Bob Horner Posted April 24, 2021 Report Share Posted April 24, 2021 Hi all Further to my thread re slipping overdrive, I picked up a recon overdrive box off EBay. The seller said it was from a mk1 Gt6 and said it had been uprated byFitchetts 2 years ago. I thought it would be worth swapping for my current box and overdrive. Anyway, I spotted it was a J type rather than D type and I assumed the overdrive was the uprated bit but it seems it is a dolomite three rail as when I got it home, the spline is different and the number on the case suggests it’s from a 1850. What clutch plate will I need to fit it? Is it as simple as that? Bob Link to comment Share on other sites More sharing options...
johny Posted April 24, 2021 Report Share Posted April 24, 2021 you will need the later 1850 fine spline friction plate as the rest of the clutch is the same. However if you want to mix and match clutch components is another matter... Link to comment Share on other sites More sharing options...
Mathew Posted April 24, 2021 Report Share Posted April 24, 2021 Off the top of my head the wiring is a little different and check the length for the propshaft! Link to comment Share on other sites More sharing options...
johny Posted April 24, 2021 Report Share Posted April 24, 2021 yes I think Ive just seen the picture of the one you bought and it looks like its fitted with the single rail rear components so will be an 1" longer than a standard 3 rail D type box.... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted April 24, 2021 Report Share Posted April 24, 2021 6 hours ago, Bob Horner said: Hi all Further to my thread re slipping overdrive, I picked up a recon overdrive box off EBay. The seller said it was from a mk1 Gt6 and said it had been uprated byFitchetts 2 years ago. I thought it would be worth swapping for my current box and overdrive. Anyway, I spotted it was a J type rather than D type and I assumed the overdrive was the uprated bit but it seems it is a dolomite three rail as when I got it home, the spline is different and the number on the case suggests it’s from a 1850. What clutch plate will I need to fit it? Is it as simple as that? Bob Dolomite 1850 with J-type is a straight fit, bar the wiring for the overdrive which no longer requires a relay, just linked in to the reverse light circuit. I have one myself which did not fit the saloon engine the car originally had but fitted the GT6 Mk2 engine it was uprated with. Clutch is the Dolomite version which fits the splines so if the box number is 1850 then that's the clutch to go for. Link to comment Share on other sites More sharing options...
daverclasper Posted April 24, 2021 Report Share Posted April 24, 2021 Mike Papworth mentioned that TR7 clutches also fit? Link to comment Share on other sites More sharing options...
johny Posted April 24, 2021 Report Share Posted April 24, 2021 Unfotunately I think its this one which looks as if looks to be a combined 3 and single rail unit... Link to comment Share on other sites More sharing options...
Bob Horner Posted April 24, 2021 Author Report Share Posted April 24, 2021 Thanks for all the responses. Does anyone know the overall length of the standard gearbox plus overdrive so I can measure and compare? Bob Link to comment Share on other sites More sharing options...
Bob Horner Posted April 24, 2021 Author Report Share Posted April 24, 2021 I’ve just measured the length of the gearbox casing from the bell housing to the edge that meets the overdrive.. This is exactly the same for the std gearbox as the modded one. Thus the only thing that can lengthen it is the length of the j type compared to the d type. My understanding is that this is the same because with a bit of machining you can fit a jtype,to a std Gt6 gearbox? Link to comment Share on other sites More sharing options...
thescrapman Posted April 24, 2021 Report Share Posted April 24, 2021 The adaptor between gearbox and OD is an inch longer. the picture Johnny posted is of single rail gears and main shaft in a 3 rail casing. A fairly easy swap, and a much stronger setup. Just needs a shorter prop shaft. you can also get an original 3rail j-type in an early 1850, using the shorter main shaft as also fitted to late Mk4 Spitfire. It has the smaller tip bearing. 1 Link to comment Share on other sites More sharing options...
68vitesse Posted April 25, 2021 Report Share Posted April 25, 2021 I have a three rail with large main shaft tip and fine input shaft fitted with a J type which is the same length as another I have with small tip and coarse input shaft and j type. When I have swopped them the only thing I need to change is the clutch plate. 14 hours ago, daverclasper said: Mike Papworth mentioned that TR7 clutches also fit? Early 4 speed gearbox fine spline, think later five speed is a rover unit. Regards Paul Link to comment Share on other sites More sharing options...
johny Posted April 25, 2021 Report Share Posted April 25, 2021 Yes Paul think you have the best set up there with a hard to find thin adaptor and a specially made 1" shorter large tip mainshaft (which are not available new at the moment)... Link to comment Share on other sites More sharing options...
68vitesse Posted April 25, 2021 Report Share Posted April 25, 2021 Overdrive bit temperamental last few days so cover off check wiring all seemed ok so decided to remove solenoid, already have a suitable spanner, but its earth connection was under a difficult to acess nut. After an extensive struggle to reach it used a pair of long nosed pliers to pull wire out of terminal, surprisingly easily. Several squirts of brake cleaner inside solenoid which can dry over lunch. O ring sizes on Buckeyetriumph. Regards Paul. Link to comment Share on other sites More sharing options...
johny Posted April 25, 2021 Report Share Posted April 25, 2021 Work of the devil as far as Im concerned😜 Link to comment Share on other sites More sharing options...
68vitesse Posted April 25, 2021 Report Share Posted April 25, 2021 3 minutes ago, johny said: Work of the devil as far as Im concerned😜 The devil and covid makes plenty of work for idle hands. Regards Paul Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 25, 2021 Report Share Posted April 25, 2021 thats good so many dont realise the working bit is ...inside they just change the body 0 rings and it doesnt improve +1 for buckeye Link to comment Share on other sites More sharing options...
Peter Truman Posted April 25, 2021 Report Share Posted April 25, 2021 is that a Dowty washer, my J types have always had plain thin copper washer, obviously extra thickness doesn't impact. Link to comment Share on other sites More sharing options...
68vitesse Posted April 26, 2021 Report Share Posted April 26, 2021 10 hours ago, Peter Truman said: is that a Dowty washer, my J types have always had plain thin copper washer, obviously extra thickness doesn't impact. Yes it is, always been there in my ownership. Regards Paul Link to comment Share on other sites More sharing options...
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