REAR DIFF NOISE, CLUNKING, THUMP THUMP THUMP :(

[gomulletgo]

Hi all,

My 89 bighorn has an issue in the rear diff area. It presents itself mainly when under load at low speeds while turning. (lots of weight in the truck, towing, up hill etc.)

The truck appears to have a LSD, both wheels turn the same way when it's up on a hoist and one is rotated by hand. If a person tries to rotate the wheels in opposite directions by hand it can be done.

I don't think the previous owner (older dude) knew it had a LSD, once I found out it had a LSD I dropped the diff oil and replaced it with LSD oil. I hadn't previously noticed any noises from the diff.

Now when under load mainly when going slow and turning it makes some really really bad sounds, consistent, but loud. It sort of clunks and thumps, and when taking off it will go thump, thump, thump, thump, thump maybe about 5 times before it goes away. The truck actually vibrates with the thumping! A back seat passenger mentioned she could feel it through the seat the other day!

Any help, advice, ideas etc. would be greatly appreciated Also does anyone have a link or manual on how to do a diff rebuild for one of these? I have a spare LSD with the wrong ratio gears that I would like to make a good LSD out of with a correct ratio open diff I have spare.

Cheers

[mudslinger]

checked your wheel nuts?

[mudslinger]

if ya need a hand drop me a line 0272593533 happy to help out

[Yarno]

Check the u-bolts for the leaf springs, one side maybe loose.

[geeves]

you joint would be first guess spring bolts second and the center driveshaft bearing third. Otherwise it could be a diff issue.
When my center bearing went it was undrivable below 20kph. Had to get from Stratford to Wellington like that Was ok till the traffic jam in Otaki

[gomulletgo]

Thanks all,

It's not the wheel nuts, I've swapped rims and the problem was still there, the wheel nuts are tight. Thanks for the offer of help Mudslinger

I forgot to mention earlier I dropped the diff oil a while back to check it expecting to find chunks of metal, not a thing, clean as a whistle.

Armed with your suggestions I went out and had a look at it, it appears one U-bolt had slipped sideways off of it's top locator pad, I'll attach a picture of the problem area, you can clearly see on the other side where the U-bolt sits in the correct place. I have dis-assembled and re-assembled the whole thing correctly.

If I don't post up otherwise you know the problem is solved

Thanks heaps guys, I thought I had a big big diff problem on my hands!

[geeves]

Mine done the same thing but no noises. It might be worth unbolting completly to check the pin in the spring pack. Mine was sheared off and several springs had moved. /The pin can be replaced with an 8mm bolt but you need to grind off the bolt after putting the nut on

[gomulletgo]

Hi Alan, I did undo the whole thing, the spring pack bolt was alive and well I don't get why the locator hole in the bottom plate is formed in the steel in such a way that it is away from the spring pack bolt, the way it's set up it doesn't locate at all, so only the locator hole on the spring perch on the axle tube actually does it's job.

[geeves]

Should be a matching hole in the bottom of the plate on the bottom of the diff. This will allow the spring to fit flat against the diff while being located top and bottom. If it isnt locating that might be why it all came loose. Forgot to mention the original pin is a rivet whit a round head. The bolt is bigger so could require substantial grinding to fit in the hole properly

[gomulletgo]

The diff started making is clunking and thumping noise again. It seems to present itself more once the vehicle has done a bit of driving say 50Km, again it presents more with a heavier load, towing etc. climbing hills, tight corners at low speeds. I'll look into what is happening again and let everyone know.

[FORGE1]

Sorry to thread jack

Just thought I would mention mine is doing something similar and its Coil Spring rear end

Its only on the initial take off and there has to be a load (e.g put your foot down or have weight on the back). But mine it like a bind up feeling then clunks and goes away once over 20kph. I have changed diff oil and greased up my Driveshaft and Universals but the problem is still there.

It did it again in Auckland in the weekend with a Car trailer and SWB bighron on the back but as it was a uphill take off it did it but a lot slower and it definately feels like something is not balanced properly until it gets up to a decend speed so maybe a bearnig but I wounldnt have a clue

If anyone else has anything they could add.

Someone mentioned trailing arm bushes (which could be replaced) but It would do the problem for longer I would think.

