Plymouth passenger car gears to truck carrier

[PT81Jan]

I have been in an intensive information exchange with another forum member the past weeks regarding a never ending subject to our trucks: how to alter the rear end to get a better road performance. We did some research, have  read many reports in the forum here and many other sources. 

We both ave a 1939 Plymouth PT81 truck. We plan to change the ratio from 4.1 to 3.73. 

What we know we could do:

1st: a swap to another rear end out of another vehicle like Jeep Cherokee,  Ford Explorer or something else (not what we prefer) 

2nd: a swap of the axle carrier assembly (11 bolt,  10 spline shafts) out of a mopar passenger car,  years 37 - 53  -> passenger gear carrier to truck axle housing (didn't find one up to now)

3rd: exchange of the truck's 4.1 ring and pinion to 3.73 truck ring and pinion (impossible to find) 

Long story short: What we would like to know is:

Does anyone know, if ring and pinions out of passenger cars fit to the truck's ring and pinion carrier? To be more precise: 3.73 ring and pinion out of any mopar passenger car to the 1939 Plymouth truck rear end carrier ? 

Thank you much !

Rear_Axle_Fundamentals.pdf

 

 

[PT81Jan]

Has anyone already made such a swap (passenger car ring and pinion into truck rear end carrier) ? 

Any input on this ? Experts knowledge is appreciated. 

Edited October 15, 2017 by PT81Jan

[Merle Coggins]

I believe some of the differential carriers are different, so the 3.73 ring gear may not fit onto the carrier from a 4.10 gear set. If you have the entire 3.73 differential assembly it would fit your axle. The only difference may be the axle shaft and side gears. 

[DJ194950]

My interchange vintage manual says that either the whole 3rd. member carrier OR the ring and pinion will fit.

I would not look for ant other mopar 3.73 to to readily avail. in models before 1950 as they would have benn optional gear ratios for almost all before that.

Also do Not look at chrylers or desotos unless they have a 6 cyl. motor, 8 passenger,limos or rears from the wagon supposedly do not fit.

Never have i personally done the car to truck rear gear swap  but sold several cars gear sets to people to do this. One person who bought a 3.73 years ago did let me know that it did fit ok.

Hope that gives some info for you,

DJ

[Los_Control]

I am doing the same swap, I feel it will work, therefor it shall! 

[Desotodav]

I have done a truck 4.1 to car 3.54 swap in my 53 truck.  The car axles are shorter than the truck axles. We changed the side gears as Merle suggested. I have another 3.54 diff center swap yet to do for my 52 truck.

[jeffsunzeri]

I swapped out the entire carrier section from a Plymouth to my '47 dodge rear end. Axles fit just fine, and was an easy 1 for 1 replacement.

[PT81Jan]

On 15.10.2017 at 9:55 PM, Merle Coggins said:

I believe some of the differential carriers are different, so the 3.73 ring gear may not fit onto the carrier from a 4.10 gear set. If you have the entire 3.73 differential assembly it would fit your axle. The only difference may be the axle shaft and side gears. 

Thank yo Merle, I only know that there are 10 bolt and 11 bolt carriers,  but I do not know the difference up to now... 

On 15.10.2017 at 10:17 PM, DJ194950 said:

My interchange vintage manual says that either the whole 3rd. member carrier OR the ring and pinion will fit.

I would not look for ant other mopar 3.73 to to readily avail. in models before 1950 as they would have benn optional gear ratios for almost all before that.

Also do Not look at chrylers or desotos unless they have a 6 cyl. motor, 8 passenger,limos or rears from the wagon supposedly do not fit.

Never have i personally done the car to truck rear gear swap  but sold several cars gear sets to people to do this. One person who bought a 3.73 years ago did let me know that it did fit ok.

Hope that gives some info for you,

DJ

Thanks DJ,

first paragraph: ring and pionion of what kind of vehicle to what kind of vehicle's rear? (passenger /truck) 

fourth paragraph: veeeerrry interesting !! 

On 16.10.2017 at 12:05 AM, Los_Control said:

I am doing the same swap, I feel it will work, therefor it shall! 

Hahaha,  cool attitude.  That is what I wanted to hear.  Would be nice to hear of the result ! 

On 16.10.2017 at 1:02 AM, Desotodav said:

I have done a truck 4.1 to car 3.54 swap in my 53 truck.  The car axles are shorter than the truck axles. We changed the side gears as Merle suggested. I have another 3.54 diff center swap yet to do for my 52 truck.

Thanks Desotodave,

I have read about a probable necessity to change the side gears in some reports. Where does the need come frome ? Lack of clearance between gears? The altered ratio should not be a problem !? (thats at least the technical part of my brain makes me thinking...) 

