Axle Advice


Rear Axle Breaks at Speed

Here's an occurrence I hear about from time to time, and it's the kind of failure that is hard to predict, but worth trying to anticipate, in a machine that is over half a century old.

Larry Shank is well known to many readers of CJ3B.info as the owner of the 1953 CJ-3B and teardrop trailer customized by his father Harry Shank, and featured in Mom, Dad, a Jeep and a Teardrop. The Jeep is well-maintained and used regularly, as Larry attends car shows and trailer camping rallies around California.

On the freeway Larry wrote in early 2018, "On the way home from a vintage trailer rally in Southern California, the driver's side rear axle broke... at 55mph... on the interstate... with the Teardrop in tow! Absolutely clean break at the bearing carrier. We were very lucky. Coasted to a straight stop as the wheel passed us by. No permanent damage to the Jeep or Teardrop."

(See also details on Harry Shank's Steering Headlight on CJ3B.info.)

Damage Here you can see where the axle snapped, and the new shape of the brake after it skidded along the pavement.

Larry says, "My friend Ron at Fresno 4 Wheel Drive and I are in the process of rebuilding with a full floater kit. Will be ready for the 2018 rallies. All else is well and looking forward to more Jeep and Teardrop trips in 2018."

Floater diagram

You might expect that kind of failure off road, but it does also seem to happen at speed on the highway, where the danger to the Jeep (and to other vehicles from the loose wheel) is much greater.

Larry's solution of installing a full-floating axle is the most reliable way of preventing the loss of a wheel if an axle shaft snaps due to torque or fatigue, because the wheel actually rides on the axle housing. But it is a heavier and more expensive assembly. A full-floater kit from Herm the Ovedrive Guy is featured in Early Dana 44 Full Floater Axle Kit at Four Wheeler.

John Goering comments: "The advantages of a full float are several. 1) as in Larry's case, the wheel stays on even if the axle breaks, 2) and maybe just as important, you still have brakes when the axle shears, 3) when you are out in the sticks and something goes south in the rear end, just pull the rear driveshaft and drive flanges and drive it home in front wheel drive mode, and 4) since the weight of the vehicle is no longer supported on the axle shaft, a full float is usually a lot stronger. A very worth while modification. I think I installed the rear full float in my 1955 3B around 1974. It has been completely trouble free for all those decades."

EBRO hub A full-floating axle is easily identified from the exterior, by the larger axle hub. Full floating axles were standard on CJ-3Bs built by EBRO in Spain, as seen here.

New hub NewUpdate from Larry: "We purchased the axles and flanges for the full floater kit from Herm, but we compiled the rest of the parts from Ron's prime collection of originals at Fresno Four Wheel Drive. Ron added his custom fabrication/machining to produce a top quality axle assembly.

"We decided to add Warn locking hubs to facilitate the possibility of flat towing or dolly towing in the future. The standard flanges/caps from Herm will be kept as emergency spares. We installed new u-joints along with all of the other updated axle components."

And here are some axle topics raised in the past on the CJ-3B Bulletin Board:

Gear Ratios

The question was asked by Robert: "I have a 1954 CJ-3B. How can I tell what the axle ratios are? My speedo doesn't work but I guess I can go about 55 with the motor screaming..."

Service Manual Oldtime: "Robert, you should have 5.38 to 1 gears in a non-modified '54 B. Unlikely that it has anything else. Also you should have a small metal tag attached to one of the differential cover case bolts. The numbers 43/8 will be embossed on that tag. 43/8 = 5.38. Your speed estimate is close but perhaps you are closer to 60mph, depending on how good your engine is and how hard you're pushing the pedal."

Dave: "The tag shows your axle's gear ratio. 43 teeth on the ring gear and 8 on the pinion. Divide 43 by 8, you got 5.38 gears, which is the optional 4-cylinder gear ratio. The standard gears were 4.27 which were much better gear for street use. The 5.38's were offroad gears and with a stock 4 cylinder you can't expect much more than 50 MPH, and thats screamin. If you do much highway driving a Warn overdrive would help a lot by reducing your engine's RPM by 25%."

Lamar: "I own two 3Bs, a '53 and a '64. The '53 has stock 5:38s the '64 has stock 4:27 gears. In the early 60s gear ratios were changed to the 4:27s. The 5:38s were offerd as an option. I prefer the taller 4:27s. Look for axles out of late 3Bs and 60s to '72 CJ-5s."

Note: Willys Service Bulletin 601 from 1962 provides details on the change in ratios.

