Vibration when changing gear (auto)
 

Hi all,

I have a Mk2 R75 V8 automatic which has covered 39K. I'm getting a vibration from the back of the car when it drops from 3rd into fourth at between 50 and 70 mph when briskly accelerating.

It's an odd one as all the auto gear changes are smooth and it won't do it urban speeds.

Any ideas I can go armed with the garage would be helpful.

Thanks

Sounds as if the torque is overpowering the clutch in the box. Could be low oil pressure. Check oil level and perhaps clean filter in sump.
Also check gear lever adjustment.

Assuming no wheel spin activating the LSD.

Thanks. What should I be looking for on gear lever adjustment? How would that effect it? The garage did have a tinker when I first got the car as it had the RV8 problem of not always wanting to start when in P. How would that effect it?

Definitely no wheel spin - the car is already at cruising speed. I think an oil change would be a first call of port - as far as I'm aware the auto transmission oil hasn't been changed since the car was new.

It sounds as if the gear change is not adjusted correctly.
If the car does not start in N or P, the lever is not correctly adjusted to trigger the inhibitor switch.
If they have adjusted that right, it is still possible that the gear selector on the box is not adjusted correctly to go into top and OD. If almost there, the box will tend to hunt as if it will try and shift, but it will be reluctant to do so.

There is an adjustable rod from the lever on the shift box to the gearbox, running under the shifting console.

It'll be drive shaft related - it's quite a common fault.

One or both of them will need replacing.

The car always starts in neutral, but is temperamental about starting in park.

Thanks for the suggestions. I've got it booked in at my local MGR specialist to see what they make of it.

Did you ever sort the problem?

Yes I did! I used FedAuto to find an automatic gearbox specialist near me, and that turned out to be The Automatic Gearbox Centre in Hove https://www.automaticgearboxcentre.co.uk/

They had the car in and adjusted the setup so it was changing properly and starting in park as it should. Interestingly they suggested that the first thing to check was the state of the atf fluid and change the filters to make sure there was no contamination from damaged or worn parts and if that came back clear to add an additive called Instant Shudder Fixx. I was very skeptical of this as I regarded this kind of treatment as snake oil which can do more harm than good. However, they assured me it would do nothing more than free the torque converter up without swelling any seals or nasty stuff like that. I let them stick it in with a full atf and filter change and the problem was gone straight away. That was last Feb and it's been fine since.

Instant Shudder Fixx can be found here: http://www.lubegard.com/~/C-230/Instant+Shudder+Fixx

Looking on the internet it appears to be a very well received and genuine product.

I'm still look for a new selector cable to replace my damaged one. So if anyone knows anything....

Further to that there is quite a good discussion here about lock up on the Ford 4r70W gearbox here :https://bobistheoilguy.com/forums/ub...&Number=284227

It seems to be a reasonably common problem, which is cured or at least helped by the right friction modifier.

Love it when a plan comes together!!http://pmcdeadline2.files.wordpress....6&h=299&crop=1