Axle, Pinion, Differential

Question:

I am experiencing what I think is pinion bearing noise in my 1977 MGB. I get a whine when I accelerate that increase in pitch from 35 to 40 MPH. I get a different whine when I decelerate. If I let off the throttle, I get no noise until it starts to decelerate. I can feel pinion bearing slop in the rear flange. How hard is it to replace the pinion bearings? Is there a good source of instructions for this? Thanks.

John’s Response:

There are only several easy repairs you can make to a differential -- after that, it's best to replace the entire differential unit. Two of these involve you: Tightening the pinion bearing and replacing the washers behind the spider gears. The pinion can become loose -- it should have some resistance to turn -- a preload of about 12 lb-ft. It is nearly impossible to judge the resistance to turn because as soon as you begin to rotate the pinion, the crown wheel begins to turn, too. But this is the only easy way to do this. Place a socket on the pinion nut and some type of long bar, bolted to the differential flange. Let this long bar carry through and come to rest on the bottom of the battery box. Tighten up the nut by 1/12 or 1/6 of a turn and judge the resistance to turn. Take your time! Instructions for replacing the washers behind the differential and pinion wheels is in my Tech Book and on the webpage (I believe). If tightening the pinion nut does not change the whine, then suffer it until you find another diff!

Question:

My car is a 1977 MGB. I have just found you and your website. It is great! I need information on resealing my pinion gear. I also have more than 1/4" of free play. My shop in Tacoma, WA. does not want to do the job, they told me to find a good use rear end, because without the crush sleeve it’s a very nasty job and hard to make it work, right!? Do you have a tech article on this or anything in your book?

John’s Response:

You have two problems: a leaky pinion oil seal and too much slop in the "spider gears" in the differential carrier housing. These can be corrected at the same time, but the first is far more serious -- you could run the differential out of oil -- a fatal error. The second is common to the Salisbury diffs and the repair is detailed in my tech book which is on the way to you. In the first case, it's necessary to remove the driveshaft, then remove the nut that holds the pinion / driveshaft flange. An air impact wrench is perfect for this job; I believe the nut is 1 5/16" dia. Then tap off the flange, pry the seal loose, fit a new seal, polish the surface of the flange on which the seal rides, and reassemble. The tricky part, of course, is just how tight to get the nut on the flange: too tight and the differential won't turn and/or the bearings will fail; too loose and the gears will chew up. The proper preload (resistance to turn) of the pinion is about 12 lb.-in. This is difficult (not impossible) to "feel" with the half shafts and wheels on the car, for if you turn the pinion flange more than 1/4 inch, the resistance to turn includes not only the pinion bearings, but the crown wheel bearings, the wheel bearings, the tires, and the brakes! You must make a tool for holding the pinion stationary. A two-foot flat steel bar is best -- drilled to accept two pinion flange bolts yet allow your socket to fit over the pinion nut. Rotate this tool and allow it to bottom out on the bottom of the battery box. Use your breaker bar to rotate the pinion nut. The nut will turn freely (well, sort of,) until the flange returns to its original position, then the torque rises dramatically. Turn the nut 1/16 turn by 1/16 turn testing the preload after each rotation. Stop when the preload (again, you must judge this in 1/4" of rotational freeplay) begins to rise. We do this job a lot without a problem -- your shop is simply not used to, or comfortable with, or unskilled in this repair. Changing the differential is a MUCH larger problem! Hope this helps.

Question:

I found this once but I can't find it again. What is Max/min allowable for axel hub splines outer diameter on a 1975 MGB and also the matching ID tolerance on the wheel hub. Do you have this info or suggest where to look?

John’s Response:

The original spline diameter on the hubs is 2.450". 2.425 is really worn. 2.400 is dangerous! The hub you can measure. The inside of the wheel hub you cannot measure (well, I can't). So, I use my finger to judge the "step" between the worn and unworn splines. If barely a step is felt, well then, it's pretty good. If a definite step is felt, well -- it's wheel time. New wheels on new hubs should not have any rotational freeplay.