Jyotin: "Here is a quick and dirty way to discover gear ratios:

  1. Jack one wheel off the ground while the Jeep is in 2WD and neutral.
  2. Turn the wheel 'till the valve stem is in the 12 o'clock position.
  3. Mark the position of the drive shaft both on the fixed housing and the shaft itself.
  4. Now, turn the wheel TWO (yes two) full revolutions and count the number of turns of the drive shaft. That'll be your gear ratio.

5.38, 4.27, 4.88 and 3.73 are the standard Jeep CJ gear ratios, so it will most likely be one of them."

Oldtime with his axle collection Robert: "Is it hard to change the gears? What are my options for taller gears, i.e. 4.11?"

Oldtime: "That's a tough one. It is technically the hardest part of the Jeep to work on. It takes special tooling to do it properly. You first should decide stock or modified. Lots of pros and cons invlved with such a choice. If you're bent toward modified then you have two other options if your on any kind of a budget.

Option #1 -- get some used axles out of a '63 to '71 CJ. These later axles often could be found with a 4.27 gear ratio. Plan on doing some brake line changes. This change gives you just over 20% taller gears.

Note: you must have the same ratio in both axles.

Option #2 -- get a 25% Saturn, old Warn or old Husky overdrive. Easy to install with no permanent modifications. Except maybe the shift tower cover. The OD also has other advantages -- just ask anyone who uses one. I'm not trying to sell overdrives to anyone but what works, works. They sell like hotcakes used. You will need patience to find one. I personally bought a complete whole CJ-3B back in 1989 for $1000 just because I wanted a second Warn OD. I am currently rebuilding that 3B. But then you see I try to drive mine on today's roads in very nearly stock condition."

Larry D: "This is interesting stuff. So if I have 5.38 gears and install an overdrive unit -- I think they are a 25% reduction -- would that result in an effective 4.03 gears (5.38 x .75)? Couldn't you get a similar result with a taller tire?"

Oldtime: "Sure U can put tall tires on to change your gearing, but to get the same results you may have to run nearly 36" tall tires. Elsewhere on the web, check out Rick Grover's Willys Speed Calculator page -- its the best I've found."

Oakes: "You could also find a V6 CJ-5 or 6 Jeep. Some had 3.73 gears but 4.27's and 4.88's are also possible."

Vents and Drain Plugs

ExplodedPete: "I have a '54 CJ-3B with the Dana 44 rear end. I cannot find a vent on this unit. Anybody know the particulars of the vent?"

An anonymous poster responded: "The vent is a small hole, about 1/8", in the left axle tube. You will find it about half way up the tube and it will be facing the rear on one side or the other of the spring perch. On one of my Jeeps I welded the axle tube breather closed. Then I drilled and tapped (1/8"NPT) a hole in the top of the differential housing, or you could also braze in a fitting in the differential cover. Then screw in a barbed hose adapter and run the hose up to the frame rail, maybe add a check valve or a small orifice fitting in the hose end to keep dirt out."

Felipe: "I have a 1965 M606 (military CJ-3B) and I can't find where both differentials drain plugs are located. The differentials are originals."

John: "They should be on the underside of the diff. (Note: see #24 in the exploded diagram.) Mine is an allen-head bolt that is flush with the case. In order for me to use it, I get on a creeper with a flashlight and a wire brush, cause the allen hole is probably filly with mud or road crud. If you can, get a Chilton's maintenance manual or one like it -- it has helped me a lot."

Rusty: "On later rear diffs you have to pull the cover to drain them."

Kevin: "Usually there is only a filler plug and not a drain plug. The filler plug is located at a top position. To drain the old diferential oil, remove the jackpot cover and replace it. You almost always have to replace the jackpot cover gasket. I always do. By doing it this way you can inspect your ring & pinion gear and the inside of the housing. When you refill the diff. oil it should come up just about 1/2" below the filler hole. This is the way I've always done it."

Andy Stock: "No modern differentials have a drain plug -- it makes it too easy for people to change the fluid themselves. I know most (if not all) older Jeep axles did, though, right on the bottom of the case."

Dana Axle Pinion Depth

CutawaySebastian Ruiz: "Does anybody knew the mounting distance for the pinion of both axles?"

Eric Lawson: "I assume you mean pinion depth from the center of the carrier bearing bore to the face of the pinion.

"All of the following is from some old notes of mine. I THINK they are correct. There is a lot more here than just the answer to your question. I hope that Derek can archive this (with some warnings about the possible unreliability of this information), so that others can add to it or make corrections.

