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ride height: fender lip vs. t-bar centers way out of wack

I spent nearly the entire day today trying to get my 84 coupe's ride height dialed in so I can get it aligned. Prior to today, I had set the fender lip heights at 25 rear and 25.5 front - just as most of you do. I did all of this on a level surface.

So I decided to check the t-bar center heights against wheel centers, to be sure that my body was not skewed. Long story short, they were WAY off on the low side, which explains my bump steer, if nothing else. So, I readjusted everything to factory adjustment specs this time using t-bars and wheel centers and not the fender lip.

The car seemed to be way high, and once I had the chassis to spec, the body was visibly up. Front fender lip around 27, rear around 26.5. If I lower the fender lips, the t-bar to wheel centers are now way off factory spec - in fact, my rear t-bar cover is actually about 8mm below my wheel center, and spec is 16mm above. On the front, I'm about 20mm low at the t-bar when the fender lip is 25.5 inches.

I read in Wayne's book and Bruce Anderson's 911 Performance Handbook that there may be spacers on top of the struts, but I found none.

All the height changes were made using the adjusters, no t-bar reindexing was done - is this my problem???

More detail - my wheels are 16x6 and 7 Fuchs with 245/45/16 rear and 205/55/16 front - they're not the exact same height, but it's not like I'm running really tall tires.

Anyone run into this? I have new rear shocks and t-bar bushings, almost new front shocks (all are Boge). Seems like it should be something obvious, but it's almost as though I have a body lift kit like you'd find on a Jeep!


Help!!!!

Craig
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'84 Carrera Coupe - B&B Headers and one-out muffler; K&N Cone intake; Steve Wong Chip; Euro height and corner balanced; 171K Miles (9/12)

Last edited by Thrasher; 01-01-2005 at 09:26 PM..
Old 12-31-2004, 09:47 PM
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Ok, I'll ask the stupid question: are you measuring to the right place? For example, it seems like the book calls for measuring to the center of the t-bar cap -- are you measuring to the center, or the bottom? 'Coz that would throw you off by 24mm pretty easy. Sorry if that's too obvious, but I'm just throwing out an idea.

Dan
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Old 01-01-2005, 12:21 AM
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I've never been able to make sense of the factory settings regarding the torsion tube to wheel-centerline relationship. I've posted this question before with no results...but I sincerely believe there was an error in the factory manuals that was never corrected over time.....and I suspect the errror continues in later publications. I recall this applied particularly to the rear relationship ( ?)

Wil
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Last edited by Wil Ferch; 01-01-2005 at 08:45 AM..
Old 01-01-2005, 08:16 AM
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On the more minor note, maybe someone can also post a pic of the spacer so that you know what it looks like removed.. that might help you make sure that's gone.. although that's not the problem your having exactly...If will doesnt know then we might all be in truoble using that measurement!
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Old 01-01-2005, 11:06 AM
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Harold, here a couple of pictures of the spacer you refer too. Sorry for the poor quality as the battery's are low. Hope this helps.
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Old 01-01-2005, 11:40 AM
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Dan: thanks - because it's probably something simple, but that's not the case - I am measuring from center. In fact, one of the descriptions tells you to measure to the bottom, then add 1/2 the height of the cap, since no clear "center" is marked.

Wil: So does that mean ignore the factory suggestion and go with the fender lip height, even though it makes my suspension sit very low? That'd be simple, because that is where I left it. I could add the bump steer kit and avoid curbs on driveways, but I think my chassis is too low. Can anyone with a Euro height car give me a reference measurement to the crossmember, etc?

Harold and CRH911S: Thanks for the pic of the spacer - it's precisely as described by Bruce Anderson in 911 Performance Tuning - big, bulky and "a great paperweight" - but definitely not to be found on my strut. Only the rubber bushing with the metal sleeve for the shock mounting stud.
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Old 01-01-2005, 06:51 PM
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sounds like others have been here, too - I found this one Porsche's way of measuring ride height vs. the fender method. What gives?

But, the guy never really got a solution to the mystery.

I measured my tire heights, and they were roughly 24.5 inches, but I'd have to roll them to measure one revolution accurately.

After finding a few more good threads in the archives, I checked my A-arms to make sure they were sloping down, which they were, but only very slightly - which means my ball joints are slightly lower than my inboard pivot points on the front - which Wil stated to be a good thing in the thread
Ride height data compiled

... this with my front fender lip at 25.5 inches, so I've essentially "hit bottom" if I want to meet that requirement.

That point was reiterated by Chuck Moreland in this thread:
Ride height too low?

