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MG MGB Technical - Spinning Freely

After a drive around the block in my '77 MGB, sitting in the drive, a smell with accompanying light smoke from the right rear indicated rubbing shoes. (Several short drives since, but no smoke) With both rear tires off the ground, in neutral, with park brake adjusted for max cable slack, wheels would not spin freely, but came to a dead stop after attempting a spin by hand. Drag was obvious. Replaced shoes on both sides. While drums were off, spinning axle left or right gave the same results. Drag was obvious. Next move is to drop the drive shaft and spin again. What's my most likely problem?
F. Doyen

If the shoes are binding and causing the smoke why are you bothering with the prop-shaft and the diff? You say nothing about the foot-brake adjuster at the top of the back-plate, have you tried slackening this? In my experience (many BL cars over 35 years) they all rub slightly at one or more points in the rotation, which in theory could mean out-of-round drums, bent half-shaft, etc. etc., but adjusting so that they can be turned with light hand pressure through the rubbing points has always ben fine for me. At every surface I remove the shoes and put a thin smear of grease on every metal-to-metal contact surface of slave piston ends, shoes, backplates, handbrake levers, hand-brake cable etc. to give every assistance in pulling-off when the brakes are released. Stretched or missing pull-off springs can cause them to not fully pull off after being applied. When adjusting mine I belt the tyre in two or three places with a mallet, or tap the drum of the wheel is off, to help seat the shoes before rotating them to judge the rub. Even then experience has taught me that the V8 needs the adjuster one click looser compared to the roadster. When that is done make sure you can pull the handbrake up one click *without* the drag on the wheels increasing, to be sure there is minimum drag when it is fully off.
Paul Hunt

Sorry, Paul...I was unclear in my presentation of the symptoms.

Because I removed the drums from both sides and spun the axles, I thought I'd proven that the drag is induced by the drive train, particularly from the transmission back, since the car's in neutral. If the brakes are out of the equation, would you agree that removing the drive shaft would isolate the problem to either the rear end or the gearbox?

In the archives, someone had said he looked for 2-3 turns of the wheel after a hand spin. With the car on stands, fully assembled, I spin the wheels at about 30 mph and push the clutch in...the wheels stop within 1 second. Brake conditions: hand brake cable backed off 1 inch (max cable slack), brake adjuster beveled pistons touching in center (max brake slack), both sides.
F. Doyen

Doyen:

That’s a strange problem. Yes I guess I would remove the drive shaft as you suggest and recheck and isolate.

If the problem persists, and if it’s in the rear-end, then it would have to be a bearing. And if it is a bearing, then it must be really bad. Can you hear any rumbling sound anywhere?

Is this a new car for you, or have you had it awhile? That is, was it running ok before or unknown? Did somebody do something to the RE.

You got be curious…

Bryan


Bryan Prindle

I've never seen a rear axle which would spin freely by hand. There is a lot of drag either from the ring and pinion or the spider gears which is normal. Certainly not free like a front spindle. It doesn't sound like you have a problem now after you fixed the dragging brake shoess.
Bill Young

Bill, though a rear axle may not spin freely by hand, would you expect a tire at 30mph to stop dead within a second?

Bryan, no tell-tale noises. I've had the car 2 months. Had to correct numerous PO induced electrical problems to get to this point. License plate still has 1978 tag and 78k miles (2 years mileage?!), so if I haven't been scammed, it's been off the road for over 20 years. The car seems in excellent shape, though.

Fred
F. Doyen

FWIW Spinning by hand I get about one rotation of the wheel (back end off the ground, brakes backed off, in neutral). I thought I had more friction than was fair, but sorry, your story makes me feel OK again! Unbolting the rear end of the propshaft is quick and has to isolate the cause, as you say. Let us know what you find.
Steve Postins

Fred. I am somewhat confused by the comment, "would you expect a tire at 30 mph to stop dead within a secoond?". Is this happening with the rear brake system connected or with the brake drum off?

