Setting Front Ride Height After Suspension Refresh - What am I Doing Wrong?
 

I am having a really difficult time setting "correct" front ride height on my '87 after redoing the front suspension bushings (everything else is identical, other than new ball joints and tie rods). Struts are same Boge with same Bilstein inserts (I left the struts on the car).

According to Bentley, the ride height is determined by measuring the distance between the center of the wheel and the center of the torsion bar adjustment cap (C = A-B):
http://forums.pelicanparts.com/uploa...1458678214.jpg

The value of C for Euro ride height is 108mm.


Starting with where the car "originally" was at (which was the same number of 4 threads showing out of the top of the adjustment cap before I took everything apart):
Height to center of wheel (A): 310 mm
http://forums.pelicanparts.com/uploa...1458678250.jpg


Height to center of torsion bar adjustment cap (B): 137 mm
http://forums.pelicanparts.com/uploa...1458678280.jpg

C = 310-137 = 173 mm


The car is WAY too LOW, nothing close to where it was before taking everything apart. Either way, I know I have to turn the adjustment screw clockwise, and I do so a few turns (I'm working only on the driver's side at the moment).

New height to center of torsion bar adjustment cap (B): 147 mm
http://forums.pelicanparts.com/uploa...1458678336.jpg

C = 310-147 = 163 mm


Turn a couple more turns clockwise.

New height to center of torsion bar adjustment cap (B): 156 mm
http://forums.pelicanparts.com/uploa...1458678365.jpg

C = 310-156 = 154 mm


This calculation makes no sense based on my measurements. Just to get to Euro ride height by calculation (108mm) I've got to modify the height of B another 46 mm, or almost 2 inches?!?!? That makes ZERO sense, and there is nowhere close to enough adjustment screw left.

With the value of B at 154 mm, the height of the fender is at about 650 mm, or about 25.5 in.
http://forums.pelicanparts.com/uploa...1458678427.jpg

Before I took everything apart, the original measured B value was 160 mm. I'm about to just set it to that and call it good, but I'd really like to understand that calculation. I'd also really like to understand why the number of adjustment threads is so different from what it was when I removed it, and whether there are now too many threads sticking out the end that are going to cause the adjustment screw to bend.

Your adjustment screw won't bend.

You can 'index' the screw. When you put it all together, and before you put the end cap on put some weight on the A arm, to set them about the right angle. Put the cap on and you should find you have a finer adjustment.

You said you are working only on the driver's side. And I see a swaybar. If there's a difference in heights, that swaybar can affect things more than you think.

Maybe try "eyeballing" it so both sides look about right and even before you start measuring?

Good point. Disconnect swaybar then set ride height?

disconnect it at the steering rack cover plate. don't let it droop, suspend it with wire where it seems to move most freely. getting the a-arm side out is a project in its own right.

are you on a level surface? are you rolling the car to n fro some to settle things after an adjustment?

What do you mean it's too low? It looks like you have almost 5cm of clearance from the tire to the fender.

You can always jack it up and remove the adjusters from the T bars and re index them by one groove.
It really is a simple procedure.

Has anyone set a chasis height block for the rear???
 

I am going through the front end of my 74, upgrading a bit as I go and have been pondering the chassis height/corner weighting ritual soon to follow.

I rebuilt the suspension on an old Ferrari, using threaded body, aluminum shocks, stiffer springs,poly bushings and adjustable drop links on the bigger bars. I borrowed scales and put considerable effort into making a level platform, with decent roll on and roll off to get the stiction out of the suspension.

This seeming endless chasing of one's tail, side to side and front to back and all of the variables in between

What if we could just set one end, (of the chassis), at the desired height, then all we would have to do is to set the height and corner weight at the "in progress" end??????? With a final all 4 wheel corner weight fine tuning, bars disconnected, drivers weight in the seat and half a tank of fool.

If we start with a level platform, set the "other end" at its desired height, this has just got to simplify/shorten the usual chasing of ones tail, front to back, side to side and corner to corner.

I haven't done it yet with the P car, but I sympathize with the OP, looking to get it right.

If I ever get through moving and setting up my garage/shop, I am going to give this method a try - Hopefully, someone else has BTDT and can offer a bit of advice/help.

dazed and confused,
chris


SUPPOSITION: if the rear of the car were supported on blocks, at the "Euro Height", (wheels off the car), then the front could much more easily be set to both the desired ride height, and scales being present, much closer to equal front corner weight.