So, it sounds like I'm probably ok, albeit about as low as I would want to go. I do have bump steer, so it looks like Pelican is about to add 12 bucks to my pending order!

BTW, these measurements are all taken on a level-corrected surface with my sway bars disconnected, front and rear.

Craig
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Old 01-01-2005, 10:06 PM
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Not to throw a wrench in the works, because it sounds like you've been very complete......but......is adding ballast equal to the drivers weight, and half a tank of fuel considered a good idea?

When I set my racecar up, it's done with scales, and 200lbs in the drivers seat. I also measure ride height, but the actual corner weights take precedence.

Without the drivers weight in the car, your low height will actually be lower on the left, increasing the bump steer you refer to.
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Old 01-02-2005, 01:11 AM
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Good call , but actually, I went with 3/4 tank of gas as an "average" weight, and had my wife with my son on her lap "guest star" as the driver weight while I measured. They were getting a little tired of the routine by the end of the day ;-)

The bump steer is not severe, though, and should be readily fixed with the spacers.
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Old 01-02-2005, 08:21 PM
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the front T-bar ft or rear centerline is not specified any where as the point to measure afaik.

I got nice factory #'s for the rear so I let the front T-bar measurements go. Nice means that I believe my tub is real straight.

I used 3/4 tank, driver's weight, rear sway bar disconnected, perfectly level ground. Almost perfect on a street car as per tire wear of 4 equal tires.. meaning rear lost about 20% more.

lateapex's act is the best, no question.
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Old 01-03-2005, 12:06 AM
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Thanks Ron,

I didn't think there was a spec on another location, but rather was just looking for some measurements to compare in practice, since the factory t-bar specs appear suspect.

I'm using my garage floor, leveled with a water level using vinyl tiles stacked to attain level with accuracy to about 1/8". I also have disconnected the sway bars, but don't see a big impact from it.

I'm going to use the Scruggs alignment on the same platform, but I think I'm supposed to reconnect the sway bars??

As an aside, I formerly was employed by the largest mfr. of wheel aligners in the US, based in St. Louis. I can verify that the equipment is excellent and precise beyond reproach.

However, unless it is calibrated on a regular basis and used properly by trained, skilled and caring technicians, I would feel necessary to go back and check their work anyway, so I'm doing it myself. I'll likely have it checked on a rack, but I'm sort of enjoying the work.

The engineers worked tirelessly to refine and innovate, but tire shops repeatedly wanted one thing - the ability to do "ok" work fast and cheap. "Ok" work being the type that is not glaringly poor enough to have the customer return for a free follow-up.

For instance, if a wheel mount for the alignment head were dropped, the electronics could be calibrated to compensate, but this was rarely done in practice. Alignment racks are installed perfectly level, but rarely checked afterwards.

The same held true for wheel balancers and tire changers as far as the technology being utilized. I guess it all comes down to whether you can find trained and competent mechanics who are allowed by the shop manager to take the time/effort to follow procedures. You will (and should) pay a bit more for that service.

Craig
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Old 01-03-2005, 10:04 AM
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Quote:
Originally posted by Thrasher

I'm going to use the Scruggs alignment on the same platform, but I think I'm supposed to reconnect the sway bars??

I always disconnect the rear sway bar, correct air psi, etc.

I set the castor at max without going thru the wheel turning and angle method. so far so good.

I use a probe, to check tire temps at inner, outer, and center to confirm street settings. I'll run at 60-70mph for about 5mi on a straight road then pull over to check only 2 tires. Temps disapate quickly. I'll do the temp act a few times to confirm the temps. I'll use a tire thread depth ga every 5k mi to stay on top of things and flip accordingly.

I went thru 20k mi on S-03's on a cross country drive.. meaning over 90% at 60-90mph. I flipped about every 5k mi and they looked evenly worn when changed them.

So I figure if the car drives straight, tire temps are balanced side to side, and tires wear nice then I done good.

fwiw, the 3/4 full gas tank is related to the difference in toe as the tank gets less. I read that the change has a less radical effect on driving than if you set alignment with 1/4 tank. I guess to avoid leaning twords toe out? The assumption is that the average fill would be 1/2 tank. I think the details are correct? Race track settings is supposed to be more track and personalized dependant.

I also use the Scruggs method on a perflectly flat platform.
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Old 01-03-2005, 03:01 PM
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This is nuts... it's not THIS hard! I thought I was close enough to start aligning, but I had 1/2 inch difference left-right in the rear (25 1/4 Driver, 24 3/4 Passenger), so I started trying to bring the left down and right up, then the right never came back up! The adjuster plate looks to be fully up, and the eccentric cam is maxed out, because if I turn it any further in either direction, the adjuster plate (outer) starts moving back down.


