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MG MGB Technical - Can't get reverse after storage

Hi,


I've been reading through your very informative web site, in particular with relevance to a problem with my MGB GT. I have been reading many posts relating to problems associated with the reverse gear and become a little bewildered with the various possible issues and solutions. My particular issue is that my GT has been tucked up in its warm dry garage towards the end of 2019 having worked faultlessly during that year. Yesterday 29th May 2020 I started her up (battery had been on trickle charge but needed to jump start it as battery cells had lost water). Gave it a good run (15 minutes or so) through the gears with no problem although didn't use overdrive. Oil pressure was good and engine temperature was normal. Back in the drive I attempted reverse but despite seeming to engage it failed to drive backwards giving a low wining sort of sound. My thought process is that a cause could be related to the months of standing idle, if so what could potentially cause the problem?


Best Regards


Alan Want
Alan Want

Overdrive either energised or stuck on - you need check whether there is power to the OD unit and if not and the OD clutch is stuck then get underneath and give the black brake ring of the OD unit a good hard thump with a hammer to free it off.

Don't reverse the car with the OD engaged - it will damage it.
Chris at Octarine Services

FWIW WSM says slipping in reverse, and freewheeling on the overrun, is caused by worn or glazed linings or a broken circlip on the sunwheel.

Whacking the brake ring is suggested to release a stuck OD, but if you didn't use OD on your drive then it's difficult to see how it could have got stuck.

If OD is powered then you would normally get a jolt just after going from 2nd to 3rd as OD engages - subject to wiring issues.

Checking for power can be tricky if anyone has been messing with wiring, even if you disconnect the normal source of power it could be getting it from elsewhere, or from damaged insulation if mice have been chewing wiring. Wiring is very different between 3-synch gearbox and 4-synch. The only sure way is to disconnect the solenoid wire underneath.

Personally, and if you can do it without needing to engage reverse, I'd try driving it switching OD in and out when in 3rd (4th needs more speed for the ratio change to be obvious). If that works as it should i.e. revs go up and down but the reversing problem still exists, then it looks like an internal mechanical problem.
paulh4

"If OD is powered then you would normally get a jolt just after going from 2nd to 3rd as OD engages - subject to wiring issues."

Not necessarily - the OD can engage while you are in neutral before you lift the clutch pedal - many times I have forgotten to turn it off and wondered why the car bogged down on changing up from 2nd.
Chris at Octarine Services

Firstly thank you for your rapid response. I decided to take the easy option to start with by taking it out for a run and operate the overdrive a few times in third and fourth. However, driving it out of the garage and onto the drive I decided to see if reverse would work. To my surprise it did! I still took it out and used OD which to begin with appeared to be a little delayed but after a few goes responded normally. I can only assume that something was a bit sticky after it's months standing idle, I was half expecting to have to give the fuel pump a wack to get that going but it sprang into life straight away.


I wish all problems could be solved as quick as that. Must keep running it more regular!


Thanks again


Alan
Alan Want

Alan,
good that it's going again - but I'd not leave it at that because if Sod's Law if you check everything will be fine but if you don't you may well regret it now or later.

The following, help or a lecture - you decide (what was that from).

Not using the car regularly causes problems and issues not using it for so long possibly more extensively and a great number - that's my first hobbyhorse done there.

Now for the second, oil level in the gearbox, have you checked, and what about the age and condition of the oil. Workshop manual has to change oil every 24-months or 24k-miles whichever is sooner.

This is your second run out in the car (15 minutes isn't really that long, 15-20+ miles is needed really) but even so as this is your second run I'd not expect the o/d to be sluggish.

If your oil is a good few years old (decades for some cars and owners) then a cleaning flush and/or thorough hot change of the oil (and clean of o/d filter) may prove very worthwhile.

What is the normal operation of o/d if it's not almost instant then it's not at its best.

O/d needs the load so when engaging and disengaging you don't dip the clutch pedal or lift off of the accelerator pedal.

All information on operation and servicing is in the Driver's Handbook. - https://www.mgownersclubstore.co.uk/catalog/Online_Catalogue_Handbooks_5.html

(Below is a example.)



Nigel Atkins

You have the choice by shimming the valve between quick and sharp or slower and softer. If quick (and sharp) is 'best' for you then that is a personal choice. Slower and softer is not an indication of a defect - unless it takes more than a second to engage.
paulh4

Almost instant was perhaps a poor description, I mean quick but not sharp but certainly not a second or more to engage.

I've been in with others driving their cars with o/d and there's a second or two delay and they say it's normal because that's what they know and are used to, same as dipping the clutch and/or fully lifting off the accelorator.
Nigel Atkins

This thread was discussed between 30/05/2020 and 31/05/2020

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