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.

[JM 35 Sedan]

X2 what JWL said

[Planojc]

Get a Mitchell OD

[dean333]

I'm told the numbers 9 34 are stamped equaling a 3:78.......

[V8COOPMAN]

9 / 34 does equate to 3.78, BUT......that does not guarantee that the originals are STILL in there. Just FWIW !

You can pull the fill plug, mark one of the ring gear teeth, and rotate the ring ONCE while counting the teeth. DD

[dean333]

How many teeth then?

[V8COOPMAN]

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Originally Posted by dean333

How many teeth then?

If it counts 34 teeth, it IS in fact a 3.78.

If it counts 37, it is a 4.11.

If it counts 39, it is a 3.54.

DD

[jimTN]

Scooder is right about the carrier bearings, 37 up are all the same but the 35/6 are different from the later. Get the cups out of the later housings and put in your 36 housings.

[scooder]

Jim,
Just to clear ambiguity, are you saying you can use a 37 up center banjo complete, in pre 37 axle casings, if you fit the bearing cups (the part that the goes in the differential end of the bell)?
I kinda thought you'd swap the pre 37 diff carrier bearings onto the 37 up diff carrier, to make it go together. Would either way achieve the same end product?
Asking purely for clarity for the OP and anyone else thinking of doing this.
I have a small pile of leftover V8 rear parts tucked away, and have a feeling some is pre 37 and some post 37. So will file this thread for future reference. Not bothered about axles and spiders, cus I know I have both variants complete in diff carriers.
Many thanks,
Martin.

[jimTN]

I am not sure Martin. Know the width of the center housing is the same and do remember swaping stuff back and forth using 36 outer housings and that is why changing the cups makes sense. If the carrier assy. is the same width on the late and early and bearing IDs are the same, you could go the way you descriged.

[scooder]

Thanks Jim,
When I get to deal with this, I'll report my findings. Martin.

[dean333]

Coopman.....on the teeth count; are you sure 39 is a 3:54? The math doesn't work out if the numbers are stamped 9 39. The other two ratios compute.

[JM 35 Sedan]

Originally Posted by dean333

Coopman.....on the teeth count; are you sure 39 is a 3:54? The math doesn't work out if the numbers are stamped 9 39. The other two ratios compute.

That is a good example why you can't always rely 100% on what is stamped on the bottom of the banjo housing but if you actually have 39/9=4.33, that is a ratio that was offered for light commercial pu's.

39/11= 3.54, 37/9=4.11, and 34/9=3.78.

How many teeth are you actually counting on the ring gear that's in the rear in question here??

[dean333]

John: haven't counted yet, relayed info to the seller (not the formula, just asked for the count).

[JM 35 Sedan]

Originally Posted by dean333

John: haven't counted yet, relayed info to the seller (not the formula, just asked for the count).

Keep in mind that in some cases, going by ring gear tooth count, there could be two different ratios with the same number of teeth on ring gear. Check this post where I give ring gear tooth count for most of the banjo rears as listed in the Green Book (bible as some call it).

http://www.fordbarn.com/forum/showth...ear+gear+ratio

[dean333]

I can't tell what year I just picked up using photos shown in the link from post #2, any help would be appreciated.

[V8COOPMAN]

That appears to be a '37-'40 bell, as the shackle hanger boss is BELOW the arm rather than inboard as on '41-'48s. That shock bracket is not factory. DD