The 'E' Type Forum

Hi
I have just bought a 1971 S3 v12 and have gearbox
Changing from third to second and back erratically
Could this be the vacuum hose, frayed pipe?
And is this a simple fix.
Appreciate any advice
Regards
John
This is my first post

John : I cannot think that any vacuum hose would have anything to do with it, although IIRC the Model 12 does have a quite sophisticated aneroid device which varies transmission response according to atmospheric pressure . The very first thing to do is to check the fluid level using the procedure set out in the manual. If you haven't got a manual you will find the procedure set out in the knowledge base on this site for 2+2 6 cylinder cars, and in nearly all respects it will be similar for your car . If the fluid level is correct , and the fluid is the correct pale pink and does not smell of burning etc, then the next thing to consider is the kickdown cable . If a temporary disconnection of the cable stops the problem then it is probably just a matter of adjustment - lengthening would be more likely than shortening

I should have a good read of the various checks you can make without special equipment - running through the gear selector positions etc to see that the box responds as it should do

Hi John...welcom to the forum.....do you have a service manual....there is a road test & fault diagnosis section that would be worth following through Series 3, has a vacuum modulator. If the vacuum line comes loose, it will rev up a lot before shifting gears kind of like giving it full throttle.....Steve

I would support the other suggestions - in order - check oil level using the correct procedure which is:

Warm car and auto transmission to proper operating temp - take it for a drive to do this. Park on level ground with handbrake on and in Park. Leave engine running at normal idle. Pull transmission dip stick out and clean the level marks. Reinsert dipstick fully home and immediately pull out and read fluid level. The difference between low and full is 1.5 pints - do not over fill.

I have driven my car with low fluid and it does cause major issues.

You mention - trouble changing from D to 2 (if by kickdown) then if fluid level is correct I would be checking the kickdown system - switch on the throttle pedestal on top of the engine etc and the cable.

If manually changing from D to 2 than check the adjustment on the cable from the lever to gearbox - when you move the lever it may not be fully going into 2.

Check all connections on the side of the gearbox.

If these are OK and you still have issues then I think it will be time for an expert.

Cheers

Garry

Cheers guys
Took her out for a run today it's ok if you put your foot down, changes ok and slowing down is ok. It only happens
On slow pulling away.
Gearbox fluid is fine, I will check the vacuum hoses
First and take it from there.
Many thanks guys
John

Hello John.
I have just completed a complete "nut and bolt" refurbishment of my 1973 series 3 Roadster. During which I dropped the gearbox oil pan and cleaned the filter, there was some sludge in the bottom of the pan which I cleaned. I refilled the gearbox with Castrol QTF as specified in the service manual. Today when test driving the car I have experienced what I believe is exactly the same problem that you are experiencing. At relatively low throttle openings and low load the gearbox appears to either jump between gears or the clutches slip. When I reduce throttle or increase throttle each side of this situation the gearbox performs normally until it reaches another similar throttle opening/load situation when the symptoms reoccur. During the refurbishment I inspected the vacuum control unit at the rear of the gearbox which is connected to the left hand inlet manifold, the manual describes a setting procedure using oil pressure gauge and vacuum gauge. This may be the problem, I will try rectifying fault and give update.
David.

John.

Update on my series 3 auto gearbox problem, found it was intermittent fault with kickdown micro switch making contact.
Suggest try disconnecting the spade connectors to the micro switch which is situated under a metal plate at the end of the accelerator cable, insulate any bare connections and test drive.
Also ensure that you check ATF oil level with engine warm and ticking over, I used castrol QTF to refill mine as recommended.
Regards David.

Do you mean TQF ?