When I leased my orchard my 3500 5 speed went with it, along with all equipment, so I have been having to tow with my AT 2500. Did two tows across WA, ID and MT, two passes and a big hill, 17% for 9 miles, coming out of the Columbia River Gorge. Last pull was with 8k on a 90° day, AT temp has been staying under 220° on the pulls and EGTs seem to quit climbing at 1150°, 20. 6 mpgs in 440 miles!!! I was stoked it did so well, would've raced right up them if it weren't for 15 mph curves. AT is stock, 135k miles. What I'm saying is it can be done, I was worried at first. Question is- is it better to go to OD off when you need to downshift or just punch it to disengage the lock-up? I can go much the same speed in either, but the AT temp runs a little higher with the TC unlocked. What's best for the transmission?
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Very happy towing with my AT
- Thread starter illflem
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Bill.
You need to change your sig to one less CTD in the family.
Sorry, but after reading your question a few times I'm not sure exactly what you are asking. Are you confusingOD with lock-up??? You said something about punching it to unlock the TC. I assume you are referring to being in OD at the time right???
Please explain a little better for my lack of understanding.
I can tell you that the lock-up clutch lining is a weak link to the TC and therefore if you are applying much power while the TC is locked up, you are stressing this lining. But like you said it runs hotter with the TC unlocked and the power isn't at strong with the mushy (IMO) stock TC unlocked.
-Ryan
You need to change your sig to one less CTD in the family.
Sorry, but after reading your question a few times I'm not sure exactly what you are asking. Are you confusingOD with lock-up??? You said something about punching it to unlock the TC. I assume you are referring to being in OD at the time right???
Please explain a little better for my lack of understanding.
I can tell you that the lock-up clutch lining is a weak link to the TC and therefore if you are applying much power while the TC is locked up, you are stressing this lining. But like you said it runs hotter with the TC unlocked and the power isn't at strong with the mushy (IMO) stock TC unlocked.
-Ryan
Ryan, my understanding, which could be wrong is that, when you punch OD off the trans shifts into 2nd which can then also can lock up. If you are in 3rd with lockup and the trans downshifts from punching or lugging it unlocks into third. The AT essentially had 5 speeds, am I way out of line?
I still own my other truck until it sells with the orchard if ever. One stipulation I made on the lease is that it only is used for hauling fruit from the leased orchard, didn't want it to become someone's daily drive, so it sits.
I still own my other truck until it sells with the orchard if ever. One stipulation I made on the lease is that it only is used for hauling fruit from the leased orchard, didn't want it to become someone's daily drive, so it sits.
Assuming the 2nd in there is a typo, you are correct. pushing the OD lockout button puts the transmission in 3rd and then allows lockup in third. With the button out the transmission will not go into lockup in third.
The transmission makes heat when doing the fluid coupling thing, and does not when in lockup. Or at least not as near as much. So from a heat point of new 3rd lockup is better that 3rd non locked.
3rd locked is better from a power point of view, however a TC from our buddy Bill K. can seriously narrow the gap.
As mentioned the lockup clutch is a weak link. I need a transmission guy opinion here, but I think when you are in 3rd locked and the engine speed is cranked up, like when towing a grade, the line pressure is probably enough to keep from trashing the TC lining. Unless you are seriously BOMBed, of course. -- I think the TC lining problem is for those who are lugging the engine at low speed, have the TC locked, and then mash in a ton of power. -- This is different that seeing the approaching hill, slowing to the correct speed, pushing the OD button, then getting back into the throttle, and running the hill at 2750 all the way. Or something like that.
My guess is 3rd locked provides the most power and the least heat, and is not damaging as long as the engine speed is kept up so their is decent line pressure in the transmission, and you dont got 400+ HP.
The transmission makes heat when doing the fluid coupling thing, and does not when in lockup. Or at least not as near as much. So from a heat point of new 3rd lockup is better that 3rd non locked.
3rd locked is better from a power point of view, however a TC from our buddy Bill K. can seriously narrow the gap.
As mentioned the lockup clutch is a weak link. I need a transmission guy opinion here, but I think when you are in 3rd locked and the engine speed is cranked up, like when towing a grade, the line pressure is probably enough to keep from trashing the TC lining. Unless you are seriously BOMBed, of course. -- I think the TC lining problem is for those who are lugging the engine at low speed, have the TC locked, and then mash in a ton of power. -- This is different that seeing the approaching hill, slowing to the correct speed, pushing the OD button, then getting back into the throttle, and running the hill at 2750 all the way. Or something like that.
My guess is 3rd locked provides the most power and the least heat, and is not damaging as long as the engine speed is kept up so their is decent line pressure in the transmission, and you dont got 400+ HP.
Sly thanks, think I've got it, maybe. This is the first AT I've owned, not very experienced with the beast. When you reengage the lock up it seems like it goes though 3 gears, whats that all about?
