1933 Plymouth rear end....better ratio than 4.375

Hi there, I'm trying to improve the top end speed without winding the little 189ci. engine too much.

I was trying to install a complete rear end from a 50 Plymouth with a 3.9 ratio but discovered that it was too wide and the drums won't work with my stock 17" wire wheels. Has anyone here found something that works ?

By the way. I have a 50's Plym rear end for sale with turned drums, new brake shoes, wheel cylinders, axle and pinion seals. 3.9 ratio $150.00

Has anyone here found something that works ?

Try this

http://forums.aaca.org/f145/chrysler-engine-183786.html

excerpt

"A friend of mine who is now deceased, collected '33 and '34 Dodges and Plymouths. Early-1960s Valiant and Dart rear ends fit perfectly in the early-1930s cars with only a change of the U-joint yoke. The leaf spring brackets are even the same. Al used to drive his stock Dodges and Plymouths on the Los Angeles freeways at 65 and 70 MPH. "

On another site I've seen a chart of Mopar rear ends and it seems likely that the early 60s Valiant and equivalent rear ends would fit without too much problem as far as spring perches and distance between backing plates. Don't know about the wheel offset or bolt pattern though.

'33 through about '35 or maybe '36 have basically the same design for the rear end. Pretty major redesign after that. I know a fellow with a '33 who found a 3.9 something rear pumpkin from '35 or '36 that worked for him. Probably for a flat land coupe but I don't have any parts book for '35 or '36 to figure out what the application was for.

A 4.11 rear end will be pretty easy to find and they used them on the PCXX (and maybe the PC) also, I think on the '34 PF & PG.

Also, apparently you can fit some of the earlier Mopar overdrive transmissions into a '33 or '34 fairly easy. I've heard of '37 DeSoto overdrives basically bolting in with a swap to use the '33 transmission top cover, a shorter driveshaft and using the freewheeling control cable for controlling the overdrive. I haven't looked too closely at the details but I've seen a couple of cars where that was done.

For what it is worth, I find my '33 with the 4.375 rear end runs out of top end about the same time as the suspension, narrow tires and tiny brakes start to get scary. So for me I live with it as it because otherwise I'd end up with a very modified car which I don't want.

So you want to cruise along at 60-65 and purring like a kitten. Here's what I did. If you can find a complete rear end from a 1970's Comet or Ford the one equil to a

Comet (I used a Mercury Comet a guy gave me. It has to be from a standard shift ; automatic ratio is too high. The hydralic brake line threads right in the Plymouth.

The Plymouth rims or wires bolt right on, the width is the same. All we had to do is splice the drive shaft. The Plymouth shaft slides right in the Ford drive shaft. End

result, better stopping, sweet cruising lower rpms, gas mileage and 70 Hp will handle it just fine. I did this in or around mid 1980s although I sold it, its still doing

fine today as I speak. Oh we did use the axle spring hangers from the Plymouth and welded on the Ford axle = Ford perches were too wide. sam

I still can't remember what Ford same as a Comet perhaps Mavrick?? same axle anyways / can't remember ratio either maybe 3:86 or 3:90's?

Thanks guys for the advice. Yes, I would like to purr along at 55 or 60 without spinning the engine at 3000rpm. At 60 with the stock 4.375 rear gears and 28.5" diam. tires the engine is spinning at 3100 rpm. Too busy for my liking.

Now today I have developed a different problem. The trans is jumping out of gear in 1st and 2nd under a load even when I hold the gear shift in place. What's causing that ???

Is it time for a rebuild? Anyone have a spare '33 PD trans ???

. . . Now today I have developed a different problem. The trans is jumping out of gear in 1st and 2nd under a load even when I hold the gear shift in place. What's causing that ???

Is it time for a rebuild? Anyone have a spare '33 PD trans ???

Never had that issue myself but understand worn bearings can cause it. I've got the bits and pieces of two transmissions stashed away. Been meaning to clean them all up and see if I could make single complete spare out of the lot but that is pretty low on my to do list. If you need a particular part or set of parts, let me know.

Never had that issue myself but understand worn bearings can cause it. I've got the bits and pieces of two transmissions stashed away. Been meaning to clean them all up and see if I could make single complete spare out of the lot but that is pretty low on my to do list. If you need a particular part or set of parts, let me know.

ThanksTod. Do you know if this trans was used in other than 33 models ?

ThanksTod. Do you know if this trans was used in other than 33 models ?

I think '34 transmission is pretty much the same. Maybe some different part numbers inside but I think the case is the same. Also I think, but don't know for sure, that the '33 and '34 Dodge would be very similar if not the same.

For '35 they added synchros for 2nd and 3rd. Not sure if they changed from the funky gear shift lever mounted on the frame cross member or not for that. '35 is the one year for which I have no parts books so I can't be sure one way or the other on that.

Hi Guys- some advice in general on the 60's Plymouth rearends. There seems to be a lot myth in reading, but truth in doing.

A-Body rears are the ones that are- bolt in as far as leaf mount spacing. 43" mount space.

