8 Lug rear end

[busterwivell]

Hey there, Boys and Girls...........
I have a 1 Ton Longhorn with a 402 and 700R4. My problem is the rear gears. As best I can determine, they are 4.56. It is an 8 lug, 14 bolt rear. I checked with a local differential shop, and they tell me the only gears available for that rear are 3.90, 4.11 and 4.56. I want something like 3.54. They tell me to get a 73 and up 8 lug rear and they will put leaf spring mounts on it to fit my truck. Before I do that, anyone have another idea? No, I won't put a 9 inch F##d in it.
Bill

[Mike C]

Is this the Eaton diff? You can find a Dana 60 from a 67-72 wqith 3.54 but you will still have perch problems. The 4x4 and Longhorns have a 40.5" spring center while the 3/4 and 1 ton 2x4 have 42.5" spring centers. You will not find 3.54 in a 40.5" center IME. Might as well go with the later 14 bolt which is cheaper and has more options. If you can find one from a single wheel one ton it will already have 40.5" spring centers and only the shock mounts will need to be relocated.

[COBALT]

Don't ask if it's an Eaton. Ask if it's an HO72 or HO52 ten bolt corporate axle - perfectly round cover like a salad bowl.

If you have this differential you're SOL on the 3.54 gears. These things only came with 4.10 and up from the factory. The only available gears to decrease reduction are 3.90, so your supplier is correct.

I have an HO52, and originally had 4.10, and wanted 3.73 put in when my carrier started having problems. Apparently years ago there was a 3.73 gear set made for the Eaton carrier in these corporate axles that you could swap in (I've seen exactly one set), but they haven't been made for close to 10 years, and any that are available are LONG gone, so no dice. I had to opt for the 3.90s and basically plan on swapping axles some time in the future.

[Longhorn Man]

With the over drive, whats your RPM on the freeway?
My last longhorn had the 4.56 gears with 9.50 16.5 tires and I was spinning about 3000 @ 70MPH with a TH350 tranny.
just curiouse.

[Stocker]

Originally posted by busterwivell
As best I can determine, they are 4.56.

Short of looking inside and counting teeth, can you jack up the back end, spin a tire exactly one rotation, and count the driveshaft rotations to get the ratio? I think if you have an open diff, you need to double the driveshaft rotations to get the right ratio...

[busterwivell]

I know it is at least 4.11, don't know how accurate the factory tach is. With the 700, I'm doing 3500 at 70 MPH with 9.50 x 15. I can run 50 at 2500 and run a good temp, but with 110 degress temps, I start warming up at 3500 RPM.

[Longhorn Man]

I really don't want to insult you in any way shape or form....but you sure you have an overdrive in that sucker?

[busterwivell]

Yes, I had a 700R4 built and installed several months ago. Replaced a granny 4 speed.

[Mike C]

There is no way you are doing those kind of r's with the 700 and even 4.57. With a .68 od should be a 3.1 final drive. Sounds like you may have 5.13 or even 5.57(!?) as crazy as that sounds. 4.11 would be perfect with the 700 and easy to find to boot.

[busterwivell]

Then the tach is off, but it shows, for example, 2700 at 55 mph in overdrive, in 3rd, it shows 3700 at 50 and runs warm. I guess I can pull the rear apart and count teeth, or install another tach, after I get home from Pomona.

[Longhorn Man]

I would verify the tach.
As for overheating at speed, you'r probably lookin at a pump that is givin up the ghost or maybe a lower hose getting collapsed from the negitiave pressure.