RV Changes Gears to Quickly and won't stay in Power Band

[SmithRV]

I have a 1997 Winnebago Grand Tour Vectra, Modle: WKM35WQ with a 3126 Caterpillar Engine at 250 HP and somewhere between 12-13 MPG. I'm having a problem when going uphill, my gears on my RV will go to high and won't stay in my power band. I have to manually switch it down to third or fourth gear and once I do that it works GREAT! But when it switches it does not switch good at all sometimes it's in 5Th gear on a 12Mile grade and it won't go above 30 with a 75 MPH top speed. When I switch the gears down manually I can go like 50 MPH on a hill so I know something is wrong I just don't know. And CAT stopped putting this engine in RV's because they didn't work good so now you can't find any help on the engine. So to Summerize My engine won't switch gears correctly it will switch to the 5th or 6th gear and I can't go up hills at 30 MPH and I have to manually switch my gears to the 3rd or 4th to get back in my power band and get the most speed. If I don't I only 20-30 MPH sometimes on a TINY hill. I'm also towing a 2007 Jeep Wrangler 4 Door X Unlimited with a BlueOx towing package.

Any help would be great.

-SmithRV

[wolfe10]

Yup, single window shift pad= "pre-select gear". The gear TOWARDS which the transmission will shift at engine RPM allows. So "6" even at a stop light when you KNOW you are in 1st gear.

Two window shift pad: Left window is "pre-select gear". Right window is gear you are actually in.

[OLYLEN]

You are reading the gear selected not the gear it is in. If you had the two gear indicator window it would show the selected gear and the second would read the gear it is in, your year only has the selected gear window. By the time you are in 3rd gear you should be near 2450 RPM and 38 MPH and the trans will try to go to 4th gear. Many times at this gear/RPM it's best to shift manually to 3rd and just wait the grade out until you can hold 4th gear. If heating then best cooling is at 2200 RPM. Some times you can down shift manually to 4th and hold 55 if you get ahead of the RPM/load.

LEN

[Bill_Satellite]

It is very important that you pay attention to the post above by wolfe10. Your engine is simply not capable of maintaining the same RPM in the same gear while the driving speed decreases.

[wolfe10]

Yes, we are not getting all the facts here.

There is no way for the engine RPM to stay the same from 70 to 40 MPH in the same gear. The Allison transmission torque converter is locked up in all higher gears. The amount of "slip" needed to fit your 70-40 would indicate a destroyed transmission-- very unlikely.

So first job is to get the tach working.

Then, PLEASE tell us the lowest RPM in each gear before the transmission downshifts when at wide open throttle.

And, as already asked, check the transmission for diagnostic codes.

[SmithRV]

Ok. Thank you all for your help I really appreciate it. I'm going to go to catapillar today and request a new transmission diagnosis test but with me towing my jeep so they can program my transmission according to the load.

[11178adm]

if your engine rpm stays constant 2000 rpm but your speed drops from 70 mph all the way to 40 it sounds to me like your trans is slipping or the torque converter has a problem, smell check the trans fluid to se if it smells burnt or is a dark brown color, dextron fluid should be red, if it has allison transyn synthetic fluid the color will be more of a gold color. you need to take it to someone that can diag Allison transmissions

[st687]

Max torque is at 1440 RPM.

[usersmanual]

Yes I understand my Power Band is half my MAX RPM my power band is 2,000 RPM I just don't understand why my RV won't automatically gear down on a Grade so that it does not kill itself. maybe I need to explain. Here is a scenario. RV is on a highway I'm going 70 MPH on 5th or 6th gear at 2,000 RPM I see a small grade ahead I understand I may lose 5-10 MPH but, Which from all understanding CANNOT be good. But the problem is even at 40 MPH on a grade I'm still at 2,000 RPM. So I gear down to 3rd or 4th my RPM stays in 2,000 but then I'll go to 40-50 and stop at 60 MPH at 2,000 RPM it seems impossible but it's happening. Even going downhill I'll stay at 2,000 RPM and I know my gauge is working because idle RPM is 500. So why is my transmission not gearing down on a grade? I don't let it switch gears automatically because it seems like it will hurt my transmission. But on flat roads my transmission will gear up and gear down fine. Also my transmission does this sometimes and not other. Sometimes I'll go up a grade in 6Th gear and stay at 60 MPH so please answer that question. I'm not trying to be rude I just don't want my transmission to kill itself one day.

