Four synchro gears in three synchro casing

[Josef]

So, I’m pretty sure I’ve seen at least one retailer offer to rebuild three synchro small chassis type gearboxes as four synchro units. Having now disassembled both types myself, it doesn’t look like you could fit the internals of a 4 sync box into a 3 sync case. Anyone tried it / otherwise know for sure? Just asking out of curiosity really. 

[Clive]

cases are indeed different, so no, it can't be done.

I believe many suppliers used to supply 4 synchro in exchange for 3 synchro boxes. After all, who would prefer a 3 synchro box? 

[PeteH]

Also, out of curiosity?. When aproximately did the factory change from 3 to 4? and in what cars?. I learned early on about "double clutching" to get 1st on the move. Art once learned not forgotten?. Even taught SWMBO, when she learned to drive, Our mini van had no second gear at one point. A "weekend engine swop" with one from the scrappy solved that for a while.

Pete

[Clive]

all heralds, vitesse 1600, spitfire 1-3 are all 3 synchro.  (or were)

[johny]

Certainly my 2L Vitesse with standard 3.89 diff hardly needs first gear so it wouldnt be too difficult to do without synchro on it...

[Colin Lindsay]

Original instructions for the Herald were to use 2nd, 3rd and 4th gears only as driving gears, so you would move away from static in 2nd; first was for very steep hills and hill starts only. Not much point in putting synchro on it, I suppose.

[Pete Lewis]

well back in the 60s and earlier 1st was really an emergency low for nasty hairpins like on porlock hill 

start off on the flat in 2nd was standard practice on so many makes not just triumph 

I added/rebuilt   a 4 sync to the 1600 but now cannot remember what case we used 

and changed from coil to diaphragm clutch both add up to Better !!

Pete

 

[PeteH]

Once reversed up Sutton Bank, 1st would`nt cope, kept stalling. (Mk1 Ford Consul).

Pete

[Casper]

Quote

Original instructions for the Herald were to use 2nd, 3rd and 4th gears only as driving gears, so you would move away from static in 2nd; first was for very steep hills and hill starts only. Not much point in putting synchro on it, I suppose.

Yes, but the change to 1200 was accompanied by a big hike in the diff ratio.

I'm pretty sure my car has a 4 synhchro converted from 3 synchro by Mike Papworth

C. 

[PeteH]

By co-incidence on my way home this a.m, from having the Camper MOT`d, Stopped to fill, and got talking to a bloke I know. He had a Dolomite Engine/Gearbox swap into a Herald some years back? that was a 4 syncro, he said?. Is that Do-able?.

Pete

[Colin Lindsay]

1 hour ago, PeteH said:

By co-incidence on my way home this a.m, from having the Camper MOT`d, Stopped to fill, and got talking to a bloke I know. He had a Dolomite Engine/Gearbox swap into a Herald some years back? that was a 4 syncro, he said?. Is that Do-able?.

Pete

Very do-able; Spitfire gearboxes and the like, and similar Dolomite boxes, being more refined(!) are a straight swap.

[johny]

Just have to check some of the ratios as there are differences...

[Josef]

On 15/04/2022 at 07:13, PeteH said:

Also, out of curiosity?. When aproximately did the factory change from 3 to 4? and in what cars?. I learned early on about "double clutching" to get 1st on the move. Art once learned not forgotten?. Even taught SWMBO, when she learned to drive, Our mini van had no second gear at one point. A "weekend engine swop" with one from the scrappy solved that for a while.

Pete

The Spit went 4 synchro for the MkIV (so 1970ish), the 2L Vitesse and GT6 were always 4 synchro I think. The 1500 RWD had the same box as the Spit IV (I know that as I’ve just rebuilt one of each, YC and FK serial numbers).

[Josef]

2 hours ago, PeteH said:

By co-incidence on my way home this a.m, from having the Camper MOT`d, Stopped to fill, and got talking to a bloke I know. He had a Dolomite Engine/Gearbox swap into a Herald some years back? that was a 4 syncro, he said?. Is that Do-able?.

Pete

Swapping a 3 sync box for 4 sync, yeah no problem. That’s exactly what I’ve just done on my 13/60. The later box is a tiny bit longer (5/8” or something like that) so requires a bit of loosening/wiggling of engine mounts and so on. The rear flange is also a touch larger so the prop shaft needs a matching flange fitting. 

[Colin Lindsay]

1 hour ago, johny said:

Just have to check some of the ratios as there are differences...

I was assuming (always a mistake on my part!!) that a gearbox from any other model fitted to a Herald would be an improvement in ratios!

