Adding tranny fluid temp sensor and towing in OD

[wrcsixeight]

I might have to tow a ~2500lb trailer across country CA to FL this summer, and I am considering adding a Tranny temp sensor to my A-500 tranny turning a 3.55 rear. It has a lock up torque converter.

Does the temp probe just go in the Pan, or on one of the cooling lines? If in the Pan, where is best?

I do have an additional tranny cooler, and a recently rebuilt cooling system(pump, AL rad,T-stat, hoses), and fresh ATF+4.

I've read how the OD is the weak link in these trannies, and how one should not tow in OD, but honestly I hate the rpm and engine noise in third gear at 55 to 60 mph, and cannot imagine driving across the whole country in third at those speeds.

Is it the heat which destroys the transmission when towing, or just the stress of the load? If the temp is monitored closely am I still likely to damage the Tranny by towing in the flatlands with the OD on?

The tranny has about 65k miles on it since the rebuild, and has been fed ATF +3 from 10k to 30k miles and ATF +4 since then with many more Pan drops/ filter changes than necessary. I have added a drain plug. It still shifts firmly, perhaps a little too firm from 2-3, and perhaps is a little late/reluctant to downshift from 3-2 without really stepping on it. I usually manually downshift in such situations.

Darn rebuilders did not use the correct fluid initially and I had TCCC/ shuddering issues around the 10k mile mark.

Considering the extra Fuel prices, trailer rental and possible transmission grenading, I am considering shipping the trailerload instead, if the trip becomes necessary.

So, where should the temp sensor go, and do you think it is possible to use the OD in the flat sections of the country without damage?

The 318 was rebuilt 30k miles ago. It runs strong.

TIA.

 

[Colt45ws]

Pan is fine for showing you what the transmission is getting.
As far as stress or heat causing a failure...eehh, they are kind of synergistic. More stress equals more slippage when shifting, more frequent shifting and more frequent unlocking of the TC due to it trying to keep the engine in the right range (more applies to hilly areas). All this equals more heat. Overly Hot fluid is thinner, so pressure is harder to keep high, and more fluid bypasses the clutches. Positive feedback loop: more slippage, more heat. As long as the transmission is not overloaded, or a freak failure occurs, failure is almost always heat related when towing. As long as you can keep the temperature within a reasonable range, it will be fine.

 

[Ken2]

Quote:
I am considering shipping the trailerload instead,
Good idea.

The location of the temp sensor gives different info. Pan, line to cooler, line from cooler all give different info and are not comparable. I prefer the pan temp, but with the light load (2500#) and additional cooler, I don't see the need for the sensor.

If you decide to tow in OD, be sure to switch out of OD in hills where it is frequently shifting back & forth. The rpms out of OD aren't the real problem. It takes so-many horsepower to pull your load up a given hill. If the rpms are increased, the torque actually developed at that load is reduced, thus the twist on rotating shafts is lessened. (Talking about hp and torque actually produced at the rpms & load you're running, not max at peak.)

 

[Cause4Alarm]

I do not recommend towing in OD....the manufacturers set up transmissions to shift into OD baby soft because of all the soccer moms buying suburbans and expeditions to haul they're only child around..... Also it doesn't take much throttle input in OD for a downshift under that kind of load so it'll hunt between 3rd and 4th causing elevated temps

 

[JHZR2]

I'd add the cooler if the van doesn't have one as good measure regardless. I'd just play it safe. Tow in od where land is flat and consistent, tow per the manual elsewhere.

 

[Jim Allen]

Nothing wrong with towing in OD on the flats if you rig can do it. The trans will tell you when it's had enough by constantly locking and unlocking the converter or downshifting. When it starts to do that, go into direct. 2500 is not much of a load, but your rig will tell you right off what it likes if you pay attention. The trans will not generate much heat with the converter locked up. Constant locking/unlocking or downshifts is the danger sign.

IMO, a 2500# load is not enough to warrant any mods, but trans temp gauge is a good thing no matter what. If you need a good excuse to add it, thsi trip is close enough ( : < ). Live a little!

