Pumpkin swap or not?

[Bob Riding]

I'm upgrading my '52 Plymouth Suburban build with a Ranger rearend, mostly so that I will have a parking brake with the 2004R auto trans I'm installing.

During all this downtime, I've been thinking about how to improve the drivability of my '40 Plymouth wagon. Currently it has a 4:10 rear end with a George Asche -installed overdrive on the stock three speed tranny. The overdrive works well and cuts in at about 25 miles an hour in second gear. The OD allows me to bring the vehicle up to about 70 mph with no problem. Sometimes I wonder how fast I need to go in a car made of toothpicks ?. 

 

I’m thinking of swapping the 4:10 in the wagon with a 3:73 gear set that I’m pulling out of the '52. Any thoughts on drivability? Would the OD and the higher gear ratio of the 3:73 gears allow me to shift later from a standing start or is it only high-end RPMs that are affected? How about hills?

[wayfarer]

The change from 4.10 to 3.73 is 10% and that is what you can expect in rpm change at each gear. It should not greatly affect around town manners.

[Sniper]

Don't forget the speedo will be off.  IF both vehicles use the same sized tires and the speedo was accurate on the donor you may be able to swap the speedometer pinion over as well.

[Loren]

Swapping the "pumpkin" is one of the beauties of the MoPar rear axle.

After you pull the brake drums they are very easy to work on. A real drum puller makes the job so easy!

Take a good look at the design. All Timken tapered roller bearings and the axles necked down in the middle to spread the torque load over a larger area.

This is really good stuff!

Then take a good look at the Ranger axle.

Enough said.

The MoPar has lots of ratios too. From 3.36, 3.54, 3.73, 3.8, 4.1 and I think I've hear of a 4.3.

If you can break the MoPar axle there is an upgrade path to the 8.75 axle which is highly respected for strength.

And for the purists it looks just like the original to the average person because it's the same design only bigger. 

[Bob Riding]

1 hour ago, Sniper said:

Don't forget the speedo will be off.  IF both vehicles use the same sized tires and the speedo was accurate on the donor you may be able to swap the speedometer pinion over as well.

the woodie has 16" wheels, while the "52 has 15" wheels. Would that make up for the difference, or would it make it worse?

[Bob Riding]

2 minutes ago, Loren said:

Swapping the "pumpkin" is one of the beauties of the MoPar rear axle.

After you pull the brake drums they are very easy to work on. A real drum puller makes the job so easy!

Take a good look at the design. All Timken tapered roller bearings and the axles necked down in the middle to spread the torque load over a larger area.

This is really good stuff!

Then take a good look at the Ranger axle.

Enough said.

The MoPar has lots of ratios too. From 3.36, 3.54, 3.73, 3.8, 4.1 and I think I've hear of a 4.3.

If you can break the MoPar axle there is an upgrade path to the 8.75 axle which is highly respected for strength.

And for the purists it looks just like the original to the average person because it's the same design only bigger. 

Cool! So pop the axles off, and swap the gear cluster, new bearings and voila?

[Los_Control]

Los scratches chin mumbles weeeel .... I asked this question awhile back ...and there are some really smart people here that told me yes, no, maybe. 

See I wanted the 3:73 out of the suburban & put them in my 49 dodge pickup. Seems I was told the only issue might be the splines on the axles.

Seems some years used different splined axles and what you can do if yours are different, take the parts needed from one pumpkin & swap to the other so you can use your original axles.

In your case, you may be able to swap the axles also if you find this issue I dunno, My truck rear end was actually 2" wider then the suburban. I could not swap axles.

 

Long story short, compare the axles/splines when you remove them.

[DJ194950]

Pull and inspect closely the 52 gear set. Check gear  lash and any noise in the bearings. I have had 3 different older Mopar rear gears sets that I sold 2 of them and all 3 were so good that No changes were made and installed. These gear sets if maintained well are great setups and will last almost forever.

I have seen the Suburban in the past and the overall condition I suspect that it may be good enough to use as is.?

 

A 3:73 may well be quite good , but if a little to tall  a 3:9 should be great. I have the 3:9 in my 50 4 dr. with the BW OD and it pulls very well and the OD is a dream to use, cruises easily to about 80 which is way to fast for my car with good but stock brakes. The 3:9 ratio are much more common than the 3:73 so car guys swap is certainly possible.

Certainly worth the try!

 

BTW , my interchange manual says this exchange is good to go! The later models auto and truck changes can get quite complicated in the interchange book.

 

DJ

Edited December 21, 2020 by DJ194950
add interchange book info

[Sniper]

1 hour ago, Bob Riding said:

the woodie has 16" wheels, while the "52 has 15" wheels. Would that make up for the difference, or would it make it worse?

Over all diameter of the tire is what matters.  Currently, my 51 sports 215/75R15 tires. which are 27.6" tall.  I have a set of 17" rims I am planning to run P245/55R17. which are 27.6" tall.  So no effect on the speedometer.

 

[Young Ed]

I have a 3.73 with overdrive in my 48 coupe. Works fine for me but I only have 15" tires. If your tires are taller the 3.73 might be a little much. 

[Bob Riding]

Lots to ponder. Thanks for the expert advice!

 

[Young Ed]

1 hour ago, Los_Control said:

Los scratches chin mumbles weeeel .... I asked this question awhile back ...and there are some really smart people here that told me yes, no, maybe. 

See I wanted the 3:73 out of the suburban & put them in my 49 dodge pickup. Seems I was told the only issue might be the splines on the axles.

Seems some years used different splined axles and what you can do if yours are different, take the parts needed from one pumpkin & swap to the other so you can use your original axles.

In your case, you may be able to swap the axles also if you find this issue I dunno, My truck rear end was actually 2" wider then the suburban. I could not swap axles.

 

Long story short, compare the axles/splines when you remove them.

Yes Dad and I did that with my 48. I am running my original spider gears with the rest of the 3.73. just check it before you install the rear end... Unlike me

[Loren]

There was a Craigslist ad in my area for a stack of early MoPar axles, they asked $100 a piece, then $100 for what looked like 10 of them. Finally they went for FREE come get em! I am not sure if anybody did and they might have been scraped.

With the "Third Member" design a person could have an assortment to chose from.

If you are a "Tinkerer" like I am, you like working out little issues even if it means repeatedly taking stuff apart and putting it back together.

Of course with an assortment of gear ratios you could really Dial your ride in.

Every time you turned up the wick under the hood you could change final drive ratios to take advantage.

Of course the spline issue is a consideration but I haven't run into it. My 52 Suburban seems to have the same splines as everything I've checked.

I found a 1956 pumpkin with 3.54 gears that I will use with an Overdrive transmission with a 1940 gear set (lower 2nd gear) and I figure that is what I'll be using. However, I am always looking for other ratios.

[48ply1stcar]

I asked the question about sucessful rear axel swaps 5 years ago.  Finally did my swap in March.  I had a 2000 Cherokee rear in my 48 that and disc brakes are the best thing I've done in the 52 years I had the car.