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Exploding Diffs - where does the energy go?

Crispin

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I was watching some of the vids from Gavland and Jimbo and one of Jimbo going up the hill had me fascinated.
See below:
[youtube:3dyx9qeu]1eDtxy52QEk[/youtube:3dyx9qeu]

In the first seconds, the front wheels are spinning, the truck then comes down hard and both front wheels stop dead.
If the CD was open, this shock would be absorbed through the rear of the drive train and into a spinning rear wheel (assuming there was one)
If however the CD was locked, this must put a huge shock load through the drive train. To have all that kinetic energy and then instantly stop - that's got to be punishing to something.

What is the weight of the wheels+tyres vs drive shafts, diff gears etc. The wheels would be storing most of it which, when stopped, would actually not send that much through the drive train?

At what point does a diff break? That? Ian? Chris? When happened with yours?

Curious as ever....
 

Paul_Humphreys

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Diff normally go under shock load (well mine did, I have done a fair few in LRs). If you watch the video it goes when the spinning wheel hits the ground.

Paul
 

Graham Stirling

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It's normally the ring gear that breaks. When the wheels stop the pinion forces the ring gear to flex. Have a look on the web for "diff pegging". Diff pegging stops the ring gear flexing by bracing the back of the ring gear where the pinion works on it.
 

Jimbo4x4

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What can I say? The LC's a hardy vehicle and can (in most cases) put up with the punishment. The angle of the hill can be factored in in this case to take weight off the front wheels so the shock load wouldn't have been near the threshold. There can't have been much more than quarter a ton spread between the two front wheels when at standstill.

The 70 is part time 4wd so there is no centre diff, the transfer box runs like a locked diff whenever 4wd is selected.

The shock load may have been transfered all the way to the auto box, as you can see the rear wheel wasn't spinning at the moment the front wheel touched down either - although I didn't have the rear locker engaged at that point so the opposite one may have been.


Graham Stirling said:
It's normally the ring gear that breaks. When the wheels stop the pinion forces the ring gear to flex. Have a look on the web for "diff pegging". Diff pegging stops the ring gear flexing by bracing the back of the ring gear where the pinion works on it.

If you do this though, what in turn would be taking the strain of a shock load? The transfer? Or perhaps something even more difficult or expensive to fix?
 

Crispin

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Was going to add though (Jimbo / auto 'box reminded me) that if you had an auto which at that point, I would assume an auto does not lock the TC, your slip would be taken up in that? At great strain but would absorb it.
 

Graham Stirling

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Jimbo4x4 said:
Graham Stirling said:
It's normally the ring gear that breaks. When the wheels stop the pinion forces the ring gear to flex. Have a look on the web for "diff pegging". Diff pegging stops the ring gear flexing by bracing the back of the ring gear where the pinion works on it.

If you do this though, what in turn would be taking the strain of a shock load? The transfer? Or perhaps something even more difficult or expensive to fix?

Probably. Once you strengthen the weakest part the next weekest part becomes the week link. The rear half shafts take a fair bit of strain as they will twist and generally spring back. Sometimes, in the case of LR's, they twist or break at the splines. I've never had my LC rear shafts break but i would guess that the flange bolts would break before the shaft.
 
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Jimbo4x4

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I know from experience with my old SJ that broken halfshafts are a PITA to fix, but at least cheaper than a diff to get hold of.

Does anyone think that with having an auto box I'm a bit safer from these dangers? Surely it must be able to absorb quite alot before anything else in the drivetrain goes?
 

Paul_Humphreys

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Jimbo4x4 said:
Does anyone think that with having an auto box I'm a bit safer from these dangers? Surely it must be able to absorb quite alot before anything else in the drivetrain goes?


No, I use to brake diffs and shafts in autos and manuals the same. Must have been my driving style :shock:

Paul
 

Graham Stirling

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I recon that an auto give you a smoother take up so that you don't risk breaking something by snapping the clutch up at high revs. But, i don't think they help if you tend to be heavy footed anyway or start bouncing the front end like in your vid.

I prefer autos personally but i've only ever bust anything in a manual and that was on tarmac.
 

Paul_Humphreys

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Most of my brakeages were done in off road trails, where you have to try hard!!

Paul
 

Paul_Humphreys

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Not driving, but set on up last week end, they said it was too hard!! The RTV and Inters, if I would have entered in the 80 I would have won!! As it was up against a lot of SJs and I would have got a lot further using longer wheel base on the cross axle sections. Trees don't bother me!!

Oh yes, off out in a bit to help put out some punch markers for tomorrow (for winching), but I have to work tomorrow.

Paul
 

Chris

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That's exactly how mine went. When the front wheels landed they had so much grip that the drive had to go somewhere else. As the back wheels were effectively carrying the whole weight of the vehicle, they could not spin either, so the diff had to go. Now, in a really well set up drive train where the pre-loads are all as new, maybe it just stalls the engine? I dunno. But from now on, no more radical air for me!

Chris
 

Jimbo4x4

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Battered and Blue said:
That's exactly how mine went.
:( I'll have to be more careful in future then. I haven't pushed this thing as hard as I pushed my old SJ as it is my only transport at the moment, but I would have thought Toyota engineering would be alot more up to task than Suzuki? Just that in 4 years of owning the SJ and very heavily off roading it throughout that time, the only damage done to the drivetrain was two snapped halfshafts (NSR after a big air, OSF trying to pull a stuck LR90 out of a mudpit in reverse - lesson learnt :p ), and a dead clutch after scooping a load of mud into the bell housing when I smashed the protection off. :?
 

Crispin

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Jimbo4x4 said:
:( I'll have to be more careful in future then.

Didn't mean for you to feel like you sitting in front of the headmaster :|

Was a good example though of what I was thinking about.
 

Paul_Humphreys

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If you ever see a Jeep doing a trial, you will see most with road or AT tyres. They have a 4.0 engine and a lsd in the rear. The idea is that you can spin the tyres a lot more with a lesser tyre than a MT.

Also with the SJs they are very light, so when they grip they tend to spin. Driving a SJ is very driffrant to driving a LC or LR.

Paul
 

Graham Stirling

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Paul_Humphreys said:
Not driving, but set on up last week end, they said it was too hard!! The RTV and Inters, if I would have entered in the 80 I would have won!! As it was up against a lot of SJs and I would have got a lot further using longer wheel base on the cross axle sections. Trees don't bother me!!

Oh yes, off out in a bit to help put out some punch markers for tomorrow (for winching), but I have to work tomorrow.

Paul

Excellent Paul, fancy coming up to marshall the Phoenix in July? It's near Dumfries this year,just down the road from last years site.
 
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