Rear end swap

[dean333]

I have a 36 Fordoor with a 4:11 rear. What years can I do a straight swap to a 3.78 without modifications? I'm thinking 36-40?? Can I swap out just a center section? Thanks guys.

[MuskegonFlatheadFan]

look here; http://www.flatheadv8.org/fordrear.htm

[Charlie Stephens]

Originally Posted by dean333

I have a 36 Fordoor with a 4:11 rear. What years can I do a straight swap to a 3.78 without modifications? I'm thinking 36-40?? Can I swap out just a center section? Thanks guys.

When you do some reading you will find out that the adjustment for the ring and pinion is accomplished by adding or subtracting paper shims between the center section and the axle housings, so the answer to your question is NO on swapping the center section. Modern rear ends have a center section that can be interchanged without adjustment of the gears.

Charlie Stephens

[dean333]

Charlie, can't I swap out a center section and make necessary adjustments with the shims? Looks like spring perches are different 36-40....will the 36 spring still fit?

[Charlie Stephens]

Originally Posted by dean333

Charlie, can't I swap out a center section and make necessary adjustments with the shims? Looks like spring perches are different 36-40....will the 36 spring still fit?

Yes you can swap out the center section and make the necessary adjustments with the shims but I thought you just wanted to swap without having to make any adjustments like on a modern rear end. If you start going between years post as I assume you are within the same year on your parts. I don't know enough about the overall rear ends to answer your other question question.

Charlie Stephens

[dean333]

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Thanks Charlie

[ford38v8]

Tim, The center section of any early Ford differential having the gear ratio you want will swap in without modification. You will need a 6/10 driveshaft coupling, and a set of banjo gaskets. Likely you will need a set of shackles also. I suggest teflon shackles from Speedway. I also suggest that you get two sets of gaskets. Split one set for a quick determination of correct shims per side to avoid complete disassembly/reassembly for each trial fit. Never rethread the banjo threads and bolts, as they are meant to thread tightly to prevent leaks. On final assembly, use thread seal on those banjo bolts.

[JM 35 Sedan]

Originally Posted by dean333

I have a 36 Fordoor with a 4:11 rear. What years can I do a straight swap to a 3.78 without modifications? I'm thinking 36-40?? Can I swap out just a center section? Thanks guys.

Not sure I understand your first question. Are you asking what years of complete assembled banjo rearends, that already have 3.78 gears installed, will swap with the complete stock rearend that's already in your '36? If that's your question, then of course another '35-'36 rearend will swap, plus a complete '37-'40 passenger car ('37 - '41 light commercial vehicle) rearend will also swap.

If you just want to swap your existing 4.11 ring and pinion gear set, that more than likely has a 10 spline pinion now, without making other modifications, you would need to find a 3.78 matched ring and pinion gear set that also has a 10 spline pinion. This requires going through all the bearing preload steps and setting the mesh of the ring and pinion gears by placing the correct number and thicknes of gaskets/shims between axle housings and center banjo housing. There is no quick and easy way of doing this correctly that I know of. All of this assembly must be done by the correct procedures or its not going to work.

[dean333]

Thanks for all the info guys, now I can make an offer for one I found.

[jimTN]

I think you will find that a used gear set will need no additional gaskets. I have put several together with just silicone to seal them. Over the years they easily wear so if anything they need tightning up. Put the side with the ring gear on first and see if there is any resistance, if so then add gaskets.

[ford38v8]

You guys...! I don't understand your confusion! All he wants to do is swap out a center section. He'll be using all his '36 parts but the center section, and will need a 6/10 drive shaft coupling, period. No other fuss.

Maybe I'm the one behind that 8 ball? I don't see the problem you guys see?

[V8COOPMAN]

Gotta be careful about axle tooth count/spiders. DD

[JM 35 Sedan]

Originally Posted by ford38v8

You guys...! I don't understand your confusion! All he wants to do is swap out a center section. He'll be using all his '36 parts but the center section, and will need a 6/10 drive shaft coupling, period. No other fuss.

Maybe I'm the one behind that 8 ball? I don't see the problem you guys see?

Alan, a stock '36 rear would have a tubular driveshaft with a 10 spline female bung welded into the pinion end of the driveshaft. A 6 to 10 spline coupler would only work with the later solid driveshaft that requires a center bearing torque tube. The only possible use for a 6 to 10 spline coupler in this case would be to cut off the 6 spline end, bore out the 10 spline bung on the tubular driveshaft, and weld in the six spline piece, IF the ring and pinion set he plans to use has 6 splines on the pinion.

Also, his question about swapping out just the center section was his second question. Go back and reread his first post to understand his first question.

[ford38v8]

John, I've never actually seen a 6/10, so I assumed it would work either way by flipping ends. It didn't even occur to me that the hollow shaft has a female spline....So, I sure am behind the 8 ball on that one!

On his question, I just understood that he meant center section from the git go. Sometimes these long distance conversations get twisted between sender and receiver, don't they?

And to Coopman, assumption on my part was that he was aware of tooth count on the spiders, or at least would have discovered the difference all in good time!

[deuce_roadster]

I didn't see anywhere the mention of the spiders. The axle ends have different number of teeth but are the same length. If you use the 40 axles, no problem, if you are going to use the 36 axles, you need to change the spider gears.

[jimTN]

YOu can use the 40 drive shaft and torque tube. If necessary, relocate the boss that radius arms bolt to. 35-40 TT and DS are same length.

[scooder]

We also have to pay mind to the carrier bearings don't we? Just asked a question about these on the modern bearing thread. Was informed that the carrier bearings need to match the axle casings. So if you use a 40 center section with 35 axle casings, you need to swap on the 35 carrier bearings.
Unless I got it all fuddled up.
Martin.

[dean333]

Ok Guys, I found a complete assy less backing plates from a 37 pickup, am I good to go?

[V8COOPMAN]

If it has the spring, torque tube and bones attached, it should glue right in place. Only thing to consider is the brake rod routing for the '36, as the '37 used cables.

If you have hydraulics, you're golden. DD

[JWL]

I REALLY doubt the 37 pickup rearend has 3:78 gears. Better do some checking before installing a 4:11 in place of a 4:11.