DCurrent Posted June 2, 2013 Report Share Posted June 2, 2013 I thought I'd better start my own thread rather than hijack anothers thread. I'm just starting to some homework on a rear end swap. I, like others, want to get just a little bit better speed with lower rpms. I take it that rear end gears are not easily changed or available for P15s, and is the reasoning behind why the changes to ford rear ends are done? Obviously the easiest and cheapest way to get the rpms lower on a p15 is to raise the revolutions of tire speed and lower the revolutions of the drive shaft. What is the best rear end ratio for a p15 with original drivetrain, no OD? Are the ford wheel bolt patterns the same as the P15? 1 Quote Link to comment Share on other sites More sharing options...
Ram Man 02 Posted June 3, 2013 Report Share Posted June 3, 2013 I bought a dodge 8 3/4" rear for my truck. im not sure what the width of your current rearend is but this could also be an option for you since they came in several widths depending on its application. but an 8 3/4" will be plenty durable and you are sticking width the mopar family 1 Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted June 3, 2013 Report Share Posted June 3, 2013 Daren; I must ask why you want to do this? Your car is a thoroughbred and you should drive it as such. Your engine is in excellent condition. When you gave me a ride in your car I was waiting for you to drop the hammer but I soon realized that your driving style was to pamper the car. You should know that your engine can run at 3600 RPM's all day long and this will give you more than enough road speed for your driving style. Dont be afraid to use your engine to its full extent. 1 Quote Link to comment Share on other sites More sharing options...
TodFitch Posted June 3, 2013 Report Share Posted June 3, 2013 Daren; I must ask why you want to do this? Your car is a thoroughbred and you should drive it as such. Your engine is in excellent condition. When you gave me a ride in your car I was waiting for you to drop the hammer but I soon realized that your driving style was to pamper the car. You should know that your engine can run at 3600 RPM's all day long and this will give you more than enough road speed for your driving style. Dont be afraid to use your engine to its full extent. I haven't had a ride in your car so I don't know the condition of the engine but I trust Don's judgement on that. . . We've been conditioned by post '73 oil crisis car gearing to assume that its bad to run the engines at 3000 to 3400 RPM all day but that is how the vehicle was designed and they are quite happy at that RPM. I have no intention of swapping out my 4.375 to 1 rear end on my '33 as it works just fine. And my 900 mile return trip from Tucson was mostly on freeways at 60 MPH. If my 80 year old vehicle can do that reliably I don't see why a 15 or so year newer car can't too. 1 Quote Link to comment Share on other sites More sharing options...
steveplym Posted June 3, 2013 Report Share Posted June 3, 2013 Here is the lowdown on the Dakota rear end swap I did a couple years ago. Fellow forum member James Curl did the same swap before I did. I have been happy with the results. http://mopar.pairserver.com/p15d24ph_forum/topic/25700-dakota-rear-diff-swap/?hl=%2Bdakota+%2Brear+%2Bend+%2Bswap Quote Link to comment Share on other sites More sharing options...
DCurrent Posted June 3, 2013 Author Report Share Posted June 3, 2013 Daren; I must ask why you want to do this? Your car is a thoroughbred and you should drive it as such. Your engine is in excellent condition. When you gave me a ride in your car I was waiting for you to drop the hammer but I soon realized that your driving style was to pamper the car. You should know that your engine can run at 3600 RPM's all day long and this will give you more than enough road speed for your driving style. Dont be afraid to use your engine to its full extent. Well it just seemed to me that lowering the rpms would be a good thing, and it might extend engine life. I just find a motor doing some 3000 rpm different from everything else I own. I guess I just need to get used to the idea of it reving so high if you think it's OK. I took it for a spin today with some friends and we loved it at 45 - 50 mph, but every once in a while a trip will be in order and will have to run her at 60-65 if I want to get there before I die. I was poking around underneath it this evening to see if I could find any markings to determine gear ratio or whatever. I only found a short series of numbers 663473-1. On another spare rear end I have from a 50 I found more numbers 180 1141544N1 of which that rear end also had the DP logo. The rear end under the 48 has no DP in the same spot. Kinda makes me wonder if the rear end under it is the original. Upon inspecting the underside, looks like I'd better replace the main shaft bearing seal on the end of the trans while I have the trans off to replace the throw out bearing. Has anyone got a part# for part 50 on page 170 of the service manual. The manual also suggests 80 or 90 wt gear lube in the trans and rear end. There are so many different types of lube out there now, anyone got a suggestion for a brand and sl, gl, ml, or pfla I might use. I just tried out quaker state lube in my Indian gearbox and I'm surprised that it isn't leaking near as much as it did with Valvoline. Thought about using more quaker state. Quote Link to comment Share on other sites More sharing options...
