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Old 02-13-2018, 08:50 PM
  #31  
rjtw
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Dr Bob, Speedtoys, thanks for the responses. Totally makes sense to count the turns -- glad to know that's more than sufficient and that corner weighting will not be an issue (at least, counting turns won't change its current corner weighting). Time to measure current height and also review this list for how-tos!!
Cheers
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Old 03-20-2018, 09:32 PM
  #32  
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I finally have time to start looking at this. Um, can anyone point me to a how-to thread here on the forum for adjusting ride height? Really have no clue what this involves (does the suspension need to be disassembled?) Mine's an 83, 5 speed, USA. And do I need any special tool(s)? Socal Tom mentioned a spring tool, above! Cheers.
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Old 03-20-2018, 10:21 PM
  #33  
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The workshop manual is pretty good, section 44 pages 2b & 3.

Don't disassemble or lift anything, that will mess up the measurement. Make a set of height gauges, we've had good luck with either Rob's style or Bob's, although we have found wire coat-hangers to be in short supply around here. Be sure you are working on a relatively flat and level floor, and turn the front wheels left/right for access-- don't lift anything.

A special tool is required, factory tool VW-637/2 or equivalent. We bought ours from 928 Specialists some time ago, on their website here: http://928gt.com/ps-26018-122-shocks...ster-tool.aspx

I hate disagreeing with Dr. Bob because I am always wrong, but the factory spec for front ride height is 180 +/- 20mm, with a footnote that says that spec applies to new cars. For cars that "have been driven for a period" the allowable range is up to 10mm less. So I interpret that to be an allowable range of 150-190 (front) for a car with some miles. (Rears are spec'ed at 173+/- 10mm, minus 10 for not-new, so 153-173mm). We shoot for the minimum spec (150 front, 153 rear) plus any difference in tire diameter from the stock 25.0" (add 5mm for current 235/40-18 Mich PSS).

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Old 03-20-2018, 10:35 PM
  #34  
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That is assuming that your 928 does indeed have adjustable struts at the front.... my 83 S (ROW) does not.... new shocks were and still are on my list of things to do.... rears are adjustable but I believe all were.
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Old 03-21-2018, 07:53 AM
  #35  
FredR
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Originally Posted by jcorenman View Post
The workshop manual is pretty good, section 44 pages 2b & 3.
.....the factory spec for front ride height is 180 +/- 20mm, with a footnote that says that spec applies to new cars. For cars that "have been driven for a period" the allowable range is up to 10mm less. So I interpret that to be an allowable range of 150-190 (front) for a car with some miles. (Rears are spec'ed at 173+/- 10mm, minus 10 for not-new, so 153-173mm). We shoot for the minimum spec (150 front, 153 rear) plus any difference in tire diameter from the stock 25.0" (add 5mm for current 235/40-18 Mich PSS).
Jim,

My interpretation of the WSM is a little different from yours in that Porsche intended the difference between front and rear ride height to be a constant of 7mm. What the specification seems to understand is that the springs with use will take a permanent set and consequently from time to time this needs to be corrected. Thus on page 44-05 it quotes the case for a new car and front height is specified as 180mm +/- 20mm suggesting that nothing needs to be done until the front ride height reaches 160mm - a hard barrier not to be transgressed i.e. something has to be done about it either with shims or as in later models with the collar adjustments. However, what the qualification words say also suggests that whatever height the front axle is at the rear axle must sit a similar amount lower relative to the design point- that is to say that there must be a 7mm difference with the rear being lower.

Now, if you turn to page 44-2b the specified front height is 180+/- 10mm and my take is that this applies once the system has settled and is no longer "new". Thus the +/-20mm differential no longer applies . Thus Porsche intended that the lowest you should run long term is 170mm on the front axle and 163mm on the rear axle.

Porsche clearly expected the front springs to permanently sag more than the rears- not too surprising given the braking force compresses the front springs more thus why neglected examples that have not been attended to end up with their "nose in the dirt/*** in the air" attitude that so many think looks right but is in fact way wrong.

