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Thread: Talked to Bilstein today about "revalving" B6 (HD) E23 shocks for lowering springs

  1. #26
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    Update. I installed my Dinan front and rear coils on unmodified Bilstein HD's. The ride quality is totally fine. However, when the car is lifted off the ground to service it, the rear strut pistons extend about an inch past the point where the coils lose preload. The spring can tip and get out of the top spring seat when this happens. Having to check that the rear springs are seated in the upper spring seats using a flashlight and mirror every time I lower the car from working on it is massively annoying. The rear ride height is also way too high compared to the front. I thought about sending one of my pairs of E23 rear HD's in to Bilstein request the droop travel be reduced and have grooves cut at 20, 30 and 40mm below the existing snap ring groove. The droop travel right now is almost 1" too great to maintain any spring preload. When I drop the spring seat that will get even worse. I don't like the idea of having to lower the spring seat on a strut that already has far too long of a piston for a lowering spring. I just ordered a pair of Bilstein E28 HD (B6) rear struts to measure them. They look like they have a shorter piston than the E23 HD, which is good. I hope it's at least an inch shorter, even up to 2" shorter. That will make the range of travel correct for this spring using the E23 spring seat. I may still have to cut lower spring seat snap ring grooves in that shock, although the E28 version already comes w/ 3 grooves.
    Last edited by BONDOSPECIAL; 11-24-2018 at 08:04 PM.
    Steve H.

  2. #27
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    Didn't Vern on The other forum warn against using the e28 rear?

  3. #28
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    I read someone claiming that they felt like the e28 HD was topping out during track day driving, but I want to measure it for myself. The piston length looks like it will be closer to correct for a lowering spring than the e23 HD. An e28 sport shock would definitely have too short of a piston for an e23.
    Steve H.

  4. #29
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    I bought e28 B6 (HD) and e28 B8 (sport) rear struts so I could compare them to the e23 B6 (HD) rears I took off my car. Here is a picture showing the strut piston lengths and spring perch snap ring locations side by side. The top strut is an e28 B8, middle is an e28 B6, and the bottom is an e23 B6.





    I had two problems with the e23 B6 rear struts with Dinan lowering springs on them. One, the coil spring would come unseated from the top perch when I lifted the car, and the spring would often tip, so when I lowered the car, it would not sit properly in the perch. Two, the rear ride height was about 1.75" too high compared to the front ride height w/ the Dinan springs because of the e23 spring snap ring location.

    Here is what an e23 B6 strut looked like at full extension w/ the Dinan spring on it. This represents full droop when installed on the car. Notice how the top spring has about an inch gap to the top perch.





    The next two photos show the Dinan rear spring installed on the e28 B8 strut using the e23 perch. Because I needed so much drop in rear ride height, I placed the e28 B8 perch snap ring in the lowest of the three grooves. Even with the perch moved down this much, the Dinan spring stayed close enough to the top perch at full extension that it wouldn't come unseated.





    I had read an anecdote on mye28 where someone claimed that an e28 rear strut would limit the droop travel of an e23 and cause unwanted issues during hard cornering. I do not find this to be true. The e28 B8 strut, which is the shorter of the two e28 struts, allows the e23 rear trailing arm to hang at full droop without limiting it. I was able to slide the e28 B8 strut locator pin into the trailing arm with it freely hanging and it went in. The rear dogbones are still limiting droop travel, not the strut.



    I found that the e28 B8 rear strut with the snap ring in the lowest position gave me a 3/4" drop over the e23 B6. This is not quite as much drop as I wanted, but it took a lot of the unwanted rake out of my stance. At some point I may cut a lower groove on the rear strut but for now this will do. Subjectively, the ride quality w/ the e28 B8 rear strut is fine. The car rides quite stiff w/ 225/40/18 front, 245/40/18 rear tires on 18x8, 18x9.5 wheels, but the struts control the suspension well and the ride is not bouncy.



    Conclusion. The e28 B8 shock works better with a lowering spring than the E23 B6 shock because the piston length is correct for the shorter spring. Either of the e28 shocks would be too short to work with stock ride height springs on an e23, but if you have stock height springs you would want to use the e23 B6 shock anyway. In an unscientific test where I compressed the e28 b6 and b8 struts against the floor w/ no spring on them, using my body weight, the B8 strut was notably more difficult to compress. I know this does not tell you much, because struts are speed sensitive and the speed at which I could compress them does not represent what would occur driving a car down the road, but I would not be surprised to find the e28 B8 strut is valved firmer than the e28 B6 strut. I have not tested the E28 B6 strut w/ the Dinan springs. Its length would also be appropriate w/ the lowering spring but I don't know how the valving would feel. E28's have much smaller diameter rear springs than e23's so I wanted to use the firmer of the two struts to ensure I'd have enough damping.
    Last edited by BONDOSPECIAL; 12-06-2018 at 08:25 PM.
    Steve H.