[johny]

Well I think its quite possible to put in a later gearbox which was set up to work with a 1500cc engine and then find you have to slip the clutch when pulling away in your 948 Herald☹️

[Peter Truman]

I thought (a dangerous action as Colin attests to) that the 3 rail 3 and 4 syncro gearbox cases were similar except the 4 cases had the 3 tension springs at the front that preload the layshaft thrust washer?

As I want another 3 rail case to convert a Midget single rail overdrive box for my Vitesse I'm interested in the discussion. When I converted a box for the daughters Spit I used a GT6 case.

[Clive]

7 hours ago, Peter Truman said:

I thought (a dangerous action as Colin attests to) that the 3 rail 3 and 4 syncro gearbox cases were similar except the 4 cases had the 3 tension springs at the front that preload the layshaft thrust washer?

As I want another 3 rail case to convert a Midget single rail overdrive box for my Vitesse I'm interested in the discussion. When I converted a box for the daughters Spit I used a GT6 case.

Did Australian Midgets have overdrive? UK ones never did, though many have used spitfire ODs into the cars.

Some 4 synchro boxes don't have the springs, very idd stuff happened in production, like some 1500 spits having scroll front "seals"

If the midget box originates from a spitfire, none of the gears (including the first motion shaft/layshaft) will be interchangeable. I have seen a 4 cylinder gearbox bolted to a six cylinder engine. They used teh 4 cylinder bellhousing (plus engine backplate? or are they the same) , and some bodgery to mount the starter. No reason that wouldn't work, but you lose the far superior 6 cylinder gearing, and need a different prop. 

But the cases are different between 3 and 4 synchro boxes. 

 

[Josef]

8 hours ago, Peter Truman said:

I thought (a dangerous action as Colin attests to) that the 3 rail 3 and 4 syncro gearbox cases were similar except the 4 cases had the 3 tension springs at the front that preload the layshaft thrust washer?

As I want another 3 rail case to convert a Midget single rail overdrive box for my Vitesse I'm interested in the discussion. When I converted a box for the daughters Spit I used a GT6 case.

The difference I spotted immediately (and he reason I started this thread!) was that there’s a major change in the casting at the rear of the case. The 3 sync box has a big chunk of metal between the reverse and lay shafts that the long bolt to retain the lay shaft locates in. It looked to me, by eye, that this would not allow you to get the 4 sync 1st gear and corresponding lay gear in to the case as one or both would foul on this bit of the casting. 
 

Neither of my 4 synchro cases have the preload springs you’re describing (both are 1972). I believe though KC, KE, KF, FH, FK, HC, DG, YC and WH cases are all functionally interchangeable for 3 rail 4 sync gear sets (info from here), presumably with detail differences, though the gear sets are not necessarily identical. FH, FK, and YC at least I know all should be the same ratios (Spitfire compatible). Providing of course they still contain the gears they left the factory with!

[Peter Truman]

My 68 Vitesse Mk2, 4 syncro gearbox is original and has the pre load springs as does the GT6 4 syncro case KC18564 which I used in the MG Midget 1500 single rail internals conversion for a Spitfire 3 rail 4 syncro box with J Type overdrive.

Unfortunately I didn't keep the old MG single rail box case, but it had the antitorque cross bar in the rear gearbox mounting bracket to stop the gearbox hitting the MG transmission case.

The MG Midget 1500 engine I brought with the single rail gearbox had engine number FP51151F.

I also have a Dolomite 1850 single rail J Type overdrive box number WH6345 as a spare to fit into the Mk2 Vitesse, once I've found a suitable 3 rail (4 syncro) case to put the internals into.

 

[johny]

Will you use the single rail as is being an inch longer than a D type or shorten it Peter?

[Pete Lewis]

my 64 3 sync  HB   box had the three damper springs  , these just reduce gear train backlash rattle at idle 

damper springs in the clutch hub can have the same tuning to reduce this normal racket 

simple old school test to check what the noise is to just give 3rd a push to make the baulking contact and load the gear train 

if it goes quiet is backlash rattle if it doesnt its something else 

later boxes without the 3 was probably  driven by  cost reduction 

Pete

[Peter Truman]

38 minutes ago, johny said:

Will you use the single rail as is being an inch longer than a D type or shorten it Peter?

Yes with J type it Is 1in longer and I believe you can use the longer single rail adapter J type adapter. When I used the MG single rail internals with the GT6 case I had to add a 1 in annulus to the Spit IV 3 rail adapter.

[johny]

That adapter might need a bit of modification but should be ok so just got to hope you can squeeze the extra inch in the chassis without too many problems👍 

[Peter Truman]

I brought a special prop shaft from Rimmers for a J type in a Vitesse ref No. RVG998 it’s 42.75in compressed and 44.25in expanded