Rear-end swap options

[rcl700]

I'm in the process of getting my 48' up and running and one of the things I'll need to do is have a custom driveshaft built or have my factory shaft rebuilt. It was in the back seat when I got the car. Iv read may posts that recommend have a modern day u joint shaft built vs repair of the old style. 

So first, has anyone on hear done this and if so do you have pictures of how the slip joints and flanges were put together? 

Second,  if I do have one made or mine repaired and down the road decided I'd like to swap the rear axle for a unit with better gear ratio for modern speeds, is there a modern rear-end that will bolt in place without again replacing the driveshaft? I found a video stating that a 1991-1994 explorer lis a direct bolt up for a 1954. Is there any chance this would be the same for a 1948 plymouth deluxe?  

Any and all help / advise welcomed 

 

 

[Loren]

I question why anyone would want to change the rear end in a Plymouth. I can think of lots of reasons why one shouldn’t bother.

 The original is a good design and perfectly adequate for a flathead powered Plymouth.

If the motivation is to lower the engine rpm on the highway, then there are much better ways to do it.

You could install an Overdrive transmission. That turns a 55 mph car into a 70 mph car, with a whole lot less work and you will not have bastardized your collector car.

A rear end that lowers engine rpm on the highway will kill your already bog slow acceleration. An Overdrive does not because it adds another gear and the rest stay the same.

 The advantage of a Plymouth Overdrive ( Borg-Warner R10-G1 ) is that you remove your old transmission, install the Overdrive transmission using the same linkage and speedometer gear and drive shaft ( if you have the long transmission. Or shorten it 7 inches if you have the short one ) add the wiring and you are done. No messing around trying to adapt a driveshaft, brakes and speedometer drive. You’re done in an afternoon.

 

 

[Bob Riding]

As to your driveshaft question, my original was not in great shape on my '40 Plymouth wagon project, so I had one made up by a local driveshaft company. It has a very easy 4 bolt connection on each end, and is perfectly balanced. Sorry I don't have better pictures.

[rcl700]

5 hours ago, Bob Riding said:

As to your driveshaft question, my original was not in great shape on my '40 Plymouth wagon project, so I had one made up by a local driveshaft company. It has a very easy 4 bolt connection on each end, and is perfectly balanced. Sorry I don't have better pictures.

So slip yoke, U-joint and flange on trans side and U-joint flange on the rear-end  side? 

[rcl700]

6 hours ago, Loren said:

I question why anyone would want to change the rear end in a Plymouth. I can think of lots of reasons why one shouldn’t bother.

 The original is a good design and perfectly adequate for a flathead powered Plymouth.

If the motivation is to lower the engine rpm on the highway, then there are much better ways to do it.

You could install an Overdrive transmission. That turns a 55 mph car into a 70 mph car, with a whole lot less work and you will not have bastardized your collector car.

A rear end that lowers engine rpm on the highway will kill your already bog slow acceleration. An Overdrive does not because it adds another gear and the rest stay the same.

 The advantage of a Plymouth Overdrive ( Borg-Warner R10-G1 ) is that you remove your old transmission, install the Overdrive transmission using the same linkage and speedometer gear and drive shaft ( if you have the long transmission. Or shorten it 7 inches if you have the short one ) add the wiring and you are done. No messing around trying to adapt a driveshaft, brakes and speedometer drive. You’re done in an afternoon.

 

 

I would love to put an r10 in but unless you have access to an good unit... it seems from the little  I know they are few and far between, as well as pricy. 

 

My goal is to respect the car but get it on the road without going in dept.. I want a car to cruze in. I have never seen someone at the grocery store crawl under to verity if that's a stock rear-end.  All that to say I asked for your thoughts and I do understand.  I'm trying to figure out what works best to get it going. If down the road I change things I'm hoping most of what I'm doing now will only help the process and not be a waist of money. 

I have not even cracked into the driveline or brakes yet. Keep seeing posts about specific special tools for removing drums. Costly brake parts with sub parts performance. I really don't know. Iv never owned a classic car. It's all new so all this information provided helps me to gain insight in to best practices. I'm sure working guy with young kid so not a big budget for dad toys ??

[Bob Riding]

26 minutes ago, rcl700 said:

So slip yoke, U-joint and flange on trans side and U-joint flange on the rear-end  side? 

