Look at my image of the hub spindles in my 500 rear axle thread. It sits on lugs about the size of a standard washer. There is no flat joint face.

These people sell shim washers. They have various thicknesses.
https://www.ebay.co.uk/itm/0-5mm-THICK-SHIM-WASHERS-HIGH-QUALITY-STEEL-DIN-988-ALL-SIZES/253287469547?hash=item3af91c11eb:m:mL7tYo9RonYTvbphx9unn2w

These look better but no M10
https://www.ebay.co.uk/itm/Flat-Metric-Steel-Shim-Washer-0-1mm-Thickness-DIN988/132407910887?var=431749054560&hash=item1ed42061e7:m:mpqQbVDm6gh_YpEyR3EoeVQ

Shim sheets allow you to make your own washers. Possibly easier to use as you can do them in pairs. 1mm = 40 thou, so 10 thou is 0.25mm (near enough).
https://www.ebay.co.uk/itm/STEEL-SHIM-ASSORTED-PACK-6-PIECES-002-003-004-005-008-010-thou/264100789800?hash=item3d7da23e28:g:~qcAAOSwgQ9VnUY6

But if you want it done properly accurately you will need a ground shim plate with the correct angle. It will be faff with thin shims but you can build up the correction layer by layer. The plate would have to be made by a machine shop on a surface grinder.

Edit - The easiest way to make holes in thin shims is with a punch. But try finding one to buy. Thin shims can be drilled if clamped between two metal plates. Drill holes then cut around with suitable shears.

This shows the stub axle casting. It sits on four lugs so shim washers would be ideal. Just grease them before the final fit and try to avoid slicing your hands.

To make life easier while check fitting for final thickness, you could use aluminium sheet though the thinnest is 0.5 mm if you can find it. 1mm is more common. It's easier to work with and might crush as you tighten down the studs to take up an angular seating. You might get a better result if the size steps are not too coarse.

DaveMcT said:

Look at my image of the hub spindles in my 500 rear axle thread. It sits on lugs about the size of a standard washer. There is no flat joint face.

Click to expand...

Quite right, as I discovered today. No need for a shim plate, shim washers are ideal. It seems 16mm O/D is standard on the M10 shim washers needed for the hub studs. It still seems a bit small, I'd prefer something bigger to cover the face of the lugs on the hub, but maybe it doesn't really matter. I'm just being picky.

Thank you for the links. I'd been looking myself at the first link for Screws City in Edinburgh. Could we send Mrs Jock over to see if they have any larger washers lying about?

Quick recap: my rear tyres have both been wearing down the outside tread, particularly near side. The front of my rear tyres was approx. 6mm inboard of the rear, and the near side rear wheel visibly pointing inboard:


After fitting 0.8mm shims to the front two studs on the N/S rear hub, I bounced the suspension & pushed the car backwards, measured 0mm difference between front and rear of the rear tyres. The car was rolled another half wheel rotation, and the front of the tyres measured approx. 2mm outboard of the rear of the tyres.

I know this is not an accurate measurement of wheel alignment, but allowing for variations in the rim & tyre, I'd say it's possibly more or less parallel, and definitely an improvement. Visually, the difference is obvious from the rear. Before and after:

I'll try and get her to a 4-wheel alignment as soon as I can to reveal just how much of a mess I've made of it! With more accurate data I can try to calculate & source more precise shims. I suspect I've pushed the N/S too far into toe-out territory, and that I probably needed closer to 0.5mm on the N/S and 0.1-0.2mm O/S.

Still, my main aim was to alleviate excessive NSR tyre wear. There seems consensus that manufacturing tolerances on the rear axle are pretty relaxed, so I'm not going to fret too much about getting it perfect. I've swapped the front & rear wheels and will monitor tyre wear.

I wasn't expecting any change in handling with such a small adjustment, and she felt fine on a short test run, but on a straightish bit of road, it feels like the dreaded pull to the left has gone! Letting go of the wheel didn't result in a visit to the ditch, anyway. It's a couple of weeks since I saw a dual carriageway, so will have to wait to confirm this. Not many straight lanes round my way...

I must admit, this job took me a couple of attempts. Because I suspected the N/S had a lot of toe-in, I started with standard M10 zinc-plated washers, 1.6mm thickness. This was clearly far too much, and the front of the tyres went from 6mm inboard to 9mm outboard of the rear. I figured that 0.1mm of shim equated roughly to 1mm of adjustment at the tyre circumference (at the highest available points to measure, under the handbrake cables at the front, and under the exhaust back box at the rear). I used 0.8mm, the closest I had to 0.6mm, to give me the above results.

