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Discussion Starter #1

I am chasing down a problem with my rear axle

The attached link shows a how much I can rotate the input flange of the diff before the wheels start to move.

Can anyone tell me if this is correct or do I have excessive play in the diff.

thanks
 

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Hmm, lot of slop there and going by your other thread its an overhauled unit?

I'm going to check mine as there was play but i dont think it was that bad.
 

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Discussion Starter #3
Yep, rebuilt 8000 miles ago!

I was reading the 105 manual I have today and it did tell you how to set the preload with a special alfa tool. This appeared to be a weight on a rod. When the preload was correct the weight caused the input flange to rotate 30 degress. This seems to be what is happening on my car, so now I am even more confused.
 

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But Mad North-Northwest
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Both my Spiders seem to have about that much play in the diff when I turn the driveshaft. No idea if it's normal or not, but they don't clunk or make noise so I've never really worried about it.

What problem are you trying to track down?
 

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What you are measuring there has nothing to do with pre load, but simply backlash. A diff has to have backlash. What is backlash?, the distance the pinion can turn before contact is made with the crown wheel teeth.

It is also perfectly normal to be able to turn the wheels back and forward a bit too for the same reason.

The only reason I believe you could not feel play at the wheels once you had loaded the driveline (referring to the test you did in the other thread) is because you loaded it. This to me indicates you have play in your suspension bushes, not the axle. Also the fact you still have play with the backing plate removed and the wheel bearing clamped supports this too.

Have you measured the play directly on the axle flanges with a dial gauge? That is what you need to do.
Pete
 

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Richard Jemison
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Differential

It is a real shame when people without knowledge post as if they are experts!
I suggest you ignore earlier post.

Using your video as the reference, I doubt that you have issues with the ring & pinion adjustments.

Most of the "slop" in the video is the differential assembly (spider gears and if LSD unit, the spider gears taking up the slack(clearance" in the clutch pack.
The more clearance in the internals of the LSD unit the farther the spider gears must turn to raise their shafts up the ramps to engage (put pressure) on the clutch pack. The LSD unit should always have some clearances (no preload) so that the clutch pack works as designed.

There is a lot of parts in the diff that reflect on the amount of movement on the input flange before the parts stop that movement.

A delicate touch on the flange can feel the initial contact on the ring gear.

To test the R&P backlash, remove the oil fill plug and wedge a screw driver in against the ring gear so it cannot turn. Then do the movement on the front input flange. Based on the diameter of the u-joint flange, about 1/8 inch is minimum movement in these differentials. 3/16" is normal for these cars with a bunch of miles.

If you have a whining noise that is indicatibve of worn parts, not just backlash issues. If it is whiuning get a replacement differential, don`t try to have it built as mechanics rarely can set them up correctly.

Video the test that I suggested above!
 

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Discussion Starter #9 (Edited)
Richard

Here a video of the test you suggested


Here a video showing how much the wheel rotates with the ring gear locked


This is a video of the problem I am trying to fix (see other thread). If you turn up the volume you can hear the play. (and no its not the brakes, hand brake is of)
 

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Richard Jemison
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slack

See I was correct as usual. (Nitwits please take note!:p)

The slack that you are getting in the wheel/axle is due to the excess clearance in the LSD unit.
The splines at the end of the driveshaft fit into the drive plates that are centered by contact with the internals of the friction assembly. It can be corrected by properly rebuilding the LSD to correct clearances. This requires a good selection of floater plates of different thicknesses.

It is not a major job other than having the necessary parts.
The LSD can be removed by separating the center and right (passenger) axle from the left tube (large steel bell). The Left tube can remain hanging in the car. Do noy remove any bearings as setup will be the same and nothing has to be reset R&P wise.
The internals should be cleaned and media blasted to remove glaze and restore LSD function.

There are not many people set up to correctly rebuild these things.
 

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Well I'll be the first to say I have no idea of how one of these Alfa LSD units work. I will say what a weird design, but Alfa7's comments make sense.

I'd take it out (and bin it) and purchase a gear type that Alfaholics sell. I used to have the same concept in my last club race car, worked beaut and no weird stuff with axles being able to float around in the centre.
Pete
 
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Ok, so this is exactly the same problem as mine (last video). Still trying to get my head around the technical comments as I haven't got a clue how the LSD works and by rocking the wheels it gives the impression the problem is localised at the outer wheel bearing end. Without opening the whole thing up and having a look I would of thought the inner bearing would of held the half shafts in place rather than them floating about through incorrect LSD setup etc but Alfar7 obviously knows his stuff..

next question is where in the UK can you get this sorted?
 

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Discussion Starter #13
Alex wrote

Strongly suggest you ring CTS in Markyate, Herts. Get Bernie to take a look at it. He's a fair-minded guy and will diagnose likely problems on the spot. I have a small amount of new internal components if really needed.


I will be contacting these guys over the next week or two to discuss.

WICTOD/ALEX

Have you discussed this issue with the specialist who rebuilt our axles?

If so, what reaction did you get. Mine has only lasted 8000 miles and has always had a 'clunk' when taking up drive. I assumed this was something else though as the axle had been rebuilt. Send me a PM if you don't want to discuss in public!

thanks
 

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How a 105 LSD (aka ZF LSD) works (potted version):
Below is a parts picture of the slippery bit of the diff.

