The Stovebolt Site Forums The Parking Lot Tons 'o Fun '49 3804 rear axle upgrade report

As many of you may know from following along, we started a project to replace the ring and pinion gear set in Ole Charlie, the Stovebolt Flagship, to improve cruising speed, lower engine RPM's, etc.

To start with, we had a mostly original and unrestored (but very good condition) 1949 1-ton pickup. It has a splasher (babitted) 235 engine that replaced the original 216 in the Spring of 1950 (engine is a 1949 manufacture, BTW). The tranny is the original SM420. The rear axle is the original HO72 Eaton axle with the 5.17 ratio. And the wheels are the 17-inch bias plys on 3-piece rims. The truck could cruise at 55 in stock form and sprint to 60. But it was at max RPM and screaming to do it.

Amtrakjoe sourced a rear axle from a '72 3/4-ton Chevy pickup with an automatic trans. We removed the center section (with the desired 4.10 ring and pinion gear)and took it to Stovebolt HQ. For peace of mind, I even took the new center section by our local transmission expert and Friend of Stovebolt, Sean at The Gearbox in Mechanicsville, MD, for a check. Sean looked at it and inspected the gear faces and the bearings and said it was good to go as is and to bolt it in and go. Of course, with a wink and a smile he offered to rebuild it for me anyway, being the good businessman he is, but he added it didn't need it.

As part of Homecoming, we removed Charlie's original center section and replaced it with the donor center section. Stay tuned for the tech tip on that, btw.

The operation, supervised by Sweet and involving myself, Mike B, Billy Marlow, Amtrak Joe, Mike Roache, Dr. Dave and a few others (I was under the truck mostly throughout the operation and only saw feet and ankles), was a complete success! The switchout was a simple unbolt, remove, replace, rebolt affairs. four new gaskets (both axle hubs, the inspection plate and the center carrier) and we were back on the road for a test.

We were a little cautious because we didn't know how the original steering, straight axle and bias plys were going to react, so we conservatively expanded the performance envelope to 67 MPH with only a slight buffet as we transitioned through 61 MPH. Engine RPM seemed beautful (not sure what the numbers were, but it seemed to be achieveing 60 MPH effortlessly.

Acceleration proceeded smoothly until plateauing at 67 MPH. Engine still not screaming but appearing to run out of HP. Controllability seemed marginal at best towards the upper right of the power/speed curve ... so we decided to end the test. Thus ended the first test drive. We returned to the shop and inspected the axle. No drips! No excessive heat!

We decided to give the steering box a tighten. After that, we went out for a second run. The steering adjustment did wonders for controllability! With much steering authority restored, we again made a run at the upper right of the power/speed curve. The truck absolutely will not pass through 67 MPH in level flight. So we maintained 67 until a down grade. Entering a down grade, a vehicle appeared to be entering the roadway from the right, so we had to slow down in caution. Vehicle did not enter the roadway, we by then, we had reached the bottom of the downgrade and had to build back to 67 anyway. Another down grade came along, and with my test engineer, Mike Roache, reading off the data from the GPS speedometer, and our chase vehicle, Sweet, verifying ... Ole Charlie hit 70 MPH! With a 90 HP cast-iron, splash-oiled wonder!

So we can verify that the '67-72 3/4-ton center section swap not only is a very easy upgrade, but does wonders for the driveability of the truck.

Even though Ole Charlie lacks the HP to exceed 67 MPH except in a dive, cruising at 65 is comfortable on both driver and engine, wheras before, even 55 was hard on the engine.

I am very pleased with the outcome. And it was really very easy as all had said. A very doeable upgrade for even a novice wrench turner.

Caveat: I would only recomend this upgrade if your other components are in good shape to withstand increased speeds: steering, brakes, tires, transmission, u-joints, engine, etc. My next upgrade for Charlie will be seatbelts. Mike and I were both a little uncomfortable hurtling down the road at 70 MPH in an AD cab with no seatbelts!

BIG THANKS to Sweet, Denny Graham, Amtrakjoe and the rest of the crew at Homecoming. I have a trailer for sale now

Pictures are here

Hy John Milliman, thanks for the update and pictures, it looks like everyone had a good time, I sure hope they did!

That was a great slide show. Now how did you get the shot from high up in the air?

3B -- You're welcome! We all had a great weekend with lots of wrenching on many different trucks. It was like Woodstock for old trucks. A Stovebolt Lollapalooza! You should come sometime. Dave Betker has been here...

Fred -- Aerial photo was courtesy of Hambone and our friend Erik Hildebrandt in his Cessna O-2 Skymaster

I hate to say "I told you it is easy" But I told you so . The real trick is to find the 4:10 gear sets.

Hi John; thank you for doing this and posting here great information. I have been looking up here and have found a couple of 4:10 pumpkins priced from $200.00 up to $400.00 just curious how much did you pay for the one you used?

