Plymouthy Adams Posted March 24, 2015 Report Share Posted March 24, 2015 (edited) the early 3.54 early hog head was discussed in post 15 Edited March 24, 2015 by Plymouthy Adams Quote Link to comment Share on other sites More sharing options...
55 Fargo Posted March 24, 2015 Report Share Posted March 24, 2015 Don, Help me understand this. Why do you say that? I've done various calculation on rpm ratings at highway speeds, 65, 70, etc. and it seems to me that if I could keep engine rpms around the 2200 range it would be better for the engine. The car came originally with a 3.9. For instance, at 3.9/1 the rpms would be close to 3400 at 70mph. But with a 3.01/1 it would be 2600. Assuming tire size at 27". What I haven't considered and don't know the answer to, is what would it be like in first and second gear? Slower than molasses? I am running 3.23 gears with y 1955 Fargo, and I live in flat land. I would be better off with 3.55 for those times with a lot of head wind or hills. yes my RPM is not that high at 65 mph, but if taking off onto a highway uphill or against the wind the 3.23 may be a tad weak, with my current engine. Having said this, I really enjoy this current gear ratio, and do not need an overdrive in this truck at all... Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted March 24, 2015 Report Share Posted March 24, 2015 Don, Help me understand this. Why do you say that? I've done various calculation on rpm ratings at highway speeds, 65, 70, etc. and it seems to me that if I could keep engine rpms around the 2200 range it would be better for the engine. The car came originally with a 3.9. For instance, at 3.9/1 the rpms would be close to 3400 at 70mph. But with a 3.01/1 it would be 2600. Assuming tire size at 27". What I haven't considered and don't know the answer to, is what would it be like in first and second gear? Slower than molasses? With 3.01/1 gearing it is doubtful your stock engine will have the torque and horse power to allow you to pull a steep hill in 3rd gear without down shifting. And with that gear starting from a dead stop on even a slight incline will require excessive clutch slipping leading to premature disc failure and possibly clutch chatter problems. 2 Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 25, 2015 Report Share Posted March 25, 2015 I think I'm on board with all of you now. I get the picture. Anything lower than a 3.54 with an unmodified engine is unacceptable. That's what I like about this forum. The answers are here. I'm at a disadvantage because I don't have any prior knowledge or experience in this drivetrain. And when I get an answer, (that's already been tried and proven), I also need to understand why. My initial thinking was to keep the car original, but modify it just enough to drive comfortably at normal highway speeds. But, I'm learning that a stock car would have a hard time doing that. So, now I'm searching for modifications that aren't too radical that will help bring it "up to speed". Sounds like a 3.54 first - then add OD - then consider changes to the engine. I've got a spare engine that could be rebuilt, but I need to learn what changes could be made during a rebuild process. And again, I want to keep the flat six. Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted March 25, 2015 Report Share Posted March 25, 2015 If you install an overdrive transmission and keep your 3.9/1 differential your RPM's would be around 2400 @ 70 MPH. Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 10, 2015 Report Share Posted May 10, 2015 Chrysler 8.25 3.55 gears 27 spline case out of a 95 Jeep. Will this work in my P15? There's a lot of good discussion here about ratios, but what other factors are critical? Assuming I'm just changing the ring and pinion. Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 11, 2015 Report Share Posted May 11, 2015 No answers on my last post, but I realize the question was kind of vague. I'm thinking the ring and pinion might work, but would still require setup, which would complicate the installation. (If I used only the ring and pinion.) I'm back to my original thoughts again now. Change the whole carrier assembly in the axle housing. And look for a 3.55 or 3.73. As I understand it these are most likely found in Chrysler products up to around 1952. I haven't found one yet. Quote Link to comment Share on other sites More sharing options...
Dave72dt Posted May 11, 2015 Report Share Posted May 11, 2015 Chrysler 8.25 3.55 gears 27 spline case out of a 95 Jeep. Will this work in my P15? There's a lot of good discussion here about ratios, but what other factors are critical? Assuming I'm just changing the ring and pinion. If I understand the question correctly, you want to install the diff carrier and gears from the Jeep into a 47 Plymouth axle housing. That will not work nor putting the ring and pinion gears themselves onto the 47's diff carrier. That's not going to work either. What will work is using the entire axle assembly from the Jeep. You may have to relocate the spring perches to match the spring locations and pinion angle of the 47 or keep looking for the correct elusive 3.54 Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 11, 2015 Report Share Posted May 11, 2015 When I originally posted the question, I was considering changing just the ring and pinion on my carrier. But after thinking about that I decided it's not a good idea even if it would work, considering what it takes to set up properly. Second option on the other hand, I do have access to a shop that is reliable that can change the ring and pinion if I had the right gears, but I still don't know how to properly identify which gears will work. Right now my thought is to consider trying to find that elusive 3.54 or even a 3.73. And, changing the whole axle would be the third option, for me. Quote Link to comment Share on other sites More sharing options...
