Troll Hunter Posted March 29, 2012 Share Posted March 29, 2012 Hi, I need some answers or views, please. My GKN overdrive recently stopped working - wouldn't engage - and since it's designed to only engage above 30mph it's not easy to try and see what's wrong with it. In the garage I checked all the wiring, and it seemed OK, so I decided to put both axles up on axle stands and run the engine in gear, at above an indicated road speed of 30mph, and examine the system, including getting under the vehicle, while it was safely stationary. I thought this would be straight forward, but when I was ready, with the vehicle up on four axle stands and engine running, I engaged gear and - horror of horrors - a wallet-crunching grinding and clunking sound from the front diff. And this was in 1st gear at an indicated road speed that didn't even register! A couple of days ago, when I last used the vehicle, all appeared normal, apart from the o/d not working, and there were no untoward noises from the transmission. How many pieces of metal were being tumbled about in there? I checked both front wheels and there wasn't any play when I tried rocking them at top and bottom, so I judged the wheel bearings to be OK. The drive shaft was OK. So I thought I'd better check the diff oil. I first checked the level and it was full to the filling plug, so loss of oil wasn't the problem. So I drained the diff oil, and it appeared not to contain any metal particles when I ran it over a rare earth magnet. However, it appeared to contain not only the original SAE 90 but also the One Shot that I'd put in the swivel housings. Once drained, I felt around inside the bottom of the diff, and couldn't find anything. I refilled the diff with new SAE 90 and checked/topped up both swivel housings. Unfortunately, I hadn't checked the swivel house levels before draining the diff, but I have no reason to suspect that low oil level in the swivel housings was the cause of the noise. And ....... I still have a horrible noise from the front diff. So, is it normal for diffs to make grinding and clonking noises when the vehicle is up on axle stands? The only reason I've been able to come up with is that when the wheels don't have rolling and road resistance the half-shafts "bounce" in their contacts within the diff, instead of being held in constant contact while transmitting drive to the road. Sorry this has been so long, but, please, give me your views, answers, etc. Many thanks. Miike Quote Link to comment Share on other sites More sharing options...
zoltan Posted March 29, 2012 Share Posted March 29, 2012 ? Any excessive play in the wheel bearings? (clutching at any straws available) If you breath on the brake pedal when it is in drive does it quieten down? A tiny amount of load would stop the multitude of shafts and splined connections chattering Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted March 30, 2012 Author Share Posted March 30, 2012 Many thanks, Zoltan. The wheel bearings all seem good with no rocking movement when pushed/pulled top and bottom, but when I touch the brakes with the engine running and in gear it quietens down quite nicely, so it must just be the slack in the transmission rattling about since there's no road resistance. I'll keep my fingers crossed when I put it back on the road. Mike Quote Link to comment Share on other sites More sharing options...
Gremlin Posted March 30, 2012 Share Posted March 30, 2012 Ohhh i had the same horror story..........but it was my center diff making horrible noises.............. i quickly took it off the jack stands and convinced myself noting was wrong..................in fact this has happen some years ago and it still drives well on the road, no noises or funny grinding and clonking............ I guess its all the backlash in the system............scary scary i must say....................... G Quote Link to comment Share on other sites More sharing options...
Maverik Posted March 30, 2012 Share Posted March 30, 2012 Every time I've drained back my front axle the oil contains one shot, it must just migrate back down half shafts. Talking about transmission "slap" I'm planning a front output nose change on my transfer box as i refuse to belive that any rotating machinery should have as much slack as that does. By the time you get to your wheels it is alarming the amount of transmission play. Mav Quote Link to comment Share on other sites More sharing options...
nicks90 Posted March 30, 2012 Share Posted March 30, 2012 it is quite frightening how much play there is in the system when you add up all the areas that can jiggle. splines into transfer box, 3 diffs, 4 splines into diffs 2 or 4 splines into drive members. as a test, lock your centre diff and put it in gear, then jack one front tyre and one rear tyre in the air and see how much play there is between the front and rear tyre when you rotate one of them. Quite scary. Quote Link to comment Share on other sites More sharing options...
landroversforever Posted March 30, 2012 Share Posted March 30, 2012 Its part of the nature of the beast to a certain extent though, lots of components with little bits of slack soon add up. Your average car has far less bits in it, I guess its probably a far newer design too! Quote Link to comment Share on other sites More sharing options...
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