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MG MGB Technical - 1976 MGB No Reverse

1976 MGB VIN GH5NUG3975099 Canada

I've been working on this MGB for the last week. It's been sitting for the last, probably 5 years or more. It took almost half the week to get it running, then the last couple of days rebuilding the Clutch Master and slave and running new lines. Now that it runs and the clutch works, it shifts into all 4 forward gears no problem, but there doesn't seem to be a reverse gear. Normally you pullover to the far left then back for reverse, but there is no far left to pull to with this stick, it just stays in the 1st and second line, any clues?
J Gagnon

I had a similar problem with a midget gearbox which had been sitting for a while. There is a reverse detent plunger and spring on the Midget 'box and the plunger had seized in its bore. A bit of penetrating oil down the bore and a few sharp taps on the gearlever in the direction of reverse and it was free.
I'm assuming there is a similar arrangement on the B but I haven't dismantled one...yet!
Dave O'Neill 2

As an update, it looks like it is #19 on this parts diagram

http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=144
Dave O'Neill 2

The spring load that keeps you from accidently selecting the reverse track is pretty stiff. Are you sure it doesn't just need a smack to put it over there?

Charley
C R Huff

Hi
As David has already mentioned, the Reverse Detent Plunger is probably the culprit in this instance, I have a 71B and had exactly the same problem as you,acess to the bolt is on the upper right hand side of the Gearbox. again as Dave suggests take it out and free it up, When replacing do not tighten the bolt too much,then go back to the gearlever and try if you can get it in reverse, if you can,t Keep backing the bolt out and trying the gearlever,until it slides into reverse easily,as it should. Check out the Youtube video John Twist of University Motors and watch the video on the Remote Gearbox linkage,John shows this Detent Plunger. WATCH THIS Video. Hope this helps you
M Brady

Thanx for all the info! Unfortunately the link to the video doesn't work. I've taken the top of the tunnel apart and removed the stick shift. The bolt that you are talking about is on the right side? I can see one that sort of angles down on the upper left side (Drivers side in Canada). How in the #@#$% do you access it? It must be stuck, because now with the stick out using a prybar on the remote control shaft, it still won't budge. I also discovered while I was underneath it, that this car has overdrive. One more question, can you get longer clutch slave cylinder pushrods? Mine seems to have alot of free play before engagement.
J Gagnon

A new pushrod will have a lot less play where the clevis pin passes through. Replacing the clevis pin , at the same time, wouldn't hurt either. Check the throwout fork were as well. Congratulations on discovering that you have an overdrive transmission! RAY
rjm RAY

As in another post there should be a spring inside the clutch slave cylinder that pushes the piston out to take up any play between piston and pressure plate, including where the clevis pin joins the push-rod to the release arm. It's this that keeps a consistent biting point as the release bearing wears down. You may be thinking of the clevis pin up at the pedal end, play there and ovalling of the holes in the pedal and the master push-rod *does* affect clutch operating by giving a low biting point.

If the push-rod were too short you would be pushing the slave piston out of the cylinder and fluid with it.

A longer push-rod may bottom the piston in the cylinder and prevent the clutch being fully engaged, hence slipping, as well as doing nothing for any play that shouldn't be there.
PaulH Solihull

Hello, try this link to the video.

http://www.youtube.com/watch?v=JWlzTemci7M

Cheers
Tony
Tony Oliver

Thanx for all the info. I removed the reverse detent bolt first and it came out with the spring. I then tried putting it into reverse and it still wouldn't go. Using the palm of my hand, I slapped the gear shifter towards reverse and after a few times it started to move and finally went into position. Climbing back into the pit under the car, I discovered the plunger had popped out and was caught by the wires going to the reverse switch (lucky for me!). I cleaned everything up and put the spring and plunger back into the bolt, holding the plunger in place with a bit of grease. There is no adjustment on this bolt, it screws into the housing and seals with a copper washer on the housing face. Now I tried reverse again and it goes in easily, too easily. It doesn't seem to have any resistance at all, I guess I'd better go and take another look. Maybe it's the plunger that activates the reverse switch that is stuck down not returning to position?
J Gagnon

I think the problem is the same thing I was talking about before. It used to be stuck out, and now it is stuck down. But, it is not the plunger and spring that you took out.

