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MG MGB Technical - Axle breather question

I have a small leak from the right side of my rear axle, wetting the brake back plate. I have read about cleaning a breather, which I had a look at today. All it appears to be to me is a small plastic cap that caps an upright metal tube a couple of inches to the right of the differential.

Is this all there is to it? I was expecting a screen or filter or something. This cap fits pretty tight, and I am surprised that it would do any "breathing". I've attached photos below.

Erick Vesterback

"top" view of the cap:

Erick Vesterback

"Underside" view of the cap:

Erick Vesterback

well I didn't realise that the cap just lifted off I thought it with the tube were one piece and you had to unscrew the tube

is the tube clear of crud and oil?

I guess the tube and cap are made of some sort of plastic so trying to take the tube out it might be brittle and break so either a stout bit of bent wire or a mirror and torch to inspect
Nigel Atkins

The tube should have a hole right through it. It doesn't breathe through the hole in the end of the tube.

You can also use a small bar or a screwdriver through the hole to unscrew the tube, in order to clean it.

All the ones I've seen have been plastic.
Dave O'Neill 2

That's all there is, a screwed in plastic tube with a snap-on cap, with an air passage between the two. Is the "wetting" inside or outside? Assuming the greater is clear a leak on the inside (drum side) is the oil seal weeping. If the outside it's the joint between the axle and the bearing cap. Sometimes this leak will respond to "nipping up" 9/16" AF bolts. There isn't a gasket, it's metal on metal, sometimes with a smear of Goo. The oil seal can give up with age or if the bearing giving up.
Allan Reeling

The cap just pulls off the small tube. I thought the tube itself was metal, and welded onto the axle or something. I stuck a small diameter screwdriver into the tube and it went in unobstructed until it hit something solid. By the depth it went in, I figure it touched the axle halfshaft. So it isn't plugged at all. I just can't figure out how this could breath much, since the cap fits on pretty snug. Where is the air passage? Maybe I need to take another pic of the tube with the cap removed.
Erick Vesterback

Here's a spare one that I have...

Dave O'Neill 2

Dave, thanks for that pic. Now I know exactly what I should be looking for, it makes a lot more sense now! I haven't noticed a hole in the side of mine, so either it is blocked, or I haven't been able to get my eye in the right place to view it.
Erick Vesterback

Almost all off road vehicles have a rubber line attached to the plastic tube. The manufacturers run this line to the highest point of the vehicle to prevent the ingress of water and dirt. RAY
rjm RAY

Erick, They don't all have the hole. The later ones are a different design. The air space is there because the cap can't push all the way down. Get back to the oil leak, where is it?
Allan Reeling

The oil leak is running down the brake backplate from the axle. So, I presume it is a leaking axle seal. I also hear a high pitched squeak from this area for a few seconds each morning, so I have purchased a new bearing and seal, plus brake shoes and springs to overhaul the brakes in the process. The brake shoes on the leaky side have been contaminated with the fluid. The brake shoes on the other side are fine. Interestingly, there is quite a bit of friction material left on the shoes. The car seems quite light on its brakes, given that they have not been changed out in the 17 years I have owned the car, a full 40,000 miles later.

I will remove the breather and check it out. I will also attempt to remove the filler hole nut from the diff before I remove the diff drain nut. If that goes well I will change the oil with 80w90 GL5 oil.