Essentially, there's a multi plate clutch for each rear wheel.
Assuming the wheels are on the ground & have traction, drive arrives via the tailshaft, through the diff & into the limited slip clutch part.

The drive ring (part #4) moves out to clamp the clutch plates (part #s 2 & 3) to transmit drive to the axle/wheel. The outward movement of the drive ring (#4) is accomplished via the ramps (you can see these as cutouts on the inner sides of each of the drive rings (#4).
If a wheel loses traction the drive ring loosens its clamping of the clutch pack & drive is reduced/removed from that wheel.

There's a whole bunch of wearing bits in there, but the most important (in this instance) is the clutch plates. As the clutch plates wear & get thinner the drive ring has to move further out to clamp the clutch plates. Because that outward movement is accomplished via the drive ring ramps it uses more rotational movement to do this. But, within reason, it will eventually clamp the clutch plates & transmit drive.

This shows up as scary amount of "freeplay" in the tailshaft rotation before the diff takes up the slack caused by the thinner clutch plates.

Hope that helps (& makes sense, I've been to a party & might have had a drink or 2) ;)

edit to add: It's not that weird a method of LSDing, Hewland used a similar system in its racing tranaxles for many years. It was similar enough that there were court battles between ZF & Hewland over who owned the design.
 

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Discussion Starter #16 (Edited)
As a self confessed 'Nitwit' ;) I have been struggling to understand how the inner end of the half shaft is centred by adjusting the friction plate assembly.

I assumed it was located by passing through the inner bearing until it finally dawned on me that there would be no way of it passing through the bearing as this would have to be a pressed fit on the half shaft to prevent play.

I think I have got it:

The splines pass through one of the planet/or spider gears. This is located by moving it in or our using the correct shims so that the mesh with the other planet/spider gears is correct. If the LSD plate wears the gears can wobble about causing the movement seen and possibly the clunk when taking up drive?

Is this right or have I just made a tit of myself.


How a 105 LSD (aka ZF LSD) works (potted

version):
Below is a parts picture of the slippery bit of the diff.

Essentially, there's a multi plate clutch for each rear wheel.
Assuming the wheels are on the ground & have traction, drive arrives via the tailshaft, through the diff & into the limited slip clutch part.

The drive ring (part #4) moves out to clamp the clutch plates (part #s 2 & 3) to transmit drive to the axle/wheel. The outward movement of the drive ring (#4) is accomplished via the ramps (you can see these as cutouts on the inner sides of each of the drive rings (#4).
If a wheel loses traction the drive ring loosens its clamping of the clutch pack & drive is reduced/removed from that wheel.

There's a whole bunch of wearing bits in there, but the most important (in this instance) is the clutch plates. As the clutch plates wear & get thinner the drive ring has to move further out to clamp the clutch plates. Because that outward movement is accomplished via the drive ring ramps it uses more rotational movement to do this. But, within reason, it will eventually clamp the clutch plates & transmit drive.

This shows up as scary amount of "freeplay" in the tailshaft rotation before the diff takes up the slack caused by the thinner clutch plates.

Hope that helps (& makes sense, I've been to a party & might have had a drink or 2) ;)

edit to add: It's not that weird a method of LSDing, Hewland used a similar system in its racing tranaxles for many years. It was similar enough that there were court battles between ZF & Hewland over who owned the design.
 

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edit to add: It's not that weird a method of LSDing, Hewland used a similar system in its racing tranaxles for many years. It was similar enough that there were court battles between ZF & Hewland over who owned the design.
Yes I understand all that but what I don't get is what supports the inner ends of the axles. There must surely be diff side bearings(?) and they should support the axles not the clutch plates. The clutch plates should only be for torque transfer.

Any pictures of the crown wheel assembly?

Actually I think I get it, still poor design IMO. The diff side bearings support the crown wheel, but with a non LSD diff the spider wheels run in the crown wheel cage with no bush I think because they only occasionally have different rpms. Thus the inner end of the axle is accurately located.

In this case the axle ends poke into the clutch plates but Alfa/ZF have allowed too much axial tolerance of these clutch plates. I guess they did this so the plates won't grab on their edges and affect the slipping characteristics. But what they should have done is machined a surface after the splines on the axles that located in maybe a brass bush outside of the clutch packs in the crown wheel cage. Extra cost is the only reason not to have done this. This design alteration would have meant the clutch packs/plates would only look after torque transfer and no matter how worn these clutch plates were the axles would still be well located.
Pete
 

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Richard Jemison
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Lsd

Actually the LSD design is a excellent one, and not a ZF design but an old British one made by many suppliers in similar form.

The design is quite durable, and there is no reason to spend megabucks for aftermarket replacement.

The design allows for increasing lock up rate both by changing the number of "clutch" disk, or more approiately by changing the ramp rate (as was done with the Montreal unit).
The design also allows "de-cambering" the rear axle housing for race setup as it tolerates some misalignment.
 

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Discussion Starter #19
Richard

Am I right that by shimming correctly as per your earlier post, the gears are moved into mesh with each other more closely and thus removing the wobble in the halfshaft?

thanks

James
 

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Richard,In your experience with conventional differentials(non-lsd)what parts do you normally find worn,ie,shims,shaft,side-gears/splines,etc.?Or can the sloppy differential assemblies simply be shimmed back to specs.?thanks,Phil D.
 
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