The photos of the shims in place are the 1.6mm thick washers from the first attempt, just to show the location. In between fighting rain showers and impending gloom, I didn't manage to get any decent pics of the final assembly.

Thank you Jock, DaveMcT & portland_bill for your advice, and also for warning about the hub stud nuts. Once I'd got them cracked, I took it easy with plenty of penetrating fluid & cleaning the threads, and they ran off OK. Not bad for a 15 year-old FIAT!

Thanks for the follow up and the info on the shim thicknesses and how they seem to equate to movement at the tyre surface. Do let us know if the pull is gone (or significantly reduced when you can get her out on a decent bit of road.
Kind regards
Jock

Thank you Jock. I'm sorry I don't have the capabilities to do this more precisely, but as a very rough guide, 0.1mm of shim between the rear stub axle and swing arm mounting plate gives about 1mm of movement at the tyre surface, so if anyone else has rear tyre wear issues, then toe and camber can be adjusted this way. I don't know what caused my near side rear wheel to be so far out of line, though. I'll try to give an update soon, once I've covered a few more miles and had alignment properly checked.

It's a seesaw effect.

For toe out, the REAR studs are the fulcrum. Being about 50mm from the front studs, this gives about 10 : 1 at the tyre tread. So 1mm shim = 10mm tread movement.

However, this is the radial measurement. Most tracking is done on the wheel diameter.

e.g.
If the wheel track is 5mm "wider" at the back than at the front you need enough shims to move it just 2.5mm so 0.25mm would be enough. That's near enough +2.5 at the front and -2.5 at the back = 5mm overall.

DaveMcT said:

It's a seesaw effect.

Click to expand...

Yes, I was expecting the wheel to pivot around changes I made at the hub, and your post confirms what I experienced. Except that I didn't get uniform movement at the front and back.

I don't have the equipment or expertise to carry out accurate wheel alignment measurements on the wheel diameter, so used a tape measure between the inner grooves on the front and rear tyre surfaces just to get a rough idea of what was going on.

Shims were added to the front two studs on the near side rear hub. With the rear studs acting as fulcrum, I found the front of the tyre moved roughly twice the distance of the rear of the tyre. For reference, here are the measurements I took:
Before adding shims: Front: 1293mm / Rear: 1299mm
With 1.6mm shims: Front: 1303mm / Rear: 1294mm (+10mm front / -5mm rear)
With 0.8mm shims: Front: 1298mm / Rear: 1297mm (aggregate) (+5mm front / -2mm rear)

Well, I managed to get alignment checked earlier than expected, but as expected, I've gone a smidge too far with my 0.8mm shim on the near side rear hub:

I now have 1.2mm toe-out N/S, 3.1mm toe-in O/S. On average not too bad And camber is surprisingly bang on at NSR, despite my extra wonky spring pan! Front alignment was also out, so was corrected at the time, I'll include the screen read-out for this.

The read-out suggests ideal rear toe-in is 1.5mm. In which case, I'm 2.7mm out near side, 1.6mm off side. Would this be right?

Now I just need to figure out if it's possible to make this kind of fine adjustment by shimming the rear hub, and if I can be bothered All the shim washers I've found give increments of 0.1mm thickness, so all I could realistically do would be take 0.1-0.2mm off the near side, and add 0.1mm to the off side to get it in the right area.

Is it really worth it?

I feel I've achieved my aim of improving the alignment enough to get rid of the worst of the tyre wear. And yet... having started, I'm reluctant to leave it at that. I'm tempted to continue to monitor tyre wear for now, and save this decision for later. Any thoughts would be very welcome.

The droopy spring pan we know is a design "feature". But if yours is drooping more than that it might be the metal thinning with rust and failing.

Measure the pan position. Put the jack under and heave it up. Measure again with jack in place. If it's moved you need to get the repair metal and welder sorts out. You could correct the droop at the same time.

Thank you Dave, that's a good idea. There is rust on my spring pans in the areas 1" in from the welds where I've seen others on this forum that have failed. I've treated it, but there was some pitting, so it's possible that the steel has been weakened there.

rmjbn1 said:

Thank you Dave, that's a good idea. There is rust on my spring pans in the areas 1" in from the welds where I've seen others on this forum that have failed. I've treated it, but there was some pitting, so it's possible that the steel has been weakened there.