"Also on the notes are bearing information for the Model 25 axle: Carrier bearings Timken 24780, bearing races Timken 24721, inner pinion bearing Timken 31594, bearing race Timken 31520, outer pinion bearing Timken 02872, bearing race 02820, pinion oil seal National 39118-2, inner axle shaft oil seals, Victor 49447.

"Continuing on with the notes for the model 25 axle: Pinion preload 10 to 25 inch/lbs to rotate the pinion -- no ring gear or seal. Ring gear backlash .005 to .01 inch. Carrier bearing preload, additional .008 inch of shims."

Sebastian: "Thanks for your help! But now I have more questions: Searching in some books I found that the distance for Dana 44 is 2.625 and for Dana 30 is 2.250, without any change for different ratios. But wait -- you must search the pinion head for any difference (-0.1/+0.2). How can the distance change for different ratios for the 23-25-27-41? For model 41 with the highly popular 5.38? Which is the distance. The D-27 with 7.2 ring size, the same as D-30, has a different distance? And the D-25 with 7.75 ring has the same distance as D-30?

Glenn Smith: "To repeat what was with the instructions in a gear set I just installed: the final determination of proper depth is by visually checking tooth contact pattern. This is obviously done by using a marking compound on the teeth. I'm no expert for sure on this, just noting this in case someone might think that the measurement was all that needed to be done. Besides, I doubt very many people have the tools needed for measurement -- anyway,I definitely don't have them. Also, the rule of thumb is to start with the same thickness of shims that you took out."

Eric: "Yes, nothing is better than a visual check of the pattern, and I always do that. However, the only time I had a problem with the gauge and the visual pattern check not agreeing was when I missed a burr on one of the holes in the ring gear. The place on the gear that I checked with the gauges said everything was OK, but looking at the pattern on ALL of the teeth showed a problem in one area of the gear. Had I not done the final check, I would have eventually had a disaster on my hands.

"You are right in mentioning that the value etched onto the face of the pinion must be added to the value I listed to determine the pinion depth for that individual gear set. The depth values given are nominal ones; they are adjusted by the amount indicated on the pinion face. This adjustment is determined by the gear manufacturer after they run the gear set on a test fixture and check the patterns themselves, so the values are quite precise. Since the values were determined for a particular set of gears, the gears should only be used as a set and not mixed with another set of gears. Also, if you get a gear set, ask if the correction value on the pinion is metric or 'inch'.

"I don't know the depth value for the model 41 axle with 5.38:1 ratio gears. I think, but I am not sure, that 2.625 inch is the correct value. If the axle is already set up and you are replacing gears, Glenn's suggestion of starting with the same shim thickness as was previously installed is a good one.

"As for the gauge, I was lucky. I don't feel right playing the lottery anymore as I think I used up most of that kind of luck. I was in a tool shop and the owner was wondering what to do with the gauge because the person who ordered it would not come in to pick it up. The person making the order had put down a 75% deposit, so I got a great deal on the gauge."

Rear Axle Shims

Steve S.: "I'm in the middle of a restore and I'm on the rear brakes. Everything is off to the axle flange. On the right side (differential side) there are 9 shims between the outer bearing and the bearing plate. On the left side there are 0 shims. Is this correct? How do you know how many shims there should be in the first place?"

Anon responded: "I think that the manual says to even up the shims from side to side. (Note: see #36 in the cutaway diagram.) The shims set the preload on the wheel bearings and there should be between .002" & .006" of freeplay. I recommend that you get a service manual to help you through your project. Good luck."

Neil Graham: "I am at the same stage as you are with my rear diff. Mine is exactly the same -- all shims are on diff side. I am fairly certain mine came this way but it would make more sense to split the shims as the manual does indicate this procedure."

Pete: "I havn't done that job yet, but I seem to recall reading about it. I think it said all shims on one side. Maybe it was the Jeep Bible by Granville King or it could be in the (Chilton?) manual I have. You should check a manual."

Keith: "My recollection is that it doesn't matter. Both axles end up inside the carrier against a small spacer that has a hole in it for the pin the spider gears ride on. What you are adjusting is the total endplay. So all on one side, or split, has the same effect.

Ernie: "My FC150 and FC-170 both had the shims all on one side too. It doesn't really matter except it will push the wheel with the shims outward more than the other wheel."

