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MG MGB Technical - Rear end noise

Just bought a '69 MGB GT. This is my first experience with a MG. Driving it around I can hear a "low rumble" in the rear end. Don't have the back seat cushion in so its just the battery tray cover between my ears and the differential. Should I be hearing the tumbling sound of the differential at work from the drivers seat. Don't know if MGs are typically noisy like this or not, nothing to compare it to. I can spin the rear wheels easily when jacked up and out of gear. No noises unless I'm going at least over a few mph. No change on accleration, coasting, down-shifting, or reverse. Same sound. Like someone shaking a brown paper bag full of wooden blocks back there. Not a metallic sound, just a tumbling sound. An occasional "pop", but not loud. The volume level is to the point where its noticiable, but not louder than the engine.

I've changed the fluid, no metal drained out of the old fluid. Fluid level is good. Have yet to pull the cover, would like to know what to look for before I dig to deep. Any suggestions?
D Gesse

D

My '65MGB makes the same noise but only on deaccleration, coasting, down-shifting, when ever I take my foot off the gas.

Ray
Ray Gordon

My advice to you is get some sound deadening material and some carpet and cover the rear shelf. If I drive my roadster with the battery cover off, the diff noise is alarming. It's been like that for 9 years now and still works fine. If it clonks when changing from forward to reverse, you can fix that cheaply, but whining or rumbling, forget it. The car is 34 years old - it's allowed a little wear. Cover it up and be happy.

Mike
Mike Howlett

Well guys:

Here’s my take on this subject. I’ve had the same sounds and symptoms on both of my MG’s and in both cases it was bad bearing in one or both sides. After I removed the rear axle bearings and cleaned them up, I could see where the ball bearings were pitted or the surface had peeled off. More than likely this is the sound you are hearing. On both of my cars all this metal that had sloughed off had scattered throughout the rear end ruining the other bearings also. Disassembling and cleaning everything up was time consuming and a pain in the butt, but now both rear ends run dead quite.

My feeling was that if I just ignored the noise, sooner or later I would be stuck on the side of road. Not a place I wanted to be.

One additional way to check the rear axle integrity is to put the car on jack stands, remove the back panel, put it in gear, and run the engine. That way it is real easy to hear what’s going on. A fresh rear end is quiet!

See ‘ya in the garage…
Bryan



Bryan Prindle

My 65 banjo rear end has some gear whine for 10 years but no problems. This is likely due to gear wear and probably the pinion to ring gear set up.

That said, a rumble is likely bad bearings and should be checked. I would start at the axles and investigate up to the drive pinion. The outboard pinion bearings are next most likely to go as they aren't lubricated as well as the inner one and are smaller. Sometimes bearings just stay noisy for a long time and sometimes they fail catastrophically...such as welded parts etc.

You should have the more modern integral housing axle. So, if you need repairs beyond axles bearings you should probably see a specialist or get a used one. But, these things are old and the chance of getting a used one that needs bearings is high.

Robert McCoy

Hi D,
Changing anything but the wheel bearings takes some specialist tools to get the ring and pinion gears set up correctly, and changing the wheel bearings takes a press, but other than that is pretty straightforward. If you do need work, feel free to email me - I can supply a rebuilt rear axle for you.
Safety Fast, Wade
Wade Keene

Thanks to everyone for the responses. Looks like I have some conflicting suggestions. I think I'll take my chances and run it while the weather is still good and save a bearing replacement for the cold months. I may replace the tank this winter and so I'll do both at the same time. Thanks again!
D Gesse

Another vote for the bearing. I accused my diff of being duff for a year before listening really hard to the bearings. Spinning the wheels I still couldn't hear it, but luckily felt the rumbling on my fingertips. As such it was a much easier fix than I expected and driving got much quieter from then on.
Steve Postins

Pull the battery tray cover and drive it to see if you can isolate the source. i.e. whether it's from the outside (where the wheel bearings are) or inside (differential). Maybe have someone else drive while you turn around in passenger seat or otherwise get situated near opening and move your head around to listen. My wheel bearings were intermittent and had a rhythmic nature and higher, slightly whiney tone but that might vary by type of damage. Mine were just slightly flattened on a couple bearings and did it only at a higher spead and not in reverse. I am not convinced it is your bearings. You might just check your diff fluid to see if it's down too low. Never know. It's easy to jump to conclustions and do work you don't have to. (Don't ask how I learned THAT one) Listen to everyone but make your own decision, like it seems you are doing, and diagnose carefully. Everyones facts are just a LITTLE bit different.