Click to expand...

Mine had a clear line of thin metal where the rust was flaking off more persistently and exposing new metal to corrosion. Mine was also lower on the left but it did not seem to have separated.

I noticed yesterday my 100HP site lower on the left rear (and that's the side where the tyre sometimes touches the inner wheel arch. The 1.2 Dynamic with its 500 axle sits perfectly level.

If the metal has thinned and you are considering welding on reinforcement, I think it would be an ideal chance to level up the spring pan by slitting a V into that weak area straightening the pan, welding up and reinforcing with steel across the front side (the side nearest the axle beam).

DaveMcT said:

If the wheel track is 5mm "wider" at the back than at the front you need enough shims to move it just 2.5mm so 0.25mm would be enough. That's near enough +2.5 at the front and -2.5 at the back = 5mm overall.

Click to expand...

I keep thinking about this, and trying to work it out in my poor brain. Having started this, I don't feel I can leave it alone until I've got my rear wheel alignment as close as I can.

If the above is true, then it should follow that:
1mm shim = 20mm overall movement at wheel diameter, as wheel alignment is measured. Therefore:
0.1mm shim = 2mm movement at wheel diameter.

If I could move my near side rear 2mm inboard and my off side rear 2mm outboard with 0.1mm shim adjustments at the hub, I should end up with:
N/S is currently at -1.2mm (toe-out). Plus 2mm = +0.8mm toe-in
O/S is currently at +3.1mm (toe-in). Less 2mm = +1.1mm toe-in

My tracking report shows the correct rear wheel alignment is 1.5mm toe-in on each wheel.

I would therefore be well within tolerance, and have my rear wheels nearly parallel too.

I currently have 0.8mm shims on the front two studs on my N/S rear hub. If I reduce this by 0.1mm, and add 0.1mm shims to my O/S hub, would I be right in thinking I should get the result I'm after?

Or, if I loosen the bolts on the triangular mounting plates for the rear axle, is there any way to accurately control how much I bring the N/S forward and O/S back to get the 2mm movement on each wheel?

Unsurprisingly, the staff at the tyre centre stated my rear alignment couldn't be adjusted so it was a waste of time measuring it, and didn't want to know about any attempts to correct toe with shims. Which I completely understand.

Would someone with experience in this kind of thing be happy to confirm if my thinking's heading in the right direction, please? Even if my wheels aren't

I would guess if you took the car back and have it re tested the results would be different.


seen it for myself. I van bought from a dealer and pulling to one side. Went back to the same garage that did it a few days earlier. Needed adjustment as toe was in the red. The actual fault was due to the tyre.


While we were there a customer was being told they needed to pay for an adjustment because it was a massive 25 outside tolerance. Looking on the screen it wasn't degrees out of tolerance not even minutes but was seconds out. No doubt no more than the wobble in the rim they are measuring from.


the old method of mechanical slip plates was more reliable than 4 wheel laser alignment

Thank you Koalar, that's a fair point. I shouldn't be taking the results of one alignment check as gospel truth.

This is the first time I've watched laser alignment done, and I was surprised to see it taken from the edges of the wheel rims. Surely this is the part of the wheel most prone to dings and wobbles, especially on a pressed steel wheel? There were no checks that the wheel rim was true which, even to my untrained eye, seemed less than ideal. That's yet another point in favour of Jock's tracking gauge!

At least the alignment check did agree with my suspicions though. My off side rear had been slowly wearing the outside tread with feathering on the tread blocks, consistent with excessive toe-in. As I was quite sure my rear wheels were sort of parallel-ish, I was expecting to see a bit of toe-out on the near side rear, which is what the tracking report shows.

I did tell myself when I started this that I wouldn't worry too much about getting the rear alignment accurate, just improved enough to get rid of excessive tyre wear. So I am tempted to leave it at that and continue to monitor tyre wear for now. After all, the steering feels fine with no obvious pull.

However, I'm confident now that I do have too much toe-in on the O/S, and that my tyres will continue to get shredded unless I can just make this small adjustment of 2mm to bring my rear wheels into tolerance.

If I could be reasonably sure that either: a) adjusting the shims by 0.1mm each side, or; b) shifting the entire back axle slightly would cure this, I would do it. Any thoughts, please?

