Sj40 front diff or transfer slips under load? Any ideas?

LJ, SJ
Boydozm
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Sj40 front diff or transfer slips under load? Any ideas?

Unread post by Boydozm » February 7th, 2016, 9:23 am

Hey everyone iv got a 1982 1litre sierra sj40 and I'm having trouble with the 4wd, with the car on the ground, hubs locked in and in 4low I can grab the drive shaft to the front diff and with a bit of force rotate it in increments with a clunking sound also slips completly under load, I have rebuilt the whole front diff only had acsses to a second hand diff centre but seems strange it would do the exact same thing,

Thank you for any help in advance

Peter Aawen
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Re: Sj40 front diff or transfer slips under load? Any ideas?

Unread post by Peter Aawen » February 7th, 2016, 10:06 am

There's gotta be something drastically wrong there!! It could be something like the diff carrier has broken or deformed, so that the driving force actually allows the crownwheel to move clear & skip over the teeth on the pinion; or possibly that the pinion/crownwheel distance was never set properly so that the teeth don't engage properly.... altho the chances of a second hand diff centre having the same issue are pretty slim, unless maybe you rebuilt it before assembly using incorrect specs - Is that possible?

Other things that could be causing this is broken or damaged CV joints, so that when driving force is applied the CV allows the half shafts to turn despite the hubs being locked; or maybe worn splines on the ends of the half shafts or in the hubs?? I guess it could also be a broken axle that's still basically in place & only separating under driving force, but I'd reckon that to be the least likely.

The fact that you can make it do any of this by turning the driveshaft by hand is more likely an indication of the designed power output available from the engine rather than anything else, but regardless of where it comes from, the diff or the axles/CV's are turning when & in a manner they shouldn't, so something is drastically wrong in the front driveline, altho I'd suggest it hasta be somewhere ahead of the driveshaft & not in the transfer case at all..... but I've been wrong before :irked:

Good luck!
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

Boydozm
I'm new, be nice!
Posts: 2
Joined: February 7th, 2016, 9:17 am

Re: Sj40 front diff or transfer slips under load? Any ideas?

Unread post by Boydozm » February 7th, 2016, 10:20 am

I understand what your saying but this is where I'm at a loss I have had the whole front diff apart replaced everything, cv's, hubs, only the diff centre is second hand and when it was apart even my olds diff centre upon inspection everything looks fine even all the splines look in good condition, I took the drive shaft off and tried the same thing, spinning the back off the diff by hand and it wouldn't do it??

Peter Aawen
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Posts: 20807
Joined: June 17th, 2005, 8:01 pm

Re: Sj40 front diff or transfer slips under load? Any ideas?

Unread post by Peter Aawen » February 7th, 2016, 10:45 am

Is it worn splines or a dodgy slip joint in the driveshaft, & not the diff turning at all?



But I'm still more inclined to think that if you can turn it via forcing the driveshaft to turn while the hubs are locked & the front wheels are on the ground (& I assume not turning as you turn the driveshaft) that your issue is still in the diff, half shafts, CV's, or Hubs rather than anywhere else.... The fact that you can't make it turn by forcing the pinion flange once the driveshaft is off is more likely leverage than anything else - put a couple of long bolts in the pinion flange holes where the driveshaft came off & then use a long pry bar across them at 90 degrees to the driveshaft rotation so you've got just as much leverage & see if you can turn the pinion then?! If you can't, then yeah, maybe start looking in the trans case, but I don't see how it'd make a great deal of difference - the gearbox isn't stuffed is it??
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

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