You seem to have had some form of problem, originally, as indicated by smoke and overheated smell. If the car has been sitting for years, it is perfectly possible that the brake shoes were not retracting properly due to binding. Checking through the braking system, as Paul mentions, is an excellent idea. Your master cylinder, caliper pistons and wheel cylinders may all have pitting or rust inside them due to the hydroscopic nature of brake fluid.

With the brake system fully functional, you can begin to troubleshoot the other systems and find if you have a problem. The only possible source of other than normal drag would be rust in the bearings/races within the rear end and in the meshing gears. Whether this would be a problem or not can be determined one of two ways.

First, there is some inherent amount of drag within the system. This seems to be common, even on cars which are in good condition and driven on a regular basis. Thus, as Bill mentions, the rear wheels do not spin freely as the front ones do. With this in mind, it might be perfectly possible that the rear end is in fine condition and you are not sufficiently familiar with what it should feel and act like to realize this. So, driving the car for a while, paying attention to what is happening and changing the rear end fluid a couple of times over the next several months may be all that is needed.

Second, there is the possiblilty of rusted bearings and/or races. The minor rust on gears, because it is seldom very deep, is not a problem. Significant rusting of these hardened parts would be a problem, but is seldom encountered unless there is water in the rear end or the parts have been removed and left exposed to the elements. So, bearings/races are the only real source of worry. Normally, these items do not fail in a catastrophic manner. Rather, they go bad more slowly giving increasing warning due to growling of the rear end. Driving the car will tell you if the condition is worsening. Feeling of the brake back plates and the area immediately inboard of them, will give you an idea if the bearings are binding and causing excessive heat build up.

If you do not feel comfortable with conducting such an experiment, you can tear down the rear end for inspection and see what you find. Removing the rear plate will allow you to inspect the gears for any rusting. Removing the two rear axles and bearings can be done at the hobbyist level and there is information in the archives on this. Same with the pinion bearing. If you have any doubts, it is possible to have the entire rear end professionally inspected and rebuilt. Les
Les Bengtson

It could also be a flex hose to the rear brakes that has gone bad from age. It could be retaining pressure and that would also add to the smoke problem.Break open a rear bleeder and see if the wheel then rotates easier. Hoses do deteriorate on the inside even though the outside looks good.
Sandy
conrad sanders


Sorry, gents. In this thread, I seem to have gotten you experts off in the wrong direction, due to my inclusion of a symptom I thought I'd shown to be irrelevant to the problem I am most concerned with. I included the "smoking right rear" as an explanation of what led me to find what appears to be a drag problem in the drive train. I believe I had a dragging shoe that caused the smoke, and I've replaced the shoes, but while I had the drums off, I spun the axles by hand, and I've tried to describe this symptom, independent of the brake issue.

Les, I spun the axle by hand with the drums off. After reassembling everything, I spun the rear wheels at about 30 mph. Brake adjust and hand brake were set to assure shoes did not contact the drum.

As the light smoke rose from the hub area, I felt behind the plate and found no significant heat.

Oil in the rear end is a deep, dark brown. I will replace the oil several times over the next several months, as you suggest.
F. Doyen

Fred - If the car has not been driven for a long time, it's possible that the rear wheel bearings do not have enough oil in them. The bearings depend on a certain amount of oil from the differential splashing up the tubes when cornering. A lack of oil combined with a crust of dry dirt could make the bearings (and possibly the seals) tight. To find out if this could be the cause, remove the brake backplates. It's not necessary to remove the brake components from the backplate -- just disconnect the hydraulic line. The bearings will be visible with the backplates removed. Look for dryness and signs of overheating. If they're not bad, squirt plenty of diff oil into them and/or pack the outside of each with grease before replacing the backplate.

Another possibility is that the pinion retaining nut has been overtightened, although my recent experience with this indicates that once the initial binding is overcome, the pinion rotates relatively freely.