Yes, that is correct.

 

[Sam Buchanan]

13 minutes ago, rcl700 said:

I would love to put an r10 in but unless you have access to an good unit... it seems from the little  I know they are few and far between, as well as pricy. 

 

My goal is to respect the car but get it on the road without going in dept.. I want a car to cruze in. I have never seen someone at the grocery store crawl under to verity if that's a stock rear-end.  All that to say I asked for your thoughts and I do understand.  I'm trying to figure out what works best to get it going. If down the road I change things I'm hoping most of what I'm doing now will only help the process and not be a waist of money. 

I have not even cracked into the driveline or brakes yet. Keep seeing posts about specific special tools for removing drums. Costly brake parts with sub parts performance. I really don't know. Iv never owned a classic car. It's all new so all this information provided helps me to gain insight in to best practices. I'm sure working guy with young kid so not a big budget for dad toys ??

 

Ok...you just validated how you should approach your "new" car so you can enjoy it with minimal cost.

 

Don't over think this. The old Mopars are very well designed and once returned to serviceable condition are very capable drivers. Drivability doesn't require replacing the rear end, driveshaft, brakes or make the other mods you have been reading about. Just fix what you have and enjoy the car.

[Booger]

I agree with Sam Get it running go from there. How are the tires, brakes, suspension before you head out on freeway speeds. Hot rod it down the road if you wish Old cars handle way differently and are made to cruise. Your safety is what matters. IMHO upgrade is not a modification. Axle swaps are a lot cheaper than R10s (if you can find one) Plenty of info on axle swaps in here.

[Loren]

To get where you want to go consider the old adage, “If it works don’t fix it.”

Your car is an assembly of components that do certain things. Only touch the stuff you know is bad or not working.

Replacing a part or assembly that you aren’t sure about won’t make the whole car any better, it just wastes your money.

If a part is out of the car, then one of two things is possible 1) the part needs service or 2) somebody borrowed the part and didn’t put it back.

Old Plymouths can be destroyed, but for the most part they are long lived and reliable. They are transportation cars and they do their job very well.

Take it slow and enjoy your car and the learning curb you are on.

[D35 Torpedo]

I don't see a problem with swapping the rear end, if you find the right one. They can be had for cheap out of a junk yard, and can be swapped back to the original easily enough. Things to consider are; leaf spacing; driveshaft adaptation; bolt pattern; and width. Bolt patterns can be changed for both wheels and pinion flange. Spring perches can be welded on to suit spring spacing. The width is crucial unless you buck up. Nothing will fit like the original. So maybe pursue a factory pumpkin with the ratio you're after first. Happy hunting.

[FarmerJon]

I belive that '49-54 are a different width rear end than the 46-48. I have been hoping to find a spare rear end in my general area, so figured up what would be a direct fit a while back. 

 

I would drain the oil out of your current one and assess its condition to start with.

If there is no signs of water, rusty water, or significant metal bits, look for signs of leaking. Also, with the wheels off the ground, make sure each wheel and the yoke spins free and smooth.

If all looks good, replace any needed seals, fill with appropriate lube, and move on to the next item.

 

I considered a lower numerical gear ratio for my '48. I wouldn't want to run less than a 3.73 gear with a mostly stock engine. With 3.90 gears it is slow enough around town, and at 75mph has more pull left, more than my loose kingpins and poorly balanced wheels will let me explore. 

 

Get it going now,, but keep an ear to the ground and you may find an affordable overdrive in a year or two.

Edited May 14, 2023 by FarmerJon

[rcl700]

1 hour ago, FarmerJon said:

I belive that '49-54 are a different width rear end than the 46-48. I have been hoping to find a spare rear end in my general area, so figured up what would be a direct fit a while back. 

 

I would drain the oil out of your current one and assess its condition to start with.

If there is no signs of water, rusty water, or significant metal bits, look for signs of leaking. Also, with the wheels off the ground, make sure each wheel and the yoke spins free and smooth.

If all looks good, replace any needed seals, fill with appropriate lube, and move on to the next item.

 

I considered a lower numerical gear ratio for my '48. I wouldn't want to run less than a 3.73 gear with a mostly stock engine. With 3.90 gears it is slow enough around town, and at 75mph has more pull left, more than my loose kingpins and poorly balanced wheels will let me explore. 