Cheers
Ray

[geeves]

if 2 piece driveshaft check the center bearing
Check u joints
check leading and trailing arm bushes
if none of the above its in the gearbox or diff

[turnturn]

Back to "gomulletgo"s original post, could it have had a Lokka fitted?
They make a clicky thump noise don't they?
And would behave like a locked diff when the wheels are jacked up off the ground?

[gomulletgo]

Hey guys,

Thanks for the input. I'm fine with that "Thread Jack" certainly sounds like a similar problem to me. Re: possible locker installed, no I don't think so. I'd like to think I've heard enough auto lockers and been in enough vehicles running them to know the difference.

So an update, it's been up on the hoist recently, the WOF mechanic has checked but made no mention of issues with the U-joints. The driveshaft center bearing needs replacing, the rear diff pinion bearing has play and oil leak. My plan at this point is to replace the driveshaft center bearing and replace the diff head with another LSD of the correct ratio. Once the old diff head is removed it can be rebuilt or whatever.

So I jacked up the back of the truck and rotated the wheels one turn and counted the driveshaft revolutions, I did it twice to be sure. The driveshaft rotated 4 and a third turns appx........which I believe gives me a ratio of 4.3

As a side note, I couldn't make the wheels rotate opposite directions to each other by hand, I didn't give it death but it seems pretty solid to me. Perhaps now that it's got LSD oil it's really bitten hard, acting more like a locker, which could ??? create drivetrain wind up and destroy the center bearing and pinion bearing? Still, I have a beach buggy with a welded diff and it acts differently. The isuzu never chirps tyres on tarseal when turning sharply at slow speeds for example.

Forge1 how did you get on with your truck? What did the issue turn out to be?

Thanks again guys

EDIT: I've got a Mu diff here, I think it's the leaf sprung model I got it a while ago, would that be the same (4.3) ratio? If it's LSD it could go in

[geeves]

with both wheels off the ground and truck in gear they will rotate opposite ways. If they dont I would be double checking the lack of locker. If there is less load on the pinion than the other axle it will turn before the axle

[gomulletgo]

with both wheels off the ground and truck in gear they will rotate opposite ways. If they dont I would be double checking the lack of locker. If there is less load on the pinion than the other axle it will turn before the axle

When I jacked the back diff to get the rear wheels off the ground to rotate the driveshaft and wheels to count the revolutions I had the truck out of gear and the front wheels chocked. You say with both wheels off the ground and the truck (running?) in gear the wheels will rotate opposite ways, that sounds like an open diff to me. Please correct me if I'm wrong. I believe my isuzu has a LSD hence why the wheels rotate the same way when jacked up and the driveshaft or either wheel is rotated. Do you think I have worked out the correct ratio of the diff? I'm starting to doubt myself now

I don't think it's an auto locker as it does not sound like one. For example auto lockers make the clicking and clunking noises while turning at low speeds any time (whether the diff is cold or warm), where as my diff does not make the normal locker "clicking" sound ever. Also it only makes the clunking noises after appx 30km of driving, once the diff is warm.

[geeves]

in gear but engine off
4.3 will be correct

[isuzurob]

as per your other thread im sure it fixed his truck as it was fine when i saw him, if it plays up only when turning, that is when the pinion and crownheel are under the most load, does it loose drive when it clunks or bangs? the mu diff will fit just make sure the ratio is correct as they come out 4.5 also

[gomulletgo]

does it loose drive when it clunks or bangs? the mu diff will fit just make sure the ratio is correct as they come out 4.5 also

No it does not loose drive when it clunks and bangs, I usually back off the accelerator when it starts as the harder you accelerate the worse the noise is. Re: The Mu Diff, I spun the pinion and the brake rotors spun opposite ways, it doesn't look LSD to me so I didn't bother checking the ratio. Still no 4.3 LSD to go back in the truck yet . Soooo many parts but not the one I want

[isuzurob]

4.3 is a common lsd in isuzu's i have 3 that i havnt fiited to my trucks yet, one of them has only done 300km since new and have a brand new lsd unit with no ring gear, normally if the teeth are broken it will clunk but normally loose drive now and then around corners, well my hilux did broke 3 teeth off the pinion, 4x4 on tarseal trying to back a trailer with a 4.5 tonne digger on it