Don, 17% is correct according to the sign. It's a steep mother, 900 ft elevation at the river 4200 ft nine miles later at the top.
Don, 17% is correct according to the sign. It's a steep mother, 900 ft elevation at the river 4200 ft nine miles later at the top.
3 gears, hmmmm. not sure I understand.
My experience. I always lift my foot when pushing the button, in or out. Maybe its different if you do it under throttle.
I believe that a transmission in fluid coupling mode does not transfer 100% of the RPMs created by the engine. so while the engine is running 2750 lets say, the transmission input shaft may only be doing 2500. When the lockup clutch is engaged the engine RPMs drop to match the speed of the shaft, as they are now connected via a clutch. This can vary according to load, TC efficiency and probably a host of other things.
Also the transmission wont down shift unless the lockup clucth is dis-engaged.
So in order to go from OD locked to 3rd locked, or visa versa, the transmission had to:
1. Go from OD locked to OD un-locked - RPM change
2. Go from OD unlocked to 3rd unlocked - RPM change
3. Go from 3rd unlocked to 3rd locked - RPM change
My experience is I usually dont see #1 as I always lift my foot off the pedal. I always see 2-3.
My experience. I always lift my foot when pushing the button, in or out. Maybe its different if you do it under throttle.
I believe that a transmission in fluid coupling mode does not transfer 100% of the RPMs created by the engine. so while the engine is running 2750 lets say, the transmission input shaft may only be doing 2500. When the lockup clutch is engaged the engine RPMs drop to match the speed of the shaft, as they are now connected via a clutch. This can vary according to load, TC efficiency and probably a host of other things.
Also the transmission wont down shift unless the lockup clucth is dis-engaged.
So in order to go from OD locked to 3rd locked, or visa versa, the transmission had to:
1. Go from OD locked to OD un-locked - RPM change
2. Go from OD unlocked to 3rd unlocked - RPM change
3. Go from 3rd unlocked to 3rd locked - RPM change
My experience is I usually dont see #1 as I always lift my foot off the pedal. I always see 2-3.
illflem,
Where is that 17% grade out of he Columbia River gorge? Goldendale?
I have been pulling a 7000# TT for several years with my 94 auto and have learned something almost every time.
SlyBones has pretty well described the way things work.
I have a lockout/unlock switch on mine and discovered early not to try manipulating OD with the TC locked. It will shift but it is very harsh. Same as jammin' gears without using the clutch.
I have traveled I-90 from here to Nebraska and back many times and very seldom do I have to drop below 3rd.
Most of the time, on any of the passes, I will wind up in 3rd with my foot on the floor and the TC locked. I like to have it locked at the top of the pass so I can use the exhaust brake on the way down.
The biggest problem I have is in the rolling hills where I try to stay in OD as much as possible. There, I really have to keep an eye on the EGT.
As the RPM drops off the EGT goes up and at some point a decision has to be made to either get out of OD or unlock the TC.
Unless the hill is starting to get steeper, I'll unlock the TC and let it slip to get RPM up. Otherwise, I just lock out the OD and let the transmission do it's thing. Unlocking the TC has never caused my transmission temperature to rise excessively and is a quick way to get EGT down.
Where is that 17% grade out of he Columbia River gorge? Goldendale?
I have been pulling a 7000# TT for several years with my 94 auto and have learned something almost every time.
SlyBones has pretty well described the way things work.
I have a lockout/unlock switch on mine and discovered early not to try manipulating OD with the TC locked. It will shift but it is very harsh. Same as jammin' gears without using the clutch.
I have traveled I-90 from here to Nebraska and back many times and very seldom do I have to drop below 3rd.
Most of the time, on any of the passes, I will wind up in 3rd with my foot on the floor and the TC locked. I like to have it locked at the top of the pass so I can use the exhaust brake on the way down.
The biggest problem I have is in the rolling hills where I try to stay in OD as much as possible. There, I really have to keep an eye on the EGT.
As the RPM drops off the EGT goes up and at some point a decision has to be made to either get out of OD or unlock the TC.
Unless the hill is starting to get steeper, I'll unlock the TC and let it slip to get RPM up. Otherwise, I just lock out the OD and let the transmission do it's thing. Unlocking the TC has never caused my transmission temperature to rise excessively and is a quick way to get EGT down.
illflem, thanks for the reply. I am familiar with those roads, both highway 2 and McNiel Canyon. I have never had the pleasure of pulling a trailer up either one though. I think my truck would handle it OK but it might not make it in 3rd.
As stated previously, my trailer gvwr is only 7,000# and is usually loaded lighter than that . The last time I weighed the combination of truck and trailer the total was a little over 14,000.
The truck equipped as it is does a fine job for us.
As you can see, I upgraded the transmission with a lower stall torque converter and a modified valve body. Both from BD. The TC is fine but I am not real fond of the hard shifting from the valve body. I have backed out the pressure screw as far as I can without it dropping out but it is still too harsh. Maybe someone has an idea what could be done. I have heard Bill Kondolay of DTT can provide VBs that are better tuned to the truck and towing requirements. If so, I may just have to bite the bullet and go that way.