 

[440Magnum]

My opinion: keep an eye on the tach and make *sure* that the torque convertor lockup clutch isn't "hunting" in and out of lock if you do tow in O/D. That in my mind is the biggest risk of damage, moreso than the O/D unit itself. Its better to run in 3rd with the TC clutch locked all the time than run in O/D and have the TCC locking and unlocking. Running under load with the TCC unlocked is the biggest single source of heat in the trans, plus the TCC isn't really designed to repeatedly apply and release under significant load.

If it were my rig, I'd probably tow in 3rd, even on the flatlands. I've driven 3-speed Torqueflites for decades, and you just can't kill them... and that's what an A-500 basically is if you keep the O/D locked out (its a 904 Torqueflite with an O/D in the tail shaft housing). The high RPM really isn't all that high although it sounds like it to ears used to running in O/D. What are you turning, maybe 3500 at 65 MPH in 3rd? A 318 can do that day after day, year after year without a hiccup.

 

[demarpaint]

I agree ^^^ I'd tow in 3rd gear and not risk the possibility of damaging the transmission.

 

[Cause4Alarm]

You guys are forgetting that rpm is not a measurement of load in any way

 

[meep]

I bought a brass T, put 2 barbs on opposing ends and screwed the temp probe in the middle, soldered a ground lead to it, and placed it inline with the hot side cooler line in my minivan. learned a ton about immediate driving impacts on trans temps. comparing it to so oem gauges I've seen, I think that even oem trans temp gauges are highly buffered.

I think OD use depends on the trans it's in. In the torqueflite with tailshaft OD, it's going to basically force more torque load back to the trans. behavior is probably the best way to gauge it. I'd def want the gauge if I was to drive it in OD.

In some of the integrated 4spd OD ATs, the reason behind it is that 4th gear combination has too much ratio going against the final gearset in the trans, with more pressure on the gear teeth than they were designed for. Read this from a technical rag several years back, please don't ask me to quote it.

Another potential issue is that some ATs run in a partial TC lockup mode, which obviously would not appreciate the added load. I doubt this AT does this.

The tow-haul button on certain ATs also boosts line pressure, which is usually kept as low as it can be to reduce pumping losses and mpg losses associated. Don't know if that is a feature of your AT or not, but it is certainly a strong argument for using it if it is.

Me--- if it's gentle, flat, I'd probably roll in OD. I'm assuming you'll be responsible with speed. On the hills, I'd slap it in 3rd and leave it there and slow down.

M

 

[FL_Rob]

Third should be right at 1-to-1 ratio anyway,in fact around town, I use regular drive, not O/D always so as not to lug the engine plus easier on the TCC,which does lockup in third ,it just doesen't hunt at all.Ive got the 4L60 GM,so Idon't know if yours will lockup in third or not.

 

[wrcsixeight]

Thanks for the helpful replies.

I'm still running numbers at this point, trying to see what shipping the load to Fla would be compared to the extra gas required and trailer rental fees. On my numerous previous x country trips I was able to average over 16mpg keeping it under 68mph, and am wondering what I could expect when towing. Any guesses?

I do not yet have a tach, but can tell when the lock up is engaging or disengaging by feel, and by the ~3 psi difference on my mechanical oil psi gauge.

I'm 99.8% sure my tranny only locks up in OD.

Agreed, the estimated 2500 lbs is not much of a load, but my roller cam 318 is only rated at 175 hp, and it is a high top Van so it has the aerodynamics of a barn door.

I rarely ever climb a hill with the OD on now, even if the engine has enough oomph to do so in OD. I notice when I do hit the OD off button when beginning to climb a hill, I also need to back off the throttle to hold speed than if I left the OD on.

But that said, it just seems like too much rpm in third at highway speeds. I've had to do it when my speed sensor failed, or when I first replaced the ECM and the sellers had the manual and automatic part numbers mixed and I had no overdrive.

The extra noise became tolerable, it was the significant loss of MPG, and the driving slower which annoyed me(and others) greatly.