Note that A-Body rears most ALL have (4.00"on 5) bolt pattern or SmallBoltPattern to the 60's Mopar freaks, I just learned this recently.

If you find the correct A-Body rear with a Large Bolt Pattern or 4.5" on 5, it will be pricey, about 700-1000 range. Just an FYI. It was a special one used for one year only (of course) Super Stock Racing Darts.

The B-body rears are the ones with the 4.5 on 5, but the mounting is about 1" wider and the rear is about 2" wider in general. The price is somewhat lower.

You still will have to move in the mounting pads. I was told that .5" out in each direction on leafs should not cause binding. I actually bought one and can place it and take photos for you guys as a FYI, it would be great info for this thread.

That is just some info if you are wanting to update your vehicle with Plymouth components. Which is what Im doing on my '33 Sedan. I may go ahead and narrow the rear as well to the A-Body specs.

If you do the Maverick route it is cheaper, but your using off brand stuff in your Plymouth, the rear end basically the Ford 8" same in 60's Fairlanes.

Now back to the original post..

As far a new gear ratio for the OP. Maybe take look or see if NOS gear sets are available some place online. either way your going to want to rebuild any rear you get to make sure nothing fail.

you can try Andy B

http://www.oldmoparts.com/parts-rear-axle.aspx

74-76 Darts & Dusters with front disc brakes used the 4.5 on 5 bolt pattern in both the 7.5 and 8.25 rear ends. Very common.  Mostly 3.21 ratio though, or taller. 6 cyl cars with drum brakes and the earlier cars all used the 4.00 on 5 pattern, and are becoming very rare. I have a 74-76 8.25 under my 33 Ply coupe to roll it around. Have 1940 Plymouth disc wheels on it and I had to space the wheels out with washers to clear the body. I won't be using that rearend in that car, just temp. I have another that is a 2.76 , man was that tall geared even in a 74 Dart Sport with 4 speed. Made the clutch stink even in reverse! Also have one with 4.11 posi. Lots of 8.25's out there.

Jeep Cherokee and Dodge Dakota pickups also used the 8.25 rearends with a different axle spline, somewhere near the same width I believe.

Oh yeah, the 8.75 A body rear ends had 4.00 on 5 with the exception of maybe some real late ones, but I can't verify that for sure.

Dave

Take it from one who has experience with 2:76 rear ends......VERY WEAK and troublesome.

I used a 74 dart in a 36, 323 ra. Posi all the dodges and Plymouth were close 55/56" backing plate to backing plate, spring perches fit nice too....

I have an extra rear from a '36 Dodge in the high 3 ratio 3.78 or somewhere around that, can't remember off hand. We can check measurements if you want. Where are you located?

Wow !  3.78 would be perfect but unfortunately I'm way over here in California.

would a 3.78 be better gearing than 3.55

3 hours ago, Sactownog said:

would a 3.78 be better gearing than 3.55

For climbing hills, yes. For speed, no.

On 4/20/2019 at 3:03 AM, Spinneyhill said:

For climbing hills, yes. For speed, no.

thanks. 

On 8/26/2015 at 7:03 AM, jpage said:

I have an extra rear from a '36 Dodge in the high 3 ratio 3.78 or somewhere around that, can't remember off hand. We can check measurements if you want. Where are you located?

Jpage,

Do you still have the 36 rear available? I'm trying to correct my 1932 Dodge and finding that the 9.5 diameter rings are non-existent, so I might need to swap the entire rear and a 3.78 ratio would be great! 

Not sure anymore, I'll have to check.

The only 2  I  have left are 4-1:1. Sorry

Maybe my opinion is unwanted here but I'll chirp in anyway.

Gear ratios:

Back in the day top speeds were much less. Cars were designed by engineers for the good all-around performance. Climbing hills, cruising on open roads too. They had to keep in mind the car weight, horsepower, and performance and yet remain priced right for the market they wanted to target. Most roads were dirt and riddled with pot holes and washboard wear back in the early 30's. Brake performance was adequate for the speeds back in the days. The lack of safety features was not a a big deal. Then cars became faster. More HP. Paved interstates were developed. The old jalopies from the early years were far inferior.  Taking a stock equipped car from the early period, and trying to make it cruise closer to today's speeds, in my opinion is a blunder. As mentioned, you may get lower RPM's at higher speeds, but what about the skinny tires? The inadequate brakes? The lack of safety? The steering ratio and suspension handling? The low engine torque and HP. None of this was designed for higher speeds.  Climbing any hills with a higher diff gear ratio could put you in danger as well. You'll be very slow on hills potentially be a sitting duck for upcoming modern traffic.  Even when stock, you'd be slow. Changing the diff, even worse. 

Many end up starting the modifications and keep going from there. Upgrading each system to accommodate the changes made. There is a market for 1930's cars with all the power and handling improvements. Then yes, you can keep up in traffic, stop, and steer no problem. Resto-mods I think is a term.  Of course the choice is yours to do as you please.  Just pointing out that the diff is only one piece of the puzzle. It was all designed to work together to be adequate for average driving in the 1930's. Cheers. - K