If it is the bearings then not too bad a job if you get an impact puller (borrow from Autozone or Checker) for the shaft and a two or three prong puller ( buy $10 one from Harbor Freight) for wire wheel hub, if you have wires. Otherwise a lot of banging with hammers and swearing goes on. Much easier with correct tools.
J.T. Bamford

Boy, I would think one would feel/hear a bearing problem by jacking the rear end up and then turning one of the rear wheels. This sounds like its coming straight from the diff. I do not have a rear seat on this GT so its just the battery cover insulating the sound - not much insulation. I will also check to see if there is anything loose back there (battery cable, etc.) Fluid was full, and there is no change in sound in turning one direction or the other. Haven't really checked reverse yet, need to find an empty parking lot.

If the bearing goes, what's the result. Trashing the other bearings? Any major damage that would be tough to fix? I imagine that when the bearing goes completely, it will just spin in the housing and cause a lot of friction. Still able to limp home if not too far.

Hate to waste the last few weeks of warm weather here in Michigan with the MGB up on jack stands.
D Gesse

At low speeds you may not even hear bearings depending on how bad they are. Mine were only at certain speeds in the 30-40 mph range, particularly decreasing speed with clutch in. Not sure on result if you don't fix but wouldn't test it if they are bad. Seems like you could ruin the surface they run on and now you have bigger and much more expensive problems. If you get organized you will be done in 1/2 day or long evening or less. Just my right rear one went. Asked a mechanic buddy and some bulletin board people and they said don't fix it (the other one) if it ain't broke (JDW quote). You might need to find machine shop with press to press bearing off and on though some people have managed to get them off or on themselves. I am just not that mechanically adept so do it the easy way where possible.

The battery cover may not be much insulation but it is some and diffuses sound. The closer you get and less between you and sound the more likely you can isolate it. I bet it's not the bearing but only believe your own ears. You might also try the tube trick where you use rubber hose to your ear and direct other end to various car parts to see where sound is coming from. Works on engine, seems like it would work on rear end.


JTB
J.T. Bamford

I have a 77B and the howling starts when I back of at about 90 MPH - its kind of a rump rump rump noise until i get below 75 then it smooths out. There was also a clunk noise that I picked up after I changed the rear shocks - after changing all the rear bushings and lubing the rear end I found out that I had the shock finger tight!!! Imaging how stupid I felt. Oh well now the thing handles like a dream. I would still like to know where the 90 MPH noise is coming from - if its from the rear bearings are they hard to replace?
JC Nelson

Okay, I feel stupid now. Prior to calling up a mechanic to rebuild the rear end, I decided to have one last look to see what was causing this noise. What prompted me was that I couldn't figure why the noise was a consistent frequency and volume regardless of speed (other than 0).

The previous owner had moved the battery from the battery trays (two 6 volts) to the rear compartment next to the spare tire. In doing so, he left the ground connected to the driver side battery tray and passed it through (and over) the u-joint on the drive shaft, into the passenger side battery tray, and then over the axle into the rear spare tire compartment. Apparently, the battery cable was riding on the U-joint and every now and then would catch and cause the "pop" sound I would hear. Otherwise, the metal to rubber contact would make this rumbling noise that the vehicle would move. When I removed the wire, I new I solved the problem as about half of the wire insulation was worn away right where it passed over the U-joint. Drove the vehicle last night after re-routing the ground cable and voila, no rear end noise.

Can I blame this on Lucas the Prince of Darkness? It was an electrical component causing the problem.
D Gesse

This thread was discussed between 05/09/2003 and 17/09/2003

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