 

Get it going now,, but keep an ear to the ground and you may find an affordable overdrive in a year or two.

We are on the same page. ?so 390 was a good fit for you with (3) speed trans? 

R10 is best option if I can find a good unit. What funds allow.....

 

I also read that some use jeep Cherokee rear-ends but can't be sure what years work for fitment 

Edited May 14, 2023 by rcl700

[Los_Control]

Reading through your post I see you are concerned with the drive line sitting in the back seat.

I'm suggesting there are many reasons for that, does not mean it is bad. Or needs replaced. Was common practice to pull the drive line for towing.

 

Take the u-joints apart & clean all the old grease out and inspect, grease & assemble ..... then decide if they need replaced.

 

@FarmerJon has good advise on checking the condition of the rear end.

 

I'm with the others, access the condition of the parts you have, drive it then decide what you want to do.

 

Another concern is the brake drums. They are not cheap for new ones .... if yours are fine then get on with your day.

 

The year for the Jeep cherokee depends on what brakes you want. They all have the correct width ... in the 1980's-90's & correct bolt pattern .... later ones came with disk brakes .... disk is fine but now you are getting into a bigger project. Staying with older drums would be easier.

 

Same with Ford Explorer .... they have correct width & bolt pattern. My 1996 Explorer had rear disk .... I would be looking for earlier.

[rcl700]

14 minutes ago, Los_Control said:

Reading through your post I see you are concerned with the drive line sitting in the back seat.

I'm suggesting there are many reasons for that, does not mean it is bad. Or needs replaced. Was common practice to pull the drive line for towing.

 

Take the u-joints apart & clean all the old grease out and inspect, grease & assemble ..... then decide if they need replaced.

 

@FarmerJon has good advise on checking the condition of the rear end.

 

I'm with the others, access the condition of the parts you have, drive it then decide what you want to do.

 

Another concern is the brake drums. They are not cheap for new ones .... if yours are fine then get on with your day.

 

The year for the Jeep cherokee depends on what brakes you want. They all have the correct width ... in the 1980's-90's & correct bolt pattern .... later ones came with disk brakes .... disk is fine but now you are getting into a bigger project. Staying with older drums would be easier.

 

Same with Ford Explorer .... they have correct width & bolt pattern. My 1996 Explorer had rear disk .... I would be looking for earlier.

Well I'm told driveshaft joints we the reason for removal. They have been out for few years..... 25+..

So have to figure out is rebuilding factory style  or modern U-joint type best use of funds safety 

[Los_Control]

KK makes sense ..... if you are going full restoration then stock .... you want a driver, my choice would be modern.

 

Again unless you find good used brake drums .... there is one guy on ebay that makes 10" drums for $400 each.

So if you need new drums, it is cheaper to do a rear end swap then buy new drums .....

 

Sooo, if there is a possible rear end swap in your future, I would do modern u-joints now, so they work with the rear end later .... sucks paying twice for the same item.

 

 

[Bob Riding]

Check out these old threads with old friends...

Overdrive VS. Differential...Another Discussion

[Adam H P15 D30]

One of the best upgrades I did to my 49 was the rear axle, I guess I fought the brakes one too many times.  When I finally needed a replacement drum, that sealed the deal.  Plus I'll never have to fight them again, not to mention those Detroit joints on the driveshaft.

I used an 8" Ford out of a Falcon and it was 1" narrower than stock.  Fit fine and I am running 8" wheels on a lowered car with no rubbing.  Below is the list I sent to Denny's Driveline and they shipped me a new driveshaft for around $400.00.  That's pre-inflation prices though.  You will need to "Flange" 2-2-349 to attach to the transmission output shaft.  Unless you are using an 8" Ford, ignore the length and rear u joint.

Here is the link for the slip joint and tube Denny's used:  https://www.dennysdriveshaft.com/p9619_1310ss_3_spline_and_slip_driveshaft_3_inch_dom_tube_1310_sli.html

 

-Flange to connect front of driveshaft to transmission is
Spicer 2-2-349
-Overall length from flange to center of rear u joint (#38)
is 58.5 inches
-Rear u joint width is 3 7/32 (#36)
-Rear u joint cup diameter is 1 1/8 (#37) 
-There are locating tabs on the rear u joint
-The driveshaft need to only be able to handle 150hp engine
MAX.