Hi, this is a bit of a weird one. When I change down a gear, say from 4th to 3rd there is a large forward rocking movement as if I have something heavy in the back that suddenly moves forwards in the vehicle. Imagine the movement of a slide hammer.

Could it be a gearbox mount, rear prop (changed the front one)

Appreciate any help
Cheers

 

I assume it is a manual transmission and not a automatic.

Does it happen when you push IN the clutch or let it OUT?

 

Hi Spike, thanks for the response.
It is a manual, and It's when I push the clutch IN from memory, before I actually change down. Its a bob-tailed Disco, so weighs a little less, not that that makes any difference, just thought I'd give all the facts.
What do you reckon? Someone told me it could be the rear prop extending too much, but I cant see it myself (front has been changed)

 

First place I would look is the bushing on the "A" arm on the rear axle.
Then look into the rear sway bar bushings.
Mine was making the truck feel unstable at speed on the expressway when taking curves, it felt like the back of the truck was going to come around to the front.
Tightened the sway bar and all is well once again.
I dont have a manual trans so I cant compare, but those are the places I would start.

 

Spike, legend. It was the bushes on the drivers side trailing arm that joins the rear axle to the chassis.

By all accounts when you put a 2" lift kit on them, you need to also upgrade the trailing arms to cranked ones to take into account the additional travel. Mine hadnt been done and the bushes seem to be the thing that does the work.

Bought a set of cranked arms and polybush kit, yet to put it on the disco, but clearly with 5mm of movement, thats the problem. Makes complete sense

Thanks for your help buddy