Looks like I will need to remove the wheel cylinder and backplate to get the bearing out. I don't have a press, so my plan is to cut the old bearing off (taking care not to damage the shaft) by cutting about 90% of the bearing steel and using a chisel to split it. I have heard of heating the bearing to 200 degrees C, and putting the half shaft in the deep freeze, and that the bearing should go on without a press. Then refit the brakes, set the adjuster and bleed. And adjust the handbrake. Should be a busy morning...
Erick Vesterback

Erick, To do the wheel bearing you don't actually need to drain the axle. Just jacking up that side a little is all that is necessary.
Leave the wheel cylinder in place,, if you have a rubber flexible to the axle, clamp it (if you don't have a clamp use a self grip wrench and two sockets). Don't do this if you have braided flexibles, blanking off the the top of the master cylinder slows the flow down. Not sure about the angle grinder, heating freezing thing, sounds like potential disaster to me. Find a local garage and ask them to do the pressing. You might find getting the bearing out of the axle a struggle. I've used long bolts or studding, put the hub back on and used the nuts and bolts to press the half shaft out. You might be lucky they are sometimes loose enough to tap out with a mallet.
Also replace the other brake shoes as well!!
Allan Reeling

MGBs do seem to be very light on the rear brakes even though they have a static weight distribution of more balanced than most modern cars. The only time I've replaced any of mine in 60k on 100 car and 100k on the either, none of them being new when the cars came to me, was when I had leaking rear slaves that contaminated the linings. Since then the handbrake has been very poor, even though after a couple times lightly sanding down the high spots the shoes are showing even contact all the way round. Drums were cleaned with brake cleaner, and only a few minutes later showed light rusting!

Getting the hub off the half-shaft can be the first challenge. I tapped some steel wedges between the back of the hub and the heads of two opposite back-plate bolt heads and that worked well. With the backplate out of the way I loosely refitted the hub, and using a mallet on the back of the hub in various places the half-shaft with bearing and cap came out quite easily.

But unless the bearing is growling you only need to change the oil seal, I doubt the squeaking is from there if the oil level is correct. The cap can be tapped off the bearing with a drift and hammer, but you may be able to hook it while in-situ anyway. Also check the oil seal collar on the half-shaft, if this is grooved it can be replaced. This has the tapered section the hub bolts up to as well as the parallel section the oil seal runs on. It might look like it is part of the half-shaft, but a knife blade tapped into the back where it butts up against the bearing should shift it.

If you do replace the bearing I'd also advise taking it somewhere to have it pressed off and the new one pressed on.
Paul Hunt

OK, so I have pulled the bearing out of the axle,and it spins smoothly and has no play. So I figure the bearing is fine and not in need of replacement. The collar which the seal rides on has a shiny ring but there is no groove that I can see or feel on it, so it seems fine. I was going to put a smear of sealant on the halfshaft where the coller rests, but I can't figure out how to remove the coller. It rotates relative to the half shaft, very smoothly in fact, as though it is on a bearing itself but obviously it is not. So, it is not even loosely press-fit, but at the same time it will not come over the splines to come off the axle shaft. It has two gaps in the taper 180 degrees from eachother, I am guessing to allow the taper to compress when the hub goes on. However, I am concerned that fluid may leak from between the collar and the axle shaft - am I wrong about that?
Erick Vesterback

When the hub is bolted up to the taper on the collar, that seals the collar to the half-shaft, so there should be no leaks. It is designed to be a sliding fit with the hub not fitted, so it can be removed and fitted simply with the fingers. It's possible wear on the splines has distorted the splines slightly so they are now sticking up in the way. However with the correct 150 ft lb on the half-shaft nut there should be no movement between the hub and the half-shaft to cause wear, unlike at the splines on centre-lock wheels. But some people have reported that even with the nut done up correctly, the hub still moves relative to the half-shaft. That should not happen, so there must be some other problem.
Paul Hunt

I've resurrected this thread as I have just bought a breather that is significantly different.

I'd been aware for some time that V8s had an improved breather, that was subsequently fitted to all cars although the Parts catalogue doesn't show that. The air path is more convoluted, going up the side of the body instead of through holes in the side, and through an insert (B). This insert has a very small hole in the bottom that in fact doesn't allow water to run through under its own weight, although any that is lying in there on a hot axle will be sucked through as the axle cools. The insert has a groove across the top. The cap snaps onto the ridge round the body.


paulh4

This thread was discussed between 18/07/2014 and 06/10/2017

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