  5. #30
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    Nice work, Its good to see a comparison of the different rear options. Your car looks great with the rear dropped down to better match the front. It must be something about the Dinan springs that is causing the rear to sit higher (or the front lower). I have my rear spring set on the 3rd ring from the bottom on my E28 B8 struts, and sometimes I feel like the rear is sitting too low and I should move it up another notch. I am going to wait until I get my 17'' wheels refinished and installed to adjust the suspension though.

  6. #31
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    Steven, note from my pictures that Bilstein stopped cutting the E28 B8 strut with six grooves - they now come with only 3. I was so disappointed when I got the struts the other day to see this. If I had six grooves like yours have, I would drop the rear even further.
    Steve H.

  7. #32
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    Quote Originally Posted by BONDOSPECIAL View Post
    Steven, note from my pictures that Bilstein stopped cutting the E28 B8 strut with six grooves - they now come with only 3. I was so disappointed when I got the struts the other day to see this. If I had six grooves like yours have, I would drop the rear even further.
    Ohhh I didn't even notice that, what a shame.

  8. #33
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    The ones I got had the extra grooves. Part #24-006071

  9. #34
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    first thing I noticed was the lack of grooves. Sure glad my car has E23 sports at the corners.

  10. #35
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    motohunter, good catch. The part # of 24-006071 you provided is an e28 B8 "performance plus" shock absorber. The E28 B8 "sport" shock I used is 24-007276. I just took a look into why there are seemingly two part # Bilstein e28 B8 rear shocks and found this explanation:

    http://www.mye28.com/viewtopic.php?f=3&t=146121

    The last two posts explain that the 24-006071 is a sport shock for the e28 528i, and that the 24-007276 is the sport shock for the e28 535i and M5. The 7276 shock is valved stiffer.

    e28 rear lowering springs are typically in the 200-220 lb/in range. I calculate that my Dinan e23 rear springs are roughly in the 250-280 lb/in rear range (hard to tell how many live coils I have at ride height). So selecting the stiffer of the e28 sport shocks seems to have been a happy accident. The only down side is I have only 3 ride height grooves w/ this version of the e28 B8 shock. Although if I dropped the rear perch any lower it would unseat the coil spring at full droop again.
    Last edited by BONDOSPECIAL; 12-07-2018 at 01:06 PM.
    Steve H.

  11. #36
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    Thumbs up

    Awesome info, thanks for going through the trouble!
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
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    Ford, MB, and GM round out the pack.



  12. #37
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    Interesting there are 2 versions.

  13. #38
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    Rear B6 HD comparison to MTech

    I hope what I have to add helps someone. Here are two photos comparing the B6 HD shock with an actual BMW MTech rear shock. The top two shocks are new off the shelf B6 HDs. The top one with the plastic cap is recently purchased; the other is a never installed 12 year old version. The bottom shock is a NOS factory MTech. As you can see, the shaft on the MTech is about 40 mm / 1.5" shorter than the HDs. The shafts are the exact same diameter.

    20181207_135609-25.jpg

    20181207_135626-25.jpg

    From what I've read in other places of the Internet and heard from others (no actual data to back up what they said) the B6 HDs and the MTech shocks for the rear are the same internally, but the shaft is shorter to work with the shorter MTech springs. Which from what I understand is what Dinan copied. Does anyone have any data to support or refute any of this hearsay? If what I've heard is true, would it be possible to just shorten the shaft of a B6 HD and have a MTech clone?

    The only thing I know for sure is that the MTech shock is exactly the same size dimensionally as the B6 except for the length of the shaft.

    Like I said I hope this helps someone.
    C
    Last edited by cfisher535is; 12-08-2018 at 04:28 PM.

  14. #39
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    From what I see it just reinforces the idea to go with e28 rears with lowering springs assuming you already have the correct perches.

    Sent from my LGLS755 using Tapatalk

  15. #40
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    Does anyone have the MTech shock specifications? and the ones for the e28? I'm no expert, so I'm not sure if there are any number that can be compared.