P.s you don't have to say sorry about that dudes post. I laughed at it it kinda is true lol. Love your forums there nice and free feeling.

your whole deal sounds crazy for sure sounds like the tach is stuck at 2K which most likely send the wrong signal to the Trans ecm
But as said a 35ft diesel pusher loaded up pulling a fairly heavy toad
with such a small engine that you claims goes up a hill in#6 gear at 60MPH must be a incredibly small incline
But based on this post your TACH is NOT responding correctly,

[SmithRV]

Ivylog wrote:

Mike Hohnstein wrote:
And they wonder why some states require a upgraded drivers license to drive a large class A.

Smith RV, welcome to the forums and many can be pretty tough with their comments... I'm a little surprised you stayed on after the above but he does have a point. Your power band is not at max rpms with a diesel engine, it's actually closer to half that for the most torque making your Allison tranny smarter. The only reason to manually down shift is to increase the rpms for better engine cooling on a long pull. Otherwise it's best to just let the Allison do it's thing.
Sorry, and welcome back.

Yes I understand my Power Band is half my MAX RPM my power band is 2,000 RPM I just don't understand why my RV won't automatically gear down on a Grade so that it does not kill itself. maybe I need to explain. Here is a scenario. RV is on a highway I'm going 70 MPH on 5th or 6th gear at 2,000 RPM I see a small grade ahead I understand I may lose 5-10 MPH but, the engine won't gear down it stays in 6th at 2,000 RPM but the speed goes 70-60-50 and stops at 40 MPH and is still in 6Th gear! Which from all understanding CANNOT be good. But the problem is even at 40 MPH on a grade I'm still at 2,000 RPM. So I gear down to 3rd or 4th my RPM stays in 2,000 but then I'll go to 40-50 and stop at 60 MPH at 2,000 RPM it seems impossible but it's happening. Even going downhill I'll stay at 2,000 RPM and I know my gauge is working because idle RPM is 500. So why is my transmission not gearing down on a grade? I don't let it switch gears automatically because it seems like it will hurt my transmission. But on flat roads my transmission will gear up and gear down fine. Also my transmission does this sometimes and not other. Sometimes I'll go up a grade in 6Th gear and stay at 60 MPH so please answer that question. I'm not trying to be rude I just don't want my transmission to kill itself one day.

P.s you don't have to say sorry about that dudes post. I laughed at it it kinda is true lol. Love your forums there nice and free feeling.

[wolfe10]

The Caterpillar 3126 max HP is at 2,200 RPM for most, 2,400 for a few. You do NOT want to run it at 2500 RPM.

Again what is the lowest RPM you see before it automatically downshifts at high throttle settings? Is this in power or economy mode?

To check for diagnostic codes from the driver's seat:

Ignition ON, engine OFF works fine.

Push the up and down arrows at the same time. If that brings up O L (for checking transmission oil level), press the up and down arrows again.

That will bring up d 1 followed by codes for any diagnostic codes. Record them.

If no codes, you will see d 1 followed by - -. If there is a d1, press the mode button to bring up more codes. When you get to one that says - - just turn off the key, you are done.

[Ivylog]

Mike Hohnstein wrote:
And they wonder why some states require a upgraded drivers license to drive a large class A.

Smith RV, welcome to the forums and many can be pretty tough with their comments... I'm a little surprised you stayed on after the above but he does have a point. Your power band is not at max rpms with a diesel engine, it's actually closer to half that for the most torque making your Allison tranny smarter. The only reason to manually down shift is to increase the rpms for better engine cooling on a long pull. Otherwise it's best to just let the Allison do it's thing.
Sorry, and welcome back.

[SmithRV]

wolfe10 wrote:
Have you checked the transmission for diagnostic codes? Done from the drivers seat with the shift pad.

And, as already asked what RPM when it won't downshift automatically that you feel it should?

No I have not checked for codes. How can I do that?

I feel it should just downshift when I go up a hill. But the engine sustains RPM's but can't sustain speed so I don't think it can sense when to downshift.

[SmithRV]

Ivylog wrote:
At what rpms is your power band?

My power band is at 2,000 RPMS

[SmithRV]

And I know the unit is capable of this because sometimes it will go great and sometimes it just does not work. It's intermittent.