Jag Diff Noise

[kyleb]

I have a 3.54 jag power loc fitted to my cobra and am about to pull it out for the third time .... First drove the car a few months ago which was a great feeling but the rear end shook like a dog crapping tacks, so after a lot of investigation decided to remove supposed reco (albeit sat idle for many years ) diff and found the wrong dia pinion bearing was fitted therefore allowing pinion to float which also added some unwanted metal to the oil... Okay no probs we can do this, fit new bearings change ratio from 3.07 to 3.54 ( opportune time ) and re-fit diff, easy right.. Ahhh No.. Put diff back in was good initially then after a few K's started to whine and graunch on gear change and transfer of power, got worse as oil heats up then eventually chopped out pinion seal and bled to death .. Check oil and you guessed it, full of sparkles.... BUGGER. OK remove diff take it to jag specialist and $1900 poorer I get the nice newly reco'd diff back assured was good to go forever.. Apparently forever is about 60 K's.. Noise and graunching back, get home and pull a sample of oil and yep sparkly, diluted the sample with fuel and put a magnet in and it came out looking like a porcupine...Hmmm... Ok, thats great get to the point you say, Well my question is this, Have I screwed something else up to cause stress on the pinion ? It has a TKO 600 fitted in line with the centreline of the car and the diff centre is offset somewhat to the drivers side and the driveshaft is about a foot long ( typical for a cobra I thought ). Could excessive angle on the tailshaft cause vibration and failure? Or is it just plain bad luck and the fact that we are all re-using second hand parts that are now getting past their useby dates? Whaddya Reckon..

[ERA Chas]

kyleb,
The shaft angle may be the source of the damage but I'm no expert. I would think the u-joint would howl before the diff.
I did notice that nowhere do you mention that you're using friction modifier in the fluid. Jag diffs will not live without it in the 80-90W. They will start by making the noise you describe.
Kendall makes a good one-just add a 4 oz. bottle when you've got it sorted.
Best luck.

[redmt]

Complimenting drive line angles comes to mind.

[kyleb]

Chas, was told to use penrite Limslip 140 and put in additive if I get chatter.
Cheers

[Rob. Smith]

The tail shaft angle will only affect the uni-joints unless there's no slip yolk. What happens with the uni's is that they don't rotate completely and eventually brunnel themselves to death.

[Rebel1]

Agree with Rob, If engine/pinion alignment was so out of alignment then you'd feel it way before you flogged the diff to bits. Remember, ideally, the centerline of the engine and the centerline of the diff pinion should be parellel in both planes or at worse within 1/2 degree of each other but can be separated by up to 4 degrees of driveshaft angle.

see here: http://www.rustynutscarclub.com/driveline.htm

Jag PL diffs require a diff lube specially blended for limited slip diffs. Back a ways the recommended oils were Castrol Hypoy L.S. , Shell S8096B , BP Limslip 90/1 , and a few others. Mind you, this is from an old workshop manual so many may no longer be available and you'd have to seek equivalents. Although I'd suggest a good Hypoid 90 with additive would be OK.

[renovationinnov]

just aquick question / did you check the back lash on the pinion - crown gear & was the 2 lapped matched
because if they where not the hard facing can destroy the crown gear repaidly& if to much backlash can load the pinion bearings causing them to spin in there housing
reason i know this a diff mob reconed a diff for me & didn't lap it in , so i had a similar sounding problem
hope this helps

[RICK LAKE]

kyleb Kyle There are 2 angle to you to have matched to eliminate vibration and damage to both trans and rearend. You have a right to left and up to down angles. Having a longer trans is not helping either. Having a 1' driveshaft is a problem to start. Sharp angles. The best thing to to find a chassic guy who can find the center line of the car, check the angles, setup the trans and rearend to offset each other. The other thing could be the trans mounts or rearend mounts if they have too much play of deflection in them. Any twisting with also stressout the pinion bearings. If you are hard driving this is only going to increase the short time. Have the driveshaft checked for balance also, the same with the output shaft bushing. You want no to VERY little play. I don't have an endplay number but if you want one I will find one for you with the T-56 trans. I think you will find that everything is out just a little and causing this problem or you could still have the wrong pinion bearing, or wrong preload. Preload should be 25 inch pounds of drag when rotating just the pinion in the carrier housing. Hope this points you in the right direction. Are you running the Jag plate setup for the rearend or a yoke setup (driveshaft)and is there any weight plate on it?? Rick L.

[ERA Chas]

Originally Posted by kyleb

Chas, was told to use penrite Limslip 140 and put in additive if I get chatter.

If you wait until it chatters, you're already hurting parts. It should go in with the fresh fluid, right after rebuild. Others suggestions may be the problem but when solved, use the modifier.

[redmt]

Preload should be 25 inch pounds of drag when rotating just the pinion in the carrier housing. ? Rick L.[/quote]

I used to build 3rd members when I was a Ford mechanic way back when. We used to set them up with 7-10 inch pounds running torque with smooth initial rotation and new bearings. Has this been changed? 25ipt seems a little tight?

[Outwest34au]

Add to the shopping list,
1 kg minced meat
2 rolls of glad wrap
12 banannas
bag of sawdust
8 pairs of pantyhose.

If you cant get the jagman to repair what you paid $1900 for try the above ingredients in no particular order.

By 60 K's did you mean 60,000 kms or just 60 kms?

