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Discussion Starter · #1 ·
Hello! I'm a complete neophyte in the realm of Jags, but excited to have my dream car! I traded for my '67 420 last autumn, and only had the opportunity to drive it once, as the snow was starting to fall as it arrived.

At that point the car drive nicely, and the transmission shifted normally. Finally had it out for the first run of the year, and it won't shift from 2-3. The 1-2 shift is butter smooth, and the 2-1 is as well.

Can someone give me some advice? I have a shop manual, but either it's not clear as to probable causes, or I'm not understanding it. I contacted the previous owner who tried to explain about some sort of switch and cable, but it was above me.

Pictures, diagrams, or anything illustrating what I should be looking for and what I need to do would be most appreciated!
 

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It sounds like the kickdown might be sticking, i'm not sure on those how its done and whether its mechanical via a cable or linkage or electrical.

If your in the UK then G Whitehouse Autos might be able to offer some advise and/or parts to help, they are very knowledgeable on the earlier DG gearboxes in the MK2's.
 

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Also to mention that some old autoboxes start in 2nd and only use 1st when you manually select it. Are you sure that what you think is 2nd isn't 3rd? The workshop manual might tell you what RPM you should be at in each gear for each speed.

On the MK2's with the earlier box they do rev quite high at high speeds when in 3rd (top).
 

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Discussion Starter · #4 ·
Also to mention that some old autoboxes start in 2nd and only use 1st when you manually select it. Are you sure that what you think is 2nd isn't 3rd? The workshop manual might tell you what RPM you should be at in each gear for each speed.

On the MK2's with the earlier box they do rev quite high at high speeds when in 3rd (top).
Thank you for the reply! I am in Canada. It's reving about 4400 rpm at 100 kph. Several other members messaged telling me about a cable kickdown, and suggested I disconnect it to see if it shifts normally. If so, I've isolated the problem. If not, it points to an internal problem. I've been told to look for something similar to a brake bicycle cable on the firewall near the carb linkage. So I think I will begin my investigation here.
 

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Your gearbox will be the BW Model 8. It does have a kickdown cable which as you have said is at the rear of the carbs and is a bicycle brake cable type affair but I doubt very much if this has anything to do with your problem but if it is then it might be an internal gearbox problem.
The BW Model 8 has several different modes which can be seen on your nacelle. They should be marked as P,R,N,D,2,1
P is for park,
R for Reverse,
N for Neutral,
D is for drive and you should get all three gears changing.
1 is for a low gear hold and will not allow the gearbox to change in to third. Used for towing up or down steep hills. Used for engine braking.
2 is the opposite and will not allow the car to select first. Used in the winter to stop wheel spin on snow or ice.
My assumption would be that the selector on the dash is not engaging the gears correctly. There again is a bicycle type cable that runs from the steering column change to the side of the gearbox where there is a lever. Behind the steering column there is an adjusting mechanism that when screwed in or out adjusts the push or pull position of the cable and affects which gear you are selecting. If I was diagnosing your problem I would suggest that this is where your problem lies. When driving the car try at moderate speeds try moving the gear change lever up or down slightly to see if the gearbox will change from second into the higher gear. Obviously do not try and select reverse or Park whilst moving forward but moving the lever between the other settings whilst moving at moderate speeds is OK.
 
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do you have a switch on the dash that reads "Intermediate Gear Hold" ? That switch prevents the transmission from shifting to Third Gear. Toggle it to the OUT position.
 

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Yes my mistake as I have an S type that has a different Nacelle but as Jose has stated D2 is basically all gears,1st 2nd and 3rd. D1 is high gears starting in 2nd going to 3rd but will not engage 1st. L is for LOW and will only engage 1st and is for towing up hill or for locking in 1st when coming down hill. As far as I am aware and I have just been through the 420 Manual there was no "Speed Hold" on the 420 model 8 gearbox but it was fitted to the S Type and Mk2 that had the DG250 gearbox. (Also not fitted to my S Type with the BW35 gearbox) This "Speed hold" was a toggle switch to the right of the steering wheel on a RHD car (left side in a LHD car). It had a long handle about 1 inch long up and down black toggle switch. It is clearly marked with a round Nacelle which reads "Intermediate Speed hold IN OUT". If you can't see it sticking out of the dash wood then you don't have it. What this did was lock the gearbox into the gear that it was in ie. 2nd and would change up or down to 1st or 3rd.
Jose is right that the symptoms are the same but you should not have Intermediate hold on your gearbox.

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