Any way to enable control over the drive-overdrive shift point?

[95Noobie]

I'm trying to get used to my shift points and understand how to deal with the odd situation where after 3rd gear there is what seems to be a two gear in one option called drive/overdrive? There is a D with a block O for overdrive around it on the shifter dial. When pulling a light trailer on flat ground 3rd gear puts the rpms too high. If it put it in Drive/Overdrive which is my only other option then the 'drive' portion seems to be the sweet spot but then once I get around 50mph it tries to drop rpms again (is this the electronic overdrive?) but puts some bad lug on the engine.

Without the trailer, if I'm hovering right around 50 and let off gas just slightly it will drop the rpms into 'overdrive' and then between 45-50 it will lug the engine badly.

The rpm range for this overdrive situation is very narrow, almost any grade in the road or even trying to accelerate 1mph will kick it back to 'D' Obviously if I need to get power or speed more aggressively I can push the pedal half way and get it to go back to 3rd gear where I can get some added power.

So it is only a 4 speed transmission right? So how does the transmission drop rpms and get both drive and overdrive out of one gear?

It would be so helpful if I could use the drive gear but not have it ever drop into the overdrive. That would be kind of like having a tow/haul button or being able to lock it in a gear using a manual shift like the newer chevy trucks have.

Has anyone else struggled to find a better way to use drive without overdrive taking over? Is there a programming change possible in the 4L60E from 1995 to disable the overdrive or change shift points so it won't come lug the engine by dropping into overdrive too early? Or is there a way to disable it via a switch on a wire?

With the 305 being underpowered for the truck/tires I can't imagine ever being able to stay in overdrive unless perfectly locked at 55 or 60 degrees on a very smooth and very flat highway.

thanks!

 

[NickTransmissions]

I'm trying to get used to my shift points and understand how to deal with the odd situation where after 3rd gear there is what seems to be a two gear in one option called drive/overdrive? There is a D with a block O for overdrive around it on the shifter dial. When pulling a light trailer on flat ground 3rd gear puts the rpms too high. If it put it in Drive/Overdrive which is my only other option then the 'drive' portion seems to be the sweet spot but then once I get around 50mph it tries to drop rpms again (is this the electronic overdrive?) but puts some bad lug on the engine.

Without the trailer, if I'm hovering right around 50 and let off gas just slightly it will drop the rpms into 'overdrive' and then between 45-50 it will lug the engine badly.

The rpm range for this overdrive situation is very narrow, almost any grade in the road or even trying to accelerate 1mph will kick it back to 'D' Obviously if I need to get power or speed more aggressively I can push the pedal half way and get it to go back to 3rd gear where I can get some added power.

So it is only a 4 speed transmission right? So how does the transmission drop rpms and get both drive and overdrive out of one gear?

It would be so helpful if I could use the drive gear but not have it ever drop into the overdrive. That would be kind of like having a tow/haul button or being able to lock it in a gear using a manual shift like the newer chevy trucks have.

Has anyone else struggled to find a better way to use drive without overdrive taking over? Is there a programming change possible in the 4L60E from 1995 to disable the overdrive or change shift points so it won't come lug the engine by dropping into overdrive too early? Or is there a way to disable it via a switch on a wire?

With the 305 being underpowered for the truck/tires I can't imagine ever being able to stay in overdrive unless perfectly locked at 55 or 60 degrees on a very smooth and very flat highway.

thanks!

You have four forward gears in the Drive range setting plus the TCC. You have only three in the D3 setting, which is where you should stay if towing heavy loads or negotiating steeper grades.

You can look into HP Tuners to see if you can raise shift points or contact Black Bear Performance or Diablew to see if either can help with pushing back the 3-4 shift until later in your RPM curve.

 

[AK49BWL]

What you're thinking is a 5th gear is actually 4th with torque converter lockup. While the RPM is higher in 4th, the converter is unlocked and your engine is spinning faster than the input shaft on the transmission. With the converter locked, they both spin at the same rate (like a manual transmission setup would work).

On my 03 Blazer, I have a toggle switch on a wire coming from my brake switch going to the PCM/ECM telling the PCM whether the brake pedal is pressed or not. Using this, I can override the PCM's desire to disconnect the torque converter lock when I hit the brake... Or force the PCM to keep the converter out of lockup. That's one idea... It is possible to program the ECM to not lock up, but I have no idea how that works on the old TBI ECMs lol... I'm assuming it's TBI as you said 1995, new enough for an updated interior but not for a Vortec engine.

Keep in mind, forcing the torque converter to stay unlocked WILL heat the transmission fluid considerably. It'd be better to drive slower and stay in 3rd with the converter locked.

