Overdrive on '03

mdub · December 2, 2003

I'm tired of the shifting algorithm going into panic mode and unnecessarily shifting into 3rd, or even 2nd for every mole hill. If I control the throttle manually, it's typically sufficient to just kick the tranny out of OD.

Is there a way to manually disable overdrive (either factory or aftermarket)? It would be great to replace the seldom used tow/haul button with a OD disable function. The driver could just press the button when entering hilly terrain. In addition to decreasing aggravation, it seems like it would help fuel mileage as well.

Any suggestions?

Thanks,

Mdub

robsawatsky · December 2, 2003

I'm not sure if I understand your question. Does your tranny not have 1, 2,3 and OD positions? Shifting down to 3 is the same as disabling OD. The only difference is that in shifting down to 3 you also get some engine braking when going downhill.

mdub · December 2, 2003

Sorry, I should've stated the question better...

There's a definite RPM difference between running in 3rd vs. running with Overdrive disabled. Watch the tachometer... after hitting a hill, the auto tranny shift algorithm first tries to pull out of overdrive (no torque converter lockup), and later shifts down to third or second if necessary.

It would be very useful to have manual control over the Overdrive disbable, without shifting to 3rd. Manual control would force the tranny to stay out of overdrive BEFORE the cruise control has already lost too much speed, thus requiring the 3rd/2nd downshift. Correct me if I'm wrong, but I believe older 1/2 ton Chevs had a button for this feature before tow/haul mode was added.

Thanks,

Mdub

Tree_Hugger · December 2, 2003

Have you tried just using tow/haul whenyou're in this hilly terrain?

lrymal · December 2, 2003

Have you tried just using tow/haul whenyou're in this hilly terrain?

Tow/haul doesn't help. Done tried it on mine.

I also have encountered this type of kick down in not only GM trucks, but other brands which have a regular type automatic transmission. What happens is that if the hill is of a suffient incline, instead of doing a slight kick down, the automatic goes into a full o-mi-gawd-it-is-a-hill down shift. Very annoying.

The only solution is to keep the truck in 3rd gear until those range of hills are behind and no more are ahead.

My '99 Pontiac Grand Am had the SAME problem. But, the solution was very simple. Its cruise control cable was adjustable and by changing its PULL on the throttle, you could keep it from pulling in all the way as it was set at the factory. I had that cruise adjusted to a very nice hill kickdown.

You can't do this type of adjustment on the '03s since the accerator is cableless and uses the computer to handle the accleration. I have no idea how the '02s and earlier are. Yes, to reinforce the statement, I tried to figure a way of adjusting the danged thing on my '03.

mdub · December 2, 2003

Yep, tried tow/haul mode, but it only seems to hold the downshifts longer, but doesn't seem to kick down any sooner.

Manual control of torque lockup would be nice to slightly bump the RPMs up, and keep them up through hilly areas. There must be a control available for the torque converter lock/unlock, because the Auto tranny tries this as a first attempt during the automatic downshift. I also can kick the tranny out of OD by bumping the throttle (without actually shifting to 3rd).

I thought I recalled seeing the Overdrive Disable pushbutton on OBS Chevy trucks ('96-'98 vintage?). Many Dodge/Jeep vehicles had this button, and it only "disabled overdrive" (disabled torgue converter lockup), but didn't actually shift all the way down to 3rd. It's just my opinion, but it seems like an Overdrive Disable pushbutton is exactly what the torque deficient 5.3 needs.

-Mdub

mdub · December 3, 2003

Irymal,

Yes, I've thought of that before -- it would be great if we could "de-sensitize" the cruise control. In fact that would possibly be a better solution so the RPM range stays low, in the good fuel mileage range. I would even settle for letting the cruise control lag 5-7 mph if it would keep the tranny from doing the hyper-active shifting.

Any suggestions from the group on ways to de-sensitize the cruise control?

Thanks,

Mdub

Shaners · December 3, 2003

My '99 Pontiac Grand Am had the SAME problem. But, the solution was very simple. Its cruise control cable was adjustable and by changing its PULL on the throttle, you could keep it from pulling in all the way as it was set at the factory. I had that cruise adjusted to a very nice hill kickdown.

Hmm... That is interesting!!! I'll have to do some research on this for the car that I just bought my wife.

It is a 1993 Olds Cutlass Supreme Convertible. When I was driving it home from Jersey to PA, the car seemed like it wouldn't apply enough throttle on the hills to kick the car down a gear to maintain speed. I had the cruise set at 68-69 MPH and some hills I looked down and it was still locked in OD going 60 MPH. I need to adjust it back so that it'll downshift, because I don't want to drop 9-10 MPH on every hill... I don't mind loosing 3-4 MPH, but this was annoying to the point where I had to manually give it throttle so that I wasn't a nuscaince on the road!!!

chevroletmb · December 3, 2003

have you tried using manual 3rd?

mdub · December 3, 2003

Yes, I sometimes use manual 3rd, but it's a little excessive to run at 70mph in 3rd. An OD Disable pushbutton would keep the RPMs at a more practical range.