If the tailshaft angle was extreme enough to be causing the problem I am sure you would feel it wobbling/ trying to drive overcentre when going slow. Even then it would have to be really extreme to put stupid load on the diff pinion which just cant happen normally with a slip yoke.

Will be interesting to see what you pin down as the cause.
Good luck with it.

[kyleb]

Yeah I wish it was 60,000 ks then I wouldnt mind so much, it was about 40 to 50 k's and thats being generous, basically drove around the block and by the end it sounded like all I had left was a bag full of bolts spinning in loose formation... Although looking at the upside I did get to drive it around for 20 mins or so..

[AC-460]

Make sure who ever has shortened the tailshaft has lined up the yokes ...from one end to the other ....lay it flat.... the caps on both ends must be pointing up and down.....if one end is either way or a quarter turn different it will vibrate and chatter like crazy...

[stephen low]

Still yet to test out my rebuild Mk 2 Jag diff but my Jag specialist fellow Evan Foley (03 9888 8089) said to run for about 500kms on a fairly standard diff oil through the early wear period and then drain and replace with a true synthetic oil.

I've an empty container in my shed of the synthetic stuff he recommends, it's something like $50 a litre I think but he said replace this oil only every 10,000km having only done top ups in between if required. I can let you know the brand when I get home at end of week but the supplier is based in Dandenong.

You premature wear has to be caused by something else more dramatic for it to happen so quickly.

[kyleb]

Hmmm.. Was told by some people to use synthetic which I did initially ( castrol SAF-XA), but when I took the diff to a jag specialist which by the way is all they do, I was told to use Penrite Limslip 140 only unless I was racing then go something else of which I forget the name, reason for this was the jag setup is old technology and not designed for synthetic oils. Unfortunately there seems to be a lot of differing opinions as to what is better which is I'm sure grounds for more discussion, either way I can't see how that would cause problems in such a short time just as you have said in your reply slowy!! Hopefully third time lucky, I am getting good at removing and installing the diff centre though.

[AC-460]

Originally Posted by AC-460

Make sure who ever has shortened the tailshaft has lined up the yokes ...from one end to the other ....lay it flat.... the caps on both ends must be pointing up and down.....if one end is either way or a quarter turn different it will vibrate and chatter like crazy...

Its not the oil... its a balance/harmonics problem

If the diff is noisy it the gears .....if it vibrates its the tailshaft ....my guess is your tailshaft hasn't been shortened correctly....try one thats not done right and it will kill everything around it...

[Outwest34au]

Don't discount the possibility that the Jagman may have stuffed up accidentily. I've seen bearings in backwards, not in at all, cracked during assembly etc over the years. When you're in a workshop with *****in customers, 10 phones ringing and trying to organise stuff it is impossible to keep an eye on everyone.
As disappointing as it all is, I would remove it, (gotta be done anyway), drain all the oil overnight into a sealable clear plastic container, then arrange a time to be with jagman when he knocks the back cover off for a look. I know I would feel better seeing it with him rather than have an arse/ face saving story that is close but not the whole truth. If he has stuffed up, pat him on the back, 'she'll be right mate, you'll sort it', then wait a few weeks for him to repair/ replace it.

Just for shi*s and giggles tho in the meantime, undo the four flage bolts but leave the flanges touching still, gearbox in neutral, and rotate the shaft as closely as possible to what it would be doing in real life, if it is a bad shaft it should show a clue. As AC460 mentioned, make sure the uni joints are phased correctly.
Once upon a time long ago, an apprentice and I working together on a truck left a diff section plug loose, it fell out 4 km from the shop, the truck drove another 50 km before a slight noise was heard and they pulled up. We refilled it there and drove it back to pull apart in the shop. Only one small bearing was damaged, cost us about $400 including time (1985 ish) to get it sorted. 1900 bills for sub 60 km is absolute frogsh*t. I hope he is a reasonable honest guy and you get it sorted with him stressfree,

[AC-460]

Have you checked the tail shaft.....if you keep changing diffs and your not fixing the problem isn't it telling you that maybe something else is causing it....you said in your initial statement that the front pinion was loose thought it may have been incorrect bearing.... the reason it was loose is because the tailshaft is hammering the hell out of the pinion...

[Outwest34au]

"and found the wrong dia pinion bearing was fitted therefore allowing pinion to float which also added some unwanted metal"
I read that as wrong bearing, it wasn't specified it had worn down a size. Anyways, I agree the tailshaft should be closely inspected for phasing as you mentioned earlier AC460, good to do it in situ, then on a bench. I just really believe it would have been like a dog with 2 wooden legs if it was the shaft bad enough diametrically and Kyleb would have felt it on the 60km trip.
If we had a visual of the metal bits that came out it might tell a story. 5 internet points for every tooth LOL.
Since all my components and angles aren't as my kit make planned it I hope I don't have similar issues, I have only done 600 metres or so on the road.

[kyleb]

Went and checked tailshaft seems phasing is ok, it was done by tailshaft services in geelong, would be one helluva stuffup if they got that wrong due to the fact that's all they do, but i'm sure it has happened, so better to check everything. Yeah, the reason the front pinion ran out the first time was the fact that they had used the wrong I.D pinion bearing, you could drop it on the pinion from about 10 feet that's how loose it was on the shaft, so much for checking your initial assembly to make sure you have the right parts...Am appreciating all the input, it helps to make sure you have'nt done something stupid.. But it's certainly looking like a worn part has been missed on the second re-build...