MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Lost drive to rear wheels

1980 mgb roadster LE.
Driving home tonight I lost drive to the rear wheels. Put in gear and nothing happened. Engine seems fine but when release cluth no drive to the rear wheels. Got a tow home and some noises from rear axle area. Any one any ideas when I crawl underneath tomorrow.

Thanks
C Martin

Put the car up on jack stands, at least under the rear axle. Start the car, engage a forwards gear and see what the prop shaft is doing. If it is turning, but the rear wheels are not (or, if they are they can be stopped easily) look at a broken half shaft. I did that once with a Sprite, but have never seen it happen with a B.

If the prop shaft is not turning when a gear has been selected, it is a clutch/transmission issue.

Les
Les Bengtson

I had an MGA where a half-shaft broke and then nothing. There was no noise, just no power at the wheels.
Samuel Sullivan

Could you check for a broken half shaft just by jacking the back of the car up and turning a rear wheel by hand (GB in neutral)? If the opposite wheel doesn't turn (backwards!) then it's a broken shaft? If something is broken starting it might do more damage perhaps?
Simon Jansen

Actually I think with my way you'd want it in gear so the prop shaft won't turn?
Simon Jansen

Indeed you would, Simon, and only jack up one rear wheel, as with both up turning one usually turns the other in the other direction. You want two out of the three locked firmly in case whatever has broken has enough remaining friction to turn a free wheel or prop-shaft, but not propel the car. It would show whether the problem was in the axle (prop-shaft didn't turn) or OD/gearbox/clutch (prop-shaft does turn).

But even easier is simply to put the car in gear with the egine running, clutch released, and simply lean out and look underneath at the prop-shaft. If its turning, it's axle. If it isn't, it's OD/gearbox/clutch. If it looks like the latter out of gear just dipping the clutch up and down you can often hear the shafts in the gearbox stopping and starting. If you hear nothing try engaging reverse with the engine running and clutch released, I'd expect to hear something from the reverse gears if the clutch and first part of the gearbox was OK. No noises from anything would indicate clutch or gearbox input shaft.
Paul Hunt

Firstly thanks to you all for contributions - it is appreciated. Tried the clutch release and lean out (actually the wife helped - yes they do have their uses) and the prop-shaft turns. So probably the axle. Assume it could be crown wheel and pinion or half shaft? Is it better to start with crown and pinion or half shaft? If it's half shaft is it always better to renew both sides? Any thoughts appreciated and if anyone's ever in Esher, Surrey you must pop by.
C Martin

Hope for a broken halfshaft. It's much cheaper and easier to replace. The crown wheel and pinion are expensive and pricey to set up. RAY
rjm RAY

Paul, was talking to a chap at work who is much more experienced in car stuff than me and he suggested just what you said. Just jacking up one wheel. I love all the stuff I learn on the BBS :)

Be interesting to hear what the outcome is.

Simon Jansen

Impossible to tell any more until you remove the cover, then all will be revealed. Odd a 4-cylinder should break a half-shaft, the same ones are used on the V8 (albeit with a different CW&P) and even Perry Stephenson who fitted a monster blown nitro engine with 322bhp and 383ftlb to his V8 said there was no sign of twisting of the half-shafts when he subsequently fitted limited slip (http://www.youtube.com/watch?v=uiDVhKpwxVM but start at 30 secs). But then again a pal with a 4-cylinder broke one too.
Paul Hunt

I don't know if this might be your problem, but when I first got my B I removed the diff to tighten it up to stop clunking noises and found that the shaft holding the spider ( planet? ) gears was about to fall out. It's retaining pin had sheared. Maybe yours has fallen out.

