Hi All

I'm well and truly confused.

I have just been reading the various bits and bobs on alignment and I need to know how to set the front castor angle.

Earl has a good write up, but my brain will not take in the bit about castor.

I know you can get away with the castor adjuster cam fully adjusted one way or another..... but which way???

Is it with the the bottom hub pivot joint as far back as it will go, or as far foward as it will go?

In other words, if you are stood looking at the face of a front wheel, the front of the car to your right, and the rear to the left, do you adjust the castor cam to push the bottom of the wheel towards the front or the back of the car?

This follows a complete refurb of the previously siezed (locked solid) front height (spring platforms), and camber and castor cam adjusters. Absolute pig of a job!

Thanks in advance
John

 

The amount of caster isn't as important as it being the same on both sides, if it's not your steering could pull to one side and be a little funky.

If the adjuster on the bottom were moved towards the front of the car that would give you 'more' caster and that's usually considered desirable on a sports car. It provides a more positive steering wheel centering at speed with more effort required to move off center.

 

If you have ever ridden a motorcycle with a long front end (raked) the steering feels more truck like (stable)
compared to a dirt bike where the forks go more straight down (less stable)
That is your castor angle.
That is the way I remember it.

 

The castor spec is ~4 deg (+/- 0.5 deg depending on MY and ball joint type): on many chassis, one side or the other will max out near to this spec ... so it becomes the limiting factor, and the other side is set to emulate it: all this occurs with the castor eccentric turned to force the center of the contact patch as far forward as possible .... ie. towards the front of the car

If preparing to drive to the alignment rack after reassembling your suspension, max out this setting and you will be OK.

 

Recent conversation with Capt Earl sugests that you start off with the minimum amount of caster on both sides. That's eccentrics full rear, pushing the bottom of the spindle towards the rear of the car. With all other alignment settings correct (toe, camber) and the rear alignment correct (toe, camber) and toe at both ends centered with the axis of the body, ride height correctly settled and correct, tire pressures set even side-to-side, tire wear even on each tire and consistent between tires side to side, you can adjust caster to make the car track straight on a level (side-to-side) road. If the car pulls to the right, add a little caster at the left front wheel. If it tends to the left, adjust the right front caster.

This is a very subjective way to adjust, mostly because it's tough finding a road that isn't sloped to one side or the other for drainage. Try driving two both directions right down the middle of your test road to confirm your settings. It's also tough since we genarally attack alignment problems only after we see uneven tire wear.

 

From the master thread...
https://rennlist.com/forums/showpost...8&postcount=24

Please correct if wrong. Bottom-line: caster is at the minimum when the lower balljoint is as far rearward as possible, as others have noted.

 

nice write up

 

Bill,
That must be correct if the 928 caster angle tends to be a number considerably higher than spec prior to adjustment ... and one of the eccentrics limits out at an amount numerically higher than spec in the adjustment process as described in your link: I know the reverse to be true in the 993 ( it is difficult to get the caster angle high enough), for the angle starts out too low, and the eccentric must be cranked to position the contact patch center more forward.
I gladly stand corrected if the inate 928 caster must be reduced to meet spec .... by bring the contact patch backwards. I had recalled moving the contact patch forward as in the 993 when replacing the ball joints on the '80 car to meet spec ... but now I'm uncertain

 

OK, so the consensus is that you start with the wheel moved rearward as far as possible (minimum castor angle) and then adjust forward to balance out any pull to the left or right.

Is this correct?

John

 

Yes. Pay particular attention to the need to readjust toe -after- any caster changes. That means you must not raise the car to get to the caster or toe adjustments too.

 

I do this on a 4-post lift with alignment turntables under the front wheels. Other than possibly some tall ramps or jacking the front wheels under the balljoints and keeping the suspension compressed, doing this on the ground is problematic.

 

Bill--

I was able to do the caster and camber adjustments at ground level. Used a mirror to see the bolts and the cams. There's plenty of room for the wrenches under the lower arm. I did put a big breaker bar on the allen socket to adjust the cams just right.

Don't have a lift (yet...).

 

OK. I guess if I can do toe on the ground (on turntables) I the caster/camber adjusters shouldn't be that hard after all.

 

Does anyone know the correct angle to turn the front wheels thro' to record the caster angle?

So far I have seen 10degs each way (20 degs total), 15 degs each way (30 degs total) and 20degs each way (40 degs total).

Which is correct for the nine28?

Basic principle is as follows:

Put front wheels on turntables, ensure they are straight forward, zero graduated scale on turntable.

Turn the wheel out from zero by ??degs, place digital level on center of wheel at 90degs to floor, zero digital level. (Rather like you where about to measure camber)

Turn the wheel in back thro' zero, and in by the same as ??degs as above, record reading on digital level. Hey presto thats the caster angle.

Repeat above after adjusting caster cams, to arrive at about 4 degs of caster for the nine28.

So far so good, but whats the correct turn in/out angle?????