Cross8 clunk

[yowiie]

guys I need s little advice
Sometimes When I am driving the cross8 on bitumen it feels like I have driven over something on the road , when there isn’t anything visible
It’s not really a clunk sound but a sound as though you have driven over a delineator
The engine seems to drop a few revs at the same time
Was in it yesterday and for some reason it felt like I was driving over corrogates, but there were none
Could this be a rear diff problem

 

[figjam]

No idea, but a suggestion.
How long since you have had the transfer case and diff oils changed ?

 

[_R_J_K_]

Check your tyre wear front to back too (or if you're running different sized tyres), if there's too great of a difference in rolling diameter the AWD system (possibly in conjunction with the traction control) probably won't like it.

 

[figjam]

^^^^ Good point. The amount of slippage before problems is ????? %. I chased this info through the local Holden dealer. They had NFI.

The answer from Holden customer assistance ……..
“ Please be advised that Holden and other vehicle engineers would allow variations as such to allow for wear and tear. However, should the variation in tyre size become extreme, the ABS module will log a DTC code and the IPC warning light will illuminate. ……………..Blah blah, refer to your Owners Handbook, ……….. blah blah, or if you have concerns, your nearest Holden dealership.”

In short, they didn’t know either.

 

[yowiie]

Check your tyre wear front to back too (or if you're running different sized tyres), if there's too great of a difference in rolling diameter the AWD system (possibly in conjunction with the traction control) probably won't like it.

I have considered this maybe the problem
Would you believe the cross8 has 245/35/20’s on it
I have only just purchased this Ute a couple of weeks ago and this is one of the problems I am having
I have noticed that the clunk is only noticeable when the car is at 60klms an hour, the revs change as though a plug is breaking down, it’s quite obvious when it happens revs change and I can feel the clunk in my seat
I am unsure if any oil change intervals in the transfer and diffs but will certainly get them done ASAP
And downsize the tyres

 

[figjam]

Standard tyres are 225/55x17, (97H) and are the same overall diameter as your 245/35x20. So that may not be the problem.
But, as a side issue, the load rating of your tyres may not comply with the placard requirements.

As for the transfer case oil change, seek out a reputable 4WD mechanic who is familiar with them ( including the earlier AWD Territories), and use the recommended oil from Holden, a bit expensive, but cheaper than a screwed-up transfer case.

 

[_R_J_K_]

Would you believe the cross8 has 245/35/20’s on it
And downsize the tyres

If the car is pretty rough anyway, going a smaller diameter will make it more comfortable.

Does your clunk coincide with a gear change?

 

[yowiie]

Hey guys
Have been away, no internet
Figjam is correct, the tyres are the same size overall with factory wheels
I am going to change the oil in the transfer case tomorrow if I can get some oil
I am having trouble locating the oil, does anyone know of another brand of oil I can use
I have googled but not having any luck

 

[figjam]

I am having trouble locating the oil, does anyone know of another brand of oil I can use

Glen Innes Holden gone ?? Try Newcastle Gearbox and Diff (Matthew > 02 4957 7197) on Monday for advice if no luck over weekend. They used the GMH oil in my case.

Edit
Does your owners hand book mention what oil to use in the transfer case ? Mine doesn’t.

The Penrite oil website https://www.datateck.com.au/Lube/PenriteAus/ states to use Trans Gear 75W-80. But I would not put too much credibility on that. Their information site, although informative, is not always correct. I was informed it was a ‘guide’ when I queried a difference between their website and owner's manual.

To the best of my knowledge, the Ford Territory AWD transfer case clutch pack is the same as Holdens. Their owners manual, ‘only Texaco Havoline 1854 Dexron111, 0.5 litres’
Have a look at the 3 Penrite recommendations.

Bit of a minefield.

 

[yowiie]

Thanks for the info
My ABS was playing up and only just replaced about 20 mins ago and would you believe the clunk has gone out of the car.
Whats your thoughts on that, would the traction control have played apart in the clunk