Ward Duffield Posted May 27, 2014 Report Share Posted May 27, 2014 Has anyone installed a 3.54 rear in a stock Plymouth with the 2.57 1st gear ratio? I was wondering how it would affect the overall driving experience. Thanks Ward NY Quote Link to comment Share on other sites More sharing options...
james curl Posted May 27, 2014 Report Share Posted May 27, 2014 I am running a 90 Dakota 3.55 rear in my 48 P-15 4 door and have no problem taking off in first gear. With a little thought second gear starts are not that difficult. My engine was rebuilt in 2007 and has gone over 25000 miles since. The compression on all six cylinders is in the 120 psi range. The engine was modified with a cam regrind, .090 0ff of the head, dual carburetors and split exhaust and a .040 overbore. 1 Quote Link to comment Share on other sites More sharing options...
mrwrstory Posted May 27, 2014 Report Share Posted May 27, 2014 I think that (3.55:1) ratio is close to perfect. I had a 3.0:1 in my stock P-15 and 'tho it worked well at 65/70 mph it was too tall for around town driving where there is more stop 'n' start. From a dead stop, 1st gear starts were more like 2nd gear starts. Quote Link to comment Share on other sites More sharing options...
DJ194950 Posted May 27, 2014 Report Share Posted May 27, 2014 I think that (3.55:1) ratio is close to perfect. I had a 3.0:1 in my stock P-15 and 'tho it worked well at 65/70 mph it was too tall for around town driving where there is more stop 'n' start. From a dead stop, 1st gear starts were more like 2nd gear starts. I agree if your motor is in good condition-unless you live in a Very hilly area-Big hills! Finding a 3.54 rear ratio rear of stock type can be hard. If you have one go for it! Best, DJ Quote Link to comment Share on other sites More sharing options...
Tim Keith Posted May 28, 2014 Report Share Posted May 28, 2014 an eight cylinder car like a New Yorker might have the 3.54 Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted May 28, 2014 Report Share Posted May 28, 2014 I installed a 3.55/1 differential from a Dodge Charger. That along with my T-5 overdrive transmission allows me to run 70 MPH all day long with the engine spinning 2200 RPM's. There are many speed calculators on the internet that allow you to plug in tire size, differential ratio, and road speed to calculate engine RPM's. One can be found on the web page of forum member Tod Fitch. It pays to do your homework before jumping into a project and guessing what the final outcome will be. Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 5, 2015 Report Share Posted March 5, 2015 Searching for rear axle possibilities for a P15. So far this is the best thread I've found. I understand somewhere here is a reference chart?? Bottom line, what rear axle swaps require the least modification. All I'm looking for right now is to increase highway cruising range. Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted March 5, 2015 Report Share Posted March 5, 2015 I understand somewhere here is a reference chart?? Read posting # 6 Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 5, 2015 Report Share Posted March 5, 2015 Thanks, I did see that. I also copied it and saved it. But on the P15 all it shows is the spring width and the track width. I'm sure I need more information. Quote Link to comment Share on other sites More sharing options...
Frank Elder Posted March 5, 2015 Report Share Posted March 5, 2015 Thanks, I did see that. I also copied it and saved it. But on the P15 all it shows is the spring width and the track width. I'm sure I need more information. Why would you need to know more than that? Cut the old ones off, weld the new perches where they belong and install it. 1 Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted March 5, 2015 Report Share Posted March 5, 2015 (edited) duplicate the angle of the pinion in relation to the perches of the old axle to the incoming donor axle.. step one..with old axle out and on stands..set a level on the perch and rotate axle till the perches are dead level...compare left and right at this time.....read the angle of the pinion with an angle meter attached to face of mounting flange, usually folks use a magnetic base unit for this..record the angle...either cut off your older narrow perches or visit a trailer supply store and shell out coinage for new units of proper width. Before you remove the wide perches from the donor mark the centerline of the axle, or if you wish, the offset on the each tube so you can just make minor readings per side as you adjust for the original axle perch centers..(center plus 20 on each side then all you have to do is split the remaining distance equally to the center alignment hole of the incoming perch) Be sure you carefully remove the original donor perch and not cut into the housing tubes. Now with the incoming donor axle on the stands..place the angle meter on the flange and rotate the axle to that of the earlier recorded pinion angle. Measure and mark the tubes for the proper width and set the new perches in place..now ensure that they are level and the angle of the pinion is still at the set angle per your reading...tack weld and verify left and right perches are level and pinion is correct angle..if so..complete the welding process. NOTE....on a car you will be working the axle flipped as the perches are on top of spring and you want to have a good vies and easy access while laying out welding...truck perches are usually mounted 180 as they usually going for more ground clearance...if lowering your truck follow set up as per car... your angle ill be opposite of install in this position also..so just note the angel degrees be it + or - you just want to duplicate is all... Edited March 5, 2015 by Plymouthy Adams 2 Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 5, 2015 Report Share Posted March 5, 2015 Thanks guys, This is the kind of stuff I'm looking for. I won't be doing this work myself. I'm too old and don't have the knowhow. So, I'll have to find someone to do this for me. And I do have some resources, but I don't know if they are familiar with this vehicle. Changing out the whole real axle would be my second choice. What I was really looking to find is what donor gear and pinion assemblies would interchange with my housing. Mainly, all I'm looking to accomplish is being able to drive the car at highway speeds, at least 65mph. And I don't know yet what rear gear ratio is in the car! But I will in a week or so. At least that's what I think I want. We're just starting on the build on this car and all ideas greatly appreciated. As you can probably tell by now, this is all new to me and I'm learning as much as I can going into this. Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted March 5, 2015 Report Share Posted March 5, 2015 in state of well tune you should be able to drive the car at that speed stock ratio...they sound busy a bit and make people nervous more so than not being able to do the job... Quote Link to comment Share on other sites More sharing options...