In making these determinations Porsche doubtless took into account road clearances and spring rates and folks who lose their alternators or a/c compressors invariably did so because they were sat too low. Lower your car below 170mm front/163mm rear and the risk of damage increases dramatically unless of course one has stiffer spring rates [as I do], one fits front skid plates [as I do] or better still one runs on excellent roads all the time [as I do]. This is why I can run at 160mm front and 153mm rear but to be fair, it is ages since I checked my ride height!

Whether my interpretation is correct remains to be seen but if practical experience is anything to go by I seem to be doing OK.
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Old 03-21-2018, 11:29 AM
  #36  
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I’m currently in the process of rebuilding/resetting my suspension (83 Euro). My concern is handling rather than “look”. As purchased, there was noticeable bump steer, needed constant minor corrections with every expansion joint or crack when driving straight and cornering was marginal. My front was at 135, rear at 160. My front tie rods angled up from the rack to the tie rod ends. I converted to adjustable front with parts from an 84 and raised the front to 175.
Tie rods now have a slight down angle from the rack. About 160 was level. I completed the front, with numerous drives to settle and am just getting ready to do the rear.
Straight line, it now tracks true, no more constant steering inputs. Cornering is now much better.
I’m not a suspension expert, but logic would seem to indicate tie rods should be level to slight down angle from the rack. With an up angle at rest, toe out would seem to be exaggerated with every compression of the springs.
Porche designed the suspension to work best at a certain road height and a certain amount of suspension deflection, and straying from that shouldn’t yield positive results.
Even if it doesn’t look cool by today’s standards.
But i’m open to arguments to the contrary.
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Old 03-21-2018, 01:39 PM
  #37  
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Originally Posted by Billu View Post
I’m currently in the process of rebuilding/resetting my suspension (83 Euro). My concern is handling rather than “look”. As purchased, there was noticeable bump steer, needed constant minor corrections with every expansion joint or crack when driving straight and cornering was marginal. My front was at 135, rear at 160. My front tie rods angled up from the rack to the tie rod ends. I converted to adjustable front with parts from an 84 and raised the front to 175.
Tie rods now have a slight down angle from the rack. About 160 was level. I completed the front, with numerous drives to settle and am just getting ready to do the rear.
Straight line, it now tracks true, no more constant steering inputs. Cornering is now much better.
I’m not a suspension expert, but logic would seem to indicate tie rods should be level to slight down angle from the rack. With an up angle at rest, toe out would seem to be exaggerated with every compression of the springs.
Porche designed the suspension to work best at a certain road height and a certain amount of suspension deflection, and straying from that shouldn’t yield positive results.
Even if it doesn’t look cool by today’s standards.
But i’m open to arguments to the contrary.
My understanding is that the front suspension was designed to have the LCAs level.

I'm not 100% sure where that puts the tie rods, but I think it would be in the same vicinity.

But I can be wrong, and as you put it: I'm open to arguments to the contrary.

I care far more about ride and handling than appearance.
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Old 03-21-2018, 01:43 PM
  #38  
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My interpretation of the WSM and other guidance leaves me with a target on my car of 175mm in front, settled. There are many testimonials here from folks whose cars sit a little lower, saying that everything is fine for them where their car sits. Good for them if they've found a setup they like.

At my previous homes in SoCal, the driveways included rain gutter depressions that made it possible to drag the nose when approaching or departing straight on, with ride height sagged to 160mm. I drove on relatively smooth roads so in general wasn't too worried about shaving accessories off the engine. I could approach the driveway apron from an angle to avoid the scraping. I did notice the dreaded inner-rib scrubbing after a while. The combination of sag-steer and chin-dragging made the height adjustment decision pretty easy for me. Meanwhile, many local SoCal owners at the time were driving with their cars a lot lower. They compensated some by having the car aligned at the lower height, and were satisfied with the results. I don't have argument with how folks set up their own cars. I've ridden in more than a few of the sagged cars and frankly they ride like ice wagons.