If the car has not been driven in 20 years, you should consider replacing the rear axle seals in any case. Just be very careful of the pinion nut. See the archives for more info. -G.
Glenn G

Visible smoke should be accompanied by significant heat at the drum, enough to burn an unwary hand, it should also take a while to develop. If there was no heat then either the smoke was coming from further into the axle like at the diff, and only escaping at the drums, or what you saw wasn't smoke at all but dust. But driving the rear wheels with the engine at 30 mph, then knocking it out of gear, and the wheels stop within 1 second, is very wrong, in fact I'm surprised you can turn them at all by hand. I've not specifically timed it but I've done that sort of thing as part of other work and I'm fairly sure that with my drums on and the brakes correctly adjusted i.e. slight rub the rear wheels continue to turn under their own momentum for many seconds. With the propshaft off and the wheels off the ground and the brakes not rubbing i.e. drums removed it should take about 4 to 9 pound INCHES (not lb ft) of torque to turn the pinion flange. Either or both of the hubs may turn during this operation. If turning one hub turns the other hub the other way easily and doesn't move the pinion flange, but locking one hub makes it much more difficult to turn the other and the pinion flange, then the pinion bearing is the problem. If one hub is locked and the other turns the pinion flange easily, but with the other hub locked and the first released it is difficult to turn the pinion flange and free hub, then it is that half-shaft bearing or differential bearing that is the problem. Withdrawing that half-shaft and trying again will tell you which of the two bearings. Of course, that is for one stiff bearing. You could have anything from one two five stiff.
Paul Hunt

I've just come in on this thread and must say that it's one of the most confusing in a long time. I'm not saying that there is nothing wrong with this diff but I just have a hunch that it is OK. If you have replaced the shoes and the cylinders are OK, adjustment is correct then each drum should turn reasonably freely by hand with the wheel off. If you are happy with that I'd be inclined to run the car on the road the reason being that if it's as stiff as you say and there is a bearing at fault then that bearing will be really shot. This has to be accompanied by noise which is then reasonably easy to pinpoint. If there is no noise, heat or smoke I would be inclined not to worry but to keep an eye on it. Be careful with the brakes however as new shoes need to bed in and if you use them to enthusiastically they can smell or even smoke.

I suppose here I am once again saying don't tear it apart until you are really sure there is a fault and running it watchfully will help you pinpoint this
Iain MacKintosh

My experience with bad bearings has been, if your hearing is good you will know when you have a bad bearing. It will usually be louder than the engine.
I had a differential with a bad rear pinion bearing and it sounded like the car was going to self destruct. When I removed the bearing it had a few pits in the rollers. FWIW, Clifton
Clifton Gordon

Thanks, gentlemen. You've given detail that should help troubleshooting.

I recognize I could keep a watchful eye and wait for the weak link to show itself, but two things motivate finding the solution now.

1) If I turn the car over to the wife as her daily driver, I don't want her stranded because the latent problem revealed itself, and if she is the primary driver, I won't be able to watch it (she understands gauges and indicators, but not other forms of subtle communication).

2) This problem has another indicator I've not mentioned, because I've not quantized it. The mileage from my F150 pickup is between 16 and 18 mpg, and if she allows me to drive her car to work, I expect something much better. It SEEMS, though I've only run about a half tank of gas (fuel, petrol, etc.) through the MGB, the gas has gone too fast. If I cure this drag problem, I hope mileage will improve.

Thanks for your advice. I will work the problem and get back with you when I have something to report. I expect to drop the shaft this weekend.

Glenn, is your rear end supporting the aft end of a car, yet? If so, why not bring it to Aledo for a weekend drive?
F. Doyen

Fred - Yes, I put the axle back in the car last week, but now I've cut a big hole in the driver's footwell, where I'm doing some rust repair. Also, I still have to replace the right rear brake line, which I crushed under the axle while working on it. With all the other work I have to do on this project car, it may be next winter before I begin driving it. Oh well, the wait should make the experience more enjoyable. FM 1187 from Mansfield to Aledo is one of my favorite drives. -G.

