Jaguar 420G gearbox issues

[GALAXIECAMMER427]

Hi all, I'm a new member. I'm hoping someone out there might be able to help me out. I have a '68 Jaguar 420G it has a Borg Warner Model 8 3 speed auto box. It will not go into third gear no matter what I do with the throttle. I have had the gear box rebuilt with new clutches, valve body, and pump. The gearbox place has now had the car for nearly 6 months, They can't seem to be able to get it sorted. al the external linkages have been adjusted and set up. As the gearbox has been rebuilt( I know it has, because I saw it on the bench with the new clutches installed) I'm now thinking that the problem is outside of the actual gearbox. This is not a vacuum operated box. it works solely on throttle position, and kickdown. Please someone help me out, I have definately lost the love for this car.

[hashluck]

Sounds like a linkage issue though you say you already looked at that and normally this stops the gearbox going back into 1st at rest.

Haynes Manual for these gives you a whole series of tests to do driving the car which helps pinpoints any issues.

In any case I would contact Graham Whitehouse in Halesowen UK

http://www.gwautos.com/

[GALAXIECAMMER427]

Hi Thanks for getting back to me so quickly. I have the proper Jaguar Manual, which gives a quite detailed list of problems and solutions, also oil pressures in at various stages of gearbox operation. The gearbox people that have the car, have been all through this, and still no joy. I would go with you that it sounds like something outside the gearbox, but all adjust have been checked and double checked Throttle linkage and Kickdown cable. Thanks anyway.

[MrAndyW]

Don't know if this relevent,but the Mk10 had a speed hold switch on the right hand dash, It kept the gearbox in 2nd or acted like an instant kick down,
I would imagine it would be the same wiring loom,so could poss be a problem there.

I've got the MK10 and 420G workshop manuals somewhere .( but not the Jags anymore)
Has it ever worked properly in your ownership or have you bought it like this ?

[hashluck]

MrAndyW said:

Don't know if this relevent,but the Mk10 had a speed hold switch on the right hand dash, It kept the gearbox in 2nd or acted like an instant kick down,
I would imagine it would be the same wiring loom,so could poss be a problem there.

I've got the MK10 and 420G workshop manuals somewhere .( but not the Jags anymore)
Has it ever worked properly in your ownership or have you bought it like this ?

That is a great shout! Those solenoids are very unreliable (or sometimes overdrive solenoids are ftted in error) thoguh normally that stops them holding in second rather than the other way round but it could easily be an issue in this area

[GALAXIECAMMER427]

Hi andy, thanks for the info. any idea where this switch is locted, the reason I ask there was a black push pull switch mounted on the RHS lower parcel shelf under the dash, like a muppet, I didnt know what it was for, checked to see if any voltage was present, which it wasn't, and disconnected the bloody thing, Although I cant see any reference to this switch in the wiring diagram, with regards to the solenoids, any idea where they are located. Thanks guys, it could well be you've got something there, like I said it would definitely point to something outside the gear box.Haveing been a Yank man up 'till now, not having owned any British Classics, I'm at a bit of a loss. These 420G's are a cow to work on, give me a good old yank any day!!!

[MrAndyW]

Will dig out the manuals and see if there's any info in there. I can't really remember if it gives locations of gearbox components.
Will have a look .

[GALAXIECAMMER427]

Thank Andy really appreciate it.

[hashluck]

Note all of these notes relate to a Mark 2 Jaguar with Borg Warner 3-Speed The Intermediate speed hold solenoid is mounted on the right hand side of the gearbox, screwed in with two screws. It has a rubber cap with the wires coming from this. It unscrews and comes out very easily. When energised I think it sends a rod into the gearbox which holds the gearbox in second gear. They can burn out very easily if the system is not set up properly but that usually means it will not hold the car in second. However I can see a scenario where if the rod were bent or the wiring duff or shorted then the solenoid would effectively be energised permanently.. I am really surprised your gearbox guys would not have found this though.

On the Mark 2 Jaguar the switch is like a paddle switch on the right hand side of the dashboard. Not sure on a 420G it could all be very different. For example the solenoid I am discussing is not listed as for the 420G:

https://www.sngbarratt.com/uk/#!/English/parts/bb6...

First things first I would wire that switch back up!

[GALAXIECAMMER427]

Thanks very much for the info. When I was under the car at the gearbox place, I couldn't see anything going into the gearbox. With wires on it.
As you say I would like to think the gearbox guys would have checked this. I have the Jaguar parts catalogue fo the 420g.and there in ferernce to a speed hold solenoid. In the link you sent(thanks) it does state mk 10 3.8, maybe this was not fitted to 4.2 cars/420G's

[MrAndyW]

Found the manuals, but don't really help to be honest. No parts locations, just a wiring diagram on the MK 10 and not shown on the 420G.
It looks like a normally open switch, i.e. the soleniod is energised when speed hold is selected.

So even with you disconnecting those wires from the switch you found it shouldn't make any difference.
Still can't help thinking that it's something to do with that speed hold area, if all the linkages are set up properly.

If the kickdown was a problem I would have thought that would affect 1st to 2nd as well.
Has it ever operated correctly?

Sorry can't be more help. They are beautiful cars, Hope you get it sorted and fall back in love with it again.
Will keep looking and see if I can dig anything else up.

Good luck and plese let us know how you get on. Andy

[GALAXIECAMMER427]

Thanks ever so much Andy. I really appreciate your time on this, if I ever get the thing back working correctly I might well fall in love with it again. I've also got a series 1 4.2 xj with a manual overdrive, which is a much nicer car to drive. You are right, the mk 10's and 420G's were lovely old buses. Not many left now.

[classic105]

Hi, do you solve your problem? or not?

if not perhaps you could check the governor.

if it is blocked or not work freely or not enough or too much spring tension, it can cause your problem and also dont shift at the righ speed too.

in fact it supply the right fluid pressure at the righ moment (speed related centrifugal system) to the 1-2 and 2-3 valves.

you can check it by removing the trap on the rear right of the box, 2 bolts one trap plate and a gasket.

you must turn the transmission shaft to turn it in the right position in front of the trap, be carefull not to drop a nut inside the box when you remove it.

good luck and let me know.

and oh i will forget, 420G are wonderfull underated jewel and set up correctly, drive like a charm and very reliable even sporty when it should.

my 2 chilldren's ask me every time i drive them to school with......so we are 3 childs into the car ahahah

[MrAndyW]

Back again !!!
Just found some good info, Don't know if you're gearbox guys have got it or not. There are 68 pages (double sided) I've taken a few photos to give you an idea.
If they're any use then I can copy and e-mail or print them off and send them.

[MrAndyW]

[MrAndyW]