For some reason, there's a serious misconception around handling that the stiffer the ride, the better the road feel and therefore the better the handling. Riding on the stiffest part of the shock travel, and bouncing off the compression bump stops is technically "out of control" on wheel or more specifically body travel. Notice when you have your Bilstiens or Konis custom rebuilt, you get to spec a damping profile. I wonder why they do that... The Kim Crumb-spec'd rates om the 928 International-supplied Eibach spring sets similarly have a rate profile that allows you to run the car more "safely" at a lower height, albeit with an effective spring and damping rate that rattles fillings at least on my car. Some folks equate that with better handling, and they may be right if everything is set up to work together. In my opinion it spoils the car for my intended purpose, GT driving at speed on available public roads.

Anyway, lots of factors will help you decide what's best for your car. Folks who have driven or ridden in mine commonly remark how quiet it is, and how well it rides. Slot-car handling doesn't enter the discussion. Jim and Sue have experimented with combinations of springs and dampers on their cars, and have mentioned that what seems to work perfectly on one of their cars does not always translate perfectly to another similar car in the fleet. Me stating that a specific combination or setting on my car will make yours "perfect" won't happen. Much of that is what a person's definition of "perfect" is on that particular day. I've had good results with the combination of mixed springs and Boge shocks on my car, at 175mm front height and generally at factory alignment settings. I dial in a little extra camber to help the modern tires, and a little less caster to help compensate with the interesting wear we have on the local highways. Tires and wheels make a huge difference in ride quality and handling, but that's again a subjective discussion best saved for later.

So what's the best height for your car? The range we are discussing, between my 175mm and a commonly-used value of 160mm, is about 5/8" difference in static height. At a scrape-the-alternator-off height of 135mm, we are looking at about 1 1/2" difference. This is what you see as difference between the top of the tire and the fender, and is functionally the difference in height at the road-to-alternator measurement too.
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Old 03-21-2018, 02:00 PM
  #39  
Billu
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Hey Joe, sorry we never jumped together at Summerfest.
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Old 03-21-2018, 02:05 PM
  #40  
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Dr bob, what do you target for rear height?
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Old 03-21-2018, 03:50 PM
  #41  
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Originally Posted by Billu View Post
Dr bob, what do you target for rear height?
I'm not close to the car or the manuals or the logbook at this moment. I start at factory-spec height with the tank 3/4 full and front passenger weight, if that helps. I just don't remember the numbers off the top of my head.
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Old 03-22-2018, 01:45 PM
  #42  
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Kim Crumb.......now thats a name that I don't here very often anymore.

dr bob,good info on vehicle loading during the alignment process.
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Old 03-22-2018, 05:13 PM
  #43  
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Originally Posted by 928FIXER View Post
Kim Crumb.......now thats a name that I don't here very often anymore.

dr bob,good info on vehicle loading during the alignment process.
I met Kim the first time at a 928 International lunch gathering the fall after my 928 stewardship period started. Mark Anderson had invited Kim to co-drive his 928 racer at a regular race on his schedule, so he was in California. This "event" was the precursor to the event we now know as "Sharktoberfest". Mark shared a picture a few years ago from that little gathering almost 20 years ago now. Some of those folks have gotten so fat and bald they probably wouldn't recognize me now. (!!)

Meanwhile, Kim was part of the 928 judging team at the 2017 PCA Parade in Spokane. He's still a serious supporter of the model within the PCA community. He was the model expert for PCA prior to John Veninger taking the current duty.
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Old 03-24-2018, 09:40 AM
  #44  
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Default Alignment sheet after 50mm change 86 specs indicated on sheet

Just replaced the tires front was 117/113mm to start now at 175 the sheet will show the change in alignment height.


Alignment before replacing tires.


Ride height not settled yet after new tires.
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Old 04-16-2018, 02:56 PM
  #45  
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I finally got around to actually looking at the front suspension this weekend (yes I can be a bit slow sometimes lol). Um, is this even adjustable? '83 S (USA). Dayum... I don't see threads... If not adjustable, and I'm way too low, do I need to replace springs? Shocks? Both? Arghhh...


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