Spit / Gt6 Gearbox Questions

[kartman24]

I have the engine out of my car at the moment and while I am at that stage I thought I would replace the tired gearbox that has poor synco on 2nd and reverse.  The diff in my Fairthorpe is a 4.1 in the Standard ten axle, I am stuck with this as the better ratios all take larger splined shafts so 1st gear is pretty redundant. The engine and box are 1300 Spitfire, I had a hunt around my stash of parts and found that I have a close ratio Spit box and a GT6 box amongst my parts, both have a better 1st gear ratio, the close ratio box feels a bit rough when turned so I took the top off it and found a bit of rust on the top of the gears where they had not seen the oil in the bottom of the box for 25 years. So I thought I would use the GT6 box which has good ratios but have found that the splined area on the input shaft is a larger diameter than on my Spit clutch plate. I have had the bottom end of my engine lightened and balanced during the rebuild so I can`t change to the larger GT6 clutch, I am stuck with what I have. If the GT6 box was dismantled would a spit input shaft fit the casing and the GT6 mainshaft? Short of that I guess I will have to take the close ratio box into a gearbox rebuilders and see if he can clean the gears up...............Martin

[Nick Jones]

What do you mean by "close-ratio Spit box"?  There is no factory close-ratio Spit box but there have been quite a few made over the years by using a GT6 box and modifying it's input shaft to match a Spit one.

 

Assuming (!) both GT6 and Spit box are 3 rail and 4 synchro then the main shaft and casing are the same but all of the gears are different due to the different ratios.  Dependent on their relative ages things like synchro hubs, baulk rings and all the little bits and bobs may be the same, but some care is needed as detail changes were made at various points.

 

The gears should clean up provided they are not too pitted.

 

Nick

[kartman24]

The `close ratio box` came off the back of a 1300 which was purportedly SAH tuned race engine which was on twin 40 carbs, I was told the box was a close ratio unit. The gears appear to be 2.8, 1.8, 1.3 and 1.00, these are approx as it was done with a chalk line on the input shaft and rear flange. The box is stamped GB, I will be taking into a local gearbox specialist who deal with classic cars to see what he thinks about rescuing it...................Martin

[Nick Jones]

Then possibly (even probably) the close ratio Spit box is basically a GT6 box with a modified input shaft and you may be able to raid your GT6 box for spares if needed.

 

I wouldn't take too much much notice of the stamped prefix - it only tells you what it was when it left the factory - anything could have happened since then!

 

Nick

[kartman24]

The 1st gear ratio is definitely not the same as that of the GT6 box so I don`t think it just has GT6 internals but hopefully I can get the two boxes over to them next week and see what they can do.

[oldtuckunder]

The `close ratio box` came off the back of a 1300 which was purportedly SAH tuned race engine which was on twin 40 carbs, I was told the box was a close ratio unit. The gears appear to be 2.8, 1.8, 1.3 and 1.00, these are approx as it was done with a chalk line on the input shaft and rear flange. The box is stamped GB, I will be taking into a local gearbox specialist who deal with classic cars to see what he thinks about rescuing it...................Martin

 

Those ratios make it almost certainly a Vitesse 1600 box

 

1st        2nd         3rd         4th

2.93      1.779     1.254      1

 

These were stamped HG as far as I'm aware no box was ever stamped GB, does it have syncro on 1st?

 

Alan

 

Have sent you PM also

[Nick Jones]

Ah, good spot! Was too lazy to look that up!  Will be 3 synchro if so.

 

If 4 synchro then it might possibly be based on some other non-Triumph BL confection such as Marina or Ital.  

 

Nick

[Atomota_Man]

Hi Martin,

What clutch diameter are you using, 6½� When fitting a GT6 gearbox into a Spitfire motor, the input shaft needs to be shorted by 1†if it is not ready. I believe that the clutch plate, with the same diameter but with the correct 1†x 10 spline center, was then sourced from another car.

You cannot fit the input shaft from your close ratio 3 synchro Vitesse gearbox into your GT6 box. Both shafts have the same number of teeth, as the ratios are the same, but the gear will not mesh with the GT6 laygear as the helical angle was changed on the GT6 gearbox. The only gear that remained the same from the 1600 Vitesse to the GT6 gearbox was 3^rd gear (part no. 132097). The original 1600 Vitesse input shaft (part no. 208820) is also 1†x 10 splines and 1†longer than Spitfire input shaft. Your close ratio Vitesse box has a special input shaft (part no. 211000) with the 208820 gear on one end and the 7/8†x 10 spline Spitfire input shaft on the other…….Frank

[kartman24]

Hi Frank, have just noticed your Atomota Man user name, I like it! Things have moved on gearbox wise, I took the herald box with the Vitesse ratios into a Classic car gearbox firm about 30 mins from here and he gave it a good look over. He could sort it but due to the level of corrosion on the teeth which had been out of the oil for 30 odd years the gear box would certainly be noisy in use, one of the selector forks was very heavily worn as well. He reckoned over £400 to completely strip/clean and repair where necessary and the box would still be noisy due to pitting in the gear teeth, so I passed. Having now looked at the casing number on what I thought was a GT6 box it is in fact a USA spec Spitfire box with the FK number. It has the round propshaft flange which would mate with my propshaft but the input shaft is a larger diameter. Can this box be adapted to fit my Herald 13/60 engine, the bell housing is different but I am assuming that is interchangeable, I am stuck with my flywheel and clutch cover plate as they have been balanced along with the crank. The ratios seem quite good compared to the earlier UK Spit boxes..............Martin

[Nick Jones]

I'm confused again......

 

As far as I can see an FK gearbox is the US spec MkIV gearbox (equivalent UK one would be FH) and as such should be a pretty ordinary 4 synchro, 3 rail box with the "4 cylinder" ratios.

Bell housing and input shaft should be the same as std 13/60.

 

It is entirely possible that the FK stamping is a complete red herring and represents only the casings first life and any combination of 4 synchro bits will fit in any 4 synchro casing including bits from the the later single rail gearboxes.  Does the input spline have  coarse or fine splines?

 

Possible it has Marina/Ital guts?

http://www.canleyclassics.com/technical-archive/close-ratio-gearboxes-for-spitfire-mkiv1500

 

Any pics?

 

Nick

[Atomota_Man]

Hi Martin, if your input shaft has a larger diameter (1†x 10 splines) you probably have GT6 gears inside. The bell housing is different, in what way, the GT6 one? Yes, the bell housing is interchangeable. If you used a bell housing from an earlier 3-synchro gearbox you will need to swap out the front cover seal housing for the one in the other bell housing as it uses a proper oil seal. Check the input shaft length, needs to be the same length as the Spitfire input shaft. As for the clutch plate, perhaps you could contact someone like Borg and Beck, they do have a technical support line (or one of their vendors) and ask for the part number for a 6 ½†diameter clutch plate with a 1†x 10 spline center. I believe that the 4-synchro gearbox is also a bit longer than the 3-synchro gearbox so your propshaft may need to be shortened. BTW, the propshaft used in the MG Midget 1500 is same length as the propshaft in the mark 1 EM…..Frank