View Full Version : Disable Overdrive while towing?
Sinecure
07-19-2005, 10:42 PM
This past weekend I towed my boat about 2 hours with my TB, while a friend towed his boat with his Explorer. I tried towing in "D" but found that the transmission went in and out of Overdrive too often, so I ended up towing in "3". While it towed with no problem in "3", I found the RPMs kinda high. I was wishing I could put it in "D" without having it go into and out of Overdrive (the Explorer has an O/D on/off switch).
So, does anyone know if it is possible to disable the Overdrive gear of the transmission? I thought I had read somewhere that the transmission in these trucks are the same transmissions bolted onto the 5.3 liter Silverado engines, which has the "Tow/Haul" button on the shifter to change shift points and disable O/D. If that is true, it would seem that it would be possible to disable O/D. Thanks.
Jman423
07-19-2005, 10:45 PM
I always understood that when you were towing something, you shoud not be in overdrive... But I could be wrong. :m2: And being in third is having the overdrive off.
02EnvoySLE Guy
07-19-2005, 10:57 PM
This past weekend I towed my boat about 2 hours with my TB, while a friend towed his boat with his Explorer. I tried towing in "D" but found that the transmission went in and out of Overdrive too often, so I ended up towing in "3". While it towed with no problem in "3", I found the RPMs kinda high. I was wishing I could put it in "D" without having it go into and out of Overdrive (the Explorer has an O/D on/off switch).
So, does anyone know if it is possible to disable the Overdrive gear of the transmission? I thought I had read somewhere that the transmission in these trucks are the same transmissions bolted onto the 5.3 liter Silverado engines, which has the "Tow/Haul" button on the shifter to change shift points and disable O/D. If that is true, it would seem that it would be possible to disable O/D. Thanks.
I think (could be mistaken) that the Silverado has a 4L80E transmission, not a 4L60E like the TB/Envoy does.
In 3, the revs are going to be higher simply because you're going from having a 4-speed transmission to a 3-speed. That 3 speed is going to be less efficient by nature. :m2:
Sinecure
07-19-2005, 11:28 PM
Right, I realize that having it in "3" disables overdrive, but I'd like to be in "4" (or "D") and have the trainsmission not go into and out of overdrive. With the higher RPMs comes more fuel consumption, which is why I'd like to tow in "D" without overdrive.
Charlie: You're right about the transmissions. While searching for an answer I found this site. Cool info.
http://www.gminsidenews.com/index.php?page=trans_guide
02EnvoySLE Guy
07-20-2005, 12:38 AM
Yeah unfortunately I don't know of any way to get around what you're talking about... but then again, you're towing. Unless you're talking about a diesel truck, good gas mileage + towing is a real pipe dream :duh: :laugh:
Jman423
07-20-2005, 12:42 AM
Right, I realize that having it in "3" disables overdrive, but I'd like to be in "4" (or "D") and have the trainsmission not go into and out of overdrive. With the higher RPMs comes more fuel consumption, which is why I'd like to tow in "D" without overdrive.
Charlie: You're right about the transmissions. While searching for an answer I found this site. Cool info.
http://www.gminsidenews.com/index.php?page=trans_guide
4th gear is overdrive, your either in it or your not. Overdrive is not meant to be used for towing, thats why the truck is having a hard time staying in 4th gear.
bmm354
07-20-2005, 01:01 PM
Putting your TB in "3" effectively works the same as pushing a tow/haul switch. In "3" the transmission is prevented from shifting into 4th gear (overdrive), so it's doing the same thing. The RPMs are higher because it's not going into overdrive, which would normally really knock the revs down. I'm sure you'd be revving just as high with a tow/haul switch, although I think the switch also changes the shift points by temporarily "reprogramming" the computer.
The '02+ Explorers have a 5-speed auto, so it probably makes more sense to have an OD-off switch with that trans.
Envoy Fan
07-20-2005, 01:31 PM
I think (could be mistaken) that the Silverado has a 4L80E transmission, not a 4L60E like the TB/Envoy does.
Most GM and GMC trucks (not all) have the 4L60E transmission.
Actually you're friend's Explorer was most likely turning about the same revs as your TB. (Assuming you have similar axle ratios, remember our trucks have 3.42, 3.73 or 4.10 gears, while ford uses 3.55 or 3.73). The Explorer 5 speed inserts an extra gear in the lower range, their 4th gear is 1:1, just like our 3rd gear and then 5th is overdrive or equivalent to our 4th. Placing your shifter into '3rd' is exactly the same as your friend pushing the overdrive lockout button on his Explorer. (Ford shifters don't have a '4th', the only way to select '4th' or non-overdrive is to use the button).
