I have a 1990 w250 4x4 with the 727 3 speed auto and I was offered a rebuilt 4 speed auto out of a 92 4x4 diesel for $350 and thought it sounded like a good deal. Question is how hard is it to change it to the four speed and what model would that tranny be. Will it bolt up to my transfer case without a bunch of trouble? By the way I am switching from the 307 gears to 354 because the 307 is just to high for the way I am using it(towing heavy things occasionaly) The guy is offering everthing he no longer needs to go with it except for the transfer case. He has switched to a getrag 5 speed. I just thought the overdrive would come in handy since I am switching gear ratios.

 

Is it out of another Dodge or is it something else. IF it is out of another Dodge, it'll be the A518, which will bolt right inplace of ur 727. From my understanding you dont have to change a thing. They are the same transmission except one has overdrive the other does not.

 

Just some wiring, and you'll need to hook up a petentiometer or a factory TPS so the ovedrive can do its thing... unless you hardwire the o/d so you have to control it with a swtich

While the trans is down, i wouldn't put the stock torque converter in there

BUy a good converter, o/d trans, 3.07 rear = awesome mileage. but if you need lower gears (i.e.. 3.54 over 3.07) then you can't run a 3sp with 3.54 rears... that will be bad.

So yea. A518 o/d trans with a 3.54 rear would work.

If you're towing, or just drive it daily, i recommend getting an aftermarket torque converter from Goerend or Hughes, so more power gets to the ground, it'll feel like a different truck

 

You need a PCM to do that and thats not some wiring, thats alot of wiring.

The easiest way to control it is either manually with a switch or setup a pressure switch with manual override.


olskooldodge,
Your transfer case will bolt right up. If the trans your getting doesn't have it, try to get the adaptor that bolts to the trans and drops down to the crossmember mounts. The 727 has it as part of the tail housing.

The A518 is a bit longer that the 727, so your going to have to do some driveshaft lengthening/shortening.

 

Yeah the tranny is out of another dodge.

Brandon,
How come it would be bad to run the 354 with the 3 speed? It doesn't sound that low compared to 410s. What would be the top end with the 354s and the 3 speed? I would propably just wire the od it to come on with a switch.
Thanks guys for the input.

Ward

 

3 speed auto, about 15%+ converter slip, and a 3.54 rear and Diesel engine is bad news.

My friend put a 3.54 rear in one of them airport tugs, it was a 90 cummins w/727 and it originally had 7.17 gears in it to pull planes.

Getting full travel out of the throttle, he could barely maintain 60mph and the engine was tached out.

Theres a reason dodge put the 3.07 gears behind the 727 trucks and NOTHING else......its a diesel.

 

I'd second Brandon in that if you're getting that A518 (the stock trans in a 92), you should definitely investigate putting in a better torque converter. If you're towing heavy on a reg basis, I would even investigate beefing up the guts of the tranny.
And whether you put a TPS like a stocker or make your own potentiometer, you need to get a diagram to wire that thing right. Maybe ask the previous owner if he can give you the hardware that goes on top of the VE for the TPS, cuz if he put a G360 in, he doesn't need that stuff any longer, you do.
While you do all this, check if your rear crankshaft seal needs replacing: that would be the right time while the tranny is down. Be careful with your oilpan gasket...

 

If I just hardwire it with a switch does it just need 12 volts at the appropriate time to get the od to kick in? This thing only sees 60 mph about once a month. I use it as a farm truck and drive it to get fuel every 4-6 weeks so I ain't too worried about top end. The engine tends to get warm and the tranmission tends to do the same when I tow with it so I thought the lower gears might help with that since I have the spare axles in good condition anyway. I might just need a better torque convertor for the 727. What do you guys think?

 

I think you should get a good torque converter in the current trans.

If you don't go over 60 then overdrive is kidna pointless i guess.

You shouldn't be towing in overdrive anyway, even with 3.54 gears. that'll heat crap up real fast.

The cummins has enough torque it really doesn't care what gears it has, as long as the power is getting back there. you know? even adding a good converter that slips alot alot less than a factory one will increase mpg and cruising rpm, I believe the factory one slips approx. 20% and goerend's (www.goerend.com) only slips 10% and has a lower stall speed to keep it in the cummin's torque range.

now that you said you rarely go over 60, I'd just invest in a converter and be done. The 727 is a good tough trans.

 

I beg to differ. You tow heavy enough with one and you'll care what gears are back there. It also has enough torque to turn weak driveline parts into junk real quick if your not careful pull out from a stop with a heavy load.

 

You can tow in OD, you just have to be vigilant.

With the 3200 rpm spring I can do 65 in 3rd though...

 

Is it a problem with a 518 and 3.07 rear end on the highway with no load at say 65mph? Will the rpm be to low on the torque curve?

 

My buddy has a 93 with 3.54s and an auto. In 3rd, I have him tuned to do 68-70 in 3rd easily, with stock pump internals. Good aftermarket convertor, though. Wont hurt anything but the fuel mileage.

Why cant you tow in OD? I did it all the time one summer, up and down I25 in CO, but I also went 70+ with a stock engine and transmission. Tranny lasted another 100K. I figure if it will stay in OD, I'm fine; if it starts hunting between 3rd and 4th, I'll lock out 4th.

3.07s with a 3spd is real close to 4.10s with OD, FWIW.