 

[Scooterwrench]

You can tailor the tranny to do what you want. One way would be to contact a tuner and describe what you want the tranny to do and they could burn you a chip or you could do it yourself with some free software and about $100 worth of hardware. Your biggest obstacle is that 305. Raising the shift points would be good for that anemic boat anchor.

 

[95Noobie]

Yes, weighing options on a 350 swap. Not sure which shop nearby could do it and do it correctly. AT the same time it would make sense to either swap the transmission or have transmission rebuilt while it is out. Since (i'm learning) the 1995 year is a special year, I would prefer to find a 1995 chevy silverado with the 350 TBI engine and the 4l60e tranny. I have my eye on two options locally both who have 'rebuilt 350s' and 'rebuilt tranny' within the last 20,000 miles or so. My transmission still shifts hard from 1st to 2nd if I have steady pressure on the gas or going up a hill, if I let off the gas right when it needs to shift it shifts like butter. Reverse slips if you give it too much gas, if you ease into it, it seems OK. It sounds like a matter of time and we will be rebuilding the tranny.

I'm not sure I'm interested in changing where 3rd gear shifts that seems to do its job well and as you say, keeping it in 3rd when towing a load would be the wisest move. I was just trying to figure out what was happening in drive/overdrive. Now I understand it is doing a torque converter lock like putting it in the highest gear on a manual transmission before it is ready and the engine has to lug.

It would be ideal if we could do some type of reprogram so the Torque converter lockup (the overdrive 'gear') didn't happen till rpms were higher, maybe when the truck was going 60 or faster which would get rid of the lug of the engine. I can ask a local tuner who helped me delete the automatic cylinder shutdown on my 2015 Suburban and maybe he can help.

If it wasn't hard on the 4th gear to keep the converter unlocked that would be ideal but don't want to create transmission overheat when it struggles already.

 

[NickTransmissions]

Yes, weighing options on a 350 swap. Not sure which shop nearby could do it and do it correctly. AT the same time it would make sense to either swap the transmission or have transmission rebuilt while it is out. Since (i'm learning) the 1995 year is a special year, I would prefer to find a 1995 chevy silverado with the 350 TBI engine and the 4l60e tranny. I have my eye on two options locally both who have 'rebuilt 350s' and 'rebuilt tranny' within the last 20,000 miles or so. My transmission still shifts hard from 1st to 2nd if I have steady pressure on the gas or going up a hill, if I let off the gas right when it needs to shift it shifts like butter. Reverse slips if you give it too much gas, if you ease into it, it seems OK. It sounds like a matter of time and we will be rebuilding the tranny.

I'm not sure I'm interested in changing where 3rd gear shifts that seems to do its job well and as you say, keeping it in 3rd when towing a load would be the wisest move. I was just trying to figure out what was happening in drive/overdrive. Now I understand it is doing a torque converter lock like putting it in the highest gear on a manual transmission before it is ready and the engine has to lug.

It would be ideal if we could do some type of reprogram so the Torque converter lockup (the overdrive 'gear') didn't happen till rpms were higher, maybe when the truck was going 60 or faster which would get rid of the lug of the engine. I can ask a local tuner who helped me delete the automatic cylinder shutdown on my 2015 Suburban and maybe he can help.

If it wasn't hard on the 4th gear to keep the converter unlocked that would be ideal but don't want to create transmission overheat when it struggles already.

You dont want the tcc unlocked unless you want to burn the transmission down. The TCC isnt your problem, the engine is the problem (you already know this, Im just reinforcing it).

Harsh 1-2 shift is likely TCC regulator valve bore wear; very common 95-2000 model years. Drop the valve body and check the pan for anything concerning. If everything looks ok, drop the valve body and install the Fitzall TCC regulator valve in place of the factory valve.

Unless that "rebuilt tranny" has paperwork, i wouldnt chance it. Def upgrade to a 350 sbc, 305s are horrible.

 

[Scooterwrench]

Have you thought of lowering the gear ratio?

 

[Sean Buick 76]

I would add a toggle switch in line so you can turn off the lockup converter any time you want. I ran for 10 years with a toggle switch and it was especially useful when towing!

 

[Supercharged111]

Have you thought of lowering the gear ratio?

The correct answer here is 350/383 swap, gear down, tune, and start saving for a transmission rebuild/swap.

 

[Scooterwrench]

The correct answer here is 350/383 swap, gear down, tune, and start saving for a transmission rebuild/swap.

If he were to go with a 383 he probably wouldn't need to gear down.