| Author |
Message |
    
Emilio
| | Posted on Thursday, May 09, 2002 - 01:05 am: | 
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why is it that the transmission will not shift into 4th from overdrive? The truck starts uphill, losing speed until i hit 58mph or so , then suddenly shifts into 3rd(which shoots the rpm's way up). Why not shift into 4th?
98 4.0l |
Anonymous
| | Posted on Thursday, May 09, 2002 - 09:13 am: |
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what overdrive? |
Leslie N. Bright (Leslie)
| | Posted on Thursday, May 09, 2002 - 09:14 am: |
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Emilio,
It IS a 4-speed transmission. 4th IS overdrive. It HAS to shift to 3rd.
-L |
hendrik
| | Posted on Thursday, May 09, 2002 - 02:38 pm: |
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> see above = L.
The automatic box has a lockup clutch which is activated in 4th gear at a certain speed and does not allow any slip in the torque converter (saves fuel, helps not to heat oil too much on motorway).
On my RangeClassic this is at 86km/h (must equal to 55mp/h). one notices a drop of rpm when it locks up. This could give the impression of a 5th gear.
(you notice that the rpm`s do not raise immediately when you floor the accelerator a little just like they do if in a lower gear).
regards, hendrik |
Emilio
| | Posted on Friday, May 10, 2002 - 07:10 pm: |
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thanks Hendrik.
This is my first automatic car so i'm not too familiar witht the workings of the tranny.
My next question is whether or not there exists a device that prevents the locking of this clutch. You can find this on most North american trucks "the overdrive off" button. |
jec
| | Posted on Saturday, May 11, 2002 - 11:50 am: |
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You're confusing the lockup and overdrive on this truck. 3rd gear is a 1:1 ratio high gear. 4th gear is about a 0.8:1 ratio overdrive gear. If you don't want overdrive, use 3rd. We use 3rd all the time in the city or in the mountains, and only use 4th gear (overdrive) when we are on the highway at continuous high speed. So the "overdrive button" equivalent in a rover is to manually move the shift lever from 4 to 3. The lockup clutch that engages at about 55 mph in 4th gear does not change the gear ratio, it only locks up the torque converter in the transmission to prevent internal slip; it is not a 5th grear. |
Jay
| | Posted on Sunday, May 12, 2002 - 03:34 pm: |
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Going up hills you want it to down shift. Its much quicker and easier. Like peddling a bike up a hill in 4th gear, you'd much rather do it in a lower gear. |
Emilio
| | Posted on Sunday, May 12, 2002 - 11:44 pm: |
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I realize that its the same gear therefore its the same gear ratio, but at the same time i feel that if its not locked up it allows the engine to rev higher (in 4th) thus allowing for more power uphill. So the reason i made reference to domestic trucks having an "overdrive off" button is because they allow the continual internal slip which brings the engine back into the higher power band.
So its not exactly "equivalent" to putting it in third because 3rd has a much lower ratio that raises the rpm's to an intolerable highway speed level. I say its intolerable because i see Honda CRV's passing me uphill(IN overdrive) while my V8 is in 3rd!? |
Bill Bettridge (Billb)
| | Posted on Monday, May 13, 2002 - 09:28 am: |
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Trans has nothing to do with being passed by Honda's - you're driving a 5000+ truck with a little 240 ci engine with 180 flywheel hp (probably only about half that at the rear wheels with an autobox).....do the math.
Don't mean that to sound harsh BTW - it's just the truth.....
Bill |
gp (Garrett)
| | Posted on Monday, May 13, 2002 - 09:43 am: |
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hey i don't want to hear anything about this slow stuff!! haha. try putting some 32' tires on NATO wheels. i can tell you about slow damit!! freaking school buses tailgate me!! white letters out helps a little, but not enough. lol. |
Anonymous
| | Posted on Monday, May 13, 2002 - 11:58 am: |
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Emilio:
If it were possible to rev the engine higher in 4th without the transmission locking up, the extra "power" from these higher revs would be turning into heat in the torque converter, not into something useful at the wheeels that would let you pass Hondas.
Torque peak should be somewhere around 3,100 rpm. That's why your transmission wants to downshift into 3rd gear. Nothing wrong with running these engines above 3,000 rpm when you need the power. |
doug james (Dgj95lwb)
| | Posted on Tuesday, May 14, 2002 - 03:47 pm: |
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These engines are supplied to TVR, in the UK. A specialist manufacturer, of Porsche-priced open sports cars, TVR has these engines turning serious hp and 7000 rpm. The ecu and PROM/map is profiled much different than LR versions, but these engines LOVE REVS. Let'er rip. |
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