The one you took out is the detent for the fore and aft location of the shift rod. The one I am talking about is the lock out for the gate selection. I believe you will find it when you remove the shift tower.

Unfortunately, I don't think you can do that with the gearbox in the car. I've not tried, so maybe someone can say I'm wrong. You might be able to get the cap off (almost out of view on the right side of the pic) to shoot some penetrating lube in there.

If you can't get to it, try slapping the gear lever some more and see if it pops back out. If it doesn't, I would drive it for a while, being careful not to accidentally select reverse, and see if the oil, heat, and vibration free it up.

A pic is attached if it helps.

Charley


C R Huff

Hi, Well it does seem you are getting closer, It,s a real shame you can not see the video made by John Twist,because all would have been revealed to you, Access to the Reverse Detent Plunger doe,s not require you to take out the Gearlever, The image Charley kindly posted, is not the Reverse Detent Plunger, The magic bolt we are talking about is nearer to the bell housing side of the gearbox and is directly above the reverse switch,Look in your workshop manual and find the reverse switch above the switch is your magic bolt and adjust the bolt according to my previous post,the bolt charley has shown is for controling vibration of the gearlever,You will need a 5/8"wrench for the magic nut which should be accesable from underneath the car,Don,t forget to post when you sort it.
Malc
M Brady

Malc,

I re-read the posts, and now I'm not sure what the problem is. In the initial post, it seemed that the gear lever would not move sideways to get into the reverse gate. If that is the problem, I think that spring-loaded plunger in my pic is the problem. If it now moves sideways too easily, I think that might still be the problem, but now from the plunger not returning.

My gearbox parts are 12 miles from home so I can't go look to check. Also, that pic is a section from an overdrive box. I think the plunger in my pic operates the reverse lights and gives the resistance for getting into the reverse gate.

But, in the last post from J, it seems like it is the fore and aft movement of the stick that is the problem since he says it goes into reverse too easily, and moving it sideways won't put it in reverse.

If it now goes into reverse too easily, then it could be the detent that you are talking about, which I don't think does anything until after you move sideways to select the reverse gate.

I think we need some clarification from J, or at least I do.

Charley
C R Huff

It sounds to me like the detent plunger has now moved, but not returned.
Dave O'Neill 2

Thanx for all the help guys! It's fixed! When I got down in the pit yesterday, I started to remove the reverse switch. As soon as it cracked loose, I heard a little click. Getting back into the car, I found that it now was working perfectly. Must have been the rod that was stuck. When I had the reverse detent plunger out the other day, I had sprayed some penetrant in the hole, before I put it back together. Maybe that helped too!
J Gagnon

Hi Charley,
Watch the John Twist,University Motors video, 72MGB Gearbox Remote Control,where you will see the Reverse Switch and the magic bolt just above it. Well it seems we all did our bit to help J out, and that is what this Website is all about.
Malc.
M Brady

Malc,

I can watch it, but the sound died on my computer so I won't be able to listen to it.

But, J got it going so alls well that ends well.

Charley
C R Huff

Hi all,
I have a similar problem in that I've had the car for 6 months and am a car novice! I have replaced various bits and bobs (starter, alternator etc etc)and have got the car starting and running nicely but now I cannot select reverse.
When I first got the car it was quite difficult to engage and after a while seemed to free up, I just assumed I'd either got the knack so to speak, or it had just freed itself up, then a couple of weeks ago it got difficult again and now will not move over to the left.
Is there anything I can do without removing the gearbox from the car?
The other gears select fine, Help!!
Regards,
Graham.
G Morriss

If it grinds when you try to engage reverse with the engine running and the clutch pedal fully down then it is the clutch that isn't releasing, which can be for various reasons.

If it doesn't grind, just doesn't go in, then it is a problem with the selection mechanism.

The first can almost certainly be resolved without removing the gearbox (and engine ...) from the car. The second possibly not.
PaulH Solihull

Sorted! Watched that video and promptly unscrewed the indent jobby above the reverse light switch, a good squirt of WD40 and replaced it and success!! I now have reverse again.
G Morriss

Well done, GM. Another satisfied customer.

Charley
C R Huff

This thread was discussed between 19/09/2010 and 21/10/2010

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