Question:

Any ideas on what would cause a 1972 Midget to break an axle every couple years? Always driver's side. Car not auto-crossed, etc. One theory holds that if the axle housing is even a bit out of line it will stress the axle. Appreciate any thoughts.

John’s Response:

Some thoughts here about that frequent failure of the half shaft. If the housing is bent, it WILL snap the shafts, no question!

I do not know how to discern a bent housing from a good one. If the hub is bent (from installation of a bearing with a press), that might cause a problem. But the most frequent cause I know is the failure of the washers under the differential and pinion wheels. I would remove the "pig" and remove the crown wheel carrier, then drive out the retaining pin and change the washers, if not the differential wheels themselves!

Question:

It is possible to change the rear wheel bearings on a 1972 GT (semi-floating axle) myself ? A couple of garages I have spoken to say the bearings must be pressed back in with specialist equipment. Is this true? Any advice you can give would be greatly appreciated.

John’s Response:

First, it would be most unusual to have a problem with the rear wheel bearings. I cannot remember the last time we changed one!

You only need a shop arbor press -- not an exotic piece of equipment, really. Pulling the half shafts from the rear axle will be as difficult as finding the shop to press the old ones off and the new ones on.
Try this: Remove the drum, hub, and backing plate. Now refit the conical washer - BACKWARDS - along with the castellated nut. Use a slide hammer with a three finger gear puller attachment, fitting the fingers around the back side of that conical washer.

Question:

Thank you for your service. This is a mess, and I hope you can help. I'm working on a 1961 AH Sprite with a broken axle shaft. The problem is, I cannot get the shaft out. I've tried using a slide hammer/puller and can only get it out about 3/8". After that, all I seem to do is scoot the car across the floor. I thought about using some sort of dowel to shove through the other side, but the pin for the differential planet gears is in the way. As you already know, this car has a banjo type axle. There is no way to access the differential without removing it, and I don't see any way of removing the differential without pulling out the axle shaft! Can you help?

John’s Response:

By now you've been successful, no doubt -- and I'm certain that you found that you simply had to hold the car down and use a LARGER slide hammer. The half shaft twisted off at the differential wheel, most likely, and the break caused the OD of the shaft to interfere with the crown wheel carrier. If you used a "new and improved" method to remove this, please let me know!

Question:
I own an early MGB (chassis #951) with the banjo style rear end. Unfortunately, the rear axle oil level ran low due to leaking seals at the wheels and the outer wheel bearings got hot. I mean very hot - smoke was flowing out of the left hand wheel well. Preceding this, that outer bearing had begun clicking. Out with my wife on a Sunday drive, thought the clicking was a pebble in the tire tread at first. Didn't want to call a tow truck with my wife along and thought I could limp it home. Mistake and expensive miles. Should have known better. Anyway, locally someone knowledgeable about the early style of MGB rear end said if it got that hot, not only are the bearings ruined but the bearing housings in the axle casting are probably distorted and I'm better off just finding a good used entire rear axle assembly and substituting this one for my old. He also suggested that I'd have an easier time finding a later style (tube type) rear end and better chances that it would be in good shape since it would be newer and the design was much stronger. My car has disc wheels by the way, and I want to keep it this way. I haven't taken my old rear end apart yet but fear the worse. Having done a rear axle swop on a GT years ago, I know that it's not too much work. Probably easier than tearing my old rear axle assembly apart, sourcing seals, bearings etc., and reassembling. Perhaps still to have problems. Anyway, my questions are these:
1) Do you agree that it's probable that my car's rear axle tube assemblies are ruined by the overheating? If you recommend that I tear it down to see, what do I look for in those bearing housings. Also, I only have a three eared gear puller style puller, can I pull the wheel hub off with this or need a more specialized tool?

