Excessive Front Diff Lash

Steve Bass

New Member
I am in south_africa
Jun 16, 2020
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Hi Guy's,

My 80 has developed what looks like a HUGE amount of lash on the front diff where the drive shaft connects. Apart from clunking when you change gear, you can turn the driveshaft by hand maybe 10 or 15 degrees.
So is likely to be a pinion issue or could a faulty half shaft/burfield cause this by allowing the slop in a knuckle to be transfered to the pinion and driveshaft???
 

frank rabbets

Well-Known Member
Mar 1, 2010
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If you drop the drive shaft off you'll get a better feel as to what is going on when you rotate the flange back and forth. The first bit of felt play will be the play between the pinion and crown wheel and the total will include that and the play in the rest of the drive which involves the cvjs and various splined joints. Chris will know as to what is excessive.
 

Steve Bass

New Member
I am in south_africa
Jun 16, 2020
11
0
1
Hi Frank,

Thanks for your reply.
So the lash is enough that it 'clunks' when you put it in gear (auto) or change down. having been under the car, the drive shaft can be moved a lot CW or CCW and I would have thought the lash between the crown & pinion would be such that if a burfield is going, the slop would be at the corner not at the diff input.
I guess i'll have to get her up on stands and start digging around.....
 

Towpack

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Oct 4, 2011
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As Frank has said, you need to disconnect the prop shaft. When you turn the input flange you should be able to differentiate (no pun intended) between the lash in the diff itself and any in the CV's which you may feel as a slight click or notch.
 
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frank rabbets

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Mar 1, 2010
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The total front lash without drive shaft on when you turn the pinion flange includes everything from the flange to the tyre. You are doing everything the engine does but by hand. Has the clunk developed over a long period? If no joy with answers you might start a new thread with "clunk when engaging drive on auto 80".
 

nielsc

Well-Known Member
I am in belgium
Jun 28, 2016
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It's play in crownwheel/pinion, spider gears and halfshaft splines in the spider gears. Not much to do about it except taking everything apart and replacing the diff center and halfshafts and adjusting the diff again.
 

Chris

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I am in europe
Feb 24, 2010
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Hello, someone mention my name? Not much I can add at this point, the guys are right. If the wheels are on the ground so they can't turn and you wind the diff pinion or prop one way until it stops (you're not going to drive the car by hand..) then turn back again, you will feel all of the play from the pinion to the drive flange inthe centre of the wheel. 10 to 15 degrees ish for all of that is not excessive. If you do this very gently by feel and you can tell that all of the that slack is in the diff ALONE then yes 10 to 15 degrees is a bit much perhaps. But what is important is the preload. If you can move the drive pinion back and forth with the lightest of touches, I'd suggest you have no preload any more. This will probably accentuate the play at the crown and pinion in relation to clunking. Front diff issues are of course very common with older high mileage 80's.
 

Steve Bass

New Member
I am in south_africa
Jun 16, 2020
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Many thanks again. Given what you say Chris, that the turning of the prop shaft will indicate all possible movement in the axle and halfshaft driveline when the wheels are on the road as well as some odd noises coming from the front near side wheel has me thinking the knuckle/burfield/halfshaft is the prime suspect.
So, here we go with the front bearings and knuckles being rebuilt.....
 

Chris

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Good place to start. With the centre diff locked and one wheel off the ground, you might get a better feel for where the issue is. Turning the road wheel gently by hand my uncover some grinding, clunking etc etc.
 

Steve Bass

New Member
I am in south_africa
Jun 16, 2020
11
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thanks! I'll give that a go. I suspect it's the near side (RHD vehicle) as there's some clinky clanky type noises coming from that side......
 

Steve Bass

New Member
I am in south_africa
Jun 16, 2020
11
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indeed :blush:

So mamanged to chat with the local Terrain Tamer guy and he's of the opinion it's the UJ on the drive shaft that's on its way out. There's no oil seeping past the wipers and the bearings are ok so it sounds a reasonale diagnosis. And if there's a lot of slack or slop in the UJ that would explain the clunking and seemingly excessive lash at the prop shaft.
So there's a couple of new front drive shafts and knuckle rebuild kits on the way in the new year.... not unexpected for 400000+ relativiely hard kms....
 

clivehorridge

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May 23, 2012
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IMHO the order of any work on this should be cheapest first.
First replace UJs,
Second check drive shafts/CVs
Last the diff pinion gears.
I‘ve had excessive front diff play for the last 5 years (460k km on it now) and apart from a whine under drive, which decreases with speed, it’s still holding up well.
I cure that with a bit more volume on the sound system :lol:
 
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Steve Bass

New Member
I am in south_africa
Jun 16, 2020
11
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1
Small update...

So it's looking like the near side CV joint in the half shaft is the prime culprit.... It's now giving a loud clicking at full lock.
Witht he front jacked up and the prop shaft disconnected, the offside wheel turns the pinion flange directly, no real lash.... Not so the near side. The wheel can move quite a lot forward and back without moving pinion flange. And popping off the diff cover shows the half shaft into the diff isn't rotating at the same time as the wheel.

So, rebuild of the front axle is under way.
Add tot hat a full cambelt service on the motor while we're there....
And on the upside, I fixed the Clim Control... seems the water valve actuator cable was jammed solid. new cable and we have heat in the cabin!!
 
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