If we can slide a couple of Euro Ride Height Blocks under the back of the car, remove the wheels and tires, the only variables, (aside from fuel and driver weight influence - easily gotten around), are going to be front torsion bar adjustment.

http://forums.pelicanparts.com/uploa...1458703423.jpg

You are correct. When I first lowered the car using the pre-suspension rebuild settings, the tire actually went up and into the wheel well.

Yup, I tried this. I could only re-index the adjuster by one spline, and it was in the wrong direction (counterclockwise on the driver's side) which made the car even lower.

I finally opted out of using the formula and just went with floor to fender opening height. I settled on 25 1/4". Still high, but the rear is very high yet. I plan to refresh the rear suspension next winter and lower the whole car at that point.

When I adjusted the front of my car I also came to the conclusion that there is something wrong with the formula. I couldn't get to the 108 mm and the car would have looked like an SUV. I settled for 150 mm because it just looked right and I have no bump steer going over bumps.

Juergen

Did you do this with the front suspension in full droop on both sides? If not, that would explain why you could only go the wrong way.

Ok, now why is the rear high if you haven't worked on it yet?

There's nothing wrong with the formula. What you guys are learning is that these cars were set a lot higher from the factory than you think and that what most people think of as the correct height is in reality a couple inches lower than the original height. "Euro" height is probably the single biggest misconception out there regarding these cars.

You can lower the height if you want. You will get more bump steer, you will lower the roll center... etc.

Have a look at this thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/143795-ride-height-factory-measurement-method.html

JR

Hey guys,

Just seen this thread and I have just started on the front suspension on my car. I have just finished on the rear and the figures that I took from the Bently Book were hugely different to what I measured on the car.
My car is at somekind of 'Euro' rideheight and after checking, rechecking, some head scratching, a lot of swearing, I decided to just reset the ride heights to the same figures I had before I started. I have driven the car a short distance to help settle the rear end and to make sure that nothing falls off and then re-measured the rear rideheights. Everything is within a few mm of my original figures, which is still massively different to the BB book, but the same as before.

I have no idea why this is the way it is but I would also be very interested to know if there is a reason for it.:confused:

Read my post above yours. What you think is "Euro ride height" is not correct. At some point, your car was lowered from it's original height to a height well below what Porsche intended the height to be. When a 911 is adjusted to the correct height, it looks too tall for most people. By now, the vast majority of 911s have been lowered and people are used to what they look like in that condition. That, and the average owner is more concerned with looks than handling, so really low cars are the new "normal."

JR

Fair point Javadog! The formula is good,just the figures stated in the Bentley Book are for a roller skate! :D

Check out this German print ad for an SC 911. Not 100% conclusive, but it does show a fairly tall profile relative to what you see here on PP these days. A quick visual check shows the rocker trim top, heading straight into the wheel center.

http://forums.pelicanparts.com/uploa...1458740938.png

No, I didn't, which would explain it. I put the caps and adjustment screws on AFTER connecting the ball joints to the struts.

I haven't touched the rear from when I bought it from the PO. Current height at the rear is 26 5/8" from ground to fender.

That rear height sounds normal, if you consider "normal" to be what Porsche set it at.

If that were my car, I would not leave the front end that low, with a rear that high. Pick whatever height you're going to pick, then adjust both ends.

JR

I've considered this exact point, javadog. I am not going to get to the rear until next winter because I've never done it before. I can't really tell for sure because I'm not entirely sure what I'm looking at, but it appears the eccentrics on the rear are adjusted all the way down, so I can only go up on height adjustment without re-indexing the rears.

I think I'll bring the front back up to what it was until I can do all 4 corners next winter. Thanks for the input.

Keep in mind that the rear height for your car was 4mm higher than earlier cars. Not a big difference, but worth noting. Rear torsion bars were also slightly larger. The later cars kept getting heavier, especially the '87-on cars that had the G50 gearbox, so Porsche modified the suspension settings to suit.

Whatever you do, corner balance and align the car before putting a lot of miles on it. Yes, you'll get to do it twice, but it will most likely be way off if you don't. You'll wear your tires unevenly, reduce your braking capability and have a lousy handling car if you don't.

Porsche got hip to the fact that owners in the US liked to lower their cars (especially back during the years when the US cars were higher than ROW cars to meet DOT regulations) and so when they made the spring plates adjustable, they set them at the factory at the lowest point of the adjustment range. This allowed the height to be corrected if the car settled a little bit after delivery, but prevented easily circumventing the correct height. Yes, you could still lower a 911 at the rear, but it took a lot more effort and expense, which probably kept some people from doing it.