2) What sort of adaption challenge would using a later model rear axle assembly entail? I seem to recall hearing that the drive shafts are different but I'm not certain, and that maybe there's a clearance problem with the original style gas tank on my car. Can this substitution work?

3) If I decide to go with a used rear axle (newer or older style), what are some inspection tips on finding a serviceable unit w/o disassembly? I'd assume checking for free play in the half shaft ends at the wheel hubs, looking for obvious leaks at the wheel ends & differential case and trying to sense excessive backlash between the ring and pinion gear set by rotating and reversing the axle ends quickly. That's all I can think of but I do have a known good wire wheel rear end in my garage from a GT. Can't use it since I don't want wires and it may not fit anyway. But it gives me a test bench to try hand or machine tool measurements that you'd suggest before I go looking at used parts. Thanks for your advice and help with this complex set of questions.

John’s Response:

I would hunt for the proper banjo style rear end. While the Salisbury, Tubed, or "GT" differential is heavier construction, those early ones "never" fail (well, there ARE exceptions). Plus, the GT diffs pick up a clunk after a while, and the banjo style diffs never seem to clunk.
If you are going to swap banjo for GT, you MUST make certain that you keep the width the same -- the disc wheel differential is wider by 3/4" on each side.
Some say that the GT differential is too large for the early cars, but I've never had a problem fitting one to an earlier car -- but then, yours is really EARLY.
Before I went through all this, I'd pull the half shafts and then pull the "pig" for a good inspection. If the pig is burned up, simply find another. If the wheel (hub) bearings are burned up, buy new ones. If the differential housing is faulty -- because one of the hub bearings spun on it -- well then, you WILL have to find another diff. Let me know -- I do have a complete WW banjo differential that is looking for a new home -- but it's folly to make any plans until you've made a full inspection of the unit you have!

Question:

I have a 1970 MGB 4 cylinder. I have noticed a grinding sound coming from the back. However, I only hear it when the top is up. It starts in 3rd gear. If I press in the clutch, the noise remains. I jacked the back off the ground and ran the car in 3rd, the noise was there, but I could not identify exactly where it was coming from. How hard is it to rebuild? Can a novice do the work?

John’s Response:

In response to your rear axle problem, here are some things to check:
First: drain the old oil and try new oil. Second: Grasp the pinion and try to shake it up and down -- there should be NO freeplay in this shaft!! If there is, you'll have to change the front bearing.
Third: You can remove the back cover of the differential and make a visual inspection of the gears -- but without the experience of having seen hundreds, you'll only note a problem if it's REALLY bad.
Fourth: The rear wheel bearings rarely fail -- leave the car in neutral and spin one wheel, then the other. Even then, hearing a problem like this may be difficult.
It is possible to COMPLETELY disassemble the differential in place. The only difficulties are withdrawing the half shafts (you need a "slide hammer") and setting the pinion back up with the correct preload -- you need a inch-pound torque wrench which will indicate 12 lb.-in. I've attached an article about the differentials -- this is NOT your problem, but indicative of the degree of difficulty you'll encounter if you disassemble the whole unit.

Question:

I have a clunk in what sounds like the driver side rear end of my 1969 MGB. It occurs when going over even very slight bumps and seems to have nothing to do with accelerating or slowing. I've checked everything for tightness and find nothing loose (shocks or springs) or visibly damaged. The shocks are the original but have no signs of leakage and are full of fluid. I'm left to assume it must be the shocks (based on browsing the web and newsgroup postings) and am prepared to either purchase new or refurbished shocks. First, do you agree with my plan of action? Should I go with new or refurbished shocks? What are the pros and cons of a conversion to tube shocks? I'm intrigued by the handling performance enhancement reported for tube shocks but since I'm not a very aggressive driver it might be more logical to stick with the stock shocks and maybe upgrade to the heavier fluid as you recommend on your web site. I gather if I go with a rebuilt original shock, it's important to have a reliable rebuild company and consequently, I would appreciate your recommendation. Thanks in advance for your assistance (again!).

