So, I'm obviously aware that towing in OD is not recommended for these trucks, however, with 4.10 gears trying to run with traffic on the interstate with a trailer is just not something I want to do. 3500+rpm for a long time won't hurt the motor, but it drives me bat**** insane haha.

I'm getting ready to throw some upgrades at my 20,000 mile 46re so it can live behind the 408 (aiming at 500lb-ft at the flywheel) that I'm building, so I figured I'd look around to see what, if any, upgrades could be done to the overdrive unit to allow for towing in OD at least on flat interstate ground. I have read on the diesel forums that guys routinely tow heavy loads with overdrive behind their cummins and v10s with their 48re/47re transmissions, so I figure there may be some carry over parts there that could work. I also vaguely remember there being an issue with not enough fluid passing through the OD unit at speed to keep it cool, and something about drilling the shaft for more flow. The trans already has a big cooler, temp gauge, and an external filter on it.

Can anyone point me in the right direction here?

Thanks.

 

Extra clutches/steels, and higher pressures won't hurt either. I am not sure there is really much of a difference between O/D units behind the various engines though. The diesel and V-10 units might have a different output shaft, but, that isn't generally the part that breaks.

 

Yeah I believe the 47re has an extra clutch in it's OD unit, the 48 may have another still. I'll look into that.

Do we know what the common failure pattern is when guys tow in OD and hurt them?

 

The Transgo TFOD Jr Shift Kit I installed in this transmission a few years back claims it prevents or at least reduces OD planetary burn up. https://transgo.com/product-details/tf-jr-shift-kit/

Not sure how much it increases pressure or whether that might be sufficient with an extra clutch or two.

I also deleted the check ball and bypassed the radiator.

 

Heat kills 'em. Keep the fluid at a reasonable temp, and that's more than half the battle.

 

Have you seen any methods you liked in terms of increasing fluid flow to the OD housing?

 

Not personally. I would have a chat with some of the major vendors of performance transmissions.... See what tricks they have up their sleeves.

 

Here's a bit of a left-field thought...but a neat idea. Probably not worth the money, but at least worth looking into.

Gearvendors makes a unit that replaces the tailhousing on a 241 transfer case. I don't believe it requires shortening the rear driveshaft, but I could be wrong. https://www.gearvendors.com/product/...ansfer-case-3/

By swapping over from the 231 to a 241 (which is a basic bolt in swap from what I understand), I could bold a gearvendors on the back and achieve 3 unique things.

1. .78 overdrive for towing that allows the transmission to remain in direct drive (3rd), bypassing the stock OD unit entirely. The gearvendors unit is extremely strong and will easily handle the torque.

2. Double overdrive for unloaded highway cruising. Current RPM @ 80mph with 4.10s and 32.2" tires is 2424rpm. RPM @ 80mph with the gearvendors engaged would be 1891rpm. This is likely to result in a greater BSFC (particularly with the stroker motor), and a MPG improvement, although how much of an improvement would be largely a guess. I don't imagine it would be a ton.

3. Gear splitting. 4 speed becomes an 8 speed, keeping the engine in the meat of it's torque band better.


If I did go that route, all I would have to do is build the main body of the transmission to handle the 500lb-ft (not hard at all), leave the stock OD unit unchanged since it would only get used during unloaded highway cruising anyway and therefore wouldn't be under load, and I should have a bulletproof setup that would also see a fairly stark improvement in performance both in terms of acceleration and towing performance with the gear splitting.

Again, probably not worth dropping 3 grand on the unit...but then again people spend far more than that for beefy transmissions. A basic set of 47re clutches and steels put into my 46re case for a couple hundred bucks should be sufficient to allow it to live behind the 408 I'd imagine.

 

Looks like this kit allows for 9 clutches to be installed in the OD housing: https://www.cascadetransmissionparts...emehubkit.aspx I believe the stock on a 46re is 4 and a 47re is 5...so that's a big increase I think.

Also dropped John from Cope Racing Transmissions an email to get his opinion.

 

I would be most interested in what John has to say.