plyroadking Posted March 5, 2015 Report Share Posted March 5, 2015 What I was really looking to find is what donor gear and pinion assemblies would interchange with my housing. I was able to just swap out the gears in my 1940 housing with an assumed mid 50's 3.73 ratio. It had 10 spline axle shaft receivers and it all bolted up really easy 50k miles ago. I recently acquired a 3.54 third member out of a 55 dodge, i will install it eventually but i first have to change the shaft receivers from 16 spline to 10 Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted March 5, 2015 Report Share Posted March 5, 2015 The 3.54 gears of the early vintage are far and few between for a fast swap...and yes swapping later years and changing the carrier gears is another way to go. One can do the math using calculator and find the speed per RPM change you will get with each .2 axle ratio change...it is not a great amount. I cruise at 70 no prob and have been to 85 with it beginning to sounding busy...while I would not do a 10 hour jaunt at that RPM I have no problem running her up a bit for a bit of exercising it legs..my rear gear is factory 3.73...running stock bias ply tires that exact fit of original.. Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 5, 2015 Report Share Posted March 5, 2015 Now we're talkin'! I've been reading that anything over 80% of max rpms is asking for trouble. And that 55 is comfortable and anything over that is pushing the limits. Guess I'll wait til I get it on the road and see what it does. And before that I will definitely find out what rear ratio I have. One question I haven't asked yet is: What was the original ratio on the P15 and were there more than one? I haven't found a reference on that yet. When I get the title and serial number, I'll write to Chrysler and try to get the build sheet also. Most of my driving will be in the 55 and under range, but I'd like to know I can take a trip when and if I want to. Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted March 5, 2015 Report Share Posted March 5, 2015 (edited) P15 is listed as 3.9 later years if sold originally in hill country..could have a 4.1 but else a 3.9 is common..OD adds another ratio in there 4.3 of course other model had other options and a source to look for if you wish to have a different ratio..the hy-drive would be 3.73 as would be the 54 first auto with the larger 230 engine Edited March 5, 2015 by Plymouthy Adams Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 5, 2015 Report Share Posted March 5, 2015 Thanks Plymouthy, I'm beginning to feel better about this. As I said, I need to find out what I have. I also just found this old thread, which confirms what you guys are telling me also. http://p15-d24.com/topic/33275-rear-end-swap/ Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 5, 2015 Report Share Posted March 5, 2015 P15 is listed as 3.9 later years if sold originally in hill country..could have a 4.1 but else a 3.9 is common..OD adds another ratio in there 4.3 of course other model had other options and a source to look for if you wish to have a different ratio..the hy-drive would be 3.73 as would be the 54 first auto with the larger 230 engine I'm a little slow here, if I understand this you say that I'm most likely to have a 3.9, but what's "the hy-drive would be 3.73 as would be the 54"? I might get lucky and find a 230 engine! Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted March 5, 2015 Report Share Posted March 5, 2015 it is as I stated...just another source for axle ratio that is higher than the stock P15 that are easily recognized and as stated yet again...per the book..the 3.9 is the only gear listed in the P15... if you do not have a book it would be a good idea to have one. This very data is taken from the rear axle section of the 46-54 repair manual.. another note for you is that axles are C10 through 52 and C16 starting 53 Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 6, 2015 Report Share Posted March 6, 2015 Seller tells me there are a lot of manuals to go with the car. We're picking it up next week! Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted March 6, 2015 Report Share Posted March 6, 2015 got your thinking cap on long before getting the car home..do read the manual..become very familiar with all the sections and such before jumping in...there are a number of safety notes also... Quote Link to comment Share on other sites More sharing options...
DJ194950 Posted March 6, 2015 Report Share Posted March 6, 2015 (edited) My 1946-1950 repair manual shows p-15 rear Stock gears as 3.9 ratios. Station wagons were 4.1. Remember though- it was easy back then to get factory ordered or dealer installed ratios as wanted! Wrecking yards also had diff. ratio drop end third members also available as desired from Plymouth or other mopar brands as many easily interchange in this era. While the build sheet may be interesting it May not answer what rear ratio is actually in your car. Man my slow typing put me way behind in responses !!! DJ Edited March 6, 2015 by DJ194950 Quote Link to comment Share on other sites More sharing options...
46Ply Posted March 6, 2015 Report Share Posted March 6, 2015 Thanks DJ, When I can actually look at the rear end, what numbers am I likely to see on it? (And as you said, that won't necessarily tell me what's inside.) I'll also see how many revolutions the wheel takes to the drive shaft. Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted March 6, 2015 Report Share Posted March 6, 2015 often stamped forward of the oil fill hole on the carrier case and again at the very top of the carrier... 1 Quote Link to comment Share on other sites More sharing options...
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