Can you explain rear alignment?

[Todd Simpson]

I'd like to know how the rear spring plate adjustments affect alignment. Ride height is easy to understand. Toe escapes me somewhat and camber makes my head hurt.

Is the entire trailing arm leaning over with lots of camber?

I just got my car back from an alignment guru and he got 3.5 degrees negative in the rear-exactly what I wanted for 95% track use. I know what the terms mean just not how you get them.

[widebody911]

There are two alignment eccentrics. The forward one adjusts toe, the other camber. As you turn the adjuster (12mm Allen) , the eccentric changes the inclination of spring plate relative to the trailing arm. Each adjuster works in a different plane, toe is adjusted my moving things fore and aft, camber by moving it up and down.

The one on the left is the camber adjuster, the one on the right is for toe:

[imcarthur]

As you adjust them you can see & feel the trailing arm move/pivot versus the springplate. The combinations of the eccentric shape of the bolts, the openings on the springplate & the interface of the trailing arm surface move it in the different planes as Thom described.

Ian

[Todd Simpson]

Thanks Thom, so now toe makes sense.

How does changing the spring plate inclination to the trailing arm affect camber? Wouldn't that (also) affect ride height?

How much play is there at the trailing arm bushing? I use monoballs but I assume that the camber adjustment still affects the angle there?

Ian-I think someone needs to draw me a picture...

[Zeke]

Originally posted by Todsimpson
I'd like to know how the rear spring plate adjustments affect alignment. Ride height is easy to understand. Toe escapes me somewhat and camber makes my head hurt.

Is the entire trailing arm leaning over with lots of camber?

The trailing arm hangs from a rubber bushing, or better yet, a mono ball. Inserting hard plastic there is not good. I'll get to that later,or it will become apparent.

The action of the arm is somewhat like a VW swing axle. You have seen those. If the owner raises it, he has a bunch on postive camber, and vise versa. The ideal camber on a older swing axle VW is when the ride height is correct. In other words, you can't have any range of adjustment on the camber, only the height, and it's respective camber.

The 911 is similar, except there is some adjustment. But, like the VW, if you lower or raise the car, the camber changes with the height. So, you establish the height you want and then the relationship of the spring plate and how it attaches to the trailing arm. This is your static camber. When the car rolls to one side in a turn, the camber increases as the suspension is compressed and the opposite side goes more positive. The general effect is to keep the contact patch square with the road.

The rear toe is set simply by moving the trailing arm forward on the spring plate for more toe-in, and back for toe out. If one of the adjustments is move considerably, it will effect the other adjustment. You end up going back and forth between the two to get exactlay what you want when sitting still at the desired ride height. I don't know if that is what you mean by "......just not how you get them."

So, the trailing arm is moving up and down in an arch just like the VW swing axle car, just not as much of an arch. That is why the hard plastic bushing is wrong as it can't follow the arch. The bolt that goes through it has to move from one angle to another throughout the suspension range. A mono ball allows this and holds the front of the trailing arm in a perfect fixed length keeping your toe and camber at the best possible numbers throughout the movement. Braking and accelerating put stress on this part and the rubber moves a bit.

I better quit at this point.

[oneblueyedog]

Thom,

What is the significance of the scribed arrows in the eccentric bolts?

[Tom '74 911]

My guess is that the arrows point to the middle of each bolts eccentricity.??

Another question - Is it necessary to loosen the (2) main bolts that connect the spring plate to the trailing arm when making toe and camber adjustments?
Thanks,
Tom

[turborat]

The 2 main bolts will adjust the ride height of the rear. Ride height will also effect your camber. The lower the car sits, the more negative the camber setting will be. Paul

[Tom '74 911]

Paul - thanks for your reply. I was actually wondering about the (2) 19mm bolts - vertical orientation - that are rearward of the toe and camber bolts.
Tom

[turborat]

Tom, the bolts arranged vertically are what attaches the spring plate to the trailing arm. These are loosened slightly when you want to make camber and toe ajustments using the ecentric bolts previously discussed in this thread. Paul

[fogcity]

Since you guys brought it up: My car pulls to the right. The tread on the inside of the left front tire is almost gone. The mechanic said I need an alignment. Do I have to have a "specialist" do this or can I just have the shop that's mounting the tires do it for me (quoted $60 for alignment)?
Thanks (sorry for butting in).

[ZOA NOM]

No. It is impssible to do a correct alignment for $60. My mechanic allowed me to perform a full, correct alignment on his machine with his supervision, just so I would understand why he charges over $200 for the job. I will never take the car to someone who doesn't understand what is involved.

[imcarthur]

Tom

As Paul said, you must loosen the 2 springplate to trailing arm bolts to align. Note: even with the trailing arm supported by a jack, there is still tension on the springplate so just loosen them. To remove them completely you must independently support them with a jack on just the springplate or you will strip the bolts & the plate will whack down violently.

Fogcity

Alignment on a 911 is not hard, just tedious. At $60, he probably has no clue & won't take the time to do it right.

Ian

[Tom '74 911]

turborat & imcarthur -
Thanks for the photos and info. That's what I needed to know. I just finished replacing my spring plate bushings so I'm fairly familiar w/the bolt arrangement, but am still learning how to make all the alignment adjustments.

fogcity - I will second the fact that whomever quoted you $60 for am alignment, probably doesn't know what's involved. I've been there, done that. Find someone who knows PORSCHES and has a good rep.

Tom

[rnln]

Originally Posted by turborat

The 2 main bolts will adjust the ride height of the rear. Ride height will also effect your camber. The lower the car sits, the more negative the camber setting will be. Paul

May I ask if ride height affect toe? If so, how? Let say raising the car, will it make more toe-in or toe-out?
My second question is if there is any torque required on these bolts, or tighten them as much as you can?
Thanks

[turborat]

rnin,

Ride height changes will effect toe and camber. Camber is effected more than toe. If I recall correctly, toe will move inward as the ride height is raised.

I would suggest taking a measurement of the distance between left and right rear tires (front and back of tire) while a full rest on the ground. This will determine your current toe.

The camber eccentric bolt is 43 lb ft
The Toe eccentric is 36 lb ft
Radius arm nuts are 65 lb ft
The ride height nuts are quite large. So I would say that torque is set a "friggin' tight" or at least 100 lb ft, probably more. You will need a thin (like used for fan blade removal on BMW) 32mm wrench to get at the bolt heads.

Paul

[rnln]

Thanks Turborat

[Zacko]

How much can you adjust the ride height on the eccentric bolt ?


/Hans

911 3.0 SC -79
SAAB 9000 CSE 2.0T -97
SAAB 9000 CSE 2.0 -97