  16. #41
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    The dimensions of e28 shock, compressed and extended, are close to the old e23 B8 sport. The old e23 B8 sport, which you unfortunately can no longer get, would have been valved for an e23. I am guessing the e28 B8 shock is valved slightly softer than an e23 B8 was because e28 lowering springs are lower spring rate than e23 lowering springs due to the e28 weighing less, but Bilstein wouldn't give me this information over the phone when I talked to them. You could probably have an e28 B8 shock, which is a take-apart shock, re valved by Bilstein if you needed it to be firmer, but I haven't had any issue w/ it not controlling the Dinan/Mtech rear spring.
    Last edited by BONDOSPECIAL; 12-17-2018 at 09:45 PM.
    Steve H.

  17. #42
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    There is some good and some pretty bad info in this thread.

    1: E23 front Sports are NOT valved the same as E23 HD. The sports are over 50% stiffer both compression and rebound, that is straight from a Bilstein tech, who was very helpful, a few years ago when I was setting up my suspension.

    2: The best data on using E28 rear shocks was provided by Eric Q, when he used to track the 'M7', and the issue was the E28 sports were too short and caused inside wheel lifting in hard corners, not about trailing arm sag. If your shocks have such poor rebound control that your trailing arm is able to reach full extension while driving, you've got a big problem.

    3: Comparing anecdotal evidence on E23 and E28 shocks is not a good idea, they are definitely not the same, and just because E28 sports ARE valved the same as E28 HDs does not mean that the E23 was done the same way.

    I have Dinan springs with front Bilstein Sports and custom valved Bilstein rears (done by Eric Q many years ago for the M7, sold to me by TCD when he changed out the suspension on that car after he got it). I honestly think the sports and customer valved rear B46-0721 are too stiff, and make the ride too harsh. I have a set of HDs that I plan to install, they rode great with the cut springs when I got the car.
    --Jay3->Sic gorgiamus allos subjectatos nunc
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  18. #43
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    Not sure if anyone has looked at this old thread. Lots of good information.

    https://www.bimmerforums.com/forum/s...lp-ID-ing-them

  19. #44
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    Thanks for the additional info Jay and for the clarification on e28 sport rebound damping. The source of info who informed me that the valving for E23 HD and sport front struts were supposedly the same was a Bilstein tech who I spoke to over the phone and via email a few weeks ago. I won't name him publicly in a forum but I spoke with him a few times because I had a hard time believing this was the case. He told me not to bother sending my E23 HD struts in because the only change that could be made to make them more like the sport application was to reduce droop travel by limiting it internally and that this would only affect operation of the car if I was going over jumps and leaving the ground and unseating the springs. I would still send my E23 HD fronts in to have them revalved if I could talk to someone at Bilstein who understood what I was trying to accomplish.
    Last edited by BONDOSPECIAL; 12-17-2018 at 04:02 PM.
    Steve H.

  20. #45
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    I would stop putting it in terms of "I want to make these Sports" and instead say "I want these custom valved to match these springs".
    The biggest problem with Bilstein shock valving is a hard initial compression, that makes them harsh compared to Koni and OEM.
    --Jay3->Sic gorgiamus allos subjectatos nunc
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  21. #46
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    I asked about matching them to the Mtech/Dinan springs and was told I needed to supply rates. I can get a close guess at rate from the # of loaded coils, spring OD, free height, and wire diameter unless someone happens to know what the actual rates are for E23 Mtech/Dinan springs. I didn't see that info published anywhere
    Steve H.

  22. #47
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    I've not seen it for E23.
    I supplied a few springs for the charts that Devinder made years ago for E28 springs, but E23 are just too physically different (front) to assume anything.
    Time to measure the wire OD, and number of active coils!
    --Jay3->Sic gorgiamus allos subjectatos nunc
    84 €735i manual, 88 528e/i
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  23. #48
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    Anyone know the compression and rebound specs for e23 HD's(current setup )? Now I feel weird putting the e28 sports on the back. I'm not tracking mine, or accelerating full throttle out of curves, or trying to shoot Steven Seagal and flying through a jewelery store window.

    Sent from my LGLS755 using Tapatalk
    Last edited by motohunter4; 12-17-2018 at 07:34 PM.

  24. #49
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    Thumbs up

    Quote Originally Posted by motohunter4 View Post
    Anyone know the compression and rebound specs for e23 HD's(current setup )? Now I feel weird putting the e28 sports on the back. I'm not tracking mine, or accelerating full throttle out of curves, or trying to shoot Steven Seagal and flying through a jewelery store window.

    Sent from my LGLS755 using Tapatalk


    :hmm: LOL
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



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