4L70E Transmission

[a990dna]

Anyone have any experience with this trans??

I'm considering a TBSS for a DD but also need towing robustness. I've been away from Chevy since the USA-1 days... and have installed a B&M kit on a 350TH. Can the 4L70E transmission be reprogrammed to eliminate any overlap if present?.... or does TransGo or B&M make a shift improver kit for this unit?

Also, has anyone installed an aftermarket converter?... or is this trans too new?

Thanks.

[Envoy Fan]

I think the TB SS will be first to get the 4L70E, unless the SSR has it.

[ScarabEpic22]

I think the TB SS will be first to get the 4L70E, unless the SSR has it.
I know the early SSRs have the 4L65E tranny, but they might have gotten the 4L70E this year.

[SBK]

Can the 4L70E transmission be reprogrammed to eliminate any overlap if present?
What do you mean with the term "overlap?" The "E" means that it's an electronically controlled transmission, so be somewhat careful with hardware modifications from a shift quality (read: shift kit) perspective. There should not be any robustness issue with this unit as long as you're staying within the towing guidelines.

No need for a converter swap either, particularly for towing. Just out of curiosity, why would you change the converter in a towing vehicle? Current technology stuff is pretty darned good. If you were swapping converters for performance, there may be some possibilities, but bear in mind that a performance converter (ie: looser) is not what you want if you are going to tow. Yes, it is a lockup converter, but towing on grades where the torque converter is operating in a non-lockup mode will always result in a lot of heat generation. Not something you want in a towing machine.

[a990dna]

What do you mean with the term "overlap?" The "E" means that it's an electronically controlled transmission, so be somewhat careful with hardware modifications from a shift quality (read: shift kit) perspective. There should not be any robustness issue with this unit as long as you're staying within the towing guidelines.

No need for a converter swap either, particularly for towing. Just out of curiosity, why would you change the converter in a towing vehicle? Current technology stuff is pretty darned good. If you were swapping converters for performance, there may be some possibilities, but bear in mind that a performance converter (ie: looser) is not what you want if you are going to tow. Yes, it is a lockup converter, but towing on grades where the torque converter is operating in a non-lockup mode will always result in a lot of heat generation. Not something you want in a towing machine.

Thanks for the info...

Overlap is or was the term that described the amount of slip designed across the various shift points. In my past experiences... most, if not all, automatics from the factory are usually designed to provide a smooth and undetected shift.

For us performance nuts, we feel the need to change that to firm shifts and remove the overlap by modifying the valve body to increase pressure... or reprogram the ECU/TCU on an electronically controlled solenoid activated valve body. I have an AW4 on my Jeep and it's a great transmission that seems to learn and reprogram firmness over time. I have 170K miles on it and it shifts better than it did when I bought it new.

As far as the converter, I wouldn't intend on changing that unless an aftermarket source had something that would increase the stall speed a bit to work on dry pavement with the AWD for those occasional 0-60 romps... but it would need to function and work well while towing... I was only inquiring not knowing the maturity of this particular trans.

Thanks again, you were very helpful.

[SBK]

I think I understand what you're saying with the word "overlap." In my world, we simply refer to this as "shift time." All of GM's 4L series of transmisssions have some degree of "overlap" when changing from one ratio to another, it's part of the inherent design of a freewheel-based automatic transmission. It is certainly possible to shorten the shift time to give a much "snappier" feel, but even in that case there's technically "overlap" during the ratio change.

GM products also utilize a "learning" type strategy, targeting a certain performance. This is why I mentioned the need for caution if modifying hardware - an associated change would need to be made in the electronics side of things to avoid having the control unit "learn" back toward a smooth shift. But from your post it is clear you already have some experience in this area, so the warning was probably somewhat unnecessary.

Understood on the stall speed change, there are nice gains in performance to be had if the vehicle in question is mainly a sport ride or straight-up performance vehicle. I would personally recommend against moving to a looser (higher stall or higher k-factor) torque converter in this type of application, given your comments which seek towing robustness. Loose converters are awesome for launch characteristics, but poor for towing and resulting heat issues.

Glad the comments were of some help!

[4DRvette]

My understanding is that the 70 series is the "super duty" version of the the 4lL60E and 4L65E that's been in Vettes for years. You might look into the Silverado SS forums regarding 4L70E mods, since I think they are part of that package also.

But, I'd agree with SBK that mods to these trannys should be apporached with care. GM paid a bunch of engineers to map the shift points, etc. correctly for the unit as desinged, so any hardware changes would require software updates to be effective for any application.

Besides, the AWD TB SS is rate at 6600lbs towing and the 2WD is rated at 6800lbs. Not sure what you're towing, but you can bet that GM Legal made sure those were conservative numbers, so it should be able to handle a bit more.

[vermorel]

If you took towing out of the mix and focused on 0-60 what would you recommend:

1. Torque Management / Tune or

2. Torque Converter

....and why