gearbox exchange

[rudi]

I intend to exhange my 3synchro/A-type OD box for a 4 synchro/J-type OD(less vulnerable to oil leaks, more reliable). Now,to my confusion, I have been told (by a gearbox:OD specialist in the UK) that a 4synchro/Jtype will not fit the original mounting points on my TR3A because the total length is about half an inch longer. A 4synchro/A-type however would fit.

This is in contradiction with the information in all the literature (how to improve.., how to retore... etc) I have read. Can anyone of you confirm or denie this from his own experience?

Next discussion is the front extension cover. I have replaced my clutch on the original box by a diaphragm clutch some time ago together with a matching new release bearing.

On this topic I was informed now that the long 2 3/8" front extension should never be used with a diaphragm clutch but the 2" cover (also mentioned in the Moss catalogue). Although I did not change the front extension on my original box the clutch is working perfect. What is the truth and if it is true what problem can I expect?

[marvmul]

The overall length of the later gearboxes (o/d and non o/d) is some 8mm more,because of the ticker (and stronger) flange of the bellhousing to the gearbox, but the sliding coupling of the propshaft will cope with that, so there is no problem.

The mounting arrangement of the gearbox to the chassis is different and you have to fabricate a new mounting. Moss is selling a kit, but I don't know if you can use it in a sidescreen car. The J-type o/d is more troublefree than the A-type indeed and most J-type boxes have less wear than the older A-type gearboxes especially if you can find a saloon box.

[rudi]

I am pretty sure that a lot of sidescreen owners shifted to a 4 synchro box. So it surprizes me to see so little comment on this subject.

Marcel, it is strange though that in any literature I could find  is mentioned that a 4 synchro box with or w/o OD would require a re-arrangement of the mountings when fitted in a sidescreen TR, this as long as it is a TR OD and not a saloon type OD, thin or thick flanged. When I study pictures of the 2 boxes I intend to believe that the overall length is the same. In fact the flange has the same thickness and the thicker parts are reinforcements that do not influence the overall length. Hence it would only require longer bolts to fit to the engine.

Anyone any comment on the long or short front extension cover?

[marvmul]

With thicker flange, I meant the mating flange of the bellhousing that is bolted to the engine : you need longer bolts indeed. This makes the box some millimeters longer, but it doesn't matter. The gearbox rear mounting is the same for all the TR's,from TR2 to the TR6 of 1972 I think. A saloon and a later TR6 with J-type o/d have a different arrangement for the rear gearbox mounting.

 

If the longer front extension for the release bearing doesn't touch the diafragm spring of the clutch cover (you surely would hear that), there can be no problem and I know it from experience. I think you shouldn't do the reverse : use the short extension instead of a long one : perhaps the release bearing can slide of the extension too far and get stuck when actuating the clutch.

[marvmul]

Rudi : on page 62 of the new TR6 Moss/Rimmer  catalogue, you can see the differences in the rear casings of the A and J type O/D (no flat piece with holes on the J-type) and a 'overdrive conversion bracket kit' is listed to allow the fitting of a J type o/d box to an  A-type chassis (TR2 - TR6 1972) : part no 211361X.

[rudi]

Thanks Marcel. See you at one of the next races, in Zolder perhaps?