My truck is a 1989 F 150 long bed with the 351 Windsor and 4x4 on 33's. I Also have the C6 3 speed. I am wondering how difficult it is to replace gears, and if anyone knows of a good replacement procedure. I am all but sure I have 4:10 gears. I haven't had a chance to jack up the rear end and test it, but at 55 MPH I am at VERY high RPMS. These trucks inconveniently do not have built in Tachs, but I am also wondering how fast I should be running her for extended periods of time. Any guidance on this is appreciated.

 

with that trans and no overdrive you probably will be running high rpm's comparatively.

 

I have 4:10 gears in my 88 f250 460 5 speed and 31" tires I'm reving at 2,000 rpm to go 55-56mph. Runs fine all day at 2,500 rpm going about 70 but I rarely am driving on interstate.

 

4.10 gears, 33" tires and a C6 would put you around 2300 - 2500 rpm (depending on how much torque converter slippage you have). 70 mph is around 3100 rpm.

Generally running your engine at those speeds isn't too bad for the engine, but it is very annoying and isn't great for mileage.

 

I ran my 88 F150 with 351w, C6, 3.55 gears, and tall tires at interstate speeds for extended periods all the time, usually between 2500 and 3200 rpm depending on speed and load. By extended periods, I mean all day except for fuel stops. It is hard on the power train and the fuel, but it is was designed for the abuse too. If everything is in good shape don't worry about hurting it, just drive. Towing or extreme speed will make overheating and other failures more likely. If your power train has a weakness, this kind of extended high RPM operation will make it worsen faster.

A gear swap is not rocket science but it is precision work and if you have to ask you probably shouldn't attempt it without a pro to help you in person. Additionally you will need a few specialty tools. It is a good learning experience, but if you need the truck and something goes wrong you will be up a creek. Having a shop do it is usually about $1000 or so an axle, and since you would need to change 2, plus the cost of the new gears... A transmission swap pretty well goes in the same direction as far as cost. Not saying don't do it, just think about how much cash you want to put out vs. the cost of buying a truck with the equipment you want already installed.

My advice:
If your truck is a toy, do whatever you want to it and enjoy. If you need a truck and you need it to drive long distances find another truck with overdrive, stock height tires, and decent gearing. If you don't need a truck for your highway trips buy a cheap small car and use your truck for truck stuff. Expensive mods beyond ordinary maintenance and repairs in pursuit of better mileage take years to pay you back, if they ever do.

 

Thank you for the advice everyone. I think I will just keep driving her how she is for now. It is my daily so I'm not going to fix something that's not broken. Maybe in the future it is something to look into but she runs fine as is.

 

A gear swap isn't hard, although it can be tedious to set them up properly if you assemble a few times and the mesh still isn't right.

No matter how you look at it, having only 3 gears is a pain in the ***. I'd look into an overdrive transmission, or just add an auxiliary od to yours.

 

Another option would be to swap in in a manual transmission with overdrive. I was only thinking about swapping in an E4OD earlier, but swapping in a manual is an option too. That said a built AOD could go in there just as well, and would probably be the least intrusive trans swap, but it would depend on how hard you really work the truck as to whether it would hold up. A trans swap could help you out a lot on the mileage front while leaving 4.10 gearing advantage in place, but it would be a lot more intrusive than a gear swap. The C6 is pretty well bullet proof as a heavy duty transmission but it just cant delivery high speed economy.

 

C6 transmissions are dinosaurs.Horrible trans for a daily driver unless you just drive 5k miles a year or something.No OD and no locking converter.Both equally important.Great for the drag strip,a toy or yard truck.Look for an overdrive trans from a salvage yard/parts truck and swap it before you worry about gears.You also have the option of buying a small 4 cyl car and using that as the dd and keep the truck as is and only use it when you need a truck....but this means you need to drive so much,that more tag and insurance are justified.

 

Now my question is are these transmissions bolt on or do they require large modifications?
Also, being that the truck is OBD1, will a different transmission confuse the computer because it was intended for what is has now? Or will it accept another transmission

 

To your first question, the answer is sort of. All of the previously mentioned transmissions were installed by Ford behind Windsor small blocks, and with Borg and Warner transfer cases. You would need to find a 4x4 transmission with the Ford Windsor small block bell housing. A 2wd transmission can be mated to a transfer case but you have to completely tear it down to do so, and it is much easier to get a 4x4 version to start with.

Different transmissions will have different dimensions so, the transmission mount, drive shafts, cables, and linkages will all change. Manual transmissions will also require clutch and shifter components. As already stated an AOD transmission would probably be the least intrusive option, but it is not a heavy duty transmission and should beefed up if you plan to put it to work. A Mazda 5 Speed with overdrive would probably deliver the best economy, and ZF5 would probably be the best of both reliability and mileage. The best way to do this is to get a complete donor with the same chassis and desired power train.

On your second question, it depends. Your current computer does not manage your current transmission at all and would not care if you swapped in a AOD or a manual transmission. The E4OD and the AODE do require a different computer and a complete harness so the two can communicate. You can also purchase an aftermarket stand alone controller and harness instead of using a factory computer and harness.

Any transmission with a Ford Windsor small block bell housing will bolt right up to your engine, but the rest of the swap would be pretty involved, but would give you the results you are after. To my mind it is significantly easier and possibly cheaper to get a different truck or live with the poor mileage.

 

it's unlikely you have a 4.10 gear... likely a 3.55.