It's becoming apparent that I must be one of the few that lives in the hilly Pacific Northwest. Otherwise, I think more people would understand what I'm talking about. I just want the ability to MANUALLY select the shift point that occurs during the first minor kick-down of the Auto downshift. It's not Overdrive, and it's not 3rd... I believe it's just the torque converter coming out of locked mode, forcing the engine to rise ~ 300 RPMs. Other manufacturers have offered the ability to manually select this maximum shift point through a pushbutton. I'm wondering if there's a way to select this maximum shift point on a 1/2 ton Silverado.

And now that I think about it, it wouldn't help to "de-sensitize" the cruise control. Doing so would only let the cruise float in a ~5mph range, and the same nuisance problem would occur if the cruise happened to be at the bottom of the speed range when you hit the oncoming hill.

-Mdub

99-2door · December 3, 2003

Sorry, I should've stated the question better...

There's a definite RPM difference between running in 3rd vs. running with Overdrive disabled. Watch the tachometer... after hitting a hill, the auto tranny shift algorithm first tries to pull out of overdrive (no torque converter lockup), and later shifts down to third or second if necessary.

It would be very useful to have manual control over the Overdrive disbable, without shifting to 3rd. Manual control would force the tranny to stay out of overdrive BEFORE the cruise control has already lost too much speed, thus requiring the 3rd/2nd downshift. Correct me if I'm wrong, but I believe older 1/2 ton Chevs had a button for this feature before tow/haul mode was added.

Thanks,

Mdub

So what you really want is control over the lock-up converter, not overdrive lock-out. No chevy truck has ever had a manual control over the lock-up converter from the factory.

Most discussions I see like this are to make the TCC lock-up whenever you want rather than to not lock up. I think you could accomplish this by doing the following:

There is a wire that goes from the ECM to the tranny for the TCC(Torque converter clutch) solenoid. If it is like everything else it is a ground signal. You could install a relay in line with the wire going through the normally closed position. Put a lighted (when on) switch in the cab. Then when you turn the switch on it will light up and open the circuit in the relay causing the TCC to no longer be able to light up.

WARNING: The ECM may see this as a TCC sol. malfunction. This may cause your SES light to come on while the lock-up over-ride is engaged. Also running without the TCC engaged can cause higher tranny temps.

If someone knows a reason why this wouldn't work please post.

mdub · December 3, 2003

99-2door,

Thanks for the info... that's exactly what I'm asking. I'm hoping it would be somewhat self explanatory to locate the TC Lockup solenoid and wire. Otherwise, it would be great if you could provide reference to the appropriate signal wire. I can easily provide the relay or switch circuitry.

If the SES light comes on, I'm assuming it will go back to normal when the TC lockup wire contact closes? Or would the SES light latch? Guess if it didn't latch, the SES light could act as a reminder that TC lockup is disabled.

Regarding transmission heating, I wouldn't operate in this mode continually, but it would be in hilly terrain. The few times I tow, I typically keep the tranny in 3rd anyway.

I also have an email into Westers to see if they're interested in providing the manual TC Lockup control through a custom ECM program.

Thanks much!

-Mdub

Tucson_02Silverado · December 3, 2003

The only way I've been able to keep CC on in Overdrive and not downshift in mountainous passes (4%-6% grade) is to be running above 75MPH, usually 80MPH. This was also true with all my past vehicles with the 4 speed auto (700R4, 4L60, 4L60E), both TA's and the Caprice wagon.

However, if you are running into an extremely heavy head wind forget about it and leave CC off.

Shaners · December 3, 2003

Sounds like about the only other option would be a pricey gear swap to 4.10's. That would add about 500 RPM at cruising speed...

robsawatsky · December 3, 2003

OK, now I've got it - your confusing torque convertor lock-up with overdrive. Overdrive is the top gear selection in the tranny - the further RPM differential is generated by the elimination of slippage in the torque convertor when it is locked up, which is a separate function from OD. Yes, I notice the RPM difference and it will lock-up in both OD and 3rd on my vehicle.

As a previous poster suggested - you don't really want to unlock the TC on hills in OD since this is exactly where you will generate the most heat. I thought most people used a manual TCC switch to keep it locked-up, not the other way around?

As another post suggested, 4.10 axle ratio would be a better but much more expensive choice.

Other than that, shifting down to 3 before you hit the hill should keep the TC locked-up but assuming you have a 4L60, the RPM diff between OD and 3 is a bit more than on the 4L80.