The other is for top gear - that's the one in the overdrive circuit. If the two switches aren't accessible when the gearbox is installed in your car, check they are working first and if you have to replace them, check the replacements work. I've not heard of problems in Jaguars, but MG owners, their cars have nominally the same devices, often have to replace/adjust them with a spacer.

 

I don't plan on using the overdrive, but it does need to be tested. The city fuel economy is 18-20 mpg, highway is 22 mpg, not to bad for a 60+ year old engine. I could see using the overdrive for highway driving, but not so much for city.

 

Overdrive (or a fifth gear in general) is nice to have for cruising and allows a rapid down change for overtaking. O/d top pulls adequately down to 40 m/h. In a light vehicle, it's not unreasonable to use the reverse switch on the gearbox as an inhibitor and make the overdrive accessible in lower gears. Though, with a JS or CR Moss box, the overall ratio of overdrive 3rd is very close to direct top.

 

I had an MGB GT V8 with overdrive in 3rd and 4th. Ideal for overtaking as already stated and often I would use it on "A" roads where I never touched the gear stick just kept flicking the O/D on and off through 3rd and 4th.
My father in the 1960s used to sprint and hill climb a 3.8 Mk2 and he set the O/D up so it worked in all forward gears. He would set off from the line in a standing start in first and then flicked the O/D into what is the equivalent of 2nd and this would get him up to about 60 mph without having to change gear using the gear stick or clutch.

 

The 3.4 came with a Delco generator. Were original 3.4 generators, Delco or Lucas?

 

When did Jaguar stop using the scroll-type pump on the rear main?

 

All of the eleven 2.4, 3.4 and 3.8 Jags I have owned used Lucas generators.
I suspect your Delco is a "ring in".
I did convert a couple of these cars to alternators. I recommend this to owners who have major generator failures such as burnt windings and poling where bearings have failed as the cost to rebuild the old generator can be eye watering.

 

So the Delco is an aftermarket replacement part, correct? There's probably not much value in one of the Delco generators is there?

 

The water pump is leaking a few drops of coolant. It's time for a rebuild or replacement. For rebuilding the pump, the manual refers to using "water resistant jointing compound". Is that pipe joint compound?

 

Not sure it is worth the hassle of rebuilding the water pump when they only cost £94 from EBay. https://www.ebay.co.uk/itm/224463631...R3MLaFoHAAAAAA
A rebuild kit is £50.

 

It's a job I have to do on my car as the pump is locked solid. While you're working on it, it's worth replacing everything that's consumable such as hoses, if you haven't done so already, and also flushing the cooling system.

Make sure the sealing surfaces are good and the gasket sits well between solid metal surfaces otherwise coolant can leak into the engine oil via the timing gear.

 

Cass
Would like to have been able to buy the new water pump you recommended in post #290 but on closer inspection of the site, the company does not post to Australia.
Even if they did the cost of postage would almost, for sure, have doubled the quoted price.
Ah, well, we in the "colonies" will just have to make and mend.
Cheers

 

The water pump I have was new (NOS), the bearings are in excellent condition, it's the seal that's bad. I've located a replacement seal based on the original seals size, that would be a cheap fix. However, all the rebuild kits I've seen come with a replacement impeller, they must break during removal. I'll experiment with a worn out 4.2 pump I have, maybe the impeller can be removed without damage.

 

Bill, Have you looked at the Davies-Craig electric pumps? Some owners have used the small version to help their Smiths heaters.

 

All the re-builders have a jig to press off impeller without damage. The new impeller, is a new design that was supposed to be more efficient than the stock one. The re-builder that I used in Oregon has retired so don't have a recommendation.
Rgds
David

 

Peter
No and I was simply remarking on how expensive and difficult it is to get parts for us in the antipodes.
In regards the heaters I live in a sub-tropical climate and a heater is way down on the list of needs.