'48 vs '85

[knighthawk]

I've got a '85 5th Ave donor car, for my '48 Dodge. Compareing the rear axle assy., ' 85 has wider and '5 long springs, while ' 48 has narrow and '4 long springs . Which should I try to keep, assuming I have a choice ?

[greg g]

I believe it will be easier to put your 48 springs on te later rear. You may have to elongate the hole for the centering pin but changing the spring shackles for the longer springs would be a pain in the but. Go to Don Coatney's photobucket side, ( I believe it is linked to his profile) as he photo documented his spring /rear end swap.

[Guest jtw3749c]

I have to agree with the 48 springs, as I have the stock springs under my 37 Plymouth and have had since I built the car 28 years ago. I have a Chevy rear end under also. Oh yea! the springs can handle a good burn out as well as a run down the drag strip.

JT

[knighthawk]

well, I'm glad to hear that, it would save me a lot work..........thanks

[Plymouthy Adams]

I have three of these cars upgraded with various Mopar rear gears..9 1/4, 8 1/4 and a 8 3/4...with all applications the stock springs were retained and the narror perches removed from the stock rear end and transfered to the donor..as for the width, that is something you need to work out..as i also used a 9 1/4 from a 79 Newport and the width is about 6 inches wider..no biggy as I built my car around a set of positive offset factory Dodge mags..fill the rear wells nicely...

[knighthawk]

well, I'm glad to hear that, it would save me a lot work..........thanks.....also, as long as we're here, this axle is a 2.2 , according to the tag on it , probabley cruises at 100 mph, what kind of power is it going to take to turn it ? you know, and not take all day to get it there.

[Guest Nile Limbaugh]

With a 2.2 gear that flathead will have a coronary trying to pull it, if it will even get started. Something in the range of 3.6 to 3.8 would probably give you a compromise between performance and economy. Somebody with more experience, feel free to jump in any time. I'm generalizing here!

[greg g]

With a 2.2 to 1 and a hundred hp,(and about 180 lb ft of torque) ya better not have any hills nearby. Remember the 318 had a torque converter (multiplier) in the mix, and if I'm not mistaken about 150 lb ft. additional twisting force. There was a thread about the fellow on the forum who runs his 48 Dodge on the salt flats and had trouble pulling a 2.8 or 2.7 in third gear. If I remeber correctly the salt is pretty flat........ Consensus seems to be that 3.55 is the best compromise to make a flatty comfortable on the highway, and still have enough legs to climb hills.

[PatS....]

You could also keep the original main leaf on the car and use the remaining springs less the main leaf from the 5th Ave.

The issue of Fat Fendered Street Rods that Don's rear end chart came from has an article on this.

I did this spring swap about 10 years ago on a '50 Dodge and it worked out quite well. The donor car was a 76 Cordoba. I used the cordoba u-bolt pads which have a shock mount built in which worked for the lower shock mount.

With the springs, the rear end swap was virtually a bolt-in other than new u-bolts and the spring center bolt.

I expected the same thing to work on my '49 Chrysler, but the Chrysler is narrower than the Canadian Dodge (same as a US Plymouth).

I'm still shaking my head on this. The max width I can use on the Chrysler is 57 inches. The 62 inch wide Cordoba rear bolted into the Dodge.

I am going to go with the rear end disc brake kit from AAJ which uses the original rear end, and if I use Cadillac calipers, I get an emergency brake to boot.

Pat

[Plymouthy Adams]

Knighthawk..with the entire drivetrain transplant of the 5th Ave..you will have the exact driving power of the donor...the rear gear should be a 2.32 ratio..7 1/4 ring gear..not a lot of meat and if you drive it normal will not be any problem..However if your intentions are to up the power in the V8 and do some really hard starts...or live in some hilly terrain, then a different ratio will be best for you. In addition, if you were to get a later model A500 4 speed OD unit say from a van or truck..you can go to the lower ratio rear gear and get some real grunt on the lower end and still serve yourself better mileage on the cruise with the OD. Remember that Chrysler small block trannys are different for the 3.9/5.2 versus the 5.9 as the 5.9 has to have an externally balanced torque converter. The use of a little heavier axle from the Dakota early series with 5 bolt lug will also be great and gives you a better choice of ratios.. 2.94/3.23/3.55/3.73 are the most common with the bigger numbers on 4WD units. The Dakota brakes are smaller but the 5 Ave will directly bolt on using entire backing plate. The 7 1/4 and 8 1/4 share same axle tubes.

[Plymouthy Adams]

one more item..I have a little song and dance I do hooking up the rear emergency brakes that allows use of the original brake handle and cable in the front and connection to the rear brakes through a unit easily fabricated and connects through donor cable and I can supply a set of bearing rollers to guide the cables and set the angle to center of the car...it does not take very long to do start to finish..have done two and have two more to do later.

[knighthawk]

what you all are telling me is, with the 318 and the complete package from the '85, it will be a fairly good driver, good freeway cruiser, but no burnouts ! O K ,. tell me why the speedometer from the '85 only goes to 85 ?

[Plymouthy Adams]

believe you will find most all of the big 3 having that same top speed indicated..not that it would not run that fast..they were telling you in a round about way of your own thinking that if I were to speed above that MPH I will do harm to the car...it was a trend to reduce speed, saving fuel an lives on the highway I think. The 86 Omni GLH I owned also had this low MPH speedo..however it was not top end pegged so would do a wrap around...look at one and tell me what you think your speed is when it comes back around to indicate 25 miles per hours again...my buddy can tell you this...when an Omni GLH leaves the road at 25 indicated second time that 2 end to end flips and 4 rolls is not uncommon..amazing but he opened the door and walked away..