Niel Hoback Posted May 11, 2015 Report Share Posted May 11, 2015 In order of ease, cost, and possibility, option 3, option 2, option 1. The whole axle swap will get you the ratio you want, fairly easy to do for comparatively little cot. Finding a 3.54 Chrysler axle could be a year-long and expensive project. Swapping in a different ring and pinion is just about impossible due to all of the dimensions that have to be exact. From pinion shaft length and diameter to bearing sizes. Then there's the ring gear that would have to have the same size hole to the same bolt pattern. Having gears made to fit the Mopar differential housing would be excellent inexpensive. A Ford or Jeep axle looks like the best choice. Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 11, 2015 Report Share Posted May 11, 2015 Thanks Niel, I'm getting there. Guess I was thinking that changing just the pumpkin would be the least labor intensive, but to find the part would offset that by a long shot. Guess I'll start studying the swaps made that are already posted. Quote Link to comment Share on other sites More sharing options...
1FSTRYD Posted May 11, 2015 Report Share Posted May 11, 2015 If 54 is the same I may have a set. My wagon was v8. I was told those were 3.54 gears. I can look tonight if your interested. Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 11, 2015 Report Share Posted May 11, 2015 I wouldn't know if it is the same or not. But I'm sure someone here would know. Is your car a P25? Here's what I've found on that model: http://www.allpar.com/history/plymouth/1946-1959/54-plymouth-cars.html Rear axle ratios on all body styles equipped with standard transmission, Hy-Drive, or PowerFlite were the same, using 3.73 gearing. Overdrive cars were the only ones to use a 4.1 rear axle. Might be interested. Take a look and let me know what you find, (at your convenience.) Quote Link to comment Share on other sites More sharing options...
1FSTRYD Posted May 11, 2015 Report Share Posted May 11, 2015 I'm not sure on what p pat form I've got. It's a 54 dodge suburban with v8. Research I found id's it should be 3.54 but I'll definitely look tonight. Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 11, 2015 Report Share Posted May 11, 2015 What I've found so far is that the late series did have a V8, but I can't find any specs on one with a V8. The sixes had a 3.73 Quote Link to comment Share on other sites More sharing options...
1FSTRYD Posted May 11, 2015 Report Share Posted May 11, 2015 I'll look tonight I'm pretty positive there 3.54 gears. Pinion seal is leaking so that will need to be addressed Quote Link to comment Share on other sites More sharing options...
DJ194950 Posted May 11, 2015 Report Share Posted May 11, 2015 I'll look tonight I'm pretty positive there 3.54 gears. Pinion seal is leaking so that will need to be addressed Below the stamped gear ratio you should also see a #2 or #4 that tells of the # of spider gears in the rear end . #4 = a heavy duty rearend. Also count the # of splines in spider gears that the axles slide into. They were built with 10 splines(most are) and also 16 spline-later years and heavy models. Most 16 spline spider rear ends can be changed to the 10 spline spiders but that means a rear gear assembly tear down using the parts from your original gear set. Best of luck. Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 20, 2015 Report Share Posted May 20, 2015 Below the stamped gear ratio you should also see a #2 or #4 that tells of the # of spider gears in the rear end . #4 = a heavy duty rearend. Also count the # of splines in spider gears that the axles slide into. They were built with 10 splines(most are) and also 16 spline-later years and heavy models. Most 16 spline spider rear ends can be changed to the 10 spline spiders but that means a rear gear assembly tear down using the parts from your original gear set. Best of luck. Unfortunately the 3.54 that is available has 16 splines. Where can I find information on changing to a 10 spline? (for a P15) How many options are there? Change spider gear? re-spline axle? Cut axle and weld new splined end on? It's obvious I don't know how or who to consult regarding this change. Quote Link to comment Share on other sites More sharing options...
DJ194950 Posted May 20, 2015 Report Share Posted May 20, 2015 The Plymouth repair manual covers the read end rebuild quite well and will give and idea of what would be required to change the two 16 spline side spider gear to a 10 spline-But--if you feel that it maybe beyond your comfort zone I'd suggest taking your repair manual to the closest rear end shop and talk to them about the time/cost to take the 2 rear pumpkins apart and build the 3.54 gear set with the 10 spline spider gears from your original rear end pumpkin. Cost will be high I'd suspect. Maybe just keep looking for an older 3.54 set from a Chrysler that had the 10 spline spiders! Quote Link to comment Share on other sites More sharing options...
46Ply Posted May 20, 2015 Report Share Posted May 20, 2015 The Plymouth repair manual covers the read end rebuild quite well and will give and idea of what would be required to change the two 16 spline side spider gear to a 10 spline-But--if you feel that it maybe beyond your comfort zone I'd suggest taking your repair manual to the closest rear end shop and talk to them about the time/cost to take the 2 rear pumpkins apart and build the 3.54 gear set with the 10 spline spider gears from your original rear end pumpkin. Cost will be high I'd suspect. Maybe just keep looking for an older 3.54 set from a Chrysler that had the 10 spline spiders! Thanks! Didn't realize the manual had this type of info. Sounds like you're saying changing the spider gears would be the best option. I'll take a look. Sure can't do this job myself. But I have a guy who might?? As you said, cost will be the big factor. Quote Link to comment Share on other sites More sharing options...
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