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I just picked her up a couple of weeks ago. She's a big fender 1969 C60 and has a 427, 5 speed Eaton (not sure which one), an Eaton 17221 2 speed rear end with 6:50/8:87 gears, hydraulic steering, air brakes, spring brakes and a semi 5th wheel. The body is clean except a couple dents and one spot by the gas pedal on the floor.

There's a laundry list of things she needs and things that I need to do but for the most part it's all there and in good shape considering she's 50 years old. The exhaust needs replaced which I already bought a set of headers since in going to replace everything from the heads back since the manifold gaskets are gone. The headlights are the only lights that work. All 6 tires are about shot, it already has 22.5s on the back and will be replacing the split rim 20s on the front with 22.5s also. The ring gear on the flywheel will have to be replaced since the teeth I was told are gone, I have to pull start it for now.

Like I said it's a laundry list of things and that's the short list. I bought this truck to pull my wife's 1972 Chevy mega truck around for now. One day I will build my own mega truck but for now back surgery and having to take it easy for a year this is a project I can do. I'm giving myself until next spring to have this truck ready to pull anything I need it to. For the time being it will only need to pull 10-15k pounds (5 years). After that it will need to pull roughly 20k pounds when fully loaded.

Most everything I can handle myself, I'm a journeyman millwright and gear head. One thing for sure I need more knowledge about is regearing this rear end I have. Currently on the down hill with the motor screaming at me I managed a whopping 58 mph. That's not going to cut it for me. Most of my driving will be on the expressway where the speed limit where I live ranges from 65-75 mph where I'll be traveling most. Using a gear calculator I've found that a 4:56/4:88 high gear should give me no problems traveling at a comfortable 65-70 mph. I don't need to go faster then that but would have a top speed of 80+ mph. With that gearing I figured I wouldn't be at the engines red line constantly. In a perfect world I wouldn't mind keeping the 6:50 high gear it currently has and just use that as my low while the 4:56/4:88 would be my new high. Now you're probably thinking this idiot has no idea what he's talking about. If you are perfect, enlighten me please! If there's other/better options I'm not aware of please tell me. From what I've gathered I could regear the low for around $500. To me that's cheaper then getting an auxiliary OD or swapping to an OD transmission. I don't mind doing either one bit but if I go that far I may as well go with a 12 valve Cummins and a NV4500. If I am all wrong please steer me correctly. A rear axle swap sounds good too but I'd really like to keep the spring brakes and air brakes but don't know how likely I am to come across that with a highway gear in it already.

Sorry for the long rant.

Hy Pvmt-Pndr, welcome, if you can find a gear set with the ratios you want and it is transferable into your rear axle housing without additional parts, then I would say make the gear swap, that job is probably the lightest work of all your options. You may be able to find a whole assembled center section with the ratios you want, the supplier will want to know the size (diameter) and spline count of your axles. Please keep us informed if you find the parts you are looking for.

I've been doing some digging and have come across two complete rear ends with 4:88 gears! They're around $5-700 each before shipping. That's cheaper then I was expecting. Once I'm back to work a whole rear end will be high on my list. If my calculations are correct I should be able to cruise at 70 mph while spinning around 2900 rpm which is perfect. I have more digging to do to find out what low gear it would be paired with. Currently with the 6:50 I have no use for first gear so I should be perfect.

Most Eaton 2-speed rears I've seen have a multiplier of about 1.36 between the two ratios. It works out pretty close on your existing rear ratios 6.50 x 1.36 = 8.84.

If you find a 4.88 gear set make sure it's for a 2-speed rear as the single speed gears will not fit in your 2-speed case.

Mike B

So I'm safe to say that the low in a 2 speed with 4:88s would be 6:24... That would be perfect! Thanks! Right now there's no need for 1st empty or even 2 low so I think I'll be safe to assume once I go to the 4:88/6:24-ish I shouldn't have a problem pulling 20k pounds at speeds and down shifting will be expected on the hills.

I've never been in one of these axles before. Am I safe to assume that I would be able to pull the 3rd member out and just swap it with the new one? I know I would have to pull the axles. Is there a go to write up on doing this that I haven't cone across yet for walking me though the process?

Glad to see that you made it over here.

Bill

Yes sir! Most of what I was looking up pointed me here. There seems to be a wealth of knowledge floating around here.

Yes, or something real close to that number (assuming 4.88's were ever available).

Yes, as long as the 3rd member cases are the same...take lots of measurements and pictures of your bolt pattern (the bolts that hold the 3rd member to the axle housing) and start looking around to see what fits.

Mike B

Thanks Mike! Much appreciated. When it comes to checking the spline count can I simply unbolt the axle from from the hub and slide it right all the way out to count them or is there more to it then that?

I've come across a few of them used. Seems like some are Chevy, Ford and IH. I assume there is a difference between them aside from the spline count or would I be assuming wrong?

A 3rd member I don't mind changing myself. I have a friend of mine who is good at changing gears and has some experience with 2 speed rear ends. If I can't find a drop in ready 3rd member with 4:88s he's already told me that he will help me do the gear swap. I've come across a few places that sell gears but I don't have enough knowledge about the rear end on this truck to call some place and tall to someone who isn't experienced and be taken for a ride and buy the wrong parts. Is there a good go to place for gears? I only know what I've posted but am learning lots everyday.

I did go out and try to trouble shoot the lights not working today. I replaced all the glass fuses and just my luck I lost all power... go figure. It's was too cold for me to do anything more today. At least I only messed with one thing so it should be an easy fix.