4th gear and overdrive

[coxfmly]

Hello,
any thoughts towing in 4th gear AND using overdrive?
Planning a long haul next week and O.D. would be a big help....thanks

[DmaxMaverick]

4th gear and OD are one in the same. Taking it out of OD limits the upshift to 3rd (direct). You can tow/haul in OD/4th, as long as it will hold the gear and not start "hunting" (shifting up/down frequently). If you get a couple up/down shifts while holding a speed, it's better to just pull it out of OD until the load stabilizes.

[coxfmly]

Hello again,
oops, I meant to say towing in 4th and using the cruise control....

thanks

[Robyn]

As maverick mentioned, its better to manually select "D" and stop the thing from constantly shifting up and down.

Running in Direct (3rd gear) with the converter locked will keep the generated heat down.

I have towed with my foot slightly on the brake, just enough to trip the unlock switch in the circuit, allowing 4th gear without the lockup clutch engaging.

This can gove you an edge on some grades, but, the amount of heat generated in the converter starts heading NORTH real quick.

Having a temp gauge on the tranny is a good idea when towing.

As long as the coolers are up to the task at hand (keep the temps down under 275F) your good to go.

Its simply a case of managing the gear box yourself.

Engine temp, tranny temp and exhaust gas temps are a MUST WATCH

If you manage these things and keep them in the sweet spot, you can pretty much do whatever you need to and get away with it.

The troubles start when temps get out of hand.

Constant searching/hunting by the tranny (actually the ECM) trying to keep the gear ration optimal can over time cause issues (things wear out)

Bottom line IS

If you manage the heat issue on the items mentioned you got the cat by the tail.

The tranny could care less what gear its in, its just the heat that will kill it.

If the engine can pull the load and the EGT's are in the safe zone and the engine temps are too, your good to go.

Tranny temps can make short excursions into the 300F range, but its not a good idea.

Tranny fluid breaks down really quick when the temps get out of hand.

When the oil degrades the lubricating qualities is not the only thing that goes way. The frictional qaulities of the oil also takes a hike too.

The tranny fluid keeps the clutch and band materials alive by creating the ability of the friction materials to "grab" the various steel components (drums, plates etc) and and do so without slipping.

Once the frictional qaulities are gone and components start to slip, its game over.

The clutch and band lining materials are in many cases a form of PAPER, while others are a semi metalic material. Makes no difference, once slippage occurs to any real degree the lining starts to "Burn" and once this happens the material will never be the same, even with new fluid.

To address the use of the cruise control.

Flat highway or slight rolling terrain will allow the cruise to work ok.
Beyond this, shut the cruise off and keep it under your control.
Again, Heat is the big issue to keep an eye on.

Have a safe and uneventful trip

Robyn

[DmaxMaverick]

No problem using cruise, with the same cautions. If it isn't gear hunting, no problem. If you hit a grade and it downshifts and stays there, no problem. If it manages the throttle similar to what you would under similar conditions, no problem. The problem with cruise, is when it can't find a gear to keep it happy, essentially the same as driving by foot. If it does what you would do otherwise, cruise is fine. Keep an eye on the temps, as they'll sneak up on you if you aren't watching.

[coxfmly]

Great information, just what I needed.
Since I don't have one at this time, is it difficult to install a trans gauge?
Not really sure if I'm going to have time before I leave, but theirs always a chance :)

Had the trans fluid changed out yesterday, should help things a bit.

Thanks

[JohnC]

One more thing to consider: When in OD you get no engine braking, so, if you're looking at a long down grade you might want to consider dropping it into D for the duration.

[Robyn]

Installing a tranny temp gauge is no biggy.

Most installs are done with an "In the pan setup"

This is fine but does not really tell the story.

If you cut the cooler line coming from the cooler back to the tranny and then install the probe in a "T" fitting you can then get a better idea of what sort of temps your seeing.

The fluid comes from the converter to the cooler, then back to the tranny.

Just be sure to put the gauge sender in the returning line.


have a good trip

Missy

[coxfmly]

Hi Robyn,
Just returned from my 1500 mile loop of Cali. Lots of flat land hauling with a few white knuckle pulls up highway 50 towards Tahoe. a few grades had me down to 2nd gear with 1050+ EGT's. Overall it pulled fine and didn't give me any issues. Going up the mountain I averaged 13.5 mpg and 17.5 cruising down highway 5.

Only real issue was the stupid 55 mph speed limit while towing. As I'm crawling along at 55 mph, I had big rigs blasting by me at 65 plus! Not the safest in my opinion and the RPM was a bit low for 4th and a bit high (3000 rpm) for 3rd gear cruising. The times when I ran in 4th at 62 to 66 mph seemed to work best for my Sub. I wonder if the 55 mph rule is a hold over from the 70's?

See ya...

[a5150nut]

Hi Robyn,
Just returned from my 1500 mile loop of Cali. Lots of flat land hauling with a few white knuckle pulls up highway 50 towards Tahoe. a few grades had me down to 2nd gear with 1050+ EGT's. Overall it pulled fine and didn't give me any issues. Going up the mountain I averaged 13.5 mpg and 17.5 cruising down highway 5.

Only real issue was the stupid 55 mph speed limit while towing. As I'm crawling along at 55 mph, I had big rigs blasting by me at 65 plus! Not the safest in my opinion and the RPM was a bit low for 4th and a bit high (3000 rpm) for 3rd gear cruising. The times when I ran in 4th at 62 to 66 mph seemed to work best for my Sub. I wonder if the 55 mph rule is a hold over from the 70's?

See ya...

No, 55 mph has always been the trailer towing speed limit in Califurnia. I have been on I5 doing 85 (not towing) and had big rigs pass me like I was sitting still. But I do remember when Nevada had no speed limit except in town. . . .