55 Fargo

There was nevr a 3.73 used in a Chrysler that I am aware of, they used the following 3.54,3.90,4.3. The 3.73 was used in Desoto cars. The speedo idea, might not be so crazy, I know what I need for the change, either a 18 or 19 tooth gear, the 19 tooth gear I have is the wrong type, as it is from the semi-auto 4 spd trans, mine is a 3spd trans from 1951, the sppedo cable goes in the left side not the right side

Here is a pic of a 1951 Dodge speedo, very different than a 47 Chrysler speedo, so maybe my theory is not so out there, this is a big round speedo, like I said, possibly it would register more accurately on this speedo, with my current set-up. But displays 10 mph faster on my Chrysler speedo........Fred

Thats true, the 3.9 could be, that could explain the 17 tooth speedo gear, but 17 tooth gears could be used with a 3.73 also, I suppose, what do you think of my speedo difference in the 2 cars dissertation............oh heck, I can just adjust for the speeds, put little red stick-on dots at the 30,40 ,50 and 60 point on speedo. Here in Canada, when they switched to metric, you could go out and buy lillte stick on numbers to place on the speedo to indicate your KMH against the MPH.

Here is another thought, the engine trans is from a 1951 Dodge, the speedo gear is a 17 tooth, the diff is a 3.73. Now suppose this exactly what was in the 51 dodge, even the tires are a close size. But, the speedo it self could be vastly different, now suppose the speedo cable is turning the correct speed for the 51 Dodge speedo, maybe it needs to be like this, maybe the 60 mph mark on my 47 Chrysler speedo, is the point where on the 51 Dodge it would register at 50 mph. Just an idea, not sure if it makes sense.

The speedo gear from the M5 semi-auto trans is not the same size as the 3spd in my car, it's too long, so I will stick with what I got, maybe get an adaptor to correct this some day..........Fred

Ed, you could be right, the speedo driver gear could be different than mine, and/or your tire size. Just found out "rule of thumb" every tooth you add on the speedo driven gear, slows the speedo cable down and of course lowers you r speedo reading...........Yhanx Fred

Tim, was on a website, for every extra speedo tooth you add, it will lower the speed of the speedo cable 2.5 to 5 %, and will of course slow the speedo down. Will try the 19 tooth gear today.

Thats true Tim, in that case I might need a 14 or 15 tooth gear, or am I thinking in the wrong direction..........Fred

Looking on this chart, with a 3spd trans, 3.73 rear end,27.1 inch tires, I should be right on the money with a 17 tooth speedo gear. Not sure what is the problem, other than if the trans driver gear is different.If I go the 19 tooth gear, and I will try this, as there are more teeth on it, this might slow the cable down and possibly slow down the speedo. On the parts car, where I got the 3.73 diff, in the 4 spd semi-auto M5 trans, there was a 19 tooth speedo gear, and maybe it was there ofr a reason, not sure. As Chrslers were supposed to come with 3.54 gears not 3.73 gears. So later I will try the gear switch in the speedo and report back....Thanx yall

The 7.10 15 is 28 inches in diameter, the tires I have on the car are 27.2, this would also put the speedo out by 2 mph. So this could be adding to the problem. My buddys van also has slightly taller tires, his speedo could be out 2 to 3 mph, so maybe I was out only by 5 mph, I can live with that.........Fred

Just pulled the speedo gear, it is a 17 tooth, the right one for a 3.73 rearend, so what might be my problem, it I am reading at 10 mph over. This was easy to take out of the trans, did not even jack the car up, just reached under and unbolted it.Fred......... ps tires are near the same size as would have been on the car in the 40s/50s

Hi Rodney, pigtails with 14 gauge would be okay, having a 12 gfauge for the hih beam side of the plug would be better, but if you can get 14 gauge pig tails, solder them together with your wire leads, shrink tube over that and yould be fine, in my books. Try not to use the crimp style butt connectors if possible, the vibration and elements have a way of loosening these up. And if you do go crimp ons, use a good quality crimping tool, for good solid crimps...........Good Luck

Hi Jim, have tried unsuccessfully to access this website you have mentioned, 3 times. I had a 4.30 in the car before, it read upwards of 15 mph of actual speed, it either has a 16 or 17 t speedo gear possibly. But now I have a 3.73 rearend, it should be very close if it is in fact a 17 t gear, in my car now. If it is the right speedo gear, my tries are 27.2 inches tall, what else could be throwing this out so far............Fred

Tim, I do have a 19 t speedo gear in hand, but there is another 19 t speedo gear in my car it's not going to matter much. I will check it and see, do I have to drain the trans to remove this gear

Tod, that is correct, but the speedo was out and reading higher with the 4.30 rearend, which was not stock and put in this car at some point in the past. I have now installed a 3.73 diff, the speedo is reading about 10 mph faster at 60 mph, where actual speed is 50 mph. So here is the kicker, my engine,trans, are from a 1951 Canadian Dodge, this car may have come with 3.73 gears,3.90 gears, or even 4.10 gears, I have no clue which. The speedo in my car is aof course a 47 Chrysler speedo, the speedo it self should make no difference, correct? So I am still wondering why the speedo is that far out at 60 mph, it should be close, or if anything, reading under as I have reduced the gear ratio to 3.73, where the factory diff was probably a 3.90 or 4.10. i do not think the diff that was originally mated to my engine and trans was a 3.54, they did not make them that way in 1951 for a Dodge car. I have no probelm off the line with the 3.73 gears, but the 4.30 had a little more zip from a dead stop, which is natural of course.........Fred

