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The front is way too low at 120mm and should sit 7mm higher than the rears. I cannot remember the exact numbers from the top of my head- the rears might be just within the allowable range. Very common for the 928's stock front springs to sag over time. Suggest you try getting the fronts up to 160mm and take it from there.
If you go for the stock setup at 170mm front, raise the rears to 163. Remember as you lift the suspension the front camber will decrease and the front toe in will increase so be prepared for a new alignment. Corner balance is the ideal set parameter to target rather than height but ground clearance is also important on the fronts. If you do end up running a bit owoer than stock i highly recommend fitting bash plates on the front- they are worth their weight in gold and also justified even when running the stock height if you have bumpby or pot holed roads in your locale!
Next topic I can assist with, cool . What is the condition of your shock absorbers? Raising the car to the minimum factory spec is the way to go.
I have done it on my GTS while updating to Bilsteins, what a difference! Wow, one of the most rewarding upgrades!
The front is way too low at 120mm and should sit 7mm higher than the rears. I cannot remember the exact numbers from the top of my head- the rears might be just within the allowable range. Very common for the 928's stock front springs to sag over time. Suggest you try getting the fronts up to 160mm and take it from there.
If you go for the stock setup at 170mm front, raise the rears to 163. Remember as you lift the suspension the front camber will decrease and the front toe in will increase so be prepared for a new alignment. Corner balance is the ideal set parameter to target rather than height but ground clearance is also important on the fronts. If you do end up running a bit owoer than stock i highly recommend fitting bash plates on the front- they are worth their weight in gold and also justified even when running the stock height if you have bumpby or pot holed roads in your locale!
Next topic I can assist with, cool . What is the condition of your shock absorbers? Raising the car to the minimum factory spec is the way to go.
I have done it on my GTS while updating to Bilsteins, what a difference! Wow, one of the most rewarding upgrades!
Hi Schocki
You assisted a lot with my transmission. Today it works very very fine !! I am so happy Now it's time to optimize my GTS !!!
I think that my BOGE shock absorbers are from 1995 and 145 000 km.
The front is way too low at 120mm and should sit 7mm higher than the rears. I cannot remember the exact numbers from the top of my head- the rears might be just within the allowable range. Very common for the 928's stock front springs to sag over time. Suggest you try getting the fronts up to 160mm and take it from there.
If you go for the stock setup at 170mm front, raise the rears to 163. Remember as you lift the suspension the front camber will decrease and the front toe in will increase so be prepared for a new alignment. Corner balance is the ideal set parameter to target rather than height but ground clearance is also important on the fronts. If you do end up running a bit owoer than stock i highly recommend fitting bash plates on the front- they are worth their weight in gold and also justified even when running the stock height if you have bumpby or pot holed roads in your locale!
I don't think it's the springs, it's the LCA bushes slowly dying. (Which exacerbates the lowered-car-eating-blocks-syndrome) significantly. Even a sagged spring hasn't really lost any spring rate, but losing bushes over time -IS- lost and progressive spring rate.
Go OE height, enjoy a good handling car based on math, not a lowered "looks like it but doesn't" based on looks.
Our 928 has the tendency to lower itself over the years below the factory minimum. Front axle should be 18cm +/- 2cm and rear axle 17,3cm +/- 1,0cm. Check out this forum on how to measure the suspension height correctly.
I would recommend to replace the original BOGE with Bilstein B6, they work really great. You have two options:
Replace all the parts of the suspension that wear over the years and with mileage
Start with the shocks and a correct ride height.
I would start with option two. New shocks with original springs. The correct ride height will also allow you to setup the geometry of the suspension like the car was designed by Porsche.
Lower than minimum cars will suffer from too much camber, especially at the rear axle.
With fresh shocks, fresh bump stops (at 120mm, your bump stops are going to be completely destroyed), fresh lower control arms, and stock pieces not modified to get additional shock travel, 150mm will work, if the roads you travel are very smooth. If the roads are uneven/bumpy, 155mm will work better. (If you modify pieces to increase the shock travel, you can also use 150mm over rough roads.)
We've been on a LONG/EXTENSIVE research/testing program to improve the handling of the 928, without affecting the fantastic "GT" touring qualities of the car (for us, the car must remain quiet, not harsh, and extremely predicable.)
We've installed just about every different product that we can buy (or make) to find the optimum "budget" combination. (We already have a "high budget" suspension, in testing.)