John’s Response:

The shock is most likely NOT the problem. You should first tighten the shock to the frame as they do come loose (rarely). Secondly, with the rear end of the car up off the ground supported on jack stands under the rear axle (not the frame or springs), grasp the shock link and violently shake it. My guess is that the shock link is faulty -- egged out at the bottom -- that's pretty common.
To change it, remove the shock from the frame, remove the plate from the bottom of the leaf spring; remove the nuts, and strike the threaded stud with a BIG hammer and "pop," the shock link will separate from the damper arm and from the rear spring plate.

Question:

I own a 1971 MGB and want to change my wire wheels for Rostyle wheels. I have found another MGB owner who would like to swap his (1979 MGB) Rostyle wheels for my (1971 MGB) wire wheels. I have removed the wheels and hubs that hold them to the axle and then looking at the MGB workshop manual noticed a difference in the diagrams showing two axles, one for disc wheels and the other for wire wheels. Is it necessary to replace the axle shafts as well? From what I can see on the outside of the axle shafts all dimensions and components look identical, is there some internal difference? I would appreciate your assistance or direct me to a response you have already made so as not to have to repeat yourself. Thanks again.

John’s Response:

Your exchange would be relatively simple if your associate had a pre-77 MGB. As it is, the exchange may be difficult.
The front hubs swap back and forth -- no problem. Just make certain you have enough shims to set up the end float; and DO NOT get the hubs switched left to right. The rear axle must be changed COMPLETELY -- the disc wheel diff is wider than the wire wheel diff. This would not be a problem, but in 1977 the factory added a rear anti- sway bar. To make this exchange in my shop, I would cut the ears for the sway bar from the 1979 rear axle and fit the works to your car, no problem. Then, I would fit your rear axle to his car, mount the sway bar, load the rear axle to it is "just" beginning to lift the car, and weld those ears onto your old diff.

Follow-up Question:

Good call. I've replaced the links and all the clunks are gone. The one that was obviously bad was on the opposite side I thought the noise was coming from. It had worn an oblong hole in the upper connector and was quite loose. I also replaced the rebound straps while I was at it- they were the originals and were cracked in multiple places with very little elasticity. I don't drive the car that much but what a joy to drive now without all the rear end noise. I truly thank you for your assistance.

John’s Response:

Question:

A fellow has offered me a 4.1 rear axle (pumpkin) from a 1960 MGA 1600. Would this fit the ZB Magnette? As easy as the early MGB 3.9? Do I need the half shafts? Does the spline coarseness or fineness differ between these gear sets? If it will work, is it just an exchange or is there more to it? Finally, what would be the approximate road speed in mph per 1000 rpm?

John’s Response:

There are three different sets of differential wheels you can fit into these diffs: 10 spline; 25 spline; and 26 spline. You can always take the wheels from YOUR differential and insert them into the 4.1 diff.
According to my workshop manual, the relative road speeds for these diffs are:
8/41 5.125 14.4 8/39 4.875 15.2 9/41 4.555 16.2 10/43 4.300 17.2 10/41 4.100 18.0 11/43 3.909 18.9
All based on a 15" rim (but probably with bias ply tires)

Question:

What is the recommended torque tightness on the Midget rear axle bolts, the U bolts that hold the thing to the springs? I can't seem to get mine to stay tightened. Even tried using "airplane" bolts (the ones with the plastic locking inserts) but this is no good either. Just bought a whole new set of nuts washers and lock washers (the split type) and presently have them down to 20-25 lbs./ft each bolt. This seems to have squashed the new rubber pads nicely, but will it be enough? Don't want to bend the mounting brackets which it seems I can easily do if go too tight. Any thoughts or recommendations? I can't find a "factory" recommended figure in any of my shop/service manuals.

John’s Response:

We don't put a torque on them as much as we watch what's happening with the U bolts, the rubber mounts, and the plates. I like to tighten them until I "just" begin to see the plates begin to distort. You can always double nut them to keep them from backing off. Is your problem that the nuts loosen - really? -- or is the problem with torque steering from the back of the car?

