It’s been a while since I started this project. Mounted a switch under the dash. And I have this relay but forgot how to put it all together to make the over Drive unit work. 58GMC 1/2ton truck 3speed trans w OD. Sent from my iPhone using The H.A.M.B. mobile app
I haven't worked on it yet, so I'm no help. But I been studying, and if it's a Borg Warner there is information all over the internet. Every vehicle that had a BW, setup was about the same.
The OD wiring harness is sold on E-Bay; like someone already said (^^^^^), all the manufacturers harnesses are basically the same, so you could easily adapt one to the GMC. GM OD brochures are reprinted and sold on E-Bay also. You'll need your relay, and a switch connected to the carburetor. The relays and switches are $$$$$! I've been collecting OD transmissions and OD parts to fit the Tri-Five Chevrolet cars. I'm down to two Muncie 319 OD transmissions, having sold one. If anyone needs one.............................................I am Butch/56sedandelivery.
If there are only a few components, it should not be too hard to work it out. How is the OD actuated? FromThrottle position? And is that box you have in the picture a standard 12v on-off type relay? (It looks like it, if it uses the case as the negative for the relay coil). Are there any other bits to the system ? (there shouldn't be, if it is just a switch activated relay type set up)
There's two basic ways to wire one of these; the way the factory did (which is what I'd recommend), or for full manual control. There's a couple of variations; you can drop the factory 'kickdown' feature, and/or byp*** the governor, but I wouldn't recommend either option. If you want to be able to 'lock out' the 'freewheeling' part of the OD no matter which wiring method you use, you'll need to retain the mechanical OD cable (definitely recommended). The manual control was semi-popular 'back in the day' as a talented operator could get 'six' speeds by splitting each gear. But the reality is you don't gain much by doing so. Using Ford V8 trans specs, the ratios go like this: 1st gear - 2.61 1st gear OD - 1.82 2nd gear - 1.62 2nd gear OD - 1.13 3rd gear - 1.00 3rd gear OD - .070 So the ratio difference between 1st OD and 2nd is only .21, and between 2nd OD and 3rd is even less, only .13. Any possible performance advantage is lost due to the time it takes to 'shift' in and out of OD. And extreme care has to be used to keep from shifting OD while the trans is loaded. Shifting under load WILL damage the OD unit. Keep in mind that the governor won't enable OD until you reach about 27 mph (***uming about a 4.0 rear axle) and will disable it once you slow to about 21 mph. So which way do you want it to operate?
Found it, do you know the number of your switch or have a multimeter. That one looks like a horn relay, I used an a/c relay just for the fact it's meant to be on for longer periods of time and the contact set inside maybe heavier duty.
You'll need a relay that is triggered by ground, and rated for continuous duty. Momentary-contact relays like horn relays will burn up quick.
Okay how about if I use a bosch relay. I have a couple of them laying around. I have the cable installed. No switch yet. On the 12v power, is one "constant hot" and another a trigger point using bosch relay; as I can run power thru the switch to the bosch relay; so the switch controls the power....
Thinking I need to use a fused power source to the switch also....... Sent from my iPhone using The H.A.M.B. mobile app
you can get a relay from ebay for about a 100.00 bucks in 12 or 6 volt other places also . these are made for the constant duty cycle you need. pretty easy after that. go on internet and find the borg warner od pages it will show how to wire it.
I still would control the ground side in case the switch fails or wire rubs through. 85 and 86 are the coil (either cane be power or ground but you need one of each), 30 is in and 87/87a are out. So you need 12v fused power to 85, 86 is ground through the toggle switch, 30 is fused power (which you can branch off of 85 so make sure it's 10g wire) and the 87 goes to the solenoid. On a friends Merc he wired up a Bosch style relay inside of his broken stock relay, the metal relay I used was also chosen for looks as they look stock. In your drawing the ground would go to 85 and the 12v from the battery would go to 30.
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