Locking Differential

Larry: "I want to put a locker/limited slip in the rear Dana 44 axle. It is a 1954 CJ-3B. What splines are the stock rear axles, and does any one know who makes lockers/limited slips for this? I've seen on CJ3B.info one guy upgraded to 19-spline axles to use a Powr-Lok, and I have seen others for 19-spline axles. Do I have to switch to 19 splines for all current lockers/limited slips being made?"

Jeep newbie: "I am a relatively new CJ-3B owner, which may go without saying after I pose my question, but I was curious if anyone could provide some info about replacing the rear diff on a '53 CJ-3B with Dana 44. I have been getting a lot of noise from the rear axle ever since I bought the Jeep, and it has only gotten worse since I put a 2-inch lift on, so I figured the diff pinion might be going. And if it's true I figured I would maybe try a locking diff and was wondering if anyone knew of a good locking or limited slip replacement."

Lock-Right installedLouie Larson: "Lock-Right Model LR2415 10-spline for the rear axle, Lock-Right Model LR2115 for the front axle. Available at any 4WD parts dealer. I have them in my CJ-3B and they work very well. Remember that if you install one in the front axle it will be difficult to steer on ice or very slippery trails. Unless you are a hardcore off-roader I suggest only in the rear axle. Lock-Rights are very inexpensive and you can install them yourself."

Randy Buchanan: "Lock-Right for rear axle is a good choice for 10-spline axles. I would not recommend a full locker for the front, as M25 axles are not all that strong. A better choice is the Power-Lok limited slip which is a Dana/Spicer product. Parts are still availible from any Spicer dealer. Keep in mind that M25 axles (axle shafts) are not up to big tires (over 31-10.50) either, and with a full locker like a Loc-Right, you WILL have problems steering, and when the going gets a little tough, with axle breakage. If you've got a non-stock motor with more HP it only makes things worse for the front end. Also you need to know that your Jeep will do 99% of what it will do, period, with the front end open. But a locker, or limited slip, in the rear is a must-have option. Until you have one, you've only got 2-wheel drive.

Note: Randy's article on Drivetrain Strength has a detailed discussion of Jeep engineering and axle strength. The "Powr-Lok" Differential Service Bulletin from 1960 describes the Willys optional limited-slip differential.

Steve: Since the noise worsened after the lift was installed, I think I'd look at the U-joints on the rear driveshaft before tearing into the rear differential. Raising any Jeep is going to affect the drive line angle, and not for the better! Try to get some grease into the U-joints, and see if there is any play in them. If the noise changes after greasing them, you may want to replace them as they are probably shot. Also, if you haven't already, drain the rear differential and then refill with 90-weight gear oil. Often you will find as much or more water in a Jeep diff than lube!"

Rusty: "If your 44 is the orignal it is a 10-spline and I believe the only new locker you can get is a Lock-Rite. You can rebuld the 44 and use any locker you want if you go to new axle shafts with a bigger spline count."

Jyotin: For what it is worth, I have found locking differentials more trouble than they are worth. I almost put a CJ-5 into a ditch because it kept wanting to slide sideways. You just have no control over when you are going into a fishtail. And, what's worse, you can't make them stop the locking action. That said, air lockers are great -- you control when they kick in and when they kick out. I had a couple in an '86 CJ-7 and they worked fine. Still got stuck though...."

Jerry Brown mentioned: "Lockers are dangerous in snow."

Rocnroll: "Read any of the magazines and they'll tell you not to go through a mud puddle unless you have a Dana 60 in the back and a 44 in the front but most people don't LIKE to spend money. Any upgrade such as the one you described is going to make you more dependable I guess. Only you can decide how much you want to spend. The Lock-Right is the cheapest because you DON'T have to change the carrier. That's one of it's benefits. It fits into your stock carrier. It's about $300-400 US. As far as custom axles go, I guess you can spend pretty much whatever you want -- just tell the shop what you have in mind and they'll give you a figure."

Thanks to all the contributors. -- Derek Redmond

Factory photo from the Images in Time collection at the Toledo Lucas County Public Library -- see also Working at the Overland on CJ3B.info. Diagrams from the Factory Service Manual, which is essential to most serious mechanical work on a Jeep. Lock-Right photo from Powertrax Lock-Right Locker Installation and Review.

Return to CJ-3B Tech Tips.

FacebookVisit CJ3B.info on Facebook.

CJ3B Home | Contents | Search | Links | 3A and 3B Community

Last updated 7 January 2019 by Derek Redmond redmond@cj3b.info
All content not credited and previously copyright, is copyright Derek Redmond