MoPar Rear Axle in pre-stepdown car

Unknown

I am putting a 1968 Plymouth Full Size car rear end in my 1940 Hudson...real tired of driving around in what seems to be first gear, listening to the poor splasher 6 thrash away.
This Plymouth housing is the same width, and wheel bolt pattern. I know others have done this swap...any suggestions, particularly with driveshaft-U-joint hookup, and emergency brake hookup? Thanks, Paul.

Unknown

Bob Elton covered that subject in a 2-part article for the WTN, 'Making the Terraplane a Highway Cruiser', Sept. - October and Nov.-Dec. of '96. He measured a lot of axles and decided upon the Dodge mid-sized rear axle from the period '64-'70, which he said was only 1'longer than the '37 Terraplane he was converting. Maybe your '40 has a wider axle than the '37 -- that would explain why you say the Plymouth axle is exactly the same length. Anyway, he chose a 3.3:1 ratio, available with a Chrysler center differential, 8.25" size.

He had to remove the spring mounting pads and he welded the original style Hudson mounting pads in the correct position on the new axle. They seemed to fit his axle just fine. You must caculate the correct angle that the new axle must sit at, to mount the pads correctly.

Larger U-bolts were needed for the Dodge axle and this required larger shock mounting plates, which he used from a later model Hudson. Special U-joints were needed which fit both the Hudson drive shaft and the Dodge differential (two cups fit one size, two fit the other). These are available from Spicer and others. The Hudson drive shaft had to be shortened. The Hudson wheel cylinders bolted to the Dodge backing plates. The clevis had to be cut from the Hudson brake cable and a bushing fitted around the cable to make it fit snugly in the hole in the Dodge backing plate. The Dodge hubs have threaded studs (the Hudson has bolts) but these could be used with the Hudson wheels. A new hole had to be drilled in the Dodge axle to correctly position the Hudson junction block for the brake lines, and you must be sure to use the original hollow bolt in the Dodge (Plymouth in your case) axle -- this vents the axle.

You have another option, of course: put a Hudson overdrive in your car. I think any of the 1941 or later ones will work (the 1940 ones are scarce) but depending upon the clearance in your X-frame, you may have to leave off the electric governor and control this function with a dashboard toggle switch instead. Several guys have installed later Hudson overdrives in their pre-war Hudsons in this way with success, and it gives you more flexiblity that just changing the rearend ratio.

PAULARGETYPE

Paul Your other opition is to go with 3.58 gears Pat McDondald in Ireland is making them they fit right in your original 1940 housing (I put 3.58 gears in my 50 convertible with no overdrive and I JUST LOVE IT) he's in the roster GOOD LUCK WHAT EVER WAY YOU GO WE NEED THE HUDSONS OUT AND ON THE ROAD
HUDSONLY
PAULARGETYPE

Unknown

I thought Pat McDonald's high speed ring and pinions fit 1938 and earlier?

[Deleted User]

Where did you get the 3.58 gears for your conversion. I am thinking of doing this for my 51 Hornet Sedan and would be happy if they fit in the original housing.



Thanks



51hornetA formerly known as 51hornet :cool:

russmaas

I did this conversion a year ago. I used the stepdown U joint ends and they make a U joint to fit the Hudson on one side and Mopar 8.25 on the other side (742) housing. I believe it is NAPA 369

Park_W

51HornetA: The 3.58 gears were standard for Hornets with Hydramatic in '51. Easiest swap, of course, is to just change out the differential assembly ("pumpkin," "pig," etc.) with one having the 3.58 gears.