purpleworm

This has probably been beat to death and I am sorry ahead of time. I want to put a switch on the brake pedal switch. I want to be able to pick if the converter is in lock up mod or not. I am tired of it hunting for gears all the time and burning out the tranny. I drive it in 3rd most of the time but with the 3.42 gears it just seems to be the right speed for some reason. My question is will it damage the tranny if I don't let it engage the lockup converter?

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91 Z28 Camaro
305 TPI
Flowmaster 3" exhaust
700R4 with 2000 Stall and shift kit 3.42 rearend
One sweet sounding system

'87FAKE-IROC-Z

It may damage the converter, probobly not the trans though. My problem is i forget i have mine in lock mode and drive on it like that for a while. That is taking its toll on my TC.

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'88 RS (originally 2.8)
-350, .040 over, vette alum. L98s, stock tpi.
-305 injectors & chip
-TES headers & edelbrock cat back
-3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
on a 2.050 60 ft.
(Damn the 2.8!)

eightTfourTA

iTrader: (3)

I put a kill switch on my TC not too long ago because the tranny didn't seem to want to downshift out of 4th in lockup. It's pretty effective in my situation. So long as you don't leave the TC disengaged while you're traveling higher than 45-50, it shouldn't hurt things. The lockup plays a large part in keeping the trans fluid flowing at higher speeds in 4th, directly affects the operating temp. (amazing what you'll learn from a few techs after the tranny gets toasted)
BUT, I would strongly suggest installing a heavy-duty trans cooler just as an added measure of assurance if you don't have one already. Just my thoughts.

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DR Stevens
1984 Trans Am 305HO L69
sucks gas, hauls ***
1991 Firebird 305 LO3
for days when I need a/c

steve8586iroc

This seams odd but if you try to do a top speed run or at least at 100mph or faster it seams the tc does not lock, nor if still excelerating at these speeds the trans stays in third gear, so how does this not damage the trans as well?

JoelOl75

Sounds like you need the 'b-fix' kit to get the 4th gear at wot shift.

purpleworm

I thought it would do a bit of damage but it has to be doing damage when it is in and out of it too. My tranny works good but I still hate the stupid thing. I would trade it for a standard anyday. I just ordered my mega shifter from summit so it should be a bit better. Well I think I will break out the relay and give it a go. Thanks guys!!!

jrr

An unlocked TCC won't hurt it at all. If anything, it shifts smoother and the car drives easier IMHO. The only thing I notice is a significant loss of MPG. It is true that GM fixed the tranny to run hotter when the TCC was locked up. According to GM, a hot tranny equals better gas mileage but I don't buy it. Heat kills transmissions and that will cost you more in the long run than any slight loss of fuel economy from keeping the fluid temps down.

If you, or anybody else, finds a way to eliminate the fluid restriction when the TCC is locked, PLEASE POST IT!

transfixleo

Driving in 3rd with L/U off is just the same a driving an older 350 that didn't have L/U. The problem comes when you are in O/D as the lower engine RPM's tend to put the converter at or near stall speed which is what generates a lot of heat, even if you have a cooler. When the converter locks, the problem goes away since there is no more torque multiplication going on. Also, the lower the gears the less of a problem this is.

purpleworm

I was thinking about this last night!! I agree now that I don't think there should be damage. I have a question to throw out there. If keeping the tranny unlocked is so bad how come a 350 turbo stays together with no lock up. It would be like driving a 350 turbo with a lockup and not using the lockup part.

THIS IS MY IDEA!!! I am getting my B&M console shifter on the 22nd. I am going to order the handle with the momentary switch in it. I will wire that to a relay which will control the lockup. One push trips the relay on and another push trips it off. That way I can wire it to an LED in my dash. I will have a good shifting mechanism and I will be able to control the lockup with the butotn on the stick. What do you guys think of this idea?

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91 Z28 Camaro
305 TPI
Flowmaster 3" exhaust
700R4 with 2000 Stall and shift kit 3.42 rearend
One sweet sounding system

transfixleo

The reason the 350 (or any other direct drive tranny) gets away with it is because the engine speed is higher than an O/D tranny. It is the low RPM in O/D that puts the converter into stall range. In fact, everyone thinks that L/U converters were added to 3 speed trannies for gas mileage. In fact, they were added to ALLOW very high rear gears, which, in turn, were used for gas mileage! W/O it, you would have the same problem that the O/D's have when L/U doesn't work since many of these had low 2 something gearing (so called highway gears). On the other hand, if you have really low gearing you could get away W/O L/U, but it is still a good idea to have it (less heat).



[This message has been edited by transfixleo (edited May 16, 2001).]

JP84Z430HP

Ok, I need something clarified here. Wouildn't the closer to equal speeds in overdrive be cooler than when the speeds are more different? I thought that the bigger speed difference would be the problem. That is why they say not to stall test at a stop for more than a few seconds at a time I thought.

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Working on:
'84 Z28 LG4 305 with 200,000 original miles!
Added dual elec fans.
145 MPH IROC Speedo
Building 430 HP 350 (ZZ430)
using primarily GMPP parts.
Short block sitting on a stand. (Man, those Fast-Burn heads sitting on it look good!)

Starting to look like the Kicker poster child!

ASE Certified Master Tech

steve8586iroc

Torque converter slipage is what causes heat. The reason GM says not too run in third or fourth gear without the converter locked up is because of lubrication problems. I personaly have a switch that prevents lock up because of a problem I had when I bought the car four years ago. With the tc not locked the car drives great so I just lock it up when I know I'll be driving at a sustained hwy speed or better.

Steve

transfixleo

At a stop there is the maximum difference in what I will call converter in speed to converter out speed (engine speed to transmission input speed). This will cook the tranny in no time. Now in L/U there is no difference in speed so no heat buildup. When not locked though the speed differential varies. Now inside the converter there is a certain dynamic going on that the faster the converter goes, the closer to coupling speed you get. Coupling speed is Non-L/U speak for near L/U. By definition in an O/D unit you are trying to slow down the engine for either greater gas mileage or increased speed. Now the high the rear gears (lower number) the slower the engine speed and the greater the difference in Input/Output speeds in the converter, or in other words you are closer to stall conditions at low engine speeds in O/D W/O L/U.
Add to this the fact that the slower the engine turns the lower the pump output, and therefore less cooler flow both for the engine and transmission. Return oil from the radiator IS lube oil. This may explain the lubrication problems mentioned.



[This message has been edited by transfixleo (edited May 18, 2001).]