rear suspension toe in & camber adjustments

[ericsinaus]

Hi have just replaced all the rear suspension bushes and outer spring plate bush retaining plates and have begun setting the toe in and cambers.
I spent one whole day adjusting these back and forth till I had it perfect with about 1mm toe in and 0.9deg to 1deg. neg. camber
Once I tightened everything up and went back to re check I found the cambers had reduced to about 0.2deg neg.??????
Does anyone have the right process as Im going to be spending another day on this most likely.
What do you set first or do you adjust both settings bit by bit.
To adjust the toe in Im using 2 straight lengths of aluminium tubing clamped to the lower section of the discs and marked the aluminium 500mm forwards and rearwards of the centre of the hub and Im measuring the distance between the 2 tubes to get an almost 0 to 1mm toe in.
Eg Ive been aiming for 1335mm at the rear and 1334mm forwards of the hub centre between the 2 aluminium tubes.
Any ideas, tips or hints would be greatly appreciated.
After this Ill most likely go and get it checked and reset if necessary at a wheel alignment workshop.
Thanks

Eric

[Alan L]

Depends how you are doing it. If you have relaxed the load at any poiint, it will re adjust later. You may need to repeat the process, or do it under full load, then roll the vehicle, or even better drive it a km or so and repeat.
Alan

[ericsinaus]

Sorry should have stated that I am adjusting the bolts on the spring plate with the hub (trailing arm) supported on jacks, so Im adjusting all the settings under its normal static load.

[PeteKz]

When I changed my spring plates to adjustable ones, I had to do several iterations to get the camber number I wanted ( -1 degree) and toe.

[75 911s]

Id put the wheels and tires on. I agree with Alan. Go drive it very conservatively, let the load settle in on those new bushings, then see where the settings are at that point. Since you've set a basic toe and camber you should be good for the test. Bring it back, then use string to set the rear toe and a camber gauge to set the camber. And yes it takes a lot of fiddling at home.

[Alan L]

Originally Posted by ericsinaus

Sorry should have stated that I am adjusting the bolts on the spring plate with the hub (trailing arm) supported on jacks, so Im adjusting all the settings under its normal static load.

There is your problem - you are not doing it on the load on the wheels - which you are adjusting. But it is a common problem either way. Usually takes more than one go.
The pro shops - at least some of them, have the car (wheels )on adjustable, floating plates, allowing the suspension and tyres etc to respond to the setting changes (under full weight load). In your case you need to move the car to allow the settings to settle under load.
When I do mine I place the wheels on squares of lino, which makes it easy for the wheels to move to the changes. But I still expect to tweek it at least once more. Under these conditions even just rolling the car back and foward is usually enough.
Alan

[ericsinaus]

Im using a magnetic electronic angle inclinometer and fixing it to the discs to get the camber and the rear axle hubs sitting on stands so the suspension is under normal empty static load, I just thought this leaves plenty of room to get at all the bolts.

I wouldn't have thought you could make any adjustments to the cam bolts let alone loosen the 2 rear bolts while the wheels were on the car for any final adjustments???

Q1. Would having about 1mm toe in over a distance of 1m front to rear either side of the axle be ok. As stated above I am using 2 straight aluminium square extrusions clamped to the discs.

q2. How does mm convert to minutes of degree as the book states about 10min I think toe in.

q3. How would string lines work as where would you line them up and tie off the string to and get them parallel with the chassis to get your toe in measurements???.

[Alan L]

"Im using a magnetic electronic angle inclinometer and fixing it to the discs to get the camber and the rear axle hubs sitting on stands so the suspension is under normal empty static load, "

No it isn't. It is the wheels/tyres you are trying to adjust - not the suspension arms. You do it via tweeks to the suspension arms - but to effect change in the wheels. Which in your method are under no load.
You may notice some time - suspension shops usually work out of a pit - underneath the car. While it is supported by the wheels.
So you have to be prepared to have a few progressive attempts at it.
String lines work just fine. There are quite a few threads on them I think. You just need some simple bars to run strings off and the trick is to get them dead parallel. I use them.
Your 1mm combined toe over 1m sounds about right. You would need to do the trig to calculate the angle - 0.5mm over 1m. Tan of the angle = 0.5/1000,
Regards
Alan

[AndrewCologne]

Originally Posted by ericsinaus

Im using a magnetic electronic angle inclinometer and fixing it to the discs to get the camber and the rear axle hubs sitting on stands so the suspension is under normal empty static load, I just thought this leaves plenty of room to get at all the bolts.

I wouldn't have thought you could make any adjustments to the cam bolts let alone loosen the 2 rear bolts while the wheels were on the car for any final adjustments???

Q1. Would having about 1mm toe in over a distance of 1m front to rear either side of the axle be ok. As stated above I am using 2 straight aluminium square extrusions clamped to the discs.

q2. How does mm convert to minutes of degree as the book states about 10min I think toe in.

q3. How would string lines work as where would you line them up and tie off the string to and get them parallel with the chassis to get your toe in measurements???.