We had just made some changes in this evolution (which looked great, on paper), settled the car, set the ride height to 155mm and aligned it. (However, we did not settle the car enough!) Took it out for a 10 mile test drive. The car felt great, at first, and then deteriorated into a complete nightmare. Both bump and rebound were terrible. The front end literally was "pogo sticking". The ride was terrible. Turned out that the car had settled to the point where the front bump stops were the main front spring. Instead of a front spring rate in the hundreds of pounds, we had spring rates in the thousands of pounds.
Bad thing to do.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Wow !! BILSTEIN B6 are very expensive !!! I will take time to check them at the best price
In a first time, I will correct ride height with my original BOGE.
Wow !! BILSTEIN B6 are very expensive !!! I will take time to check them at the best price
In a first time, I will correct ride height with my original BOGE.
I dont think that the threads on your BOGE shocks are still moveable. They are most likely frozen solid. Plus the fronts are not really adjustable.
That's why I recommend only to do the shocks first. Believe me new, adjustable shocks make a huge difference! Safe up some money, wait for a good offer and get some. This is not a time critical update for your car or absolutely necessary because your car is not driving right now.
What you could check before you start, if the lower bolt on the rear axle can be removed. If not, your're in a world of hurt! Here a picture of the bolt I'm talking about.
0/
I don't think it's the springs, it's the LCA bushes slowly dying. (Which exacerbates the lowered-car-eating-blocks-syndrome) significantly. Even a sagged spring hasn't really lost any spring rate, but losing bushes over time -IS- lost and progressive spring rate.
Go OE height, enjoy a good handling car based on math, not a lowered "looks like it but doesn't" based on looks.
Jeff,
Have you never heard of spring sag? Front springs are notorious for it- there is even a rule of thumb that says toss the spring when they have sagged one inch! In the case of 928 stock springs that would take a lifetime I suspect but maybe not give Fabien's experience.
For sure the bushes do get tired but that will not impact the ride height of the car at rest at or so I would think but stand to be corrected. It does impact the time it takes for the car to recover its natural ride height after being lifted
Ride height has come round again ! if you are up to checking ride height why not check alignment - yourself, with the car settled as normal on home ground.
Plenty of tools, even Laser assisted tools, available for domestic use. in the UK we have, for example, TRACKACE. about £75 / 100USD - there are probably others and better ones, but this is the laser based one I have used over many years. A bit fiddly at first use, practice makes it easier. I have found it to give repeatable readings if you are careful, ( a laser is involved!) have the time, and a flat floor. AND: do the rear toe too, -- after 30 / 40 years use it will have had some heavy knocks.
rear toe setting made a big difference to my straight line stability.
I have no connection with TRACKACE or any other alignment measuring provider.
Have you never heard of spring sag? Front springs are notorious for it- there is even a rule of thumb that says toss the spring when they have sagged one inch! In the case of 928 stock springs that would take a lifetime I suspect but maybe not give Fabien's experience.
For sure the bushes do get tired but that will not impact the ride height of the car at rest at or so I would think but stand to be corrected. It does impact the time it takes for the car to recover its natural ride height after being lifted
I have but I believe that 90% of out sag is the lost spring in the bushings...and we all gleefully overlook it by thinking its a Buick.
I have but I believe that 90% of out sag is the lost spring in the bushings...and we all gleefully overlook it by thinking its a Buick.
Jeff,
In the static position there is no torsional spring reaction in the bushes. Easy enough to measure the free length of springs when new and when exhausted. The front end droop cannot be explained by other than spring sag and if it could all well and good- I am all ears as they say. The car does nought to sixty in approx 6 seconds and 60 to zero in 3 seconds as I recall - that in a nutshell does for the springs long term and I would bet that the 928 springs last longer than most but they do not last forever.
Indeed I sometimes think folks generally have little perception of what really happens in the bushes- supposedly they follow Young's Law but if they did they would return to their natural position as soon as the weight of the vehicle is imposed on them but as we know that just does not happen- so clearly something else is going on. To this day I do not think I have ever heard of this anomaly being discussed in the forum yet alone resolved- it just seems to be accepted with no thought given to it.- that is not a problem per se but I do find it intriguing.
Before to change the ride heigh, I think to replace my BOGE by new BOGE (not BILSTEIN B6). Which parts to order ? I see that BOGE has been replaced by SACHS.
I will order these parts :
Front vibration damper SACHS 314617 : 928 343 055 07. 105 USD on RockAuto
Additional front spring (shock rubber stop) : 928 343 527 02
Rear vibration damper SACHS 664008 : 928 333 051 16 (can't find it. Out of stock everywhere ...)
Additional rear spring (shock rubber stop) : 928 333 518 10
Do you see something else to buy ?
Where to find rear SACHS ?
02-25-2022, 04:32 AM
. What is the condition of your shock absorbers? Raising the car to the minimum factory spec is the way to go.