I would be surprised if any Pandas of this age had any true wheels


just noticed you are running the recommended 26psi at the rear. Depending on the tyre manufactures side wall construction. If you are spirited on roundabouts it could be tucking under slightly. I run 30 psi at the rear although its makes it a bit harsh.

rmj, I just can't tell you how interesting I'm finding this thread. I can see that you are "infected" with the same pursuit of perfection that also plagues a number of us on here. Can't quite make up my mind if it's a curse or not?

Interesting to hear that you noticed the lack of pre-measurement checking of the wheel rims. Was there any checking of suspension, ball joints, bushes, etc, etc? I would guess probably not and if not then the whole thing becomes a bit of a lottery doesn't it? The good thing from your point of view is that there's relatively little to wear on the rear so your rear results are probably fairly accurate. Very early on in my working life the garage at which I was employed bought a new set of Dunlop gauges (the "good old" mirror type) and the Dunlop guy (he'd be a "technician" today) who delivered then gave us a good hour of instruction as to how to get the best out of them. It's stood me in good stead all my life. Alas I've very seldom seen a "proper" 100% job done in any garage where I've worked. Time constraints and rusty/seized adjusters being the main culprits but apathy plays a big roll too. I liked the old Dunlop gauge because every time you went to use it you would put the measuring pointers together and zero the scale. This calibrated the gauge and eliminated any inaccuracy. I've never worked with modern electronic laser gear and I concede the modern electronic tools may well be even more accurate but if someone has tripped over them it may well be that the calibration is now going to be out until the next time the calibration is done? Or is calibration checked each time before using?

During the rebuilding of Becky's front suspension it gave me the chance to very closely examine all the mounting points and bodywork and I found not the slightest sign of any deformation or problems which might account for this slight pull to the left. Now with the toe correctly set there has been really no change in the way she steers so I think it highly likely that something's not quite right in the back and it does look as if, just by eye, there is just a very little bit more toe in on the N/S/R - not as much as you had though but she too pulls, just slightly, to the left.

I find all this very logical. If the rear N/S is slightly toed in then the rear of the car is trying to go towards the centre of the road all the time so with the steering wheel straight ahead you will find yourself heading for the kerb. A slight amount (in Becky's case a very slight amount) of right lock will correct this but the steering will still want to self centre so you end up holding on to that infinitesimal amount of right lock which is counteracting the right steer of the rear axle and keeping you out of the gutter but it feels to you that you've got a slight pull to the left - in fact it's just the steering trying to self centre. That also is why you feel it less at low speeds and more out on the open road at higher speeds. Now I've got the interesting problem of working out some way of measuring this. I'm determined to do it myself! (good job I'm retired with plenty of time on my hands! Oh, but I was nearly forgetting, I've got the Honda's brakes to sort out and my older boy's Punto needs a big service, a gearbox oil leak fixed, radiator fan only runs on high speed and the clutch likely needs a new master cylinder (very slight leak on the front pulley seal on the engine too). Once I've sorted all that out I'll try to find a minute to "play" with Becky".

Kindest regards
Jock

The axle mounting brackets bolt under the car but there are no dowels or fitted bolts. A small amount of misalignment is inevitable, but they always pull left so it might be the same manufacturing issue that made the axles with a drooped spring pan.

Jock
Could you check the rear with your tracking tool and check the axles are parallel to each other? Ive looked at mine but cant see a useful datum to work from. I have a significant pull to left but tracking checks say (before and after the rear axle stripdown) say its spot on.

The laser alignment tool should be adjusted for wheel runout before measurement starts. The tool is usually attached to the wheel rim at three points, so an initial reading is taken with each 'leg' at the bottom, rotating the wheel a third of a turn each time. A mid-position can then be set as a datum.
I'd hope this is done, and may well not be noticed by an observer, but may be worth watching closely, or asking how they account for an untrue rim.

portland_bill said:

The laser alignment tool should be adjusted for wheel runout before measurement starts. The tool is usually attached to the wheel rim at three points, so an initial reading is taken with each 'leg' at the bottom, rotating the wheel a third of a turn each time. A mid-position can then be set as a datum.
I'd hope this is done, and may well not be noticed by an observer, but may be worth watching closely, or asking how they account for an untrue rim.

Click to expand...

I have watched. No account of runout taken. As with anything. Its down to the quality of the staff and time allowed for the job.

My previous car had alloy wheels with between .5-1mm runout on all four wheels.

words case all the errors add up. Best case they cancel each other out. Most of the time it will be somewhere in between.