View Full Version : reduced to tears and very frightened

24-05-05, 08:40 PM
Chaps imagine the scene, car is all but done and three weeks from SVA, all thats left to do is secure the seats, fit a clutch spring a bonnet stay and re - bleed the brakes.

So I endeavour to take her for a little spin down our quiet lane next to our house. All is well, revs fine, speedo looking good everything as expected. IN fact its all going so well the suns shining, birds tweeting etc etc.

However the rear end seems to be making a clonk of dis approval when direction is changed. If I select first and pull away either hard or without any throttle just on the clutch there is a clonk from the rear end. It doesnt do it again in any gear change until you stop and select reverse then as soon as the load is taken up it clonks again, accelerate in reverse and nothing until you go forward again.

Hope you get the picture

I have torqued everything, diff is reconed with new bearings, pinion seal and backlash spot on. Hubs have new bearings and seals and the output shafts also torqued.

I have jacked the rear up and put on axle stands and lied under the car while running with someone simulating the above mentioned. Nothing is moving or flexing, its all solid and appears to be as it should. My worry is its internal of the diff but then surely if everything is renewed it cant be.

Could it be the PowerLok engaging or something that i shouldnt worry about.

Im just so scared il get her finished we will have a heat wave and il have to take her **** apart to change a diff.

Any ideas or anyone experienced the same please shout and re assure me its all ok


Grease Monkey
24-05-05, 08:52 PM
By the sound of things you have play between the output of the gearbox and the wheels. Also if it only happens when you change direction it must be quite a stiff join as there's no backlash during normal driving.

One thing i've noticed, having jacked mine up to adjust the handbrake, is i have some play in the hub itself. With the hand brake on full, new UJs on the driveshaft, the wheel can be turned about 2mm at the tread without the driveshaft / disk moving at all.

Tracked it down to how the hub sits on the splines. Not sure how much of a problem this could be in the long run, but it could explain your clunk when changing from forward to backward.

The other suggestion could be the propshaft (or halfshaft) to diff flange. If the bolts have any play at all, then even if they're all torqued up the prop could spin slightly before power is tranferred to the diff.

24-05-05, 08:56 PM
Thanks Adrian il check the same when its jacked up. I honestly dont think its much to worry about and the echoing of the noise throgh the chassis makes it sound worse than it is but never the less I dont want anything to come off whn im at warp factor. IL check my play on the hubs and have another good look. Like I said everything is tight and as it should be so hopefully no SVA implications


Purple AK
24-05-05, 09:11 PM
Have you guys used Loctite on the hub splines? Could be the problem if not.

Grease Monkey
24-05-05, 09:15 PM
I'm thinking about it (loctite) when i'm happy everything is finished and not going to be taken apart again.

The only problem is i put my UJs on backwards (All 4 of them, whats the chances of that?!! :angry: D'oh) so the only way i can get a grease gun to the UJ is to take the hub off the spline.

24-05-05, 09:18 PM
Loctite now theres a thought, should go well with the duck tape, expanding foam and sealer thats holding other various parts of the car together tee hee.

If the splines are the problem then il by a bulk load of the stuff and squirt away


Grease Monkey
24-05-05, 09:21 PM
Loctite was standard fit on the original assembly by Jaguar, which is why it took 4 Jag mechanics half and hour plus the entire first half of the rugby world cup final to get the damn thing off the spline.

Lucky they had a telly in the waiting area.!

I guess one other thing you could check to see if the play is on the prop or half shaft flanges is chock the front wheels and try to drive it forward slightly this should set the play in the forward most position. Score a line across the 3 diff flanges the repleat in reverse and see if they still all line up.

Purple AK
24-05-05, 09:23 PM
Seriously. I'm sure the Jag splines should be assembled with Loctite (someone will correct me if i'm wrong) thats why they are normally a bitch to disassemble. Pullers etc :(

24-05-05, 09:33 PM
The splines must be 'glued' with thread lock or the metal will fret i.e. chafe and you'll b****r the splines in no time.

24-05-05, 09:34 PM
also fit 90 degree nipples to access the UJs and shim with washers so they point inwards when tightened up.

24-05-05, 09:43 PM
Read the Snake Torque article "It's Not Rocket Science". It's features in articles on the forum front page.

24-05-05, 09:45 PM
Read the Snake Torque article "It's Not Rocket Science" featured in articles on the forum front page.