On 16.10.2017 at 4:33 PM, jeffsunzeri said:

I swapped out the entire carrier section from a Plymouth to my '47 dodge rear end. Axles fit just fine, and was an easy 1 for 1 replacement.

Thank you Jeffsunzeri, 

Entire carrier of a car into a 47 Dodge truck? 

 

To all: your feedback contains more info than I did expect. To be honest, I was thinking that swap might be too easy to be true.  Most reports are of complete rear end swaps or to put in an overdrive or an other transmission in combination with a more modern rear end.  Every single info regarding my question  is a great help ! Thank you again, Jan

Edited October 18, 2017 by PT81Jan

[Desotodav]

I remembered chatting in this tread some time ago about a diff ratio change from 4.1 to 3.54 in my 52 DeSoto truck...

 

I dropped two diff centres at the diff shop this morning. The one on the left of the attached photo is a 3.54 from a 54'ish Dodge car and the one on the left of photo is the 4.1 from my 52 truck. I should know within the next few days how well this change will work. My 52 truck has a 10 spline axle and the car diff appears to be about 15... so hopefully it will all work out as well as it did when I did the same swap in my 53 Dodge truck !!!

[PT81Jan]

21 hours ago, Desotodav said:

I remembered chatting in this tread some time ago about a diff ratio change from 4.1 to 3.54 in my 52 DeSoto truck...

 

I dropped two diff centres at the diff shop this morning. The one on the left of the attached photo is a 3.54 from a 54'ish Dodge car and the one on the left of photo is the 4.1 from my 52 truck. I should know within the next few days how well this change will work. My 52 truck has a 10 spline axle and the car diff appears to be about 15... so hopefully it will all work out as well as it did when I did the same swap in my 53 Dodge truck !!!

 

Hey Desotodav,

took several month to find and get a diff center/ pumpkin assembly that fits to the truck`s rear end. Every car diff center what I found had the 16 spline side gears. My PT81 truck also has got 10 spline axles.

If your pumpkins are of the same type (10 or 11 bolt flange) a swap of parts shouldn`t be a problem. If they have got a different number of bolts, a swap most likely will not work.

Two possibilities:

> Take the 3.54 ring and pinion out of the car diff pumpkin and put it into the truck diff pumpkin.

Watch out the pinion bearings, the taper is different between cars and trucks ! Just if you should think about to leave the roller bearing piece on the pinion shaft and the bearing shelf in the pumpkin.

The ring gear has to be mounted a bit out of center due to the larger pinion diameter. Just works with a 3.73, maybe not with a 3.54. You could then remove a bit material off of the ring gear carrier on a lathe. Works, too.

> Take the 10 spline side gears out of the truck`s diff pumpkin and put it into the car`s diff pumpkin. I didn`t check this out myself, but according to feedback of others this also should work.

If you need more info, let me know.

Good luck ! Jan

 

Edited June 26, 2018 by PT81Jan

[kencombs]

4 hours ago, PT81Jan said:

> Take the 10 spline side gears out of the trucks diff pumpkin and put it into the car`s diff pumpkin. I didn`t check this out myself, but according to feedback of others this also should work.

If you need more info, let me know.

Good luck ! Jan

 

I'm amazed sometimes at the interchangeability of Mopar stuff.  Many years ago I took a 3.54 center section out of a 55 chrysler  and put it into my 65 273/4bbl/4speed dart.  Had to swap axle gears as noted.  Worked fine.

 

Same chrysler donated its' 12 brakes for my 58 ford pickup.  A little more work to make the swap, but much better than the little ford's.  Needed them because it also donated its' hemi to the same 1/2t.

[Desotodav]

I knew that the 3.54 car diff which I dropped down to the diff guys was a good one... but I didn't know that it had been recently rebuilt and had all new bearings! The guys changed the 3.54 car diff over to suit my 10 spline truck axles and I hope to be driving the truck again tomorrow.

They are also going to piece my 4.1 back together from spare parts from my shed as I had that 4.1 diff totally rebuilt about 3500 miles ago.... and I have just a few spare diffs at the shed. I even found a few truck diffs with the 15 spline count - wished I found them earlier as that would have made things even easier.

I actually took the opportunity to have a little clean up at my parts shed and will do a run to the scrap metal yard tomorrow. I still have a few diffs in trucks in the other shed, so I figure that stripping out the centres and scrapping the rusty carriers would save me some room in the small shed.

My home-made hub and axle pullers worked hard! I have the hub puller tensioned on one of the diff hubs that wouldn't budge and hope to find it free in the morning.

 

The next project at my parts shed is to have a couple of transmissions rebuilt and get rid of some that had been in the weather for too long!