Herb
H J Adler

I have now removed the cover and the pinion and crown appear to be doing what they should. On the cover one bolt (with the handbrake bracket) was a pig (hammer and chisel job). When I turn the left wheel it turns the pinion/crown but the right wheel does not. I now need the big socket to remove the castle nut on the right wheel to investigate further. Watch this sapce. Again thanks for the contributions.
C Martin

1 5/16" socket. If you have wire wheels make sure it is less than 1.8" outside diameter to fit inside the hub, it should be if it is 1/2" drive non-impact. It's tight, 150 ft lb, you will probably need a breaker bar, remove the centre cap from stud wheels or the spinner from wires and jack the tyre down onto the ground for undoing and retightening this nut. Both sides are standard thread i.e. righty-tighty lefty-loosey. The hub should be tight on a taper, I freed mine by tapping metal wedges between the back of the hub and the heads of the bolts holding the backplate on. You may need to disconnect the rear brake pipe to get the back-plate off. Refit the hub loosly, then tap on the back of it working round the hub and it should withdraw the half-shaft, bearing and bearing cap. Getting the broken end of the half-shaft out can be a fiddle, if it has broken at the diff end. Check the tapered collar on the half-shaft the oil seal runs on and replace if grooved or pitted. If sound remove it to refit to the replacement half-shaft. Might be an idea to replace the oil seal anyway, grooved side facing inwards, tapped in just flush with the face of the bearing cap. Grease the lip of the seal before fitting, even though in use it is lubricated with diff oil. If you have wire wheels when replacing the hub on the splines make sure the holes in the hub for the split-pin line up with the holes in the half-shaft!
Paul Hunt

When you are turning the left wheel is the car in gear? If not the driveshaft will turn but not neccessarilly the right wheel due to a slight drag on the brake shoes. RAY
rjm RAY

You said: When I turn the left wheel it turns the pinion/crown but the right wheel does not.

Did you do that under the conditions that Paul mentioned with the other two components locked? That is, car in gear to lock driveshaft and the opposite wheel on the ground or otherwise locked.

Charley
C R Huff

Hi Folks:

Question, is the gearbox an Overdrive? If so a possible cause(s); I have seen many late 4 synchro 3rd motion shafts that were sheared off, thus no connection to gearbox output; and there is the possibility that the drive inner section of the cone clutch could be damaged or shattered. Just some out load thinking!

Rich Boris 67B roadster
Rich Boris

Paul thanks for the procedure. I got a 33mm impact socket from Halfords (UK store) which fitted. It was a snug fit but fine. The bearing was a pig to get out but your point of loosley assembling the hub and knocking off worked but it took some careful bashing with a rubber mallet! And hey presto one broken half shaft. It had broken near to the hub end so I was able to get a long nose clamp on it to withdraw else not sure how I would have got it out. Not sure how it broke (I was just crossing a junction when it happened no hard acceleration etc.) Looking at the break I noticed a blue spot so I'm hopping it was a Leyland Friday afternoon job. Let's hope the left hand shaft was built another day! I'll try and upload some photos. Thanks to all for the contributions.


C Martin

Second picture of hub end. Whilst I'm here and everything is in bits any recommendations for painting the axle and brake hubs, spring etc. I need to clean the dirt/rust off but would like to finish with painting. Any suggestions.
Thanks to all.


C Martin

Glad to hear it was easily extracted. One thing I forgot to mention is the bearing and the new half-shaft. The bearings are a tight interference fit on the half-shaft, I've heard tell of putting the half-shaft in the freezer and the bearing in the oven (send the missus shopping for the day), but other than that it really needs pressing on by someone with the appropriate hydraulic press. When I changed my axle I gave up trying to get the old bearings off, let alone the new one on, and got the rebuilder to do it.
Paul Hunt

Paul, bearing came off with a bit of love and affection (brute force). Got bearing kits from Moss as they are reasonable. (some reason the kit is cheaper than just the bearing). Havn't tried to get it back on yet so here's hoping. Otherwise as you say I'll take it to a garage. Any recommendations on preparing/painting the drums, axles. They have surface rust and dirt and would like to stop any further rusting and smarten up. I've read about POR-15, Dinitrol and Eastwood rust encapsulator. Chap in Moss just said wire brush amd Waxoyl. I'd like to paint the drums but happy to clean and spray axle etc. with say Waxoyl Any thougts. Many thanks for your input it has been invaluable. I owe you a few pints.
C Martin

From the looks of that break, there was a flaw in the axle (unless it is just a shadow that makes it look like it was fractured almost all the way through for some time. Cheers - Dave
David DuBois

Could you give us a better close up of that break? Very odd place for an axle to break.
The Waxoyl approach is about the only practical way to clean things up, unless you want to take the whole car apart and not drive for seven years! Black barbecue paint works great on drums.