[bob westphal]

Maybe something has slipped by me but why in the 'H' would anyone want to replace the P-15 rear axle assy. and keep the flattie? There is nothing wrong with the original assy. except you might not like the gearing. If your going to modify the car, modify it with a complete drive train!

[knighthawk]

an OMNI going 100 plus ? WOW ! I owned an Omin once , all I remember is it was really good in the snow.. I'll probalbey plan on using this 318 and package then, for now anyway, cause it's basically free, UNLESS I stumble across a '69 Caddy 472 ,..........lots of ideas !........... P S ......this '48 I got did NOT come with any drivetrain, just the rear axle .

[Young Ed]

Lots of people keep the flathead and change the rear end for the exact reason you mentioned. Don C still has a flathead but a modern rear end. One of my friends in the 39-47 truck group also has a flathead with a modern rearend. I hope to have a flathead with a 5spd and a modern rear in my 40 plymouth pickup someday.

[Plymouthy Adams]

knighthawk..the Omni's I spoke of were GLH models, both with Turbochargers and 5 speed trannies..(earlier GLH was just a trim package)..the lettering GLH was for Goes Like Hell and by golly I guarantee you..you were not disappointed..it was the only car I ever owned that the cops would turn around and follow..only reason I sold the car...it was truly a fun car to drive.

[Ed Griffin]

It wasnt an Omni nor was it turbocharged but we had something from the same family, a Plymouth Champ, 80 something and I really enjoyed driving it with it's double stick shift (low & high ) range setup. I thought it was just luck or the conditions but apparenly they must really have been good in snow. During the time we had the car we had some really bad weather, snow and ice, not just a dusting either. Many folks were getting stranded across the city and the Champ was hauling people home from work, passing cars all along the way. This was my first front wheel drive car and I saw others on the road , FWD that were stuck. But this car would just keep on going over places I was sure we would get stuck in only because I was passing spinning wheels. For a car with FWD and a mitsubishi 4 cyl I was really impressed on how well it did during the time we owned it. Even when it was over the 100,000 mile mark i drove it to the Keys to work and it ran great. Basically you couldnt kill the car. Ended up selling it to a fellow that was down on his luck for a 100 bucks so he could have a ride but he did n 2 weeks what I never could do, killed it by letting the water pump go and driving it anyhow.

[Plymouthy Adams]

Ed..I remember them..I was around a couple of the Colt RS twin sticks..them little things were a trip..excellent parking lot racers...I have pics somewhere of a very elderly gentleman doing some motorcrossing while in Illionis..made plenty of rear wheel lifts while on the course..fun to watch..

[Don Coatney]

Maybe something has slipped by me but why in the 'H' would anyone want to replace the P-15 rear axle assy. and keep the flattie? There is nothing wrong with the original assy. except you might not like the gearing. If your going to modify the car, modify it with a complete drive train!

Bob;

I did it for a couple of reasons. Gear ratio being one and modern brakes with e-brake capabilities being another. When I installed a T-5 transmission behind my flatty I also lost the original transmission mounted driveshaft emergency brake assembly. With the Dodge Charger differential I now have a 3.55/1 ratio and working e-brakes.

[Plymouthy Adams]

After having owned a completely stock 49 Plymouth with stock 218 flattie, standard tranny, and 3.9 rear gear...I can say that I will not own another...thre are so many other combinations that make these car more at home on the highway and me happier behind the wheel..I will say though I am happy with my 230 flattie with automatic tranny and 3.73 rear gear...the difference in driveability is like night and day..

Edited January 8, 2018 by Plymouthy Adams

[knighthawk]

couple more questons here : bolted under the end of the tail shaft on the '85, is a chunk of iron, about 4'' x 6'', what is that for ? Also would you guys know what tire size belongs under the '85 ? I junked the body already, but forgot to write down the siz ( off the door post ) I remember is was 205, and either 70 or 75 ?????? I need four tires the same size to lay this out .

[greg g]

If you look at the speedo closely you will see that 55 is centered and highlighted eiter by larger numbers, diffeent color, or different Font. This was part of the Government's late and not lamented effort to impose the 55 MPH national speed limit. The 85 was also federally madated as an indicated top speed, also in a subliminal effort to get you to slow down. Save Gas and Save lives. was probably a lot cheaper than airbags. Some cars even had an overspeed warning chime which went off if you exceeded 60. I remember Buick had a little yellow dot on an adjustable stalk in the speedo for a while in the late 50's, early 60's, which the owner could set that would set off a buzzer if the needle indicated a speed over the setting, but that was driver/owner controlled. The chime was built in as OEM, wonder how many of them survived past the 3000 mile check up. I had a rotary engine MAZDA that had an over rev buzzer. It went off around 7500 RPM. just as a reminder to up shift, as the rotarys would rev with no vibration till the the carb couldn't keep up with demand. A fellow used to road race a similar Mazda, and was asked how it drove it that fast. His reply was that "When the over rev buzzer stops buzzing, I down shift!!!!

[knighthawk]

I remember the speed minder buzzer, also had a '60 buick maybe that's what it was om. I remember too, you could crank it up out of your way , so it didn't go off so often. Rmember the speedometer on the mirror ? I gave a young guy a ride one time in my 60 Buick, I saw he was playing with the vent window. Asked him, ''what you doing over there ?" says; I never seen a car with crank out vent windows before !

[Guest mikeys toy]

The only mopars that used 7-1/4's were a-bodys

the 5th ave, should have an 8-1/4. Chrysler's been using that rearend since '69, so gears are available for it