FourOnTheFloor

Possibly more of a general question than 993 specific, but: I just had an alignment done, for the first time in awhile (forgive me…)
I went to a shop that was “recommended” by the garage that I used to take the car to (I stopped because they no longer have a Porsche mechanic on staff). To see if the alignment guys actually knew what they were doing, I asked them “if they had the special tool for measuring the kinematic toe on the rears?”. “Mumble mumble, grumble grumble, we do what the computer tells us… “. Which I took to mean “we have no idea wtf you are talking about, please go have a coffee or something and leave us alone.”

The ‘alignment’ they performed consisted of a correction to the camber and toe on the front, but no adjustment at all to the caster - which was and is hugely out of spec. Front searching around here, I found that caster should be: 5 deg 20' + 15' - 30' (max diff L to R 15'). Mine is L 4.8deg R 3.8deg - so both well off target and significantly different.
Also from reading here, I understand that adjusting caster is rather involved, so I get why this shop wouldn’t touch it. However, having concluded that I won’t be going back there for alignment, my question is how important is caster? Do I need to get this fixed by someone who actually knows what they’re doing?

Many thanks for opinions, advice and suggestions for where in Montreal to go next time to get this done properly.

1997 C2 Cab

boomboomthump

Is your car lowered? If so, it may be hard/impossible to get it to spec and may explain why it is lower than 5.

Either way, it should be adjusted so both sides are equal.

orangecurry

Caster is important.

My car is stupidly lowered, lower than RS and does not have RS uprights - I do get bump-steer, but I find it acceptable.

(I've just had the suspension all taken off, and put back on, so ignore the 'Before' settings.)

I then took it to an alignment specialist I use for all my cars - he sets up race and rally cars, and travels round the world for critical events with the teams.

This is what he can do.

FourOnTheFloor

Thanks for the replies!

boomboomthump The car is not lowered AFAIK. The before value for the front L was 4.9deg which is just in spec, and from OrangeCurry's post, it doesn't seem to be impossible to achieve the correct value even with a lowered car.

OrangeCurry - whoah! That guy obviously really knows what he is doing! All of the settings except rear camber are on spec to within the measurement precision of the machine!!

I agree that the caster values for L and R should at least be the same - what I'm trying to get a sense of is whether or not I really need to deal with this right away. Finding a good shop (that isn't the dealer) is probably going to take some time. I read someplace that changing caster involves undoing the fasteners that connect the strut to the chassis. This sounds to me like it has to be done on a lift, not the alignment platform - which would suggest that the trial and error process would painful!

boomboomthump

Interesting on orangecurry’s results. I’d seen mention here over the years that on cars lowered a lot, it’s tough to get the caster in spec.

The other thing to keep in mind is that some aftermarket top mounts (camber plates) such as Rennline are 964 style but advertised as 964/993 application. They have the shock centered in the strut tower, which reduces caster. 993s have the top of the strut offset to the rear, which was a design change for the 993 vs 964.

Perhaps the folks having challenges getting the caster in spec on cars lowered a bunch are running 964 style camber plates.

Sounds like you have neither factor in play. Just adding this tidbit for anyone reading this in the future.

nk993

that looks like a screenshot from Chris!



yes, super important point. I learned this to my detriment after already paying for the ****ty top mounts. Luckily the coilovers were adjustable from the bottom to stay within spec, but its not ideal

Bill Verburg

on a lowered car measure caster w/ the racing gauge that hangs from the caliper bolts

caster should be equal side to side

the more caster the less that end wants to turn, ie it reacts more slowly

A/Xers may want less caster to get around the cones quicker

track guys may want more(to a point) to keep the car stable.

a simple way to estimate rear caster is to look at where the wheel is in the wheel well, as the KT arm is lengthened it moves the wheel down and forward, less caster, as it is is shortened it moves the wheel up and back closer to the mufflers, more caster

There is a circular adjustment cycle, when one thing is adjusted it changes the others so each must be rechecked in turn until all are where you want them

here's a guide

orangecurry

I believe the all-round negative camber is a deliberate consequence of the aggressive setup, which includes the 'lowered' chassis constraint.

Finding these people who know and care about what they do is what is difficult. ( @nk993 it's not Chris at Center Gravity. )

nk993

ah interesting. please share the name if you recommend them

orangecurry

Off topic for most Rennlisters as he is based in Europe.
@nk993 I'll check with him first - it's only polite. He's also one of those busy people who answers comms occasionally / sporadically / when chased