727 in an 800... Cooling Question

[Buck Dodson]

So,

I have a sii 727 with a d-20 in this 800

Not quite all stock and biased toward trail use, but it is driven to the trails, not trailered. When I did the swap from the bw-11 tranny, I put in a rebuilt tranny. I toasted the 727 while wheeling. The rebuilder rebuilt it again, and said I needed a better cooler because several items were "fused" in the tranny.

I am running a stock 800 radiator which has no provision for an automatic. My cooling is from an aftermarket cooler mounted in front of the radiator and a combination of rigid and tranny rated flex lines for the tranny to cool connection.

1. Since the cooler is a continous flow through, it shouldn't matter which line (pressure line or return line) is connected on the cooler, correct?

2 should I be consider a radiator swap to something with a built in cooler and perhaps still run the aux cooler?

I'm in the process of pulling the tranny again due to another issue, but I would sure like to put a tranny in and leave it for a while, so I would really like to eliminate the cooling issues from the discussion...

Btw, the stock radiator is cooling the 345 without problems, and I'm not afraid of modifications...

 

[Dealbreaker74]

I'm sure mayben will chime in on this one too, but here's my two cents...
The heat exchanger in an auto-trans radiator does a great job at soaking the heat away from the tranny fluid. Where as the air-to-air cooler you installed is more of an auxiliary unit to support a heavily loaded truck or towing. Its helpful, but on its own, not nearly as efficient as the one in the radiator. Think about burning your finger on something hot; would you blow on it or dip it in water if given the choice?
The 727 transmission was designed to have a radiator cooler as part of the package. The b/w got around this by using cooling fins on the converter, right? On the highway you're probably fine, but the bottom line is, you're really asking a lot of the aux cooler to carry the entire load when you're loafing around at 5 mph on the trail. I'd look into a radiator that has a trans cooler in the tank, and also a trans temp gauge to keep tabs on everything.
Run your trans fluid output line to the lower port in the radiator where the fluid is coolest (this only applies to a cross flow radiator). The output can then go to your aux cooler. If its a squiggly tube and fin design, it doesn't matter which is "in" or "out".

 

[Michael Mayben]

Let's not confuse the borg warner transmission heat exchanger scenarios with what is needed for a torqueflite! Many applications of the bw slushboxes in ihc stuff (including vehicles with significantly higher gvwr ratings than any Scout 800/sii is capable of dealing with) had no coolers whatsoever oem. In some applications an oil-to-water cooler (marine-style) heat exchanger was added in order to bandaid the shortcomings of not having provisions for transmission cooling. That was done in a rubegoldberg fashion so that an alternative radiator did not have to be spec'd up for the at-equipped vehicles only. Seen those sv water tubes with the "auxiliary" tap for the cooler? Seen the lower radiator hose mikkeemouse adapter for the same??

Some of the borg warner units did use a fan incorporated into the torque converter (along with a vented bellhousing), that did nothing for controlling transmission temps in an effective manner on a truck, but might have been better than nothing in a studebaker or a jaguar.

The front cooler fitting on the tf 727 is the outlet side. That is plumbed to the inlet side of any proper transmission heat exchanger.

The rear fitting on the transmission case is the inlet side, which is oil return from the heat exchanger.

Proper transmission heat exchangers do have directional flow in most designs, that is based upon the incorporation internally in some sort of "baffle" design that directs the liquid through the heat exchanger in a controlled manner for most effective operation. Prf coolers are baffled based upon their design and manufacturing process, tube and fin and serpentine coolers have directional flow also incorporated into either the tubing itself or in the assembly of the tube runs in the manifold system.

In my experience the tube and fin units (the low end of the price scale) are not effective heat exchangers unless they are huge in surface area relative to the frontal area of the air-on side of the vehicle in slow speed driving. At ram air speeds above say 25mph, they are only marginal.

If no radiator-based heat exchanger is incorporated, then some sort of thermostatic control should be installed to maintain a minimum transmission oil temperature. Optimum temps for oil entering the transmission is in the 180*f range under any load condition. We've discussed that time and again here in these threads.

If a transmission heat exchanger is improperly plumbed, then significant restriction to oil flow can be expected.

 

[Buck Dodson]

We've discussed that time and again here in these threads.

It almost sounds like you expect me to search

I think I'm going to solve the cooling problem before sacrificing another 727 to the gods...

 

[Buck Dodson]

And the next questions is...

In my new 80 traveler with a 727, the tranny was rebuilt at some point, but has an issue. Trever and I drove it home from roseburg, and it would start out fine is 1st, skip 2nd and shift into 3rd at a somewhat normal 3rd gear shift point.

Going back down, it shifts from 3rd straight to first, skipping 2nd. Reverse works fine.

I have looked through the service manual in the trouble shooting section and I can't really put my issue in any of their catagories.

I have not dropped the pan or tried to adjust the bands. Does this problem sound like it can be adjusted on the kickdown adjustment (best hope) or the the low reverse adjustment?