Question:

I am doing a complete rebuild of 1970 MGB Roadster and as part of it I was going to install a new ring gear. I would like to know what is the ID of the ring and what is the OD where it fits to the flywheel? In other words what is the interference fit? The reason I ask is because I think the old ring gear was slipping because there is a ridge that the old ring gear had to get over to get it off. I can't imagine that ridge should be there. It would seem to me the two dimensions should be in a manual since you should check them before installing a new ring gear. None of my 4 manuals have anything.

John’s Response:

In my 30+ years of working on MGs, I've never seen a slipping ring gear from any engine, any year. Further, I am not certain if I have ever had to change a ring gear on a 68- MGB since the starter motor is pre-engaged and doesn't damage the teeth on the gear during operation. Yet, from the description of your flywheel, it certainly seems that the gear may have been slipping. I do believe that a less expensive route would be to find a used flywheel (with a good ring gear) and substitute it for yours. To answer your question, I do not have those measurements.

Question:

I'm trying to put together an MGA/early MGB rear axle to hang in the rear of my MGB GT race car. This axle came to me in pieces missing all the bearings. Two questions:
I have an old shop manual that calls out special tool "pinion setting tool #18G-191-82. What are the dimensions of this gauge? Might you have generic numbers for the bearings in this diff?

John’s Response:

The critical measurement here is the distance from the center of the carrier bearings to the head of the pinion. If that's off by 0.005" you can get howling. However, I do not know that measurement. If you want to call at the shop, today, I can give you the Timken numbers for the two pinion bearings and the carrier bearing (times two), but I don't have those numbers here at the house.
I am not certain where you can find that pinion depth number. Barney Gaylord has a large site at www.MGAguru.com.
I've been bothered that I do not know this number. I know I can get it from experimentation, but someone out there must have it already.

Question:

I need to replace my pinion oil seal on my tube axle. I am concerned about having to use special tools as per workshop manual. I do have standard torque wrenches. Do you recommend this operation? If not, I am not sure who could do this here in the Milwaukee area. Thanks for your advice.

John’s Response:

This is a difficult task to do at home as you need a special tool and the drive flange can be very difficult to remove. Basically, you're going to remove the front flange of the differential, pry out the seal, fit a new seal, and refit the flange. The flange is sometimes stuck, stuck fast -- so you need to tap it forward with your hammer, turning it slightly between each tap so nothing is bent or stressed. When the flange comes off, you will want to polish the contact surface with some fine grit paper (600 or so).
The old seal comes out with a pry bar or with a long, heavy screwdriver. The new one is inserted and tapped into place with a hammer -- carefully!
Now comes the part that needs finesse. Reinstall the flange, fit the nut, then begin to tighten the nut, constantly feeling the restriction to movement of the front flange. You are searching for a pre-load, or resistance to turn, of about one foot pound. The "feel" is a very slight tightening. The problem here is that the flange rotates independently of the crown wheel by as little as 1/8" on its circumference -- and you must gauge the preload in that distance! Further, you should not use an air impact to turn the nut as there is little control. You should use a long 1/2" breaker bar. But you have to keep the flange from turning, so you'll have to make up a tool that you can bolt to the front flange. I've used a 3/4" piece of rod, about two feet long, with two 5/16" holes on one end. Run two 5/16" bolts through those holes, fix them tightly with nuts, and use that, passed through the 5/16" holes in the differential flange to keep the flange from turning. You could bolt this tool to the front flange, but then you wouldn't be able to feel the preload.

Tighten, feel; tighten, feel; tighten, feel. Eventually you'll begin to draw the two taper bearings close together and achieve this very slight resistance to turn.
I'd be pleased to review this with you on the phone. Of course, it would make a good addition to our YouTube videos. BTW, don't forget to refill the differential with oil!