_shel_ny Posted June 3, 2013 Report Share Posted June 3, 2013 (edited) GL-1 from NAPA. about $13 a gallon. EDIT: as corrected in following posts. GL-1 for trans. Edited June 3, 2013 by shel_bizzy_48 Quote Link to comment Share on other sites More sharing options...
52b3b Joe Posted June 3, 2013 Report Share Posted June 3, 2013 (edited) HI Daren, any 80-90 wt is good for you car as long as it says GL-4. If I had to guess, based on the 663473-1, you have a 3.73-1 ratio. You can also jack up the back of the car and count how many times the drive shaft turns to one revolution of the back wheels. If you do have a 3.73, then that is a nice ratio to have with your car. You should be able to cruise 65 all day. Our 41 Desoto has a 3.73 and I've had it up to 75 mph on I-75 in Toledo and 475 when the speed is needed. Once in a while my dad will take it out on a long stretch of road in near our house in the country and will open her up to 85 or so. If you have a healthy engine, then you shouldn't have anything to worry about. Edited June 3, 2013 by 52b3b Joe 1 Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted June 3, 2013 Report Share Posted June 3, 2013 GL1 is not for differentials....only the gear box and OD units....... the rear gear is in need of high pressure additives (Hypoid) for the shear protection...these are rated in GL4 as a minimum amount to the GL5 which is a higher content of these additives... they are two different and distinct lubes.......do not confuse or misuse these lubes...your repair manual is very clear on this in the lubrication sections of your repair manual... 1 Quote Link to comment Share on other sites More sharing options...
52b3b Joe Posted June 3, 2013 Report Share Posted June 3, 2013 GL1 is not for differentials....only the gear box and OD units....... the rear gear is in need of high pressure additives (Hypoid) for the shear protection...these are rated in GL4 as a minimum amount to the GL5 which is a higher content of these additives... they are two different and distinct lubes.......do not confuse or misuse these lubes...your repair manual is very clear on this in the lubrication sections of your repair manual... You are right, it is GL-4 thanks for catching that. Quote Link to comment Share on other sites More sharing options...
DCurrent Posted June 3, 2013 Author Report Share Posted June 3, 2013 GL1 is not for differentials....only the gear box and OD units....... the rear gear is in need of high pressure additives (Hypoid) for the shear protection...these are rated in GL4 as a minimum amount to the GL5 which is a higher content of these additives... they are two different and distinct lubes.......do not confuse or misuse these lubes...your repair manual is very clear on this in the lubrication sections of your repair manual... OK thanks, I didn't know if there was an improved oil over the old numbered stuff. So GL-4 or 5 is for the rear end and GL-1 through 3 is acceptable for the trans? Quote Link to comment Share on other sites More sharing options...
DCurrent Posted June 3, 2013 Author Report Share Posted June 3, 2013 HI Daren, any 80-90 wt is good for you car as long as it says GL-4. If I had to guess, based on the 663473-1, you have a 3.73-1 ratio. You can also jack up the back of the car and count how many times the drive shaft turns to one revolution of the back wheels. If you do have a 3.73, then that is a nice ratio to have with your car. You should be able to cruise 65 all day. Our 41 Desoto has a 3.73 and I've had it up to 75 mph on I-75 in Toledo and 475 when the speed is needed. Once in a while my dad will take it out on a long stretch of road in near our house in the country and will open her up to 85 or so. If you have a healthy engine, then you shouldn't have anything to worry about. That's good to know. I tried counting the revolutions by the drive shaft spinning countering the wheels. It seemed the shaft spun four times to almost a full spin of the tire. I'll have to do it again to remember what I come up with. The darn thing just revs so much that I'm just afraid to push it. When you start out third at 25 mph and then your at 55 in the same gear, well you get the picture. I just don't want to tear it up. Quote Link to comment Share on other sites More sharing options...
Guest bewillie Posted June 4, 2013 Report Share Posted June 4, 2013 Only let ONE wheel turn. Jack one wheel off ground and turn it two turns. As you do this count how many times the drive shaft turns. If the shaft turns 3 1/4 (or close) you have 3.23, 3 3/4 times you have a 3.75, if it turns 4 1/3 times you have a 4.11 and so on. Quote Link to comment Share on other sites More sharing options...
DCurrent Posted June 4, 2013 Author Report Share Posted June 4, 2013 Two turns! I did not know that. thanks for the tip. Only let ONE wheel turn. Jack one wheel off ground and turn it two turns. As you do this count how many times the drive shaft turns. If the shaft turns 3 1/4 (or close) you have 3.23, 3 3/4 times you have a 3.75, if it turns 4 1/3 times you have a 4.11 and so on. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.