MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

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 - Popping out of third

Been driving my car for almost 500km now and working out it's quirks. Slightly seeping freeze plug, heater valve body unscrewing (I have a quarter turn ball instead of the normal one), I think my tappets need redoing since it's ticking away like a sewing machine and soon will do the first oil/filter change and retorque everything.

The most annoying problem is it occasionally pops out of third. Only when on the throttle overrun when the car is pulling high vacuum (I love my vacuum gauge - it's a very interesting instrument). So if I am coasting down a hill off the throttle it sometimes pops out of third. If you clutch in and reengage it you get a little grinding of the gear as it goes back in. As if the clutch wasn't pressed in fully. It's not very often though and I am planning on rebuilding a OD box (currently I have no OD) I have soon anyway. Just interested in the cause.

Simon
Simon Jansen

Hi Simon,

Join the club. It's very disappointing to do all that work and find that the box is crook. With mine it always jumps out of 2nd on overrun, and occasionally out of 3rd.
Also synchros on 2nd and 3rd don't work, so double D'ing all the time.

My solution, rather than spend money on an old 3 synchro box, is to fit a Nissan Bluebird box. 5 speed all synchro, and it's almost a direct swap. Some fiddling with the cross member and drilling of dowel pin holes, modified drive shaft and speedo cable and possible change of starter motor. Cost to buy all the parts, so far, around $Aus 300. Starter motor $Aus180 plus the mods to the driveshaft and speedo cable.

I was offered a 4 synchro box, but fitting it to my Mk1 was a lot more involved than fitting the Nissan box.

At the moment I'm waiting on viewing another guy's MG, who has done this, so I can better appreciate what exactly is involved.

Herb
Herb Adler

You have a worn out synchro hub or possibly a weak retaining spring. Most likly a worn out synchro hub. The 4 synchro conversion is a fairly easy swap. Mine required very little modification and it was an od trans as well. The od is a great invention and it makes driving an MG something very special. RAY
rjm RAY

Hi Simon,
A common problem on $ syncro boxes. An easy fix is to lower the box (rear X member)Take out the inner detent spring bolt & replace the spring with a 22H75 spring from a 3 syncro box - shortened 1.5mm. The later box - possibly yours - had a plunger on top of the spring & a ball under it whereas the early box had the spring & a ball nosed plunger. The plunger can be withdrawn with a magnet stick on the side of a 1/4 bolt. It is bit awkward if the car is only on stands.
Garth
Garth Bagnall

Simon-
Let's check the simple stuff first. Inspect both the bushing on the end of the gearlever and the bushing in the top of the selector lever. If either of these bushings is worn, then you will not attain the correct amount of engagement travel of the synchronizer hub, which can in turn result in the car popping out of gear.
Stephen Strange

Are you sure about that? Surely gear lever travel is limited by the socket it fits into, not by the gear lever itself. That's why a missing bush causes the gear lever to flap about. My V8 came to me with it missing, but I never had any problems of jumping out.
Paul Hunt 2010

This thread was discussed between 01/06/2010 and 09/06/2010

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now