Front diff remove/repair

Hi all,

Back story: A while back I hit a big rock at speed. There was no visible sign of damage apart from a bent panhard rod, which I replaced with a heavy duty one. However since the accident the Jimny has shaken violently at speeds over 20mph. I have since changed the King pin bearings and track rod ends but the wobble is still there.

I took it to QwikFit for an alignment test to see if anything like chassis damage became apparent. The mechanic took it for a drive and said that I need to see a gearbox specialist as the shake appears to originate from the front diff. So I'm guessing I've damaged the part where the axle joins the diff. Is this something that an average DIY mechanic can fix? I assume it would cost a fortune for someone else to do it so I'm thinking about having a go myself. However the most complicated thing I've done to date is the King pin bearings. Has anyone done anything similar?

Just thinking.
Shaking could be the following:

Something's no longer connected, broke or loose on the front end = should be easy to see and check visually if you jack the front end up. Also while its in the air check your tyres and wheels are still round etc.

Something that rotates is bent - check wheels above and make sure the front drive shafts and prop are not rotating, ie in RWD only. If they are turning try to find out why (jammed hub etc) disconnect and test drive again. If it still wobbles then disconnecting them has eliminated their influence. If it only wobbles when they are rotating check half shafts and front prop. Hope you can visualize what I am try to say.

Something is miss aligned. This could be a bent axle or tracking. Not sure how to check this, but assume tracking check would highlight issues.

If it's a bent item then a second hand unit is going to be the best option in my opinion.

Swapping the axle, prop shaft, half shafts etc is not complex. If you can do kingpin bearings you can do the rest if you have the time and tools.

Just trying to help.

Mike

As suggested if it is running properly in 2wd the front drive line shouldn't be rotating and is therefore not going to make a vibration even if it is bent. It's much more likely something is happening to the wheels as they rotate causing them to not run true. So something like a buckled rim, an egged tyre, or damaged hub/bearing assembly.

Thanks both for the excellent replies. I have manual hubs fitted and the wobble occurs in both 4x4 and 4x2 modes on those. That said, I haven't checked to see if the hubs are disengaging when I switch modes. They both make a reassuring clunk when I turn them though so I just assumed they were working correctly. Silly question time: to disconnect manual hubs is it just a case of taking them off?

Also I've swapped front and back wheels and the wobble remains on the front axle, so I'm thinking that the wheels are fine.

When changing the king pin bearings I removed the half shafts and these didn't appear bent or damaged either.

I haven't actually replaced the front wheel bearing (only the king pin bearings). Would a wheel bearing that's had a big knock cause a wobble like this? I assumed the wheel bearing was okay because it's been through an MOT with this damage, so I assumed that if there was significant play then this would have been highlighted.

So would it now be sensible to assume it's either a damaged manual hub, bent prop shaft or wrecked wheel bearing?

Not necessarily. It could be possible though unlikely that the wheel mounting flange is bent. Effectively any part that isn't fixed when the wheel rotates needs to be examined as do any bracket locations that can affect the relative position of the axle to the thrust line of the car. As in if the axle is not either straight in itself or mounted square to the car could result in weird oscillations. It is also possible that the front prop is remaining engaged at the transfer box end some how and is spinning when it shouldn't, if it is bent that could be a problem.

When you smashed the rock did you stop against it or continue over it before coming to rest? I'm just wondering if you managed to catch the rear prop because that would give you the constant oscillation if it were bent. A mechanic ought to have spotted that though, oh yeah kwik fit, probably not.

Right okay, looks like it could be a number of things so need to strip it all down.

I actually hit two rocks and continued over them. For context I was driving down a narrow lane that I wasn't familiar with, and as another car approached in the opposite direction I darted into a makeshift passing place not noticing the big rocks. It was quite a bang and I nearly tipped over. Its quite possible I hit the rear prop, but the wobble is definitely coming from the front as it shakes the entire front axle. To be honest I haven't even looked at the rear end for this reason.

I had a mechanic/friend take a look a while back they couldn't see anything wrong. I feel the same way about kwik fit but I only used them as they were the nearest garage that would do a wheel alignment check and hopefully spot anything else that could potentially be causing it.