I hope I haven't wandered too far from the purpose of this thread. I like the auto transmission for most of the obvious reasons and as long as it is not mistreated, I feel it will haul our trailer about anywhere we want to go.
As stated previously, my trailer gvwr is only 7,000# and is usually loaded lighter than that . The last time I weighed the combination of truck and trailer the total was a little over 14,000.
The truck equipped as it is does a fine job for us.
As you can see, I upgraded the transmission with a lower stall torque converter and a modified valve body. Both from BD. The TC is fine but I am not real fond of the hard shifting from the valve body. I have backed out the pressure screw as far as I can without it dropping out but it is still too harsh. Maybe someone has an idea what could be done. I have heard Bill Kondolay of DTT can provide VBs that are better tuned to the truck and towing requirements. If so, I may just have to bite the bullet and go that way.
I hope I haven't wandered too far from the purpose of this thread. I like the auto transmission for most of the obvious reasons and as long as it is not mistreated, I feel it will haul our trailer about anywhere we want to go.
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Suppose you are driving up a grade in D, with OD off. TC is locked, RPM varies exactly* with vehicle speed. You are holding the go pedal steady. You then push the OD button once. This causes the PCM to disengage the TC clutch, and the engine speeds up due to the TC slippage. The PCM then tells the transmission to engage the OD unit, and the engine will slow down just a bit. After some period of time, the PCM tells the transmission to lock the TC, thus the engine slows down a lot and, once again, engine speed varies exactly* with vehicle speed.
Think of it as though you were shifting your 5-speed. You're in 4th and you keep your foot steady on the go pedal. You slightly depress the clutch, and the engine speeds up. You depress the clutch completely and shift into OD and mostly release the clutch. The engine slows down a bit more than it speeded up. You fully release the clutch and the engine slows down more until the clutch is firmly engaged.
The AT is really a 3 speed with an OD unit bolted on the rear (if I interpreted the service manual correctly). With some internal changes, I'll bet one could get OD to engage in 2nd gear, and maybe even 1st. I can just see it. 2nd+OD, yielding a, perhaps, . 85 final ratio!
* - exactly if the TC clutch (or something else) is not slipping, more if something *is* slipping.
Make sense?
Fest3er
To Cooker,
The TC could be part of it but with the stock VB combined with the tighter TC, the shifts were quite normal.
On the positive side, with the enhanced VB it no longer "oozes" into TC lockup, it shifts in very quickly.
To Duraque,
The TC lockup scheme I finally arrived at consists of a couple of relays and a miniature three pole double throw toggle switch wired to give me 3 options: Locked - Normal - Unlocked.
The switch is mounted in the ashtray along with a red LED that lights when the TC is manually locked and a Green LED that is lit when the TC is manually unlocked. Center position allows the TC to be controlled by the PCM.
The relays and other associated wiring are in a small electronics project box mounted under the dash.
I discovered early on that manually switching in or out of OD, with the TC forced into lockup causes pretty hard shifting so I included a circuit to disable my lockup scheme for a few seconds any time the manual OD switch is pushed.
The ability to manually lock the TC allows usage of the exhaust brake. Nothing else is needed. Whatever gear I am in at the top of the hill is what I use going down the other side. I just make sure the TC stays locked. Otherwise, the EB is useless.
Most of the time good braking is provided for my setup when in 3rd with the OD locked out and TC locked. Heavier loads would probably require 2nd gear with TC lockup.
If anyone is interested, I could post a schematic diagram and better description of my TC lockup scheme.
The TC could be part of it but with the stock VB combined with the tighter TC, the shifts were quite normal.
On the positive side, with the enhanced VB it no longer "oozes" into TC lockup, it shifts in very quickly.
To Duraque,
The TC lockup scheme I finally arrived at consists of a couple of relays and a miniature three pole double throw toggle switch wired to give me 3 options: Locked - Normal - Unlocked.
The switch is mounted in the ashtray along with a red LED that lights when the TC is manually locked and a Green LED that is lit when the TC is manually unlocked. Center position allows the TC to be controlled by the PCM.
The relays and other associated wiring are in a small electronics project box mounted under the dash.
I discovered early on that manually switching in or out of OD, with the TC forced into lockup causes pretty hard shifting so I included a circuit to disable my lockup scheme for a few seconds any time the manual OD switch is pushed.
The ability to manually lock the TC allows usage of the exhaust brake. Nothing else is needed. Whatever gear I am in at the top of the hill is what I use going down the other side. I just make sure the TC stays locked. Otherwise, the EB is useless.
Most of the time good braking is provided for my setup when in 3rd with the OD locked out and TC locked. Heavier loads would probably require 2nd gear with TC lockup.
If anyone is interested, I could post a schematic diagram and better description of my TC lockup scheme.
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