Hi Guys, I was given an 89 f250 diesel 2wd XLT Lariat 7.3L IDI(I think) Automatic trans from my boss yesterday. The truck starts up great, and runs fine. It has about 170,000 Kilometers on it. I took it out on the highway today and it seemed like it didn't want to shift into overdrive. The truck shifts incredibly smooth, so I'm not sure which gear it is in when it red lines, I think 3rd. I have about a max speed of about 85 Kilometers an hour, which is not very quick. I've checked the ATF and it was a little low so I toped it off. The fuse for overdrive isn't blown, so I'm kinda stumped. Has anybody ran into this issue before? Any info would be greatly appreciated because I am moving and I need the truck to haul a load for about 8 hours. Thanks,
-Pete

 

it probably doesnt have overdrive

 

1989 should have the E4OD overdrive transmission, but being the transition year, some might still have the older 3 speed. There should be an overdrive cancel switch and an overdrive symbol in the shift quadrant if this truch has the E4OD. Under the hood, there should be a throttle position sensor on the injector pump and NO vacuum lines.

Only thing I can suggest for now is to scan for codes if there are any. I don't know enough to really figure out whats going one.

Does the cruise control work? what about the tachometer?

 

Is there a button on the dash that says OD on it and does it light up or flash? If it's there, then you have the E4OD and you need to find out if the OD button is woking. If you don't have the button it has the C6 and it has no overdrive.

 

Dave beat me to it!

 

Thanks for the replies! The truck does have cruise control, though it doesn't seem to work. I can't see any button for OD on the dash but there is a fuse for it. The shifter says (from left to right) "P R N D 2 1." There are a bunch of after market buttons and switches on the dash for what looks like an amp that is no longer installed, and I'm not sure what else. I've tried flicking them but they do nothing. The truck has a push button for the starter located to the right of to heater control, it doesn't look stock. It sounds like I have the C6 trans with 4.10 rear end from reading the responses and other posts. I can reach a speed of about 55 MPH at about 2500 RPM.The truck red lines at about 3700 RPM. If I take it on a long trip, what RPM should I feel safe about keeping it at?
Also, If I were to get my mitts on a trans with OD, would it be worth it to install it? I've read that it doesn't increase MPG by much, but would my highway speeds increase significantly? Or would that be the work of the rear end?
Thanks again for the help.

 

I beat the lightening.....

Mad.Scientist, I feel your pain. My truck came into the world with the exact same tranny and rear end. It sucked big time, but cruising at 55 MPH will hurt nothing other than your fuel bill. If you are moving a 5th wheeler across the country like mine did in a previous life, then its great.

Yes, you could swap an E4OD into there, but its more involving than just bolting it up to the engine. You will need to install a computer (factory or aftermarket) and the related wiring. The drive shaft will have to be shortened, and depending on what year of transmission you find (must be 1989-1991), rebuild and upgrades would be a good idea. I love the E4OD, but its not as reliable as the C6 if you compare both of them in stock form.

You certainly will gain from having an overdrive transmission in terms of top speed and economy at legal freeway speeds. Other option is swapping the differential gears. Going to 3.08s will get you almost as much RPM drop as swapping the transmission. Its not recommended if you need to tow more than 5000lbs all the time, but the truck will still move a decent load.

I ended up doing the gear swap first and drove it that way for a couple years until I could afford the E4OD upgrade as well. Its a little extreme with a final drive ratio of about 2.2:1 in overdrive, but now it eats up miles like theres no tomorrow.

One other option is too look for a used gear vendors overdrive. Sometimes you can get them for a little more than $500. For the price of a new one, I would sooner go with an E4OD, but others may disagree.

 

Thanks Dave,
That was a ton of helpful info. It looks like I'll be topping off the fluids, and doing a quick tune up and hitting the road for a long haul. Being that I am an Engineering student and a roofer, I shouldn't need to be hauling too many heavy loads. I might keep my eyes peeled for a rear end over the next year or so.
Thanks again.

 

Your best bet would be to look for a 3.55 ratio, 3.08s are extremely rare. I don't know of any that were factory by 1989.