Technical Rear axle tracking

[DaveMcT]

My 100HP has always pulled left and I've just got around to sorting it. Two separate garages with laser alignment said it's straight (both rears 0 degrees on camber and toe angles) but the pull is still there and has got too annoying to ignore any more.

I was suspicious the back axle is mis-aligned by a couple of mm but could not get accurate measurements to prove it. The rear axle stubs bolt on to the axle frame. Shims under front or back mounts will alter the wheel toe or camber.

So the back end was jacked up, and I loosened the stubs axle nuts. Two layers of coke can material give 0.22mm of shim. Probably 0.2mm when compressed. The 15" wheels are 190mm radius so the mounting stud spacing will give about 0.7 mm of toe change. The car pulled left so I shimmed front of left side and rear of right side.

All back together agains, a test drive showed less pull, but still not as it should be. I added some 0.5mm aluminium shims to the 0.2mm already done. That gives about 2.5mm toe change at the wheel rim.

Result! The car now tracks straight. I could hallucinate that it's still a little more keen to go left than right, but it's not enough to worry about.

 

[Ians Panda]

Hi Dave, i have a panda 2011 where the rear wheels are toeing in about 2mm each wheel, but i think fiats tolerance for the rears is about 6mm total for both so i suppose it's within tolerance. The trouble is i can go through a set of rear tyres in about 15 to 20k miles. They tend to wear from the outer side. When you used old coke can material, did you cut holes in for the stub bolts to go through? if you could just explain in a little more detail about how you did it, i may attempt it myself. My car doesn't pull either side like yours but it the tyre wear i want to fix.

 

[DaveMcT]

I used 30mm dia aluminium shims (0.7mm thick) slotted to fit over the M10 studs. The slots set to face away from the taper being created. I will eventually fit full washers but that will have to wait until the brakes need to come off the car. Aluminium is good because it will spread the load by compressing slightly.

The studs are 50mm apart and the radius to tyre treads is 140mm. 0.7mm shims give a 2mm camber or toe change. 1.5mm would give about 4mm change. Anything more significant would ideally need a tapered plate or even better a new axle.

The studs are at least 1/2" too long and will be rusty so good luck loosening them. The risk is the nuts unscrew part way then spin when the threads strip.

This is a new replacement Panda axle for £145. You can clearly see the hub spindle mounting brackets (four M10 studs and nuts each side). eBay item 153516226784

The question is why are both of your wheels toeing in. They should be at 0 degrees. Has the axle been damaged?

You could consider fitting a Ford Ka or Fiat 500 anti roll bar axle along with 500 springs and rubber buffers top & bottom. It has a 25mm wider track at each side but the body will accommodate 5J wheels with 175 tyres. It wont cope with 100HP size wheels. Everything is a perfect straight swap as the only difference is in the rear wheel mounting brackets.

This one is a bit more cash but looks as new and you get all the equipment (brakes, cables, hard lines etc.) image shows the mounting bolts. All it will need is a pair of rubber brake line hoses or better some 600mm long braided hoses going in one from chassis hard line to brake.
https://www.ebay.co.uk/itm/Genuine-...497803&hash=item28a8cffe21:g:90gAAOSwcMNgIl7a

 

[rmjbn1]

Hi @Ians Panda, I also fitted shims to my rear hubs to cure excessive tyre wear caused by too much toe-in.

I fitted a combination of 0.1mm & 0.5mm M10 shim washers from Screws City in Edinburgh.

I know @09 johno did similar but used gasket material, and I sort of wish I'd thought of that

More details on my thread here. I would advise to clean the threads of the hub bolts and soak in penetrating fluid, and take it easy backing the nuts off.

I'd guess you only need a thin shim on the front two hub bolts on each side as the toe-in doesn't seem excessive on your car. Maybe between 0.2mm & 0.5mm?

 

[rmjbn1]

The question is why are both of your wheels toeing in. They should be at 0 degrees. Has the axle been damaged?

My 4-wheel (mis)alignment shows rear should be +1.5mm toe-in each side (0 to +3.0mm each side is within tolerance)

Fitting shims to the hubs did get rid of both the pull to the left and rear tyre wear...

...BUT tyre wear transferred from my left rear to left front. I then fitted new front wishbones when one ball joint failed the last MOT.

I've read suggestions that worn front wishbone bushes / ball joints can show up in uneven rear tyre wear.

It seems like tyre wear is much more even since fitting new front wishbones, but I've not done much mileage since - I'm still monitoring it.

Still, worth bearing in mind.