In November, KurtV and I replaced the rear torsion bar bushings, and when we replaced the spring plates, we checked the angle to be sure it was the same on each side, so the preload should be the same. We left the adjuster eccentrics centered to allow adjustment up or down.

Since then, I've been tweaking the eccentrics to get things dialed in for an alignment. Now my passenger side rear will only adjust up to 24 1/2" at the max of the eccentric, and the driver side is right at 25".

I'm sure it was going up to (and even over) 25" on the passenger right just a few days ago, but not anymore. I'm thinking about re-indexing the rear passenger t-bar, but if we got them equal before, I don't want to mess up corner balance by having 2 different pre-loads.

I did reindex the front passenger t-bar down a notch to get its adjuster more equal with the driver side. Its adjuster screw was backed out all the way to get down to 25 1/2", now it's in the middle, like the driver side. I don't think this should've had a big impact on the rear, but perhaps?


Any ideas?
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Old 01-04-2005, 11:28 AM
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I have the same problem in my carrera 86 euro.
I need help too.
Old 01-06-2005, 04:15 AM
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I use a 3ft wood ruller attached to a small carpenter's level at the wheel hub center to prevent any misalignment height readings. It's easy for me to be 1/2in incorrect without using this method.

also

Quote:
Originally posted by djmcmath
Something that may be of value is a quick refresher on the Ferch method of corner balancing. It isn't necessarily perfect, but it's a decent way to estimate corner balance without spending a fortune getting it done professionally.

Basically, the problem that you're dealing with now is that the car has four corners, each of which is adjustable in its loading. What you need to do is reduce it to a tripod, on which only 2 points are variable. The easiest way to do this is to pick up the back at a conveniently provided center-point (like say, underneath the engine), then measure and compare the front ride heights. Correct as necessary. The same goes for the back two corners -- pick up the car by a center-point at the front, then measure the rear corner heights.

Thanks to Wil Ferch for thinking this up; I've used it plenty of times with great success. BTW, each time you make an adjustment, you really have to settle the suspension by running around the block, preferably a couple of times.

Cheers,

Dan
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Old 01-06-2005, 10:50 AM
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Ronin/Dan - thanks for the tip. I'm really only looking to get "street" close, so this will be good.

Let's say I start with the front: I assume I'm only lifting the rear of the car with the jack until both left and right front tires clear the ground. Is it ok to measure now or do I need to first remove both rear wheels, lowering the jack until the fender lip is restored to where it was with the wheels?

Seems like the rear would need to be dropped to its original height, or a different front/rear balance would be measured. Even though it sounds like I'm really just comparing left-to-right here, it could have a different result as more weight is moved from the jack to the front suspension.

So, once I've done both front and rear, there's really no guarantee that I'm anywhere near the 40/60 F/R ratio, right?

Would the next step be to repeat the tripod, but using the a center point between Front and Rear and checking heights again (on both sides, of course)? This would get me closer to a 40/60 ratio, but I'll need to adjust both sides up or down an equal amount to not mess up the L/R ratio.

Is this the Ferch Method?
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Old 01-06-2005, 11:26 AM
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I never used the method.
I can only guess that removing a small bit of spring tension from the rear by a rear center jack will enable you to level the front.. If raised to high then the front adjustment might not respond as easily.

Do a search of tripod for the recent thread I coppied the reply from.
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Old 01-06-2005, 01:01 PM
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I did some searching in the archives and saw several references to the tripod method, but only left-right (one axle) balance.

Wil, anyone?

Is it necessary to do the same from the jacking point on the rocker panel to lift one side to check F-R balance (i.e. Does it change the height) I'm thinking that will affect the 40/60 ratio that is ideal.

Or am I overanalying this because it's 20 degrees in my garage and I'm too much of a wimp to crawl on the floor and do the work?
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Old 01-06-2005, 09:41 PM
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I use this angle finder placed on the door sill to rake the car. The ground must be perfectly flat, air psi correct, driver's weight, etc, etc. It costs $15-20. Spec is 1deg.. Error to the high side imo.

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Old 01-07-2005, 06:27 AM
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ok, thanks - I have one of those tools myself.

Technically, I guess it's still using the body and not the chassis, but I could calculate the chassis slope by measuring height at front and rear torsion bars and dividing the distance between the two, just for "fun".

If nothing else, that'd be one indicator of the "trueness" of my body.
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Old 01-07-2005, 08:55 AM
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