Can you Pick that sound !



g'day folks, i need your help identifying a odd sound i am getting in my XF.

here are the characteristics:
-It comes from the rear of the car.
-its a knocking sound (in time with the wheels. eg. knock knock.....etc)
-occurs only when clutch is out and the car is in gear. (eg. rolling to a corner in 3rd with no gas, it makes the sound)
-doesnt happen with clutch in.

First thing that came to mind was the diff, then i was thinking uni joint.
But then i read somewere it may be a brake problem.

Now, i have no idea. :oops:

Any ideas/thoughts would be good.

*While im posting, any cheap/easy ideas on how to fix a noisy lifter. that constant ticking is giving me the 5hits.

My 87 xf has similar sounding problem, it's a waggon with rear discs, and very worn rear susp, shackle rubbers have never been replaced.
That' what I'm suspecting in my case.
Im hoping the noise will be gone when rebuilt springs with new bushes go in.
Don't think it's coming from the brakes though, rebuilt the calipers 7months ago working perfectly.
Does it occur in all of the gears, or just one? If it occurs in all of the gears, is the knocking matched with the engine revs, or does it increase with the speed of the vehicle?

Lastly, have you done any heavy braking, enough to lock a wheel up for 50m or more?

I've found the easiest way to cure noisey lifters is to change the oil once a week for a month (cheap stuff from Coles is good!). If that doesnt cure the problem, you'll need a set of lifters.
cheers guys
Yer, it increases with the speed of the car....but mind u i can only notice it when i am slowing down..
Eg. i come to a intersection in 3rd and roll to a corner it knocks, as i get slower it becomes slower (if that makes sense).

Nah, no heavy breaking...

happens in all gears.

what u thinking disco?

I'm thinking diff centre. Jack up one wheel, and check the "play" before the tailshaft starts moving. Spin it by hand in the normal tailshaft direction, and listen.

Get under the car too, and check your uni joints. Be safe. Brakes will "click" or scrape if they are hanging up, not knock. Could even be your shaft is bent or way out of balance, or the output bushing is worn badly on the tranny (or the yoke, but less likely).

The Ford factory manuals (and the Ellery's condensed versions) have good bits on diff/driveline diagnosis.

Regards, Adam.
I'd concur with Addo. If the pitch rose/fell with the speed of the engine, I'd be inclined to suggest it would be gearbox. Speed of the vehicle says to me diff/tailshaft/tailhousing. In addition to Addo's ideas, try jacking her up (both wheels, carstands stylez), and rotating both wheels backwards and forwards. The opposite wheel should spin in the opposite direction (its an open diff, yeah?). Anything that would make a knocking sound should be able to be felt through the wheel as you rotate it, if indeed it is diff related. Do take Addo's suggestion on checking out the uni joints, a uni joint failure would be quite character building (tailshaft falls out onto the road, back end gets polevaulted!)
can't help your rearend noise but I would suggest addding about a pint of ATF when you change your oil until the lifter stops ticking, if that doesn't work you need a new lifter.
Ok, i got the car up on axle stands the other weekend..
I got under the car, and it seemed the sound was coming from both of the inner wheels..the right, more so then the left.
I was thinking maybe the wheel bearings could be nakad and on the way out.. maybe/maybe not?
The noise occured when the wheels were spun in both directions, one at a time and at the same time.
The only way i can describe the noise is, when u try to imitate a horse galloping with your mouth you get that "trot, trot, trot" sound..or in my case "knock, knock, knock."
hopefully this makes sense to someone.. :roll:

Bent axle, bro'. My XE gets a little bit of a canning by me, and one day I ouched a kerb. ( Was practicing my single wheel burnout technique in the Zingary Richmond Rugby parking lot...)

Axle was bent for some time. Flat spotted tyre and lockup in wet on asphalt surfracings were the big clues. Shockie got hammered. I grabbed an 87 XF 3.3 5-speed diff, and changed the offending axle shaft over.

If you've got stock offset 6.5 inch rims, grab a staight edge or wire or tape 53 inches (about 1350 mm) and jack up the thing. Measure the run out minimum verses maximum, moving both wheels at 180 degree intervals. Any major variances indicate a problem.