24-05-05, 10:53 PM
i have the same knock
its done 8000miles like it and i put it down to being the powerlock diff as nothing is loose and no play in anything.

maybe it is maybe it isnt

it hasnt broken yet,and if it aint broke,then dont try and fix it

anthony,i will be watching this post to see if you come up with a solution to the knocking noise,if you find one let me know as im stumped also.


24-05-05, 11:27 PM
I think you will find it is the slack between the driveshafts and hub splines, as mentioned earlier use Loctite and all will be well.

Not that I know much about Jags but a friend used to work for Jaguar and this very subject of clonks from the rear end came up.

Paul B
25-05-05, 11:36 AM
Try the propshaft couplings. Even if they feel tight, the torque from the motor can cause them to twist in one direction with a clunk. When you select reverse, the torque goes in the other direction and, hence, another clunk.

The bolts should be a snug fit in the holes and they should be very tight (make sure you use high tensile mild steel bolts). Try retorquing these and have another drive, see what happens and let us know.


25-05-05, 07:58 PM
Well chaps just torqued everything AGAIN and yep everything still tight.

I have checked for this play as suggested on the hub splines and woo hoo result, slight movement on the rear near side hub. With handbrake on there is about 2 or 3 mm movement of the wheel on the hub without the driveshaft turning. Im going to loctite these up after everything has been set suspension and camber wise after SVA and hopefully the prob will be solved.

Its worth noting that when trying the test of forward and reverse loading as mentioned in the first post this wheel has a shudder when the clonking happens which would indicate further more the movement in the spline.


25-05-05, 08:39 PM
i have the same knock
its done 8000miles like it and i put it down to being the powerlock diff as nothing is loose and no play in anything.

maybe it is maybe it isnt

it hasnt broken yet,and if it aint broke,then dont try and fix it

anthony,i will be watching this post to see if you come up with a solution to the knocking noise,if you find one let me know as im stumped also.

russ:) :) :) :rolleyes: ;) Osgood:angel:

25-05-05, 10:10 PM
Anthony - what you describe sounds exactly like the noise I had in my old diff. It was caused by the crownwheel moving against the crownwheel carrier. The crownwheel is held on to the carrier by something like 7 bolts, all of which have to be tight and loctited. Sometimes the torque reversals through the diff cause the crownwheel to become slightly loose - i.e. the bolts are no longer clamping it firmly against the carrier, and the bolt holes in the crownwheel elongate just a bit, and the unthreaded portions of the bolts themselves fret and wear.

What you then get is a deep "clonk" as the diff takes up drive. Nothing further until you reverse the torque across the diff (in your case by accelerating in reverse, in my case, sharp deceleration in first or second was enough) - and then you get the clonk again.

You could try whipping the diff rear cover off and retorquing the bolts for a temp fix, but I feel the only permanent fix is another diff. I would not like to comment on how long your diff will last before it breaks, mine took a lot of punishment for over two years and about 10K miles before I replaced it.

Try eliminating the hub drive splines as the souce of the noise by loctiting them first before you let this particular diagnosis stop you from sleeping.


26-05-05, 04:57 PM
Thanks Wilf unfortunatley after reading that I thought loctiting stuff was to simple. This sounds an absolute pain in the rump now and I believe a winter project will be to take her butt off and replace the Diff.

It should be ok for this summer and the running in period so will keep some of the horses from full gallop untill im sure its not going to kill me by breaking up


26-05-05, 09:06 PM
It would be some kind of failure to break up - would involve the shearing of all of the bolts holding the crownwheel onto the carrier, and that is unlikely IMHO. Mine got all of the ponies my engine puts out on a regular basis, clonk or not, for 10k miles, and it only got marginally worse. I have been told of diffs that always clonked, maybe it is not so bad as you think.

As I said - eliminate the hubs first by doing the loctite thing (don't use the ultimate strength loctite or you will need a 100t press to separate them ever again !)

Changing my diff only took me 3 days solid work, so it can't be all bad can it? LOL.

27-05-05, 04:05 PM
Thanks Wilf just run it down the road again (yes I know il be taking my sleeping bag with me soon) but I just cant stay away from her.

Its only really bad if you are listening for it, I dont think an untrained passengers ear will notice it.

Im not worried if I do have to change the diff as long as its raining and cold at the time and not in the middle of summer when I should be out doing number 11's


27-05-05, 09:15 PM
11's?? Maybe I am getting old?

Grease Monkey
27-05-05, 09:33 PM
LSD Mate,

Fitted to the cat that is, not taken orally,

Leaves No 11's on the old black stuff.

28-05-05, 03:01 PM
Why, the very thought, I couldn't possibly.................