Slick 60's

Ok, so I moved to Oregon and left my truck in Montana at my dad's house. I'm going to get it this summer, I'm planning to drive it home. The problem is that the current gear ratio is at 3.70, and I put a C6 auto in it.

The gear ratio is not fit for the highway, and I'm planning on driving it home, so I'd like to do a quick and easy punkin change.

My tag ID is WDM C13.70 5DC 302

I'm pretty sure it's a 9" with 28 spline shafts. I tried to interchange a punkin I had from a '84 Bronco earlier, but it was 31 spline, and the axle was MUCH wider, so no hope of easy rear end swap there.


The plan is to get a punkin here and drive it over in the trunk of my car, then do a quick and easy punkin swap (I'm only gonna have 1 day). That eliminates a full rear end swap. Also, I will have no time whatsoever to scrounge for parts once I get there, so I need to find the parts here first.

Can anyone tell me what models of cars or trucks and what years would have an interchangeable punkin for me with a better rear gear ratio. And I would also be willing to entertain suggestions as to what ratio I should shoot for. The original vehicle the drivetrain came from had 3.00 gears. I would like to be able to go over 55 mph without listening to my freshly rebuilt 351W SCREAM in agony.

Thanks all.

almost every pickup from the 50's to the 80's had a 9 inch and I think most of them had a 3.00 or 3.25. I'm sure someone else will chime in. good luck

I run 2.75s behind the big block in "Christine" I pulled a way over loaded dual axle trailer 2800 miles with it and did no have any issues. 351 shoud have enough torque to pull a 3.00 or 2.75 set.

472 CI with EFI and a C6.

Garbz

I'm not positive on spline counts, but in addition to trucks, Lincoln's, LTD's, big Merc's, etc. all had 9" rear ends through the 1970's. Most of them all had highway friendly gears in them too. Go hit the boneyards.

Make sure your yoke is compatible as well, there are a few diffferent ones if I remember correctly!

Even with a conversion u-joint, the heavier pinion yoke is also LONGER, which would mean that the drive shaft may be too long and screw things up. I know from experience. Changing the yoke is not impossible, but it can be tricky since there is a crush sleeve in there and it may crush too far with the subsequent torque with the new yoke.

But like all the other posts -- there are LOTS of 3.00 and 3.25 chunks out there. Learn to ID a 9". The 3.70 in your tag tells you that you have a 3.70 rear currently. If you are luck, in a junk yard you can find one with a tag still and ID the ratio that way. Otherwise, you can count revolutions.

Remember ratio is drive shaft revolutions to axel revolutions. And that assumes that both axels are turning forward. If one tire is on the ground, the other will turn twice as fast, unless its a locker.....

Trucks usually had the 28 spline axles up to 1972. Most cars had 28 splines also. The exception being high performance late 60's and early 70's muscle cars.

I had a 78 with 3:00 gears behind a dead stock single exhaust 302. it had adequate power and got 20 MPG with a C4.
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Where at in Oregon are you, I have a 67 F100 that I'm parting out, it has a 9" rear end and it had a auto trans.

I'm in the Portland area. Hillsboro to be exact.

Ford in Montana: send me a PM. I know where there are several pumpkins in Albany if that is not too far. I believe at least one is 3:25 but can check on the others.

geeze it seems like it would almost be easier to swap the whole rear than hassle with the "punkin" thing. if you can find one of the same type you wouldnt need to mess with the seals or the splines or any of that BS.

Bigtrip -- trust us, swapping a "punkin" or center section or whatever you want to call it is pretty easy. Vastly easier than swapping a whole rear end.

Probably the most complicated part of swapping a center section is pulling the axels, which entails getting the drums off, and THAT can be a pain sometimes. But if they are hard to get off, it probably means that they are groved and needing to be turned and new pads anyhow....

Now, there is of course all sorts of pitfalls that are not directly due to the swap that could give you trouble (remember Murphy). When the axels are out, you may find that the seals are shot. And if you are really unlucky, the bearings will be gone too, which is a bit complicated in a 65, as the retainer is pressed on. Easy to do if you have a press and tools. Trouble if you are doing this in a distant parking lot......

But the punkin swap itself is just 10 bolts and lots of mess!!!!

I'm not worried about getting it apart. I've already had it apart to check everything out, and I rebuilt the brake system while I was there, so all my seals and brakes are good. It should fly apart easy since it's already been out fairly recently and nothing's fused together after 40 years of being assembled.

What concerns me is compatability. Yoke length, spline count, seal size.....

I just don't know which tag codes would interchange and which wouldn't, and since the truck is 600 miles away, I can't exactly just whip out the measuring tape on the thing.

Maybe the Chilton manual would have measurments and compatability info I could look up at the library? Anyone know this?

I could always just hit the local U-pullit if I knew for sure what would fit and what wouldn't. Or if someone close by has one, I could double check compatability if they're willing to give up the tag info.

if seals, bearings, brakes, and all that have already been replaced swapping the center might not be that bad.

I'm in Prineville, about 175 miles from you, sorry

Its a 9" with 1310 ujoint. That was common and you can look up the dimentions of a 1310 ujoint and then when junk yarding, you can measure and verify. So long as you do that, I think all the 1310 pinion yokes are the same lenght. That will in turn assure that the drive shaft is ok.

A 9" from a 60s to mid 70's car or truck will do ya. Pull an axel first (you gotta anyhow) and count the splines. If its already out (the punkin) then count the splines.

Seals -- well any used chunk might leak at the pinion seal. But that's usually a slow leak -- worst case scenario, you'd be pulling over every 200 miles and squirting some oil in. But the 9" is a tough rear, you could run it low on oil and it would make it a long way.

How you going to get the chunk to your truck? Its a heavy little peice, about 70 lbs. Not exactly carry on luggage......

Just gonna haul it in the trunk of my car, no big deal. My only fear here is getting the wrong part and not being able to do the swap when I get there, hence the big questions. Thanks for all the info guys.

One more question for everyone. I checked and availability is extremely limited for parts for older vehicles here in the Portland area. The u-pullits here don't have any older trucks to pull parts from. Closest thing is way the heck out in Damascas, and they only have 3. God only knows what gear ratio is under them, or if they've been pulled already. I guess the trend is that older stuff gets crushed. Even if they do have what I need, they want $120 for me to come all the way out there and pull it out myself in the summer heat.

I have a rear end from an 84 Bronco. It's a 31 spline 9 inch. Obviously I can't just do a simple punkin swap, but is there any reason I can't just use the ring and pinion from that? I can always putter my truck home at 55mph for the whole 600 mile trip and do it in my own garage.....

Just trying to save a buck, and some headache.

If you get in a pinch and can't find a rear end. Look for taller tires for the rear.

Taller tires or new rear end., Don't forget your speedo is going to be off.