I am a keep right except to pass type driver, and if I feel I am holding up traffic by driving only the speed limit, I will speed up. I usually drive through the night on such journeys just for the less drivers on the road, and less wind, and time my passage through/around the big cities to avoid rush hour traffic.

When I used to use ATF+3, I would add a bottle of lubegard red, but have not done so with ATF+4.

 

[IanInCalgary]

A reliable way of determining whether 3rd or OD is the appropriate gear is to drive at a steady speed in 3rd then, while keeping the gas pedal at the same position, shift into OD. If the truck slows down, you're better off in 3rd. If the truck speeds up, you're better off in OD.

The gear that results in the fastest speed with a steady gas pedal will result in less heat developed by the engine.

Generally, a tow vehicle works best when the engine operates slightly faster than at the torque peak. This isn't as easy to determine today as it was when cars had carburetors since the engine management systems in modern cars create "artificial" torque curves.

It sounds like your ideas of shipping the material instead of trailering it is the way to go. If I was committed to trailering the material I'd be sure there was an additional transmission cooler and confirm which gear to drive in, then take it slow. I've towed my boat across the country that way and it is a very relaxing way to travel.

Ian

 

[SteveSRT8]

Remember that when towing sometimes more rpm is easier on the driveline than less.

That's an old school auto, I agree it probably only locks up in OD.

It's all up to the driver. Easy does it, and do not apply any throttle in od, manually downshift it and watch your gauges!

 

[wrcsixeight]

Thanks again.

I know the previous owner towed something significant as there was a trailer brake installed, but I had to have the tranny rebuilt 5k miles into my ownership.

I should really see how it tows such a weight at highway speeds and inclines before committing to it. I'm seeing that buying a small enclosed trailer would only be a couple hundred bucks more than renting one. Wonder how much they are to register. I might have use for one at the destination if I do make the journey.

 

[meep]

man I'd just slap it in 3rd, ease up on the pedal and call it a day. when pulling a trailer you really don't want to be flying anyway for safety concerns. the van already has the aerodynamics and mpg of a shoebox. slow down, keep the lights on so people know you're there, and enjoy the cruise. Keep it out of OD. It's a cross country hall, not a cannonball run...

 

[demarpaint]

Originally Posted By: meep
man I'd just slap it in 3rd, ease up on the pedal and call it a day. when pulling a trailer you really don't want to be flying anyway for safety concerns. the van already has the aerodynamics and mpg of a shoebox. slow down, keep the lights on so people know you're there, and enjoy the cruise. Keep it out of OD. It's a cross country hall, not a cannonball run...


Exactly! Years ago when the Turbo 400, Turbo 350, Torqueflite, and C6 ruled they all towed fine in 3rd gear, they had no OD back then in those transmissions. Lock it out of OD and enjoy the ride, if noise is an issue turn up the radio and/or blast the AC.

 

[rslifkin]

If that tranny is like mine, it'll lock in OD only with OD turned on, and lock in 3rd with OD off. You can tow in OD, but make sure it's not hunting for gears. If it downshifts, turn OD off (especially on hills).

A big tranny cooler is also a good idea, if you don't have one already.

 

[OVERKILL]

Originally Posted By: Cause4Alarm
I do not recommend towing in OD....the manufacturers set up transmissions to shift into OD baby soft because of all the soccer moms buying suburbans and expeditions to haul they're only child around..... Also it doesn't take much throttle input in OD for a downshift under that kind of load so it'll hunt between 3rd and 4th causing elevated temps


There are many transmissions designed to tow in O/D, the 4R100 in the 5.4L-equipped Expedition is one of them.

It varies by manufacturer and what transmission is used.

OP: If your tranny isn't supposed to be used to tow in O/D, don't tow in O/D. it is really that simple. Why risk breaking something?

 

[mechtech2]

You were smart to get the additional cooler. I hope it is in SERIES with the stock one! [not just replacing it]

The temp sensor should go in the pan. Maybe in the OUTLET line to the coolers.

And yes, over heated fluid kills auto trannys.