The Stovebolt Site Forums The Shop Area Engine Shop Can I relpace a 4:56 gear with a 4:11 ring-pinion

I have just purchased a 68 C-20 that I am going to make a clean daily driver out of. The rear gear is 4:56 which is much to low (50mph=2500rpm). I want to keep the column shift and hope to find a T-85n trans with overdrive (and will keep searching until I do?). A 4:11 rear gear would be much better. I have found a complete rear end in 4:11 and understand that that is the only other option with this housing but was wondering if I possible just to change the ring and pinion to 4:11 in my existing housing. This is the 12 bolt (round pattern) with the external bolts and bearings in the break drum. I cannot find any info about it on LMC Truck.

If you have the Eaton axle it is possible to remove the complete center section and replace it with the 4.11 geared differential from another truck. Provided you can find one...

My one caution is to make sure you have an Eaton rear, and not a Dana before you start this swap. The 'round pattern' suggests it is an Eaton, the Dana would never be described as 'round'.

The 4.56 and 4.11 are not the only options with this housing. There is also a 5.17 that was optional in 3/4-tons and standard in 1-tons.

Well I guess I can show my lack of knowledge quickly as I am not familiar with the Eaton axle but from looking at the diagrams at LMC Truck it is not the Dana rear end. I cannot find any supplier that list new gears for this but now that I know the name as Eaton it might help in the search. I have a picture put do not see how to attach one. Thanks again for the info.

Back when we were using that axle in dirt track race cars about 30 years ago, it was pretty common to keep two center housings around, one with a 4.56 gear, and another with a 4.11. On the "short" 1/4 mile tracks which measured 1320 feet around the outside wall, we used the 4.56. A "long" 1/4 mile, measured around the infield, needed a higher gear, so we would swap for the 4.11.

If you want to swap only the ring and pinion, you'll also need the ring gear/spider gear carrier housing, which has a different side-to-side spacing than the 4.56. Leave the 4,11 as a complete assembly, pull both axles, and swap the whole center chunk. It's less than an hour's work. If you try to mix & match parts, you're almost guaranteed to get a gear howl, as the tooth contact pattern is extremely difficult to match up once a set of used gears have their running relationship disturbed.
Jerry

Edit: If you have managed to find a 4.11 axle, you should also consider buying a Powerball lottery ticket. The odds of scoring either one are astronomical, since the 4.11 was only used behind certain 3/4 ton rigs with an automatic transmission. It's scarce as hens' teeth!
Jerry

There are actually three different styles of the GM corporate HO72

2 pin no load bolt
2 pin w load bolt
4 pin w load bolt

Thanks again for the info. There is a Chevy truck used parts place close to where I live and according to him he has the 4:11. I guess that I had better check again and make sure... price was mentioned and that may be the kicker. What seems to be the most elusive is the T85n trans. Missed one on Ebay last week from a 68 Chevy car. Thanks again I'll let you know what I find and if anyone knows of a T85 let me know.
Jerry T.

Thanks again for the info. There is a Chevy truck used parts place close to where I live and according to him he has the 4:11. I guess that I had better check again and make sure... price was mentioned and that may be the kicker. What seems to be the most elusive is the T85n trans. Missed one on Ebay last week from a 68 Chevy car. Thanks again I'll let you know what I find and if anyone knows of a T85 let me know.
Jerry T.

Thanks again for the info. There is a Chevy truck used parts place close to where I live and according to him he has the 4:11. I guess that I had better check again and make sure... price was mentioned and that may be the kicker. What seems to be the most elusive is the T85n trans. Missed one on Ebay last week from a 68 Chevy car. Thanks again I'll let you know what I find and if anyone knows of a T85 let me know.
Jerry T.

Not trying to rain on your parade, and I hope you know how to set up the rear gears,, not a swap for the novice. Needs to be set up correctly or you will be doing it again... PLease no offense just trying to save you some trouble.

Thanks again for the info. There is a Chevy truck used parts place close to where I live and according to him he has the 4:11. I guess that I had better check again and make sure... price was mentioned and that may be the kicker. What seems to be the most elusive is the T85n trans. Missed one on Ebay last week from a 68 Chevy car. Thanks again I'll let you know what I find and if anyone knows of a T85 let me know.
Jerry T.

Where in Tennessee are you? I teach school in Nashville, and my farm is near Fayetteville off US Hwy. 64. I'd be glad to try to help you identify what axle you have. The "round" description pretty well narrows it down to the Eaton with the removable center chunk, but I can take one look and know for sure. There are a couple of oldtime wrecking yards near my farm that might be worth looking into, if your current source doesn't pan out.
Jerry

Try swapping for a complete Dana60 from a late model van. A Dodge is just about perfect and Ford is within a couple inches. You'll at least have some better gear and parts options.

Why do you want a FORD T85 with non-syncro first gear???
If your truck has a three spd column shift now then it should be the Saginaw all-syncro three spd. You just need an OD version of what you now have and a new, shorter drive shaft.
SM 326

>>with the external bolts and bearings in the break drum.<<
That is usually described as a "full-floating" axle.

Thanks again for the info. There is a Chevy truck used parts place close to where I live and according to him he has the 4:11. I guess that I had better check again and make sure... price was mentioned and that may be the kicker. What seems to be the most elusive is the T85n trans. Missed one on Ebay last week from a 68 Chevy car. Thanks again I'll let you know what I find and if anyone knows of a T85 let me know.
Jerry T.

Trivejb

I did a similar swich but only needed to change out the gears from 3.92 down to 3.23 to help out the RPM's. I had a DANA 44 rearend. Is it possible to complelty change your rear axle to a DANA? That way you can find even lower gears.