OEM calipers & alignment questions

[JohnB]

Folks,

Took my car to the Merchants Tire folks for rotation/alignment today. While they had the wheels off I noticed the brake calipers have Ate logos on them. Is that OEM? Clearly I should have seen this before now but never thought to look. It's funny what you notice when it's suddenly at eye level.

I was also told the front wheels had to be "loaded" per their alignment instructions and they don't have the equipment. Something about pressing them to toe in at roughly 125 lbs. What's with that and is it correct?

Bottom line: got rotated but no alignment today and they wouldn't touch the center caps so no dings.

[Dave at Pelican Parts]

ATE (Alfred Teves E-somethingoranotherinGerman) was the OEM for all 914-4 brake calipers.

The factory instructions for some of the alignment process call for the suspension to be compressed slightly (I think that's what they mean) when the measurement is taken. I don't think most places bother, though.

--DD

[Scrappy]

The theory would be to load the car "as it would be driven" for correct alignment. If you infrequently carry passengers, sitting your butt in the drivers seat while the alignment was being done would more than adequately suffice. You would also take into consideration the amount of gas in the tank average, etc.

Of course, if you don't wanna do this and want to spend your time sipping Starbucks liquid gold (cost not taste), you could throw a sandbag in the driver's seat equal to your weight.

If your girlfriend is with you all the time, take her along and let her sit too.

I would assume the "Factory Loading" would be a maximum suspension deflection for a fully loaded car.

Ain't theory wonderful?

[JohnB]

Then I guess the big question is whether not compressing the suspension changes the alignment.

On the other hand, I'm glad I was watching the guy doing the work. Ultra cool optical alignment equipment, but he had pulled up the settings for a 911. Maybe it's better I didn't get it done there!

[JohnB]

Oops, crossed msg!

The guy seemed to indicate this wasn't a compression by weight as much as a different kind of compression. Regardless, I'd rather go somewhere that knows what they're doing and get it done right.

[no substitute]

Ask some of the racers or auto crossers in your area. Often there's an alignment shop in a given area that's Porsche savvy.

[Dave at Pelican Parts]

Ask if they have or can get the shims for the rear camber.

--DD

[JohnB]

Good pointers, all, thanks.

[jamcleod]

try Porsche independent shop: ASG, Autothority, Autobahn, Dulles Int'l Motorsports, Currys, Dr Johns should all know what it takes. (sorry if i left off any, these are in NVA local to your place) all support local PCA club.

[JohnB]

Yup, I know 'em. D Int'l and Dr John's are VERY close to my house. Thanks, Jim.

[ken180]

The Porsche spec book specifies the "toe-in" be set with the front of the tires being pushed towards each other. Most shops do not do this.

Ken

[Scrappy]

PITA rest of the theory:

ANYTIME you deflect the suspension, you alter the camber angles, toe in angle, etc. The bottom suspension arm traverses an arc under deflection. Depending upon where the arm is initially set, the severity of the arc change is effected. Ideally, the arm is parallel to the road surface, but when the car is lowered (or raised), whether intentionally or by weight, the arm will deflect in an arc from it's original setting and thereby effect the initial settings.

Old, unequal "A" arm suspensions exhibited tremendous change due to both arms trraversing arcs, but they were unequal in length so the severity of length change from the piviot in the arc was greater for the shorter one. Balancing this setup required wierd intial static settings so that handling would not be adversely effected under load.

The McPherson strut was an attempt to ameloriate some of these conditions, by trying to make the wheel travel more vertically in a straight line. The system still has an arm on the bottom that traverses an arc though.

Now we could go to the examination of arc change created under body roll conditions.........,

Enough of this...............,

[JohnB]

Thank you, Doctor, good explanation.

The question remains whether I really need to make sure the suspension is loaded per Porsche spec or is it really insignificant in the end.

[Dave at Pelican Parts]

I don't think it's significant, myself... But I have not been there watching every minute of the alignment process when I had my car done, so I could be saying one thing and driving another.

--DD

[ken180]

What can be said - it is a Porsche specification. Its your call.
Your best bet is to take it to a shop that does a lot of 914s. I do my own alignment and have found the "push" is not required. It may be, if the bushings are a bit worn.

Ken