque converters, but it hangs with it well.

I plan to drop the tranny oil pan and replace the solenoid As much as I would hate to do it. I hope I don't forget to put a pan drain before the next time. :lol

 

[evariste]

I'll try to explain all what I understood of the lockup converter behavior during the last months, and the "bypass" I have installed. As my english is a little bit poor, don't hesitate to ask questions if you don't understand what I mean.

As you may remember, I discovered that there was a problem with the converter lockup when the speedometer cable failed. As the measured speed was always zero, the computer never tried to lock up the converter. And driving the car was really fine...

What I understood is that the computer triggers a converter lockup wire when : 1) The speed is more than 25 mph AND 2) the throttle pedal is not fully depressed. On my car, as the throttle position sensor is out of order, the converter lockup is always triggered on as soon as the speed is over 25 mph. Not so good.

I have two things to do to fix definitely this problem : I can have the minimum lockup speed rise to 40 mph (I think) using the hypertech chip. I also need to have my throttle position sensor fixed to make it work properly. Too much for me now.

Looking at the wiring diagrams, I discovered that when you brake, the converter lockup is automaticaly released by a switch located behind the brake pedal. So I added a manual switch on one of the wires leading to this switch. When this switch is off, the converter never locks up, when it is on, the converter can be locked according to the orders given by the computer.

It's not so handy, but it works. In heavy traffic, or in town, I put the switch "off", and on open road I put it "on".

I hope this will help you !

Evariste

 

[GerryLP]

Evariste,

That's a very good approach. But now that you mention that -I plan to replace the stock carburator with either an Edelbrock 750 or a Speed Demon 750 (both available with electric choke and vaccum secondaries).

What concerns me is that if I replace the carb for one without the computer hook up, then I may totally loose the converter lock-up feature in my car, unless I install a manual switch or someting.

I will only be concerned if my fuel economy without the lock-up feature drops dramatically (1 less mile per gallon I can live with)

What do you think? ;help Anyones' input requested.

Any L81'ers without the computer hooked-up out there?

 

[22229stingray81]

lockup

GerryLP,

I have not yet done much with my lockup problem. I dissconnected the solenoid harness next to my tranny and nothing changed, just got a check engine light. I feel that there is a major problem and need to take it to a corvette transmission shop which is quite a ways away from me, and I do not trust just anyone. So Im going to deal with it until it gets unbareable. I am thinking about just dissconecting the lockup all together (does anyone know how much mpg it loses without it going on on the highway?); though it seems to have more power with the lockup coming on so early, it is very annoying in traffic. Ill keep you all posted on any changes and repairs, thanks for all your help again.

-Tatortot

 

[evariste]

Tatortot,

Just try this : look behind the brake pedal. You should see (not so easy) a connector with a purple wire and a pink/black wire. Just disconnect it and try to drive in this configuration. If your car has a smooth behavior, then you can guess something is messing your computer...

Evariste

 

[22229stingray81]

Evariste-

Thanks for the break down, Ill try it tomarrow as soon as I can, Ill let you know what happens, thanks again.

-Tatortot

 

[22229stingray81]

Well I looked under above back and all around. I couldnt find that color combination of wires.. There was a connector right above and almost touching the brake pedal itself that had a green wire, a blue wire, and browish purpleish (maybe faded black?) with a white stripe wire.. could this be it? I suppose I could just pull it and find out but I dont want to mess up anything really badly... Any other suggestions? Am I just not looking close enough maybe?


-Tatortot

 

[evariste]

I know it's not so easy.

If you want to really get access to it, it's better to remove the heater's hose.

If your car has a cruise control, you should have 3 connectors :

- 1 for the brake lights with a white and an orange wire.
- 1 for the cruise control release with a tan and a dark green wire.
- 1 for the TCC realease...

Try to find the orange and white wires. They separate from the main harness juste beside the TCC's one. Notice that it is also the horn relay's place (strapped over the harness).

Have a nice week-end !

Evariste

 

[22229stingray81]

Thanks for being patient with me, Ill try again tomarrow. You also have a nice weekend!


-Tatortot

 

[22229stingray81]

New development

Well today I was cruising at about 55mph and I hit the accelerator a little and the lockup actually went off.. then I hit the brake after it came back on again and it went off again.. Seems like the lockup in 3rd gear is starting to work... Still have the same problem in second gear though.. wont come off unless I stop completely. I guess things can fix themselves? Any thoughts would be appreciated.