 

[koalar]

Hi Dave, i have a panda 2011 where the rear wheels are toeing in about 2mm each wheel, but i think fiats tolerance for the rears is about 6mm total for both so i suppose it's within tolerance. The trouble is i can go through a set of rear tyres in about 15 to 20k miles. They tend to wear from the outer side. When you used old coke can material, did you cut holes in for the stub bolts to go through? if you could just explain in a little more detail about how you did it, i may attempt it myself. My car doesn't pull either side like yours but it the tyre wear i want to fix.

each side 0 to Plus 3 mm official specification

and plus 1.5 mm is optimal. Your car is close to optimum

you problem isnt the toe assuming its been measured correctly

 

[koalar]

The question is why are both of your wheels toeing in. They should be at 0 degrees. Has the axle been damaged?

Strange fiat specify plus 3mm as standard and plus or minus 3mm but don't specify rim size

thats 0 to +6mm total and don't specify a max or min per side just total.

 

[DaveMcT]

Are we talking toe change in mm or degrees? IIRC my tracking was laser measured in degrees of toe and camber angles.

After fitting new wishbones with new track rods (inner and outer) and tracking corrected on a laser system, mine was pulling left more than it did before the new parts went in. I tried setting more toe at the front which helped but it still pulled so I put it back as was.

The tracking was rechecked. Front and rear were all correct at 0 degrees. However, I suspect there is no measure across the car to confirm the axles are parallel and square to the car's centreline.

My recent MOT failed because a rear axle pivot bolt was not done up properly. I have to take the blame from when I removed the axle for de-rusting. But two MOTs have subsequently missed it. Anyhow, after tightening the bolt properly and checking the other side (which was fine) the car's pull to left was slightly worse. This points the finger at rear axle sitting off-square with the car.

Moving my rear tyre treads on both sides by the same amount (2mm to left) has kept them parallel. The slight steer should make the car pull to the right. However it now runs straight so I have to assume it's cancelling the effect of axle being off square to car's centreline.

I dont have the kit to do even a rough check of axle alignments as there is no datum line to work from. For now, the car tracks straight and can easily be put back to factory at any time.

 

[koalar]

Are we talking toe change in mm or degrees? IIRC my tracking was laser measured in degrees of toe and camber angles.

as I said mm

which works out at +0.1486404064255509 degrees on a 155 r13

 

[DaveMcT]

The adjustments are indeed tiny.
Wheel radius is about 285mm. Tyre circumference = 1790mm. 1 degree is about 30mm along the circumference.

 

[Ians Panda]

After reading everyone's comments i think i'll leave it because as koalar said, i'm close to optimal. Also someone mentioned about the wishbones, i'm not a mechanic but i think you mean the suspension arms? Well my last mot failed on the suspension arm bushings which i have now replaced the other day. so i'll keep an eye on tyre wear.

I don't think it's been in an accident before i bought it Dave but who knows, it didn't come with full history, although the nearside rear quarter panel is of a very slight colour difference.

 

[jrkitching]

Be aware that the Panda is reasonably camber sensitive; a slight pull to the left on a typically cambered road is normal.

Most of these aren't even set up correctly when they leave the factory; uneven and rapid rear tyre wear was common when these cars were new. You just have to improvise as best you can.

However, I suspect there is no measure across the car to confirm the axles are parallel and square to the car's centreline.

Getting the rear wheels parallel to each other, and aligned with the centreline of the chassis is the place to start. If that's not correct, you'll never get it to run straight without tyre scrub by fiddling with the front geometry.

Moral of all this: if your car isn't pulling to one side, or wearing tyres unevenly, leave well alone, and don't let anyone mess with the tracking.

I don't think it's been in an accident before i bought it Dave but who knows, it didn't come with full history, although the nearside rear quarter panel is of a very slight colour difference.

It doesn't need to be a full-on accident; just sliding a rear wheel into a kerb is enough to distort the twist beam. Once that happens, the rear wheels won't run parallel, and all bets are off.

 

[koalar]

some photo may or may not help

there is a subtle difference to outside edge wear

cupping, feather edge, scalloping and so on

probably the most common reasons

under inflation, gauge can be wrong

body roll due to worn springs shocks, fairly common on 15 year Old cars

over driving around corners

poorly made tyres

out of balance tyres

worn out wheel bearings

wrong tyres for rims

probably more I have not come across yet like the front mentioned by someone in a previous case

 

[DaveMcT]

Mine has always pulled left. After a few weeks of ownership, I noticed it was tram lining on motorways. Replaced both bottom arms along with inner steering arms and track rod ends.
It actually pulled more to the left because the right front was not trying to drag sideways.

I had the back axle out for grit blasting and zinc metal spray. It all measured up fine. Pulling s the same as nothing changed. Since passed two MoTs.

It failed the last (third) MOT - loose pivot arm bolt on back axle. I know not good. Fortunately it has a stiff locking nut that was not screwed up all the way. Its probably been like that since I did the axle. Tightened it and the pull to left was worse.