Be my guest:
https://nineelevenheaven.wordpress.com/adjusting-the-toe-on-a-911/

[PeteKz]

1cm at 1 meter is about 1 degree (Radian Rule). 1mm=0.1 degree=6 minutes (corrected)

[Alan L]

0.1 deg = 6 minutes, right?.
The spec for my SC is 10' +/- 10'. Per wheel.
So anything between 0.0 deg and 40' (combined distance) is in the park.
Alan

[PeteKz]

Oh yeah--I got something backwards.

And I like about the middle of the toe in spec, or a bit more. Definitely not the outer edges of the toe spec. I find that the toe on the rear helps my car and tires to not be as twitchy over ruts in the road.

[AndrewCologne]

See link above, ... the formula is simple:
Toe-in (a) in inches = sine(toe angle in degrees) * rim diameter in inches

So in case of 10' minutes toe on a 16 inch rim/wheel we divide 10 minutes by 60 where 60 mins = 1 degree and put this into the formula from above:
sine(10’/ 60) * 16 inch = 0.047 inch

Measure the distance to a parallel to vehicle existing string from both rim edges a1 and a2, the difference should be 0.0047 inch in case of 10' toe in.

[tonyduc]

Here is a mm to degree conversion chart for various size wheels. It’s from an FCP Euro video on alignment, they did it on a Mini but an excellent tutorial.
Tony

[PeteKz]

I'll repost here: The toe at either end is very easy to check if you do it this way:

Figure out the front and rear track of your car using the wheel offsets you chose. The wheelbase is 89" or 2260mm/260cm. Do a little geometry on a piece of paper to figure out how far inboard or outboard the front wheels are compared to the rear wheels, then figure out where a string from the front to the rear wheels will rest at the rear wheels, for the toe you want, and vice versa for the rear. This is the same you have to do to use the string method. Then get the front wheels pointing straight ahead, get down on the ground and sight along the edge of the tire to see whether it's where it should be. You could measure with a ruler from the outside edge of the tire to a line of the tread as your visual reference. I just eyeball it, because I've done it so much that I know what 1" inside to outside looks like.

ON my 1973 with 16x7 ET23.3mm Fuchs on both ends, the front to rear sight line should fall 1"-1.5" outside the edge of the rear tires; and the rear to front sight line should fall 3/4"-1" inside the edge of the front tires. After noting that, it's easy to visually check the toe any time. An advantage of this method is that you have a long baseline to measure against, so it will be as accurate as the string method, but much faster, and more accurate than the methods that use shorter baselines. If you really want to make sure, you can then push the car forward or backward 1/2 wheel rotation and check again. If it's different, then a wheel is bent, and you just average the two measurements.

[Alan L]

There is a real easy way to do camber too. Spirit level and measuring tape. See pic.
You will see a set screw about half way down the level. And a packer at the bottom. The packer is to clear the guards on the 930 with the level at vertical. Subtract that value off the set screw mm to the top of the rim. Then x the final mm by a trig value to get degrees camber. Takes about 1 minute.
I do caster with plumb bob and measuring tape and trig.
Alan

[ericsinaus]

Thanks everyone for your advice, charts and the tutorial was very good.
Shame I spent about 5 days trying to get this right and at present the rear wheels are basically parallel. Ill have to take it for a run now and come back and do it all over again and try the string lines and remeasure what I have done and crosscheck my initial method with the info I have now.
Will be interesting to see how it handles with. the wheels parallel.
thanks everyone.

[Alan L]

Parallel is in spec. Just that it is at one extreme end of the range.
Your 1mm combined you had initially (on the hubs) is closer to spec (assuming it translated to the wheels which it likely wouldn't). 2 mm would get nearer the mid range. With the string line you need them dead parallel to make sure you don't have 2mm on one wheel and 0 mm on the other.
Good luck
Alan

[ericsinaus]

In setting up the rear suspension what is the correct body position.
Can anyone tell me now that Im starting all over again in setting up the rear spring plate position what the body position should be.
Currently when I put a sprit level on the step sill doorway the rearof the car is a little lower than the front. Eg. bubble is slightly forward on the spirit level.
Should the rear spring plate position be set so that the spirit level on the door sill be level.
Currently the rear wheel arch opening edge is 610mm from the garage floor at the axle centre.
For the sill to be level Im guessing the ground to wheel arch height may end up being 620mm to 625mm.

Any advice would be greatly appreciated.

[tobluforu]

I know this will not answer any questions, but when I auto-xed I leveled my floor in garage, bought a fancy laser, and all sorts of devices to align my car. It was such a long, and somewhat frustrating/arduous process, that I stopped. Bringing it to a shop, paying them is worth it. Especially one that will place weights in the driver's seat, etc. It's the only time I bring my car to a shop, and it's well worth it imo.
Anyhoo, have fun and good luck