Noisy Rear Diff

[niallinireland]

Hey all
The rear diff has become noisy at low speed turning, a loud knocking, very evident at T-junctions and the like, any low speed-big turn basically, also on motorway straight line speed at about 60-70mph (95-110kph) there's a noticeable low hum out of the rear axle. I pretty certain the it’s the diff humming cos its about the only thing left in the rear axle that has been worked on or replaced.
I did a search for msg about LSD and rear diff and came across JamesW msg about adjusting a LSD, but I know it not my brake and bearings.
Basically all I want to know is can it be repaired or is it a straight replacement needed. I'm giving it too my mechanic on friday and going to get him to look at it, but like to know what to expect, worse case scenario...

Cheers
Niall

[James W]

Hi Niall,

Been there done that.... What you need to do is find a diff or gearbox specialist as if you strip down the diff it needs to be set up again correctly with shims measuring the backlash and other things thats not so easy for us who don't do it regularly. Most mechanics won't attempt this nor shouldn't.

So in many cases a swap is easier, it gets you straight back on the road and can be done by yourself or your mechanic.

So assuming a spare diff isn't as easy for you to find find a specialist and they will have to evaluate it. It may be bearings but if it's that bad that the gears are worn you'll be forced into a replacement diff anyway.

The first mision is to find out what ratio it is if replacing

[niallinireland]

Cheers James

My mechanic's good but, wouldn't even ask him to try the re-conditioning of the diff in that case. I'll get him to look for a diff, that he's good at, got me replacement hubs for nothing ;D ;D
Any ideas where to find details for a ratio, i remember there was a russian or japan site that had loads of detail on different models. Anybody got a copy of the link.

thanks again lads
Niall

[James W]

What you need to do is to identify what your diff is.
Back near my post re adjusting an LSD there should be a method for identifying your ratio. but again.

Mark the drive shaft and one wheel with a bit of tape or something. Jack up that wheel, climb underneath and get a mate to slowly turn the wheel. Go for 10 times to increase the accuracy. As one wheel is fixed on the ground the drive shaft should then turn at twice the rate of normal... (or half?) So 90 times for a 4.5 ratio for example. See the old posts.

I believe there are only two ratios. 4.56 if memory serves me right or 4.7? can anyone confirm that. Maybe in an old post?

[Bruce]

Where can I find the post about " re-adjusting an LSD" please.
Cheers Bruce.

[James W]

Adjusting an LSD.
clubisuzu.proboards29.com/index.cgi?board=Justabout&action=display&thread=1092000356

DIff ratios:
clubisuzu.proboards29.com/index.cgi?board=Justabout&action=display&thread=1091161145

[niallinireland]

the plot thickens!!!

got the jeep off my mechanic this evening...

right before i tell you what he said, give you a quick run down on my recent service history

I have to get the jeep tested once a year to get a cert of road wordiness to get my tax, one of the issue that came up was a small leak from seal between the rear axle and the trans axle. Replaced it with my mechanic while I was there, filled the rear axle and off I went and pass my test.
There’s been no sign of a leak since, checked periodically, when mechanic went to investigate my diff to-day loosen the drain plug to let the oil out to have a look and all that came out was a egg cup-full of oil. Repeat!!! no sign of leak anywhere, from trans axle seal, half shaft seals or bleed valve on top of diff….

Completely dumbfounded me and my mechanic…..

HELP!!!!!!

Only thing that is in question is the oil mechanic used…..

Could this just have boiled off???

If it did, why is there no sign of oil on the underside of floor where the oil would have come out of the bleed valve???

BTW test was done in last wk in august.....

Go to work sherlocks

Thanks for the tip on checking the ratio james

[geeves]

If its lost that much oil in that time without leaving a trace then I recon it was lost before it got into the diff. Diff oil is heavy and stays around wherever it lands and you can definatly smell it. I have a small leak in the pinion on mine that drops less than one drop a month on the garage floor unyet the rear underside of the car is covered in the stuff. I lose less than a cupfull a year from the diff

[James W]

It takes very litte oil to make a mess. I had a seal go and make a real mess underneath but repeated checks showed the level as fine or very close.
An egg cupp full of oil can sit in the bottom of the diff even when you drain the oil. Have a look at the bung it slightly to one side and not right at the bottom. I jack up one wheel to get every last drop out when I get water in, even then I doon't get it all....

So was oil forgoten to be added?

But you say checked periodically? What happened since the last check?

[niallinireland]

i know the mess the diff oil can make, had a leaking half shaft seal before also.
definitely oil put in after changing drive shaft seal, i was standing beside him when he did it, i cranked the pump for the oil tank we fill the diff from.....
Also checked the diff two weeks ago when i had to tighten up my handbrake after getting a new cable put in a while back absolutely no sign of a leak, had a good look to make sure….
No sign of a leak under where i park either

Still dumbfounded…..

[geeves]

Do you park outside Someone might of been round your way with a basin, spanner and poor sense of humour. ie stolen your oil. If it hasnt run for long without oil it might be ok but otherwise you could be looking for a new diff. Was the oil you removed clean or was it glittery If clean I would refill and see how it goes. If its sparkling then theres metal filings in the oil which is not good.

[niallinireland]

park outside alright, but live in the country unlikely somebodies stealing my oil. i'll have to check with my mechanic about the metal fillings, but she seems to be runnig all right. Will be keep a VERY close eye on the oil level from now on.
If i though it had have been a chance of my oil doing a houdini i would of kept an eye on it. Thanks everybody for you help

Niall

[Garth]

Hey Niall, My rear diff was making very similar sounding noises to what yours has been doing. It would get really bad after driving for several hundred km's. The truck has done about 200,000km's and the guy who had it before me never changed the diff oil in 7 years, but the oil was still looking good when I drained it.
anyway, back to how I fixed it. I initially drained the oil and refilled it with Penzoil LSD diff oil, which quietened it down until my next long trip. From there it eventually got really bad and I removed the diff for a look. We couldn't see anything obvious so I decided to strip down the entire diff head for a look. It turned out that the main crown wheel bearing nut was a bit looser than I thought it should have been. checked out the rest of the diff and there was no obvious wear. reassembled the whole thing and put about 400ftlbs torque on the crown wheel nut. back into the truck and she's run sweet and quiet for the past 20,000kms. Unsure what torque it should be but it certinally worked for me. Just an idea.
The diff head isn't hard to strip yourself, just be careful of the really powerful little springs in the LSD mechanism and make sure it all goes back together the way it came out. Hope you get it sorted.
Cheers

Garth

[KrisA]

A Russian website I found quite interesting was http;//english.auto.vl.ru Didn't quite go to diff ratio's though.