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 - Thread size for manual gear knob

Just received my birthday present (a new knob !) more technicaly a new manual gear shift knob for my 1970 MGB (not origional style but timber)from Moss.
Labelling clearly states for MGA & B, although someone has hand written 8mm on the box.
Looking at the knob I presently have fitted (after market timber knob)and it now appears obvious that the previous owner has drilled out the nylon bush and forced it on, he may have had the same problem. Now I know why my current knob continues to turn around.
Measured the thread on the shaft and it appears to be 3/8" diameter can someone advise me of the thread size ?
D G Levy

Hi,

From memory, the thread is 5/16 UNF. Modern cars appear to have standardized on 10 X 1.25 mm, which would be close to that 3/8". If it is a standard gearshift, though, I would expect it to be 5/16". 8mm is close to 5/16", so the fact that the box has 8mm on it could be that it is 5/16". Just gently try it.

Herb
Herb Adler

DG. There were two thread sizes used with the four syncro transmissions. The early rod was a single piece and the ball section has two vertical cuts, one on each side, to fit projecting bolts, in the shifter recess. This early gear shift had a 3/8"-16 UNC thread. This gear shift lever looks like it could be fitted to the later (side filler) transmissions with no problem. This is the gear shift lever your transmission should have if you have the top filler tranny as original.

The second form of gear shift lever, the one made with the rubber insert (which can deteriorate over the years) uses a 7/16"-20 UNF thread. In addition to being made in two pieces, joined together by a rubber insert, the ball section has only a single vertical cut in the side and the transmission has only a single locating bolt. (This single bolt is why the early model lever might be used in the later model tranny without modification to the tranny or lever but the late model lever can only be used in the late model tranny without modification to one of the systems.)

These measurements are made within the last ten minutes from two examples in my collection. I do not have an example of the three synco gear shift lever to check out for thread size. Whether the three syncro and early four syncro gear shift levers use the same thread would be useful to know. If anyone has a three syncro and could add the thread size to the information here, it would be available in the archives for future reference.

Les
Les Bengtson

Hi Les et Al,

The thread dimensions I gave, above, are for a 3 synchro box.

Herb
Herb Adler

DG

The MGA and early MGB (3 synchro with chrome gear lever) used a 5/16"-24 thread. So if the box states both MGA and MGB then the knob is probably 5/16"-24.
Steven 67GT

Be aware that on 3 sychro gearboxes non standard gear knobs can cause extra transmission noise. I got a wooded one with an inlaid MG badge from B+G and the zssss from the gearbox went up. I went back to the OE plastic one and its lot quieter.
Stan Best

Thanks to all for the quick reply. I assumed that one imperial thread size would have been used for the old MG's and a metric size for the MGF, It appears it is not that simple.
At present I am waiting on a origional looking Knob, which is what I origionaly was after, ordered from E-Bay it will be interesting because there was no choice on thread size, the wooden knob will be returned to Moss.
If need be I will take a more careful OD measurement and borrow a thread gauge from work to sort it out.
David Levy

David. If imperial sized nuts are still available in Oz the simple solution is to pick up a 3/8"-16 UNC nut and see if it will thread on easily. If so, you have the correct shifter for your model year. If the nut is too small, you may have the later model shifter, which can also be checked if you can find the 7/16" UNF to try.

As to the shifter knob, over the years I have lathe turned 1.25" aluminum round stock to make up MGB gear shift knobs as gifts to friends. I like them better than the factory made ones and it allows you to make the knob so it will fit lower on the gear shift lever, making for a slightly shorter throw.

Les
Les Bengtson

As Les has done I have 'turned' wooden gear knobs of various woods, ( Probably the same in the USA, there are some lovely hard woods around her in Australia, with crazy wood grain patterning, or figuring on them as they sometimes say in the rifle stock world. ) And to make things easier I sometimes just jam a plastic tube into the centre, which allows any thread to be cut into it. Unfortunately, then can somestimes work loose with spirited driving! I pulled the whole lever out of a ford box once!. Mike
J.M. Doust

I had the same experience that Stan described (noise & vibration) when I switched to a wooden knob several years ago. I even tried filling the hollow wood knob with expanding foam, which helped a little but eventually purchased a new plastic knob, as orginal. Problem solved. The knob on my 1972 has a 3/8-16 thread.
Joe Dufresne

This thread was discussed between 10/03/2011 and 11/03/2011

MG MGB Technical index

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