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727 to a518 swap

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Old 02-22-2018, 06:02 PM   #1  
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727 to a518 swap

I have a 89 cc dually with a 727. I don't tow alot with it and the 727 has met my needs. My only real complaint would be highway use. Front seal is leaking pretty good so thought I might as well gain od by swapping to a518. I did take a short ride in the truck before the a518 came out. It seemed to shift out well. I'm not real concerned with beefing it up for towing but would like to do what I can to make it last as long as possible. Any suggestions of stuff I should be sure and do or add while I'm doing it or tips as to what I will run into while doing this swap would be appreciated.
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Old 02-23-2018, 06:58 AM   #2  
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I am not much of an auto guru, but I will help the best I can
The driveshaft, if 2wd, will need to be shortened about 6 inches. If it is a 4x4 the front will also need to be lengthened and the 4x4 shifter linkage and bracket will be different. Or see if you can get the A-518 driveshafts from the donor truck.
You will also need to work out an OD button and wiring.
Most people recommend getting a better flex plate installed while you are there as the factory one is known to rip the center out of it.
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Old 02-27-2018, 07:13 PM   #3  
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Got the swap nearly complete should finish tommorow. I have the factory dash switch which I'd like to use. Can anyone tell me which wires control the switch and which controls the light in the switch? There's 4 wires total.
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Old 03-03-2018, 06:24 AM   #4  
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Using a toggle switch till I can get info on factory od switch. Got tranny in shifting fine1-3 can't get of od to work. Hooked up Hobbs adjustable switch 40-60 psi. My truck being an 89 never had temp sensors on tranny. I haven't hooked up either temp sensors thinking I didn't need to. Can either or both temp sensors be my issue? If so how would I go about hooking them up to my truck which never had them?
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Old 03-03-2018, 12:57 PM   #5  
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Being 2wd, a 47RH swap would not have costed you much more. OD control on 91.5 to 93 is done through the PCM plus a TPS. The pre 91.5 doesn't have the capability. Have you considered a pressure switch in the transmissions pressure port. There is information about it in the faq section.
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Old 03-03-2018, 01:36 PM   #6  
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Yes I have a Hobbs variable pressure switch that goes from 40 to 60 psi in the port. I then ran from it to a switch in the dash so I could turn od off by interrupting the ground signal comming from pressure switch. From the other pole of switch i ran to orange wire on od control on drivers side of tranny. Then ran power to blue wire. From all i' ve read this should be correct. My only concern was should I have done something with the two temp sensors.since my old tranny didn't have them I just left them out. I have been told that I shouldn't need them now and that their being left out shouldnt be the cause of od not working. I really don't know. Any input will be appreciated
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Old 03-03-2018, 04:07 PM   #7  
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Almost sounds like you are using the wrong connector. There are 2 connectors on the transmission, both on the drivers side and both toward the rear of the main case. The 2 pin is for the OD and sits above the 3 pin connector. The 3 pin is for the back up lights and neutral safety switch.
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Old 03-03-2018, 04:13 PM   #8  
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On 91.5 - 93, there are 2 thermo switches to inhibit OD. Neither on the transmission. The overtemp sets in the cooling line, while the under temp screws into the head.
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Old 03-03-2018, 04:43 PM   #9  
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My 89 never had either temp sensor. I used my cooling lines which had no outlet in them for a sensor. I've been told without a computer or tps I shouldn't need either sensor anyway. I don't know going to check all connections I guess. Tranny does great except no of.
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Old 03-04-2018, 10:31 AM   #10  
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You only need them to help protect the engine and transmission from temperature extremes. Not mandatory, you can do it manually.
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Old 03-06-2018, 06:10 AM   #11  
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Went back over wiring found a bad place in the12v wire. od working great now. Thanks for everyone's help and advice.
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