trans and t-case questions

[digglesworth]

So I was out wheeling this past weekend and my tranny was getting very warm. After talking to a buddy, he said put it in 4lo and that I needed to put the strain on the motor and get some off the tranny. This helped tremendously. I usually run around the easier stuff in 4hi to be able to carry a little more speed through the easy stuff. This time was the first time I ever let my truck shift into second gear while in 4lo. That helped a lot. But with the 4:1, even 2nd gear only got me up to about 10mph... Which is ok. But the truck had to get up to about 3500rpm before it would shift. That was higher than expected or would have even preferred... There wasn't a whole lot of difference between D, 1, 2 or whatever gear I left it in. Putting it in 2 was what I wanted but getting the rpms up to 3500 seemed like I was really givin my truck hell. And as soon as the revs would drop a little, WHAM! Downshift right back into 1st. I love the 4:1 but it seemed like the tranny was having a hard time deciding what gear to be in. My pcm is tuned and shift points changed.... I wonder if that has something to do with it. Can someone explain how our trannys work? Puttin it in 2 will allow use of 1st and 2nd gears only? 3 is 1st through 3rd? It's not like putting it in 2 will hold 2nd gear no matter what? Will the transmission hit 3rd gear in 4lo? I know you're not supposed to exceed a certain mph in 4lo but im just curious.
..

 

[derian06]

I asked this question/ had similar symptoms like this awhile ago and got the response that it is normal and you shouldn go above 10 mph anyways

But i'm curious as to what the 1st 2nd and 3rd gears on the shifter actually do as well

 

[abearden]

The 1st, 2nd, 3rd, etc on a shifter forces it down into that gear. Basically, makes that the top gear the transmission will auto-shift to. If it's set on 2nd, it'll still be in 1st going slow, but it will rev up instead of shifting to 3rd normally.

 

[digglesworth]

Thats what I thought abearden... Now I'm curious about my pcm tune effecting my shift points causing it to hold a gear for longer....

 

[poncho1965]

I can hit all the gears in 4 low while in D. 16-17 mph


Mike

 

[4speedfunk]

Me too....with 5.13s. Put it in DRIVE and go.

 

[digglesworth]

Good to know.

 

[kflips]

I thought the wiring harness restricted use of 3 when in 4 low. Guess I was wrong. Learn something new every day

 

[poncho1965]

I understand what you're saying Digg....it acts as if it doesn't want to shift, but in drive it will. Be gentle on the throttle, when it shifts its a neck snapper. I like to use 4-lo off road, my tranny/engine temps/brakes are happier. I only use 1-2-3 gear selection when descending to make it hold the gear, depending on the grade.


Mike

 

[CaseyS]

I remember reading in some literature that one of the things the engineers did in designing the offroad and traction control systems was to hold the 1-2 shift point longer in low range to avoid shifting while crawling.

I think it was in this book
http://www.amazon.com/Hummer-Launch-book-Larry-Edsall/dp/0760321957

Interesting that I thought a 2 on the gear selector forced a second gear, but I don't remember. In my standalone controller it does. Kinda nice for gaining a little speed for a momentum obstacle in a forced second - low range.

Edit: and yes, the 1-2 in low range is a neck snapper

 

[digglesworth]

1-2 wasn't so bad. It was much harsher going 2-1... Like it chirped the tires in the dirt.... Casey, that would make sense to hold 1st a little longer... I'll just have to get it back out in the dirt and drive around a little more in 4lo to get a feel for it. It's always good to know ahead of time though how it's supposed to act. Thanks guys.

 

[4speedfunk]

Manually shifting (especially down shifting) an automatic is a good way to destroy it. If you want to do that...get a manual tranny or install an AT valve body that is made for manual shifting.

 

[digglesworth]

I was in 2nd gear rolling down a slight incline. Shifter was in 3. I think I was between 1500-2000rpm. I moved the selector down to 2 thinking it would hold 2nd. I guess the rpms dropped enough to kick it back down to 1st . So I guess the safest thing to do would ne to just leave the SOB in D and forget about it. It'll just do what it needs to.

 

[f5moab]

Manually shifting a modern trans, including downshifting, should not cause a problem since the TCM will not allow it to damage itself. Try shifting in 1st gear at high speed...nothing happens. If it does something is broken or not programmed correctly.

Most of the newer GM trucks (and probably others too) have a manual shift position, and that is just a suggestion, the controller will prevent the trans from downshifting if it could cause a problem. Many times, when coming down a hill, it will allow a downshift from 6th to maybe 4th, but not into third, until the speed decreases.

 

[4speedfunk]

Good to know. I used to downshift ATs in high-school (ahem...early eighties). T-350s, T-400s, and power-glides....all would go into 1st gear at any speed. Trust me...I did it! This usually resulted in dragging the rear tires a hundred feet and complete loss of vehicle control (ditch...tree...totaled). Not to mention, grenading the tranny all over the pavement. So, it makes sense that GM would lock out the ability to do this.

Sigh. Those were the days. I was much happier when I was that stupid.

 

[06 H3]

dumb and happy is the way to go.

I added a 4:1 so I always thought my shift points were off and yes they are violent but I have learned with time if you time it correctly and let off right before a shift it will go smooth.

Btw, I like the standalone trans controller deal so you can choose a gear and hold it but it has its downsides too...Like CJ said trans parts all over does not sound fun.

 

[poncho1965]

dumb and happy is the way to go.

I added a 4:1 so I always thought my shift points were off and yes they are violent but I have learned with time if you time it correctly and let off right before a shift it will go smooth.
.

Exactly! I've had 4:1 from the beginning, you learn how it acts and adjust throttle accordingly.


Mike

 

[f5moab]

Good to know. I used to downshift ATs in high-school (ahem...early eighties). T-350s, T-400s, and power-glides....all would go into 1st gear at any speed. Trust me...I did it! This usually resulted in dragging the rear tires a hundred feet and complete loss of vehicle control (ditch...tree...totaled). Not to mention, grenading the tranny all over the pavement. So, it makes sense that GM would lock out the ability to do this.

Sigh. Those were the days. I was much happier when I was that stupid.

Yes, those old, non computer controlled transmissions could be destroyed (as well as over-revving the engine). But these new computer controlled transmissions are protected from damage to keep warranty down and to keep the customer from having to go into "tennis shoe" mode.:giggle:

Most, MAYBE not all, will even prevent the damage caused by backing up and then slamming into a forward gear, the controller causes a long enough pause to protect the trans. Makes rocking in snow a bit harder, but it does work. And I remember back in Saturn days, our transaxles, on a very cold startup (around 10 below) would keep the transaxle in 2nd gear to warm up the trans fluid faster.

 

[CaseyS]

Now that I am thinking about it a bit more, my standalone supports an manutronic, or paddle shifters. That would be real handy in low range. I could idle from obstacle to obstacle in low range overdrive.

 

[cbetts]

This is all good information for me. I have never wheeled an automatic so I just don't think about how to overide one. I typically start off in third when I am in low range unless I am about to crawl over an obstacle. Now I know why people tend to start off slower than I do.

 

[poncho1965]

I looked really hard for a manual 3. In the end I'm happy with the auto, crawling obstacles is so easy [emoji2]


Mike