P.S. Let me know if you need a replacement rear axle. I have a couple of spares.
Glenn G

IF my problem IS the rear end, I'm wondering if a rear axle kit (bearings and seals) should be a consideration? How difficult would the job be, and what tools will I need, beyond hacksaw and hammer? (There, there...it's only a joke...take your nitro pill and calm down).

Glenn, I enjoy 1187, but my favorite is FM5. I live 2 miles south of I-20 on FM5, just across the railroad tracks. There are lots of beautiful country roads in the area to enjoy with the top down.

With the driver's floor out in your car, would you say you have a Flintstone-mobile? You need to start building up the foot callouses, to get ready for that first drive.
Fred Doyen

Bearing (ho ho) in mind stiffness of rotation could be anything, like bent shafts or other distorted parts, as well as 'simply' stiff bearings, It is impossible to say how difficult it would be to fix. Most operations use the sort of tools any home mechanic is likely to have, but the Workshop Manual shows a case stretcher being used before you can get the diff out, and a pound-INCHES torque gauge to measure and set the pinion drag. However others have said this is dangerous and you should count the turns on the nut instead. However that would only work for something like replacing the oil seal, not if other parts have been replaced. And since I mention it the Workshop Manual, its Bentley equivalent, or possibly even a Haynes Manual, would be useful reading.
Paul Hunt

Fred:

Sometime you fail to mention the obvious. Since this is a new car to you and you may not be aware of it, on older cars the rubber brake hoses will swell up and plug causing the brakes to jam. Whether or not this is the problem and just as a matter of course, I would definitely suggest you replace all three of them. I have on every MG I’ve owned, and yes I’ve had this problem with my brakes.

It could be that yes you adjusted the brakes properly, but once you reassembled everything and then hit the brakes, you caused them to jam again because of the plugged hoses.

I also had a family PU do this; It took me weeks to figure out what was going on. When I finally removed the hose, you couldn’t even blow through it.

Bryan


Bryan Prindle

Paul, you've scared me, and since Glenn offered only an axle, rather than a rear end, I am going to evaluate all the options, like putting it under observation for awhile.

Bryan, my next task is to whip the brakes into shape, which includes new rubber brake hoses. Again, though, this is independent of the drive train drag I'm experiencing.

Though I've benefitted greatly from everyone's advice, I've held this thread open too long. Thanks for your help, and I'll see you in other threads.
Fred Doyen

You know, one way to decide if it's the brakes or not would be to remove the brake drums, put the road wheels back on, get it up on stands, run the wheels up to speed (30 mph is probably more than neccessary) and then see if it still slows to nil in one second. (Just don't touch that brake pedal.)
Matt Kulka

Fred - When I said I have a couple of rear axles, I meant the whole thing. Let me be more specific, since I'd really like to get rid of one of them -- I keep tripping over it. "Rear axle" is the term I use to describe the assembly of differential, housing, axle shafts, wheel bearings and hubs. I have two of these for sale, with brakes, to anyone who will pick them up. They are both wire-wheel rear axles, meaning they are about 1-1/2 inches shorter than rear axles for bolt-on wheels, although one has hubs fitted for bolt-on wheels. I'm hoping to get $50 for this one. For info on the other, and contact info, please see the Texas MG Register web site: http://www.tmgr.org/classifieds.htm . I just converted from wire wheels to bolt-ons, so I'm trying to find someone locally who wants to go the other way. Would really like to find someone with a/c parts or an overdrive transmission to trade. -G.
Glenn G

Matt, good suggestion...I'll try it.
Glenn, Jimmy Hilton told me about your wire wheels. I already have some, and I'm just looking for tires as my next purchase...but I don't recall reading about the rear end. I'll check it out.
Fred Doyen

It is unusual but I have discovered that some reliners put too thick material on the shoes. I have had them so large (literally) that on TURNED drums they still dragged... so bad I couldn't get the e-brake cable to reach.

Turning the axle without the leverage of the road wheel on there is not always an easy thing. Esp. if any of the other three points are stationary.

Good luck with the oil changes/careful road testing.

Mike!
mike!

This thread was discussed between 06/12/2004 and 10/12/2004

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