49 plymouth rear end gears

[wayfarerstranger]

what gears are in the rear end of these 49`s , and if u wanted to change out the gears to make it runs better at highway speeds which would u use and where would u buy them ? and has anyone on here ever done this ? just don`t sound look like a lot of fun to swap out a new rear end . this thing will really windup when u get around 50 or so ..

[claybill]

your rear end ratio is most probably a 3.9 to 1........some were 3.7 but very very hard to find.

[Normspeed]

My manual says the 49-52 models could be had with 3.73, 3.9, 4.1 for hilly terrain, and that the overdrive models had 4.3 to one. I think a lot of the earlier and later ones can interchange, but certain years the axles changed. By 53 the axles had more splines so the side gears had more splines as well.

[wayfarerstranger]

are the rear ends marked ?

[wayfarerstranger]

which rear end seems to work the best ?? what is the purpose for the different rears ?

[Plymouthy Adams]

Only the 1949 P17 model would have the possibility of a 3.73

but like Claybill stated above..find a set and transfer the hoghead..probably the quickest means to get where you want to be. Quick search for american car axle widths will bring back lots of measurements...remember this though..the 49 has the most narrow axle width fo them all.

[jimwheeldon]

I read somewhere that the biz coupe was standard with the 373 and the others were all standard with the 3.9...am i wrong? Also to reiterate the original ? Is there higher avilable gear swaps out ther, or is a OD or axle swap the only remedy for high rpms at highway speeds? Thanks

[Plymouthy Adams]

I believe the P17 was the shorter wheelbase car of 11 inches and thus confined to the Suburban wagon and the Concord sedan. Then again, this is just according to the book which may or may not be accurate and again the statement that areas with hills and such oftern got the other ratio for better hadling the ups and downs. Still boild down to a crapshoot trying to locate a 3.73..these however are prevelant in 53/54 era Plymouths...

[Normspeed]

Chance, the lower ratios (4.1, 4.3) give you better acceleration from a stop. But, they top out earlier and use a bit more fuel. The higher (3.73) might be a little slower from a stop but they give you lower rpms at highway speeds. There's not a huge difference from 4.1 to 3.73 but it probably helps. Not sure if there's any higher than 3.73 that would bolt into the stock housing. Some of the complete rear end swaps can give you even higher final ratios. For really quiet highway running an overdrive is nice, or even a 5 speed swap like Don Coatney's.

[Plymouthy Adams]

per the formula

at 60 mph..where tire height is 27 inches

60MPH x 4.10 x 336 / 27 is 3061 RPM

60MPH x 3.9 x 336 /27 is 2912 RPM

60MPH x 3.73 x 336 / 27 is 2785 RPM

finding a very nice 3.54 would be excellent..

60MPH x 3.54 x 336 / 27 is 2643 RPM

And with todays highway this gear would be the lowest ratio I would run if I were to go to the trouble to change is all out...I would be more inclined to stay at the 3.0 to 3.23 area. Again the slower take off but with the torque available..no problem..once rolling and such at 30-35 MPH this would start coming on real good with the longer stroke. Be very much like the slant 6 with the miser gears in the mid 70's after the first energy crisis

[wayfarerstranger]

what kind of car would have the best gear ratio if i wanted to just swap the entire rear out ,, thanx for all the input

[Plymouthy Adams]

in the 49..the narror width rear axle is what you need to consider first in replacement..followed by ratio available from the donor car...I have never looked real close at the 49 swaps as I have never upgraded one of these...again..I would look to a 3.0 to 3.23 for where I live and how I would consider driving the car.

[Normspeed]

Tim, what years were the 3.54's available?

Check my math on this, but by switching from 4.10 rear gears to 3.54 you'd drop your final rpms by around 16%.

In comparison, an Overdrive drops the final RPM by about 1/3, or 33%, no matter what rear gear you have. Applying my fuzzy math to the figures from your post, looks like:

At 60 with a 4.10 you're turning 2020 rpms in OD

At 60 with a 3.54 you're turning 1744 rpms in OD

Did I figure that right?

That would give you some great gas mileage. But you'd need to drop it out of OD for the hills.

[Plymouthy Adams]

Actuall I got figures of 2142 with 4.1 and OD and 1948 with the 3.73 and OD still given the 60 MPH and the 27 tire height...

3.54 can be found in some of the 53/54 more common and in the earlier cars I think a lot of the bigger Chryslers/Desoto with the M6 tranny.

[Dodgeb4ya]

1949-50 NewYorkers/Imperials W/ 131-1/2" WB with the straight "8' used the 3.54 ratio gear set. Won't fit the Ply/Dodges though. The gear set case is way too big.

Bob

[Howard Tarnoff]

I gave this a lot of thought early on in the build and went with a 9" F*rd from Currie and 3.25's with my overdrive. The overdrive has 2nd gear out of a Chrysler that I got from George Asche, a much longer gear.

If anyone needs a complete rear end assembly, brake to brake, we still have mine. It is Media Blasted and painted Magoo Blue and I would be happy to give it away to anyone willing to pick it up in RI or pay for freight.

Magoo had 35,000 miles on him when we took it off the road for the restoration. I had driven it two prior years with no issues in the rear end, no leaks and the brakes a fine.

[Howard Tarnoff]

Here is the picture of the rear end that is free for taking:

http://lh6.ggpht.com/CrusinDuck/SAnQCQe_nVI/AAAAAAAAAYk/N_rOryiBz6w/s144/PICT1413.JPG

Here is the Currie 9" with Disc brake set up:

http://lh6.ggpht.com/CrusinDuck/SAnPtQe_nHI/AAAAAAAAAWw/ifTKI2PQTs8/s144/to%20file%201%

[mikehalek]

Howard, Is your car up and running yet? Would be very interested in your thoughts on your rear end ratio and od performance. Thanks, Mike

[50PlymouthSled]

Wow, every day you learn something new. Though I would say, for my present situation of living, I would run a high gear and an OD for the freeway, but I don't have many hills to contest with, just a fast flow of traffic. So as was before mentioned, just choose a gear for your location. :]