Back axle and panel light switch.

Technical MGB discussion
Dave Wheatley
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Forename: Dave
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Location: SW Scotland

Back axle and panel light switch.

Post by Dave Wheatley »

Just joined up, so here goes. Bought the car last week, GT reg. October 1978. I appear to have an oil leak at the rear hub, and on consulting the workshop manual there seem to be 2 different types of axle, 3/4 floating and semi floating. Anybody know which type is likely to be on my car?

Panel lights not working. The panel light dimmer rheostat is seized solid which is probably the cause. I can't get the knob off to take it out, and will probably have to smash it and go for non adjustable panel lights unless I get it off.

Thanks for the forum here. I will in all probably need more help here, but I've been messing around with old cars since 1960 (1946 TC), so I may be able to chip in with generic help here in future.
Thanks, Dave
1978 MGB GT
1967 Morris Minor convertible
1972 Ford Cortina
No modern!
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Peter Cresswell
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Re: Back axle and panel light switch.

Post by Peter Cresswell »

Hi Dave
Welcome to the forum.
All GTs had the semi floating axle, which is also known as the tube axle. It was made by Salisbury tranmissions. The crown wheel and pinion and diff are built into the casing by removing a cover plate on the back. They are a very tough axle and replacing the oil seal is fairly straightforward (Haynes manual is ok), but check the one already fitted has been fitted the correct way round. The oil seal lip should face outwards, and also there is a cone shaped collar which must be in good condition. You can get all the parts from any of the main suppliers, including from some a bearing kit which contains the oil seal should you think the bearing also needs changing.

If the rheostat doesn't turn then that is likely to be the problem with the panel lights. According to the parts books the rheostat is 'Control Panel Lights' and is part No BHA4278 and it is common to all MGBs. Not easy to get to though! This might help: http://www.mgb-stuff.org.uk/electricste ... gaugelight, and if you go back to www.mgb-stuff.uk you will find loads of useful info under 'Spanners' in the black box on the left (under the Union Jack).
Pete
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965
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Peter Cresswell
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Re: Back axle and panel light switch.

Post by Peter Cresswell »

The bearing from the early roadster axle (3/4 floating or banjo axle) was often fitted to TCs and helped stop the halfshafts from breaking. The bearing carrier needed a bit of modification as the bearing is a double race instead of single. I used to race a TC and standard halfshafts were then ok at 130bhp!
Pete
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965
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Charles Farran
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Re: Back axle and panel light switch.

Post by Charles Farran »

Hi Dave,
The dimmer thermostat has always been viewed as worth than useless as with the original guage bulbs they are poor lightwise before using the dimmer.
Before removing / obtaining a replacdment you han simply move one of the female connectors off the back to the same side as the other one & you should complete the panel light circuit assuming the internals of the dimmer have broken down. Many of us have now replaced the guage bulbs with LEDs which i think are an excellent upgrade! ( If you go down that route, then if you want to be able to dim then you will need to have a more up todate dimmer as well as dimmable LEDs.
Cheers Charles
1980 Roadster
Dave Wheatley
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Re: Back axle and panel light switch.

Post by Dave Wheatley »

Thanks Peter and Charles.
Regarding the oil seal my workshop manual for the semi floating type definitely says "lip facing inward". I'm glad it's not the 3/4 floating axle. My Standard 10 is like that. It took a 16 ton "press" to get the hub off the halfshaft!

Once I've fathomed out how to get the knob off the rheostat panel switch I will dispense with it altogether.

Another thing, I'm suffering from running on - only a couple of bumps. I've read the thread on here, and I'm wondering what this mysterious "anti running on valve" is, and if indeed I have one. Round here there is no super uleaded, so at the moment I'm chucking in "lead substitute".
1978 MGB GT
1967 Morris Minor convertible
1972 Ford Cortina
No modern!
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Charles Farran
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Re: Back axle and panel light switch.

Post by Charles Farran »

Hi David,
There is a tiny hole on the knob of the dimmer switch just behind the knurled rim. If i recall rightly if you use a small blunt nail you can press a spring in on the spindle & the knob should pull off.
Cheers
Charles
1980 Roadster
Dave Wheatley
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Joined: Fri Sep 28, 2018 4:55 pm
Forename: Dave
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Location: SW Scotland

Re: Back axle and panel light switch.

Post by Dave Wheatley »

Charles Farran wrote:
> Hi David,
> There is a tiny hole on the knob of the dimmer switch just behind the
> knurled rim. If i recall rightly if you use a small blunt nail you can
> press a spring in on the spindle & the knob should pull off.
> Cheers
> Charles

Ta for that Charles. I'll have another look tomorrow.
1978 MGB GT
1967 Morris Minor convertible
1972 Ford Cortina
No modern!
Vic Butler
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Re: Back axle and panel light switch.

Post by Vic Butler »

David, anti run on valves were fitted only to USA cars and maybe other exports.
When I bought my 1977 BGT in 1979 it ran on badly but I tuned it out.
Don't have that problem with mine now, running on HS6's and a Stage 2 head.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
Dave Wheatley
Posts: 182
Joined: Fri Sep 28, 2018 4:55 pm
Forename: Dave
Surname: Wheatley
Location: SW Scotland

Re: Back axle and panel light switch.

Post by Dave Wheatley »

Vic Butler wrote:
> David, anti run on valves were fitted only to USA cars and maybe other
> exports.
> When I bought my 1977 BGT in 1979 it ran on badly but I tuned it out.
> Don't have that problem with mine now, running on HS6's and a Stage 2 head.

Thanks Vic, the manual that I have is a USA one, so that explains it. My car only gives a couple of 'bumps' after switching off. I am a bit suspicious of these new fangled HIF 4 carbs, so I may look around for some older ones!
I'm not sure if any mods have been done to the engine, so for now I'm assuming it's standard.
What's the feeling about hardened valve seats? I've had my Standard ten for a good few 000 miles now, and it doesn't have hardened seats, and I keep an eye on the valve clearances which haven't changed in that time. I will be using the MGB as primary transport, perhaps it might be advisable to do the seats? They may well have been done already.
Dave
1978 MGB GT
1967 Morris Minor convertible
1972 Ford Cortina
No modern!
Vic Butler
Posts: 669
Joined: Wed Dec 21, 2016 6:07 pm
Forename: Vic
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Location: North West Hampshire

Re: Back axle and panel light switch.

Post by Vic Butler »

Dave, just keep an eye on the valve clearances. The only way to check whether the head is unleaded is to remove it. You could use an additive, Castrol Valvemaster is reputed to be the best.
If and when the head needs removing at any time then you can check if it's been converted and have it done if not.
I'm very pleased I ditched the HIF's on my car in 1981. HS's are less complicated and much easier to work on.
If not already done it would be worth fitting plain throttle discs to your carburettors. It is easy but a bit fiddly and can be done in situ if the dashpots and pistons are removed and the opening to the manifold blocked with a clean rag.
. Vic
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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