-Tatortot

 

[GerryLP]

TCC Solenoid

Tatortot,

Last night I worked my TCC problem. I tried ordering the correct TCC solenoid for the 81 vette (AC Delco 1997591), but this part number is discontinued, and I could not find it even at www.gm-restorationparts.com The dealers kept sending me to a tranny shop and the tranny shops sent me to the dealer...:crazy

Instead, I had to order the TCC Lock-up solenoid (AC Delco P/N 1997592. If you have access to a 81 Corvette Shop Manual, then you can see in page 7A3-15 that the alternate solenoid looks like the solenoid wiring for TH350C model 8VZ, 8VA,8T3...etc at the upper-right corner of the page. The alternate solenoid costs around $50.

Well, page 7A3-14 at the very first paragraph, tell us that the model code is stamped IN the right side of the bell housing. I looked all over, but I could not find the model for my tranny. So I turned it in my mind every which way I could and then it occurred to me that the alternate part number solenoid that I had to settle for and my stock solenoid were only different in that the negative wire (black) and the "D" pin wire (so identified at the tranny plug connection) were crimped together on the alternate P/N solenoid. My stock solenoid had the negative wire and the "D" pin wire separate from each other.

So, after searching for locking wire terminals similar to the stock ones and not finding any at the usual places (Auto Zone and the like), I decided to reuse the terminals on my stock solenoid. I clipped the ones from my old TCC solenoid and I also clipped the alternate solenoid wires to match my stock solenoid. I used No-crimp connectors (by Swenco) to connect them to the alternate solenoid.

I then installed a new 3rd gear switch (AC Delco P/N 8643710) to make sure that I would not have to go back to the tranny pan drop process in a while. I then wired the transmission valve body as it was as stock. For which, by the way, I could not find the exact configuration in the shop manual.

Not trusting my brain power :duh I also installed a B & M tranny oil pan drain kit -in case this repair did not work. It will make my next pan drop less messy. I also had a bit of a scare when my last pan bolt felt like it was stripped. I regained my composure, and used a tap die set to chase the threads with a 5/16 -18 die. (or is it a tap? :confused ). The stock bolt would not work anymore, but a longer one (1" long from Auto Zone) did. Luckily it was at the shifting cable plate hole where it stripped, so the excess lenght was taken up by the plate itself.

I am glad to report that the transmission is shifting fine and my problem is gone. I think that the reason was that the stock solenoid was installed with a gasket, and the gasket was leaking (the solenoid surronds a small hole on the tranny valve body). If the gasket leaks, then you'll experience a delay in the lock up where it seems that the gear changes and then the converter locks up (it sounds very much as if one were to let go the clutch (in a manual tranny) at low RPM for a thrid gear. The alternate solenoid, by the way, has a built-in rubber seal instead of a gasket to seal between the solenoid and the valve body.

Now what remains is for me to follow Evariste's instructions to by-pass the TCC lock-up for whenever a Mustang pulls up next to me . The best of both worlds -TCC lock up for fuel economy and By-pass TCC for fixing Mustangs.... :L

 

[22229stingray81]

Wow.... that is way over my head. I would get confused at dropping the trans pan (haha). I did find it very interesting how you were able to substitute the replacement alternate part, thumbs up on that! And thank you for sharing all the part numbers and websites with me. I have one question though... when the lockup comes on, you loose acceleration? I think my vette feels more powerful with the lockup coming on so early, but I could be wrong. So lockup; good for fuel economy, bad for power?



-Tatortot

 

[GerryLP]

I have one question though... when the lockup comes on, you loose acceleration? I think my vette feels more powerful with the lockup coming on so early, but I could be wrong. So lockup; good for fuel economy, bad for power?

First let me say that, generally speaking, the converter locks in two ways. Hydraulically and mechanically. With the hydraulic lock-up there is an amount of slippage that varies with the type of converter (the stock converter has minimal slippage). With mechanical lock-up there is a direct connection between the engine and tranny (no slippage).

In my case, I installed a 2,400 stall converter. It is designed to allow my engine (through large amounts of slippage at low RPM's) to reach the best engine speed (while my car is not moving) so that my engine's cam power range can best be utilized.

The mechanical lock-up happens when parts in the converter connect and form a solid link between the engine and transmission through a fluid signal (solenoid operated). Mechanical Lock-up prevents my engine do that unless something else allow the engine reach the target RPM for my cam (such as the rear wheels spinning to allow the engine reach the RPM). This is so because of the mechanical linkage formed through the lockup feature.

On the other hand, without lock-up AND while driving normally around town there is that large percentage slippage happening in the converter because the engine speeds are relatively lower. The result is a large waste of gasoline. To put matters in perspective, I was averaging 18 miles per gallon in everyday driving around town (this is with my new cam too ). When I disconneted the tranny harness to dis-engage the lock-up feature my gas consumption went up to about 12 miles per gallon. So lock-up helps save gas. It also prevents converter shaking which is really bad :blow for the tranny.