JR

That's full droop. When you install the caps and adjuster screws at full droop, you're setting the height near its maximum. When you set the car down on the ground, the suspension compresses a bit as the t-bars are loaded. You have to account for that compression/travel by jacking up the suspension a bit before you install the cap & adjuster screw.

Comparatively speaking, if you were to install larger t-bars, let's say a fat 23mm front bar for racing, and installed the cap & adjuster screw at full droop? When you set the car on the ground it would look like a SUV. This is because the stiffer t-bar reduces suspension travel. So in the case of a larger t-bar, you have to jack up the suspension quite a bit more to get the height where you want it (be that desired height right or wrong).

As JR aluded to, most importantly you must do an alignment. The front end of these cars are ultra sensitive to ride height and I can guarantee your front toe is all out of whack. It may feel OK but it'll handle like crap and eat your tires.

The rear end is not nearly as sensitive to height. You can adjust the rear height, even if your spring plates don't allow for it & you have to disassemble the spring plate. You can get the alignment close by marking the toe & camber eccentrics (reinstalling them as you marked them) and your alignment will be somewhat close. Still, it's very foolish not to do an alignment after futzing with the height.

This is the part that's confusing to me. When you say, "jack up the suspension a bit before you install the cap and adjuster screw", do you mean compress the shock by rotating the A-arm upward? If you do that and then put the adjuster cap and screw on, then when you put the car on the ground I would expect the car to be even LOWER because you've compressed the shock (bringing the wheel further up into the wheel well), and the torsion bars STILL have to load up, thereby dropping the car even further.

When I put everything back together, A-arms in full droop, and put the cap on and set the adjustment screw to what it was before taking things apart (3 threads exposed between the top of the cap and the stop on the top of the aluminum crossbar), the tires were up into the wheel well it was so low. If I jacked the car up, removed the cap and screw, compressed the shocks (by rotating the A-arms upward), put the caps and screws back on, then the car would be even lower I feel like.

You understood me correctly and you understand correctly what's going on with how the suspension behaves depending on the positioning of the A-arm and the indexing of the t-bar cap.

What I didn't recognize is that you already did it at full droop and it ended up with the height too low. In that case I would remove the nut on the top of the damper shaft and push the suspension down to have more droop before you index the t-bar by installing the end cap. And you can't do that if you have the sway bar connected because it'll be resisting you from the other side of the front suspension.

Don't, for the love of god, pull the swaybar, or you'll be disassembling EVERYTHING again to get it back in.

I seriously dread installing that thing.

Agreed with Matt. You should leave the swaybar in the A-arm and disconnect at at the rear where the U-tab fixes it to the body.

1000000% agree with Matt that I HATE the front sway bar installation. That thing is a mofo to wrestle with. It laughs at you and begs you to cross-thread the bolts as you struggle to get the belly pan and U-tabs to line up and let the bolt into the hole

To maintain the intended nose-down attitude (about 1 degree) your fender lip measurement should be about 1/2 inch higher in the front compared to the rear. I know it's counterintuitive.
So your front should be 27 1/8
If it were my car I'd lower the rear.
A good target would be 25 1/2 front, 25 rear.
That assumes you haven't got some unusual wheel/tire combinations on it.

Hahahaha, oh man, I thought it was just me with the sway bar!!! I think my body is still sore from pushing and pulling on it to get the U clips to line up and get the bolts in.

I finally understand everything completely. This being my first time redoing the suspension, this site is invaluable, thanks so much. I literally would have been incapable of doing this myself without your help.

Just think - the front was the easy part and I struggled with it. I can only imagine how difficult the rear is going to be...

Matt

The rear is easy, though I admit I haven't done the trailing arm bushings. Just mark everything before you take it apart, measure the spring plate angle, line it all back up with the marks and you'll be darn near the right height and close enough on alignment to drive safely to the alignment shop.

A trick for the rear spring plates is have some longer M10 bolts handy. Turns out the bolts for your CV axles are perfect because you have an '87 with the larger bolts that have the same thread pitch as the mounts for the spring plate bushing brackets. You use the bolts to "press" the cover plate & bushings into the chassis. Using the power of threads (make sure they're lubed with oil or antiseize goop) is WAY easier than trying to whack them into the chassis with a plastic mallet.