I think that proved (as best as I can) that the issue is with the back axle. The 0.7mm shims that steer the rear wheels a tiny bit left have solved the pulling. The tyre treads have moved just 2mm to left but the car now tracks straight.

 

[jrkitching]

loose pivot arm bolt on back axle. I know not good

Don't beat yourself up over this; it's an easy thing to miss, particularly when the bolts & threads were likely well corroded.

Looking back over the years, I've made plenty of worse mistakes than this!

 

[DaveMcT]

Don't beat yourself up over this; it's an easy thing to miss, particularly when the bolts & threads were likely well corroded.

Looking back over the years, I've made plenty of worse mistakes than this!

Thanks.

I'm actually not especially worried as the bolt had a number of threads beyond the nut. Being a very tight self locking type, it has sat like that for two years with no problems and would probably have lasted the car if it had not been spotted.

My point was that properly tightening the bolt worsened the steering pull suggesting the axle or the pivot mounts are not in line.

 

[rmjbn1]

someone mentioned about the wishbones, i'm not a mechanic but i think you mean the suspension arms? Well my last mot failed on the suspension arm bushings which i have now replaced the other day. so i'll keep an eye on tyre wear.

Hi. Yes, for wishbones read suspension arms.

I also replaced both front suspension arms for my last MOT (ball joint failure), after suffering excessive tyre wear. It would be interesting to establish if there is a connection.

I did read this in another thread, and that it would be impossible to get alignment correctly adjusted whilst there is play in either the suspension arm bushes or ball joints.

I'm also going to continue to monitor tyre wear, and will report back once I've done a reasonable mileage.

If my tyres do continue to scrub themselves to pieces, I'd go for another four wheel alignment now I have new suspension arms before changing anything.

 

[DaveMcT]

The correct settings are zero degrees on toe angle.
Front toe is via the steering arms.
Front camber is not adjustable.
Rears are officially not adjustable but shims can be used to make small adjustments.

You can get a general measure of front toe by checking the tread warmth after a couple of miles on straight road. I use the dual and do part in RH lane and part in LH to reduce the effects of road camber. The warmer side of the tread is where the scrubbing is going on. Adjust steering tracking until they are cool across the tread.

However. I did that with my car then a couple of weeks later took it to be four wheel laser aligned. They said I had far too much toe in. They corrected it to Fiat spec and the car pulled like it had before I had messed about replacing the track rod inners and outer ends. The warm tyre tread was back with a vengeance.

The only way to really know what's really going is to get the car checked on a body alignment jig. However, shimming the back axle has done enough to fix the pull.

 

[09 johno]

I used the old fashioned method of string and chewing gum (well blu tack !)
with the wheels straight ahead attach a bit of string to the inside of wheel rim (as long as the rim is not buckled) attach the other end to the same point on the opposite wheel mark the string as it touches the rim, now transfer it to the rear side of the same wheels, mark it again and see if there is a difference between front and rear no difference = 0deg.
To test, check tyre pressures are correct then put a wide band of blackboard chalk (which won't harm the tyres) across the width of the tyres in 2 or 3 places, then go for a short drive, but not on wet roads!.
look for where the chalk has worn away, if worn on the inside edge too much toe out, if worn on the outside edge, too much toe in.
Laser alignment is ok and is only a check, by the chalk method the full weight of car and driver is taken in to account on the moving suspension parts.

 

[koalar]

The correct settings are zero degrees on toe angle.
Front toe is via the steering arms.
Front camber is not adjustable.
Rears are officially not adjustable but shims can be used to make small adjustments.

You can get a general measure of front toe by checking the tread warmth after a couple of miles on straight road. I use the dual and do part in RH lane and part in LH to reduce the effects of road camber. The warmer side of the tread is where the scrubbing is going on. Adjust steering tracking until they are cool across the tread.

However. I did that with my car then a couple of weeks later took it to be four wheel laser aligned. They said I had far too much toe in. They corrected it to Fiat spec and the car pulled like it had before I had messed about replacing the track rod inners and outer ends. The warm tyre tread was back with a vengeance.

The only way to really know what's really going is to get the car checked on a body alignment jig. However, shimming the back axle has done enough to fix the pull.

Zero degrees on the rear is marginal and just on the edge of tolerance

Fiat have designed a little toe (same in most cars) in into the rear axle (3mm)

it reduces oversteer and gives better High speed stability

Tracking straight is controlled via the electronic self centring (there is very little caster built in to the panda)

if I turn the steering wheel clockwise and recalibrate the steering it will pull to the right. If I turn the steering wheel anti clockwise and recalibrate the steering it will pull to the left.


If I now shim the rears to correct the pull. I now have a car that travels straight line. But is both wrong at the front and back. Increased its oversteer and reduced its straight line stability.