Hi Phil, that makes sense, but my speedo is 10 mph faster than actual speed @ 60mph,which is really 50 mph, this is with a 3.73 rearend and 3 spd trans. Now depending on what speedo gear I have, it could be as it is now, or if I get a speedo gear with less teeth it should bring it to a more accurate reading. I am not saying it has to be dead on, 2 mph in either direction is acceptable, but for me 10 or so mph is not. Just came back from another test drive,this time on the highway, had it up to 65 to 70 mph on the speedo, which is about 53 to 58 mph, with the 3.73 gears, the engine isn't winding up so much like it was with 4.30 gears. I do find at about 45 to 55 mph the exhaust (smithy muffler) is loud, I do not have a tail pipe yet, but will get one, and hope it tones it down at that speed.

Hi all, just took out the 47 Chrysler, had a friend follow in his Van, his speedo is accurate. My car was reading 60 mph, my actual speed about 51 mph. I thought after I had switched my rearend from 4.30 to 3.73, it would have corrected this, but it didn't, it has improved as before 50 mph would read 65 mph in the car. Now the engine and 3 spd trans are from a 1951 Dodge, I would think a 51 Dodge and 3 spd standard would have come equipped with a 3.73 rearend, may not though. Does anyone know, what the typical tire size was for a 1951 Dodge, I would think 6.70 15s, I have P205 75 15 tires, they are rated at 27.2 inches tall. Would there be any other item, I have not mentioned that would cause this speedo to read high. Any idea what the sppedo gear tooth count should be for a car with a 3 spd trans and a 3.73 diff. Would the speedo it self have anything to do with this problem, I do know the odometer is not turning, maybe everything is stiff and needs a good cleaning, but whay would it read a higher speed than the car is going. Having said this, at 52 the rpm is noticeably lower with 3.73 gears then with 4.30 gears.......Thanx Fred

Supposed to be 8 Pat, 2 on each back corner and 2 on each front corner, oh I am assuming the P15 is like the C38. All the 46 to 48 Chrslers have 8 bolts, maybe the Plymouths and later model Mopars don't.When it comes to securing the seats down, you know how I can be, remeber the coke boxes, went 50 mph with those, now my front seat is bolted down with 8- 5/16 bolts.

Hey Robert, I am also 6' 3", I have done a lot of under dash work, it's not always fun, if you can lay in there with your feet pointing ou the passenger door, it is not as bad, or take out the fron seat, that is pretty simple usually what 6 to 8 bolts. Why would you use a flashlight, get a trouble light or better yed and LED portable light.I laso have to clean the glass on mine, in fact it is cracked, I have to go under to dashes, once in the parts car, and under the driver car.............Fred

Sitting here on Halloween night, in the country no kids yet, the weather is cooler, but no snow, so it's good for the kids. Yesterday was 63 degrees here in Southern Manitoba, today it was 45 degrees, winter is around the corner. Maybe it's time to revive the " Winter In Manitoba' thread, nah you guys had enough I think..................Fred

Just went for a test drive, no unusual noises, thankful for that fact.The speedo is a lot more accurate, had the car up to 50 mph on my gravel road. 50 mph felt like 40 mph with the old 4.30 diff. So far so good, touch wood................Fred

You Betcha Buddy, but want to see if it's okay at low speeds first...........Fred

Hi all, did the swap today on my 47 Chrysler, someone had put a 4.30 rearend in years ago for some reason, unknown to me. I installed an exact match differential carrier with 3.73 gears, as the splines and everything were identical, it was a nice swap. The only diference was this, the 4.30 when you turned it by hand, was stiffer than the 3.73, and the 3.73 had a little more play. I did not swap the pinion seal, as I did not want to mess with it, if it needs changing, will do it later. As it is a very dark and rainy night, I did not go for a test ride, but did back down my 200 foot driveway, no noises going in either direction, so far so good. Thanx everyone who endures my many posts on this subject, and thanx for the endless advice. Special thanks to Tim Adams, who called me today and offered some more advice to me, this truly is a great forum, with some fine gentleman on it.......................Fred

Hi all, what type of grease is recommended and would be the best to use in the rear axle outer bearings. As I will be doing a diff swap, I want to grease the axle bearings at the same time.......Fred

What year is the project truck, if it is 1952 or later, and it has the original diff, then it may vvery well be a 16 spline, you could always use the axles, backing plates and drums if they fit off the parts truck diif and use them on the project truck. To help your curiosity, go measure the out side of the diff housing, from say the axle end flange to the centre of the pumpkin, compare measurements. Or lift the project truck up, pull one drum and bacing plate, then pull the axle and compare. That would only take about anhour, that way you know ahead of time............Fred