In the stock Corvette tranny, the mechanical lock-up helps in that the shifting is crispier, minimizes slippage, and helps corral every bit of engine horse power reach the rear wheels.

The by-pass action that Evariste, Nut, and Mike :BOW are telling us helps us select the lock-up feature at our own convenience :Twist

 

[22229stingray81]

They say you learn something new everyday... looks like I learned todays "something" and much more! Thanks very much for that explination, I understand how the mechanism works much better now. I thought it was nothing more then a gas saving mechanism, boy now I know! Thanks again for taking time to explain it.

-Tatortot

 

[GerryLP]

TCC By-pass is a go

I am glad to report that the By-Pass switch operation was a success. I placed a small duck bill illuminated switch at the air ducting chanel right next to the center console island above and aft of gas pedal. I drilled a 1/2" hole into the channel, but the channel already has other factory-drilled holes. The one on the front of the ducting (facing the gas pedal) worked great to route the wires ot the TCC switch. I found a good grounding point at the brake booster mounting stud inside the cabin.

I can reach the switch easily and it works like a charm. Thanks Evariste, Nut, and Mike for your inputs in this issue and everyone else's inputs to make this a nice little project. ;worship

I used a 3-blade illuminated switch (power, signal, and ground), but the electrical current for the actual signal is not enough to make the switch glow brightly at nite. All I see is a faint glow when I disengage the lock-up circuit (By-Pass).

Maybe I need a 4-blade switch so that the switch light can have its own power source???? Comments?

 

[22229stingray81]

Well I have new activity on my lockup. I attribute it to the very cool weather I have been having in va (39 for a high yesterday). During the summer, in the heat (90 degrees +), is when I started getting all the problems. Usually as soon as the car accelerated the second time the lockup would come on regarldess of conditions (after a cold start). I now realize it is because of what temperature it is. Now that it is so cold outside it wont come on till the 4th or 5th acceleration, or 3 minutes of straight driving. Yesterday while on the highway whenever I needed power the lockup (in the middle of acceleration) would come off, my rpm would rize a little, then when I stopped the acceleration, the lockup wouldnt come right back on.. it would take about 30 seconds... i think this is because how much cooler the car is running now... so.. could the heat have something to do with all of it? Now that its much colder it is actually starting to work close to normal... any comments would be appreciated.

-Tatortot

 

[GerryLP]

Tatortot,

You owe yourself to perform this simple check (and maybe you have already done it). Disconnect the harness at the tranny, and while the engine is running at 2,000 RPM and with the tranny in neutral (make sure you have the vehicle wheels blocked so that it won't roll and apply emergency brake) check the voltage at the "A" and "B" wires of the harness. Are you getting 12 volts?

With the diagnostic code display lead grounded AND the ignition in "ON" you should be able to get 12 volts across the "A" and "B" wire at the connector. Remember to keep the brake switch closed (brake pedal pressed). If 12 volts are present on the connector then the problem is internal.

And your cold weather observation makes sense to me. My car's tranny would not act-up until it warmed-up while driving. I think that the seal between the TCC solenoid and the valve body hole withstands the pressure because of the cold temperature of the transmission fluid. While cold, engine oils and tranny fluids have a higher viscosity. While hot, the fluids have a lower viscosity. When the viscosity is higher the fluid pressure increases and this is sufficient for the hydraulic signal to move the converter rotor towards the converter stator and lock-up.

When the transmission fluid reaches warmer temperatures, the viscosity drops, and the fluid pressure also drops. The transmission is having a hard time maintaining a fluid signal strong enough to maintain the converter coupling through a fluid sygnal. It literally "leaks" past the gasket or seal when the fluid is hot.

To complicate matters, your normal driving acceleration, slowing down, brake action, and internal pressure switches are cycling the TCC lock-up solenoid on and off and on again.

I am not sure if you have changed the solenoid already, but if you have not, then I am willing to "bet" that the solenoid is your problem.

 

[22229stingray81]

GerryLP,

Thanks for the test outline. I will do it this weekend. Im pretty sure I can handle hooking up a voltmeter to it.. I hope.. haha. Ill let you know what I find. No I have not yet changed the solenoid. I think the job is way to complicated for my mechanical experiance thus far. My mechanic still insists there is nothing wrong, so until I can get it into the corvette transmission shop, Ill just have to live with it. Still a pleasure to drive it even with the lockup going on and off. Thanks very much for bearing with me on my mechanical inclination, or lack there of, ill keep you posted.

-Tatortot

 

[GerryLP]

Tatortot,

Aren't we all in the same situation on other issues? I am glad to help on this one, but don't feel bad about that -you'll learn something here every day. I also do learn daily...