FRM
FR Millmore

Picture of break. I'm not a metallurgist but it looks like there was a flaw in the casting. Interested in any other thoughts from anyone. My only concern is to get it all back together and the other side to go. But if you keep thinking like that you would never buy an MG would you?


C Martin

I'd like to take FRM's suggestion a little bit further, just to warn you.

Most complete seven year restorations start with saying: "need to clean the dirt/rust off but would like to finish with painting".
Willem vd Veer

Ok it's much more fun driving it. I'll paint brake brake plate and drum and waxoyl the rest.
C Martin

I 'wire brush in a drill'-ed and Hammerite Smooth finished the backplate, just Hammerited the drum. The axle isn't going anywhere left as it is, it all depends on how much time you want to spend de-painting and de-rusting. Waxoyl is best left for cavities, water let alone grit abrasion is going to remove it, I wouldn't even put Finigan's Underbody Seal on the axle, just Hammerite.
Paul Hunt

Glad that it wasn't anything worse, broken half shafts are sort of a Spridget tradition, but like FR I think it is an unusual spot for a break, must have been a flaw in the metal from the beginning. As for removing a stub of a broken half shaft, here's a tool I once made up for that very job. Worked like a charm and made removing the broken stub quite easy.


Bill Young

Bill great tool I would never have thought of that. I have managed to get the bearing back on the shaft with spacer but it will not fit right down flush. There is literally a 1/8 inch gap between the bearing and the spacer/collar of shaft so the spacer moves slightly up and down. Will this be taken up when I torque down to 150 Ibs or do I still need to get it pressed into place. By the way I did the freeze shaft /heat bearing job. Nobody mentioned the grease in the bearing and how it would cook (burn). My wife was out but when she came back she asked what I had been cooking. Response was just some stuff for the dog. She gave me that knowing look. Lifes fun eh.
C Martin

Looks like a major inclusion. These are not castings, but forgings. The inclusion would have been in the center of the ingot the bar was drawn from, and the only part of that shaft that was driving you for a very long time is the bright part. Overdesigned and poor material.

Nice "getter" Bill! Made one meself once. Works on small dogs and kids too.

FRM
FR Millmore

You'll need to get the bearing pressed all the way down. Any shop worth their salt can do it in 5 minutes while you wait. RAY
rjm RAY

I think from memory (mine is coming up to be a 6 year 'need to clean the dirt/rust off but would like to finish with painting') I wire brushed my rear axle and POR15ed it. I don't really like using that stuff and rather prefer to get rid of rust than paint over it but on a rough lump of steel like the rear axle it worked well. It's so rough you can't easily get it clean apart from sandblasting and if you do that you must be VERY careful none of the media gets into the works.

Simon

Simon Jansen

All done and back together again. Used wire brush on drill and by hand, smooth black hammerite and then waxolyed. Lots of surface rust which actually came of quiet easily. Greased everything not near the brakes. Reconnected hand brake and brake pipe then bled, adjusted. All seems to be fine (touch wood). I managed to get the bearing fully down by resting on two large blocks of wood making sure they supported the inner race and gently hitting shaft with rubber mallet. Took some time but got there. Probably get garage to press next time.
Had to put wheel back on and lower car gentley without wheel nut to torque up castle nut, kept some weight on trolley jack and enough on wheels to stop them spinning. Lifted back up to remove wheel and insert split pin. Fortunately when I took the wheel off the split pin was lined up with a slot. Replace wheel and nut. Once again theanks for all your.
C Martin

This thread was discussed between 01/11/2009 and 08/11/2009

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.