I paid $350. I would say that your price range is within the acceptable window This one had minimal pitting on the ring gear but it doesn't seem to be an issue. It's quiet!

HI John

Thank you for taking this time to keep us all in the loop on this swap. I am hoping to be able to find and purchase a set of those gears in the near future. I really want an old truck that will run down the interstate roadways and not gasp for air as I think they do when in stock form. (I am looking for 60 MPH) I will heed your advice and do a full inspection and replace all worn front end parts. Brakes too as we go along.

So if anybody has a set of those gears that they would care to sell to me and ship out to my my place in Mechanicville NY (upstate NY)I would be greatly appreciative of it.

MikeC

Mike -- The trick, apparently, is to find those axles and center sections before the dirt track and rock crawler guys do. The one I have was sourced from a wrecking yard near Philly, so it's still possible to find them here on the East Coast.

60 mph, even with the splasher 235, is a cake walk now.

Gee Mike, Your on East Coast? The last one I had my hands on came from your neck of the woods, I traded a 5:17 for a 4:11 with a guy who wanted mine for a "Rock Crawler" Jeep, We each paid the freight for what we wanted. You live out there, freight should be very manageable. I then turned that to a guy in the Los Angeles area. His name I do have upon request. Good luck in your search, I would buy a dozen of them if they showed up tomorrow. The one I have in my 1 ton I purchased for $25 dollars back in about 2005. Jerry

Awesome news. I have a 4.11 rear sitting in the shop waiting to get plunked in. Paid $250 from a local yard that specializes in 67-72 chevys. I didn't tell thim this, but I was taking that rear home almost regardless of the price. No freight, just pull up, load up, drive off. easy.

Where did you source your new seals from?

I'll fetch mine Monday. Comes from a 72 C30. $200 for full axle. I'm only taking the center out!

John, Now that you have the rear gear upgrade, How do you plan to tackle the speedometer difference?

If I remember correctly, doesn't one the online suppliers have a ratio adapter for the speedo gear on the tranny?

Any good speedometer shop will as well.

Well, I'm deciding to forego any speedo upgrade and I'm relying on the speedo app on my smart phone for now

Drove ole Charlie to work (on base at NAS Pax River) friday -- automated speed radar sign by the NCIS office matched up perfectly with GPS App.

Would be interested in knowing if anyone successfully located a speedo gear that works for the 4.10 upgrade. Part No and supplier.

I think Denny G has studied this . To the best of my knowledge, Other than an adapter there are no solutions. Jerry

I made my own new face for the speedometer on the computer. It came out pretty close and by using my GPS, I learned where the error was. I know the approximate error in the odometer and I only use it for maintenance.

or a ratio adapter. Whatever is needed to correct it short of guessing or redoing the face.

Redoing/adjusting only the speedometer face will leave the odometer inaccurate. A ratio adapter solves both.

Man am I late to the party on this one....

Getting Charlie off the trailer has been one of the greatest Stovebolt accomplishments. Now that John has long-drive envy, I look forward to being his wingman on many adventures!

As for the speedometer in the truck, John will likely need to do both a speedo repair since it is not currently working, then install the adapter Grigg mentioned. This is what I did to my truck a few years ago.

The truck John brought to Kansas last year was much more advanced. Pedal to the metal equals exactly 62 mph.

Here's one source for the ratio adapter and I expect advice on what you might need.
http://www.mrspeedometer.com/MrSpeedometerCatalogue.pdf
I've never bought form them.

I got my gear set off of EBAY....cost me $250.00 and then $90.00 to ship it...next stop is Jim Carter trucks for the pumpkin gaskets...anybody on here have a source for the axle shaft gaskets??...
I will probably have gears swapped before I even find out if the truck will start...I want something that'll run 55mph on the interstate roadway system...in stock form I have read they wont unless these gears are in place...
MikeC

How did they ship something of that weight?

I got some with the other crap I bought from Rockauto. Just a common Felpro #55350, IIRC. Check to make sure, but that should be them.

After reading through this post I decided to check around again on CL for a 4:10 gear set. I've looked for years without even finding an Eaton HO52 or HO72. Well, I got a hit on a HO72 dually axle out of a 1967 C30. So I asked the seller the gear size and he came back with 4:10 gears. I thought for sure that it would be a 5:14.

So after he verified the stamp I picked it up. Came with all six dually tires. Four are split and the fronts look modern. Anyway I'm really interested in the gear set. Although the duallys may look nice under my other flatbed Chevy! Unfortunately the split rims look to be severely compromised by rust so may have to ditch the axle.

Anyone know if the brakes are a direct swap for my old huck brakes

Hi Trucknix

I was not at home but my wife was and she said it was the big brown truck (UPS) and the shipping stamp on the side said the weight was like 90lbs...the drivers must hate me as I have had all kinds of truck junk dropped off via that wonderful big brown truck...

MikeC