Hope this doesn't cause more confusion,
Ray
paulyjsob
07-20-2005, 02:38 PM
I understand what you mean. I tow a 3000lbs trailer and typically on flats, I have it in "D". At 70mph it runs at about 2100 RPM... If I shift it to "3", RPM's go up to about 3100. But, while in "D", the car will downshift into from 2100 RPM to about 2700 RPM, then if I put it in "D", it will shift to 3100 RPM. Its seems like the 2100 RPM is the overdrive, 2700 RPM is 4th, and 3100 is 3rd.
Sinecure
07-20-2005, 05:43 PM
I understand what you mean. I tow a 3000lbs trailer and typically on flats, I have it in "D". At 70mph it runs at about 2100 RPM... If I shift it to "3", RPM's go up to about 3100. But, while in "D", the car will downshift into from 2100 RPM to about 2700 RPM, then if I put it in "D", it will shift to 3100 RPM. Its seems like the 2100 RPM is the overdrive, 2700 RPM is 4th, and 3100 is 3rd.
Thanks Pauly. That's exactly what I mean. While I was towing in "D", at around 70 MPH, the RPM's would go to & from around 2100 RPM and 2700 RPM. When the gear selector is in "3", it's steadily at 3100 RPM.
It always seemed to me that the term "overdrive" was something extra after the last posted gear. So if you have a 4 speed automatic transmission, you really had 4 gears + overdrive. All my vehicles have performed this way (as pauly described).
MoJoe
07-20-2005, 05:54 PM
I think (could be mistaken) that the Silverado has a 4L80E transmission, not a 4L60E like the TB/Envoy does.
In 3, the revs are going to be higher simply because you're going from having a 4-speed transmission to a 3-speed. That 3 speed is going to be less efficient by nature. :m2:
The 1500 Silvy's have a 4l60E. A huge weak point of the drivetrain. The 2500's and up use the 4l80E. The 1500HD uses either the 4l65E or 4l80E
But to let you know on the towing in OD, when I tow with any vehicle, I just look at how it handles the weight of the load, and the terrain I am on. A lot of hills, I use D, not OD. When I am on flat surfaces and am cruising, I use OD as long as it does not shift in and out. You do not want to overheat your tranny and start smoking clutches.
That doesn't sound right, forcing a downshift from D should result in the same rpm as the selector being in 3rd....The tranny has down shifted to 3rd gear. Unless, you're not actually dropping to 3rd gear while towing and only pressing the throttle enough to unlock the torque converter and shifting the TC between locked and unlocked.
Some quick calculations would be that the rpm difference between 4th (.69) and 3rd (1.00) would be approximately 45% higher. So that 3100RPM would be 3rd with the 3.73 gear ratio. When you're in 4th (OD) and see the tach rise to 2700, you're not actually dropping or locking out overdrive....you're still in 4th or Overdrive just that the torque converter is being instructed to unlock by the PCM. (If the tranny was actually down shifting, you'd see the same 3100rpm on the tach). - The Ford tranny works the same way with its button, however your buddy with the Ford my have the 3.55 gears and you have the taller 3.73 and thus run a couple of hundred rpms higher.
Ray
02EnvoySLE Guy
07-20-2005, 10:07 PM
The 1500 Silvy's have a 4l60E. A huge weak point of the drivetrain. The 2500's and up use the 4l80E. The 1500HD uses either the 4l65E or 4l80E
But to let you know on the towing in OD, when I tow with any vehicle, I just look at how it handles the weight of the load, and the terrain I am on. A lot of hills, I use D, not OD. When I am on flat surfaces and am cruising, I use OD as long as it does not shift in and out. You do not want to overheat your tranny and start smoking clutches.
Ah. I've never had much dealings with GM fullsize trucks; I've got friends who own F150s and HEMI Rams, and a few superduty Fords. I only know one guy with a chevy, and his is a 2500. :undecided
That's what I get for opening my big mouth :x
MoJoe
07-20-2005, 10:23 PM
Ah. I've never had much dealings with GM fullsize trucks; I've got friends who own F150s and HEMI Rams, and a few superduty Fords. I only know one guy with a chevy, and his is a 2500. :undecided
That's what I get for opening my big mouth :x
You were not far off. I think all the trucks and suvs should have 4l65e's and higher. We also need a nice 5 speed auto :duh:
rcam81
07-25-2005, 06:17 PM
I went on vacation last week pulling a 3800 lb boat and all of the other stuff that goes with it. I started out in drive. The trans did ok on the flat hiway. When I got into the hills of Mi, I pulled the trans back into 3rd. The engine cooled back down(it got up to 230 degrees). The rest of the trip, I pulled the boat in 3rd. The tach read 2700 to 2900. I got 14.4 mpg to boot.