| |
|
|
Automatic Better Economy Than Manual
Randy.. as you know I live where it is high and hilly.
When pulling heavy loads through mountain passes with my Tundra I just find the range with the automatic tranny and lock it in there.
When I am climbing Donner Pass with the 5th wheel in tow I put it in "2" and leave it there. It will do 60 mph all day at the peak HP rpm.
Coming down the other side I can lock it in the same gear and never touch the brakes for miles.
Don't all automatics work that way?
|
|
 Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
And what temperature your transmission cooler when you reach the top? With the manual and the Cummins I travelled the passes out of California (north to Vancouver and east to AL) with 4000lb load in the back. I was in 5th gear both up and down the passes and never touched the brakes.
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
Mark, if your 5th wheel has any amount of weight,your transmission temps must be near off the scale. If I am not mistaken, the trans. torque converter in your Tundra has lock up capability in OD and 3rd. I doubt that it has lock up capability in 2nd gear. That means the torque convert is slipping against the fluid during the entire climb up the hill and generating phenominal amounts of heat.
To give you some idea of how much heat can be generated. Up until I got fed up with my 3/4 ton 93 Suburban and traded it in on the Dodge Cummins; I used it to tow my Sea Ray. I estimate that the load was somewhere between 9,000 & 10,000 lbs. My Suburban had the HD tow package, 4.10 posi rear axle, the the 4L80E HD auto. trans. I further modified the trans. system with an extra aux. external trans. oil cooler, added a Mag-Hytech double deep oil pan (which doubled my trans. fluid capacity) and ran Amsoil synthetic trans. oil. The torque converter had lock up capability in OD and D (3rd). Just towing my boat 45 miles through a variety of moderate TN hills would heat the fluid up to the point that the transmission would expelled hot oil out of the vent tube. The problem was that the truck did not have the power to hold the torque converter in lockup, nor would the computer allow it even with the chip that boosted engine out put and shift points as well as firming up shifts. The result was that I would either have to gradually back off the throttle in hopes of holding lock up on the torque converter long enough to make it to the top of the hill or as usually happened have to gradually keep increasing throttle to keep any type of minimum speed going up the hill. I would be in 2nd gear doing 25 mph with the throttle to the floor. When I would get home, I had a real nice undercoating of Amsoil synthetic trans. oil on my truck undercarriage and my boat hull. I have NEVER had an issue pulling any load with the Cummins and the 6 speed manual. Even the GM Duramax diesel pickups have this problem with the Allison transmission. GM used to offer a manual ZF 6 speed with their Duramax diesel pickups but stopped doing this early on (I suppose due to the high failure rate). This issue may have been resolved by now. As I said previously, there is NO OEM automatic transmission that comes as OEM equipment offered in the US that is truly capable of adequate towing capacity. You can move up to vehicles over 1 ton capacity but these are not vehicles that the average bear drives.
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
Somebody correct me if I am wrong.
My reading has shown that it is the constant shifting up and down that overheats the fluid.
The 5th wheel weighs over 5000 pounds and the tractor and trailer go closer to 6000 pounds.
I don't have a temp gauge on the transmission, just a warning light. I have never seen it illuminated.
I think it only locks up in OD.
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
Maybe we should leave this to Randy as he certainly has more experience with these couplings. Certainly when using air as the working fluid.
If the transmission is not locked it is a viscous coupling. The impellor of one side pushing against the other. Work is being done on the liquid and it heats. The work will also be placed on the fluid when in 2nd comming down the hill.
Degradation generally doubles for each 10 degree C (18 F)increase in temperature. Therefore for example you come up the hill and the temperature increases from 120 F to 220 F the fluid degrades at 5 X its normal working rate.
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
Mark, watch your tachometer closely when towing in this configuration. If you watch the tach closely, you will notice the rpms jump up about about 200 rpm without the transmission downshifting to a lower gear as you gradually add more throttle. This 200 rpm jump indicates that the computer has unlocked the torque converter and it is now in fluid coupling mode which generates serious heat. As you add more throttle to maintain road speed, the transmission will eventually downshift to a lower gear and you are correct. This adds to the problem.
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
Realizing experts have addressed this and I am just passing along info...living on flat land there are many dump trucks running around here with auto trans. Have been for years with good service. Would also hate to have to find manual trans in farmers pickup here and construction pickup. The farmers know manaul trans and now they are buying tractors for true farming with auto trans. I have a tractor with HST and it will pull find (yes have subsoiled with it), just ues the proper range and not try to control it with light foot on high range.
kt
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
Hydrostatic drive multi-gear range tractor transmissions and automotive automatic transmissions are apples and oranges. Totally different and unrelated working off of different principals.
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
So let me re-phrase the question.
You are hauling a big load uphill. OD is out of the question.... it just will not stay there, not enough power.
So it's in 3rd some of the time but it can't hold road speed there either and about every 30-45 seconds it downshifts into second to maintain the speed. You have 40 miles of such road ahead of you. Now what?
It is never going to achieve any sort of lock-up on the torque converter.... do you just let it shift up and down twice a minute?
This is where I lock it in 2nd and hold at a constant 4500 rpm's and 60 mph, let it climb the pass and hope those double tranny coolers will do their work.
I won't let it hunt back and forth between 3rd and OD either. When it starts doing that I lock it in 3rd until things level out.
Don't you think that this is easier on the engine and drive train?
|
|
Add Photo
Bookmarks: |
|
|
|
|
Automatic Better Economy Than Manual
There was no reference in my earlier post auto trans and HST were the same. I thought the reference to the HST in tractor pulling subsoiler would have been realized it was in reference to an earlier post in this same thread about HST not having been used for such heavy work by another.
Now, really are they apples and oranges? Are you sure they are not just different variety of apples? Maybe orange and grapefruit?
|
|
Add Photo
Bookmarks: |
|
|
|
Gas Generator Weather Protecti
12-09-2005, 10:30 
Pics
Reply
Digg It 
Del.icio.us 
