Hi. I have a very nice 78 f250 4x4. 429 thunder jet with some mods. C6 3spd. Pulling about 3000 rpms at 60mph. With 35 " tires. Would like to get rpms lower. 37" tires should drop it to 2800ish rpms. What is your opinions on revving this high? Ok? Any opinions on the gear vendors adapter? I think it turns it into a 6 spd and the tallest gear is about 20% taller then the stock 3rd gear which is 1: 1. Thanks in advance. Truck is 4we with 4.10 s

 

You won't see the full potential on a C6 as it has no lock up converter and will just build tons of heat in the transmission.

 

Why not swap the gearing to a more friendly ratio?

 

You are right so he would need to add a large trans cooler. Is there a 4sp lock up over drive trans that will bolt to his motor?

I guess you have not done this?
If he was to go to say a 3.90 or 3.73 gears, he has to do front & rear, it will be a dog from a stop, if he lives where it is hilly the trans may run in 2nd gear more and not 3rd that is 1:1. and it will also build up more heat in the trans as the converter will be slipping more so a large cooler will be needed.

As for turning the C6 3sp into a 6 speed know that the GVOD unit has a safety where it will not shift to OD unless doing 30 MPH. They do not want you starting in 1st OD as the unit can not take all the TQ so the controller is hooked to the speedo cable to know when it is at 30 MPH or more to shift.
It also CAN NOT be used in 4x4 mode as it fits on the back of the transfer case to the rear axle. The controller also has a lockup so it will not go into OD if in 4x4.

I would also find a calculator and run the numbers of what you have now and then with the GVOD unit.
Thing to remember for speed is your speedo right for the size tires you are running? I am guessing not so before you run the numbers you should get that fixed.

Now if you had a stick and wanted to use OD in 4x4 look at the Advance Adaptor's Range Splitter. Being it goes between the bell housing and the transmission you can use it when in 4x4 and you can also split all gears.
Dave ----

 

Thanks for the replies. Sounds like a lot of hassle. I did account for speedo difference . What your thoughts on this motor pulling 3000 rpm all day long. I generally don't do a lot of freeway driving. When I do I stick to 60 to 65 mph . Approx 3000 rpm.I enjoy the off the line power so lowering gearing is not an option. May just do the 37 s and call it a day.

 

An E4OD from a 460 will bolt up. It's electronically controlled so it will need a shift controller, too,

 

I've been meaning to call the local transmission shop to inquire about the e4od. I've read they weren't that reliable but can be built to be solid.

 

The E4OD isn't the best transmission Ford ever made but for what you're doing it would be fine.

The gear vendor isn't the ideal solution in my opinion , but it will work for you. I have a friend with a '79 4x4 with built 460 and a C6 and he has used it for towing for many years. no problems at all.

I have the same problem as you, a '76 high boy with a 428 CJ and 4.10 gears , way too low geared. I bought a gear vendor to solve it but you can't put one on a high boy the drive shaft is too short now I find. if I were you I'd either just live with it or put a E4OD in. I have a 4spd so it's not an option.

 

If your 429 is 1971 or later, it will. If it is pre-71, the crank pilot is larger, same as a 390.

 

Mine is from 1970