Why are these Spitfire gearbox's so weak ?

[Paul H]

21 minutes ago, thescrapman said:

Paul, Clive probably had the gearbox rebuild by Bob, who went to work for Mark O'Malley out at Stoke Ferry after Clive died.

one thing to try, disengage OD before changing from 4th to 3rd. Couple of my cars crunch if I hurry a change down with OD engaged. Seems to be worse with a J-Type box.

Don’t have that issue with my D box . The initial problem I had a week after the box was done was I couldn’t get into 4th gear so had to use 3 + overdrive . They sorted the issue but fobbed me off with the reason other than it wouldn’t happen again . I didn’t push them as it was the week Clive died. 
Paul

[Clive]

Historically, these boxes were not great when from the factory.

Back in 1986, when I was 20, I bought a dolomite 1500SE. Rare as anything now, and surprising I ever bought another Triumph.

Anyway, when purchased it had about 50K on it. But the clutch was slipping. The seller said he had just had a new clutch fitted by the local BL main dealer. And had the bill. A quick call confirmed they would sort the clutch. But the other issue was the box was crunchy and very noisy. I sourced a good used one, which the main dealer (or at least the mechanic fitting it) agreed to put back in. Slipped him a drink, and all good. But the mechanic did say that a lot of "these cars" needed recon gearboxes from 40k. He wittered on about marinas, spitfires too. All teh same gearbox. So yes, they had a reputation for being weak even back then. 

Yes, some do last 100k+, but probably driven with a bit more sympathy than the common and garden drivers of then new cars. But compare the innards to a ford box of the era, and the differences are obvious. The Triumph box has miniature components in comparison. Just not built for engines like the 1500, let alone the straight six (the vitesse/GT6 really should have used the big saloon box.....)

[DVD3500]

I "souped up" my MKIV with a Weber downdraft carb, better cam and exhaust headers ... the clutch was slipping so I replaced that too....

The first time I made a... "spirited" start after that the first gear shredded.... So gearbox out again...

I reckon the old clutch was slipping and making up for the weak first gear.

When I started my current project I knew I was going to get almost 100 BHP and/or LB/FT of torque so I called Mark Field late of Jigsaw and he sent me a 1500 gearbox that he says should handle it fine as long as I make sure to check the oil and be careful off the line...

We shall see... if this one blows I will likely go with an MX5/Miata 5-speed..

[wimpus]

So.. my main problem was no overdrive and then found the parts of the spacer on the drainplug.

 

Yesterday I had a go at fixing the od.

Bought the OD tool to remove the plugs under the sump of a J-type.

Still hard to get to as there is an exhaust in the way.

 

The pressure filter was indeed blocked.

Fitted my clean spare one & filled the oil.

 

Still no go.. nothing.

 

So tunnel out, the oil drained again in a clean container (to re-use again).

Solenoid was also working fine.

But found 2 parts of the relief valve that where stuck in each other.

Got those apart, gave it a good clean.

Blew through all the oilways to (thanks to my handy Volvo overdrive j-type manual and an old spitfire manual).

 

And .... it low works !

Tested the pressure to, bought a gauge in the US to test all the Triumph overdrives (mostly to fix a friend his one ..).

Pressure was around 315/325psi.

 

[wimpus]

A short video.

 

Look... the ground moves ! 🤣