Shimming front upper links to adjust camber

mrtask

mrtask

Well-Known Member
My car is fitted with shorter springs to lower the ride height. At the front, the wheels tilt inwards at the top, so my tyres are wearing unevenly on the inner edge. I recall reading on here that adding shims between the innermost mounting point of the front upper links and the bulkhead can rectify this issue. I've not seen the shim in question. Here's a photo I've 'borrowed' from a post on the faceache P6 club page. The person who posted it wondered what the items are, and somebody suggested that the four items on the left were just such shims for the upper links. Can anybody confirm this? Why are there two different shapes? Has anybody here done this themselves? At some point I'm going to need to change the rubbers on the swivel pillars that contact the front spring cup, at which time I'm thinking about reverting from poly bushes to Wadhams' rubber bushes in the top links, and perhaps adding some shims if anybody here can advise on design, thickness etc.

front-upper-link-shims.jpg
 
mrtask said:
Thanks for the suggestion @sdibbers. How many shims did you need to use?
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Blimey, now you're asking! In my case it was more to correct castor instead of camber, so both pedistals were shimmed. I think it was only about 0.0625" of shims needed. After alterations and 50 odd years of driving yours will no doubt need something else.
 
These are sensitive adjustments. You should get the front end measured for castor and camber before changing anything. Excessive castor will increase steering load. Too little castor will remove self centering in the steering, which I can tell you can be VERY scary to drive! Shimming BOTH bulkhead mounts will reduce castor; shimming only one will change mostly camber.
 
My Rover has had the top links shimmed since at least the mid 1980s, and quite possibly before, even back as far as 1978 when my Dad bought the car. JP is right on the money, it is not something to fiddle with. Ideally you should take it to a steering specialist, bringing along the Rover specifications so they can set it up properly. I recall watching a fellow do my Rover's steering back in the late 1980s. He loosened the top link bolts allowing them to move sufficiently to place shims in behind whilst observing his instruments. Shims were readily available at that time, I never brought my own, in fact I never bought any, they always came from the steering places. My wheels splay slightly out at the bottom when on the ground, quite the opposite when both front wheels are off the ground.

Ron.
IMG_1840r.jpg
 
There are some front end things you can measure easily,other aspects not so much. There are camber gauges out there that show them magnetically connected to the front hub, or even to disc rotor. Pretty much impossible with our front hubs, and its complete nonsense to expect to get a camber measurement from a hanging suspension with a wheel removed. Toe can be measured and adjusted using the stringing method, but camber and castor really needs a kit which involves a frame that can be reliably clamped to a wheel, with a camber gauge centrally mounted. getting castor from camber change usually involves turning the wheels +/- x degrees from straight ahead, and turn plates make this easy -but are heavy and $$$. these can be simulated with friction reducing wet (or oily) plastic under the wheels.
The bungy cord was necessary to keep the frame firmly in place against the wheel. This kit had the toe being measured quite a long distance from the wheel rim, where I believe it should be measured, despite the fact that I cannot find ANY mention in our manuals of that - implies that intention was that wheel alignment is only done by specialists.
KGNovMO.jpg


Castor can be calculated from measuring camber with the wheels at x degrees left and then right;-
castor = 57.3 * ( camber change/ Turn angle change)
If camber is positive or negative in both turns, subtract lower from larger; if one is + and other is - , add together.
eg if you turn wheels 20 deg each way, and the camber change is 3deg, then castor is 57.3 * (3/40) = 4.3deg.
The 57.3 (actually 57.296) is 180/ Pi, ie 1 radian in degrees.
 
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I'd advise against adding or subtracting shims to get a specific number value for the suspension settings. The manual does have some very specific numbers and the description and tools to set them. If the top link mounts are in fact out of tolerance I would adjust the car frame to get it square rather than packing up a link. just fixing the link angle will undoubtedly cause something else to be out. The P6 is also nearly impossible to measure accurately due to the amount of twist in the rubber joints and the need for the wheels to move latterally as the car height changes. There is also a change in both caster and camber as the height changes but due to the top link being at right angles to the bottom link the normal calculations don't apply.

I'm not saying do nothing. I'm saying start with ensuring ALL the moving joints (ball joints, rubber bushes etc) are in perfect condition then check the heights/measurements in the manual and ensure your frame is straight first. You do need to check all the bushes in the rear suspension as well as they effect the tracking of the front wheels. I think chrisyork has an article pinned on p6 suspension which is well worth a read.
 
At this time remove from availability and access to body jigs I think adjusting the car frame to correct front end geometry is so far out of reach as to be up there with Unobtainium. Only doable in a perfect world, maybe 20-30 years ago. I suspect that in Oz at least, if a P6 frame needed the use of jigs to check it, it would be promptly written off by its insurer.
If the problem is heavy steering due to bad castor that can be corrected by shimming ( as in Ron's case above, and in my own experience), guess which approach is both economic and doable? If something else goes out of spec, what will be the downside - bad tyre life, handling ? I agree that all other possible causes should be examined first, but even checking the frame is straight is no longer practical, unless you have access to a set of body jigs, and are up for the stripping work required to get a shell on the jigs. Fortunately my camber and castor were within spec, only the toe was badly out, which i put down to the sidelinks being aftermarket, and no alignment done after they were fitted.

To go back to the original question, the front camber spec is 1degree + or -. The shape of the front guards , IMHO, tends to accentuate the appearance of negative camber. To repeat - get the front end measured before doing anything. Bad toe in can also cause inner tyre wear also. when I adjusted my toe, I had a 24mm ring spanner spare, so I cut it in half (little room to swing the whole thing in there), then cut part of the ring out so it would slip over the track rod. Note that 24mm is very close to 15/16" - 23.8mm.
 
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Following all these suggestions with no little interest!
@jp928 that's a handy tip regarding making a handy spanner to fit the track rod.
I had a new track rod and both side rods replaced last year, as well as a new N/S upper ball joint. The other three ball joints at the front are still good. I also had the power steering pump overhauled and fitted with new seals and bearing. At that time we swapped the front tyres for the rear. Since then I have noticed the tyre wear at the inner edge of the N/S front tyre, but much less so on the O/S front.
This will have to wait until I can afford to spend more money on my car! I just had to shell out for having the N/S rear brake calliper removed, the handbrake mechanism freed off and the handbrake adjusted again. Shame, as both rear callipers are not more than two years old! Much as I love this car, it is intent on bankrupting me! That's what happens when one has to have any work carried out by a pro, rather than doing it oneself.
 
I have to respectfully disagree about not being able to correctly setup front end alignment. The jigs are an old school method for measuring geometry. Modern systems perform the same task but require an experienced operator to correct a P6. I’ve successfully used toe plates and camber levels to adjust the geometry before when the car is at rest on a level floor. You can also use the method a camber level in conjunction with angle slide plates to calculate castor angle. Bear in mind that suspension bushes, ball joints etc should be in good, serviceable condition before taking measurements. Also bear in mind that the bulkhead can move with constant stress from the suspension over 50 years of driving (hence the need seen to sometimes shim the top mounts to correct caster angle). It’s not rocket science, but it does need to be approached methodically and with care.
 
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