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Old 11-23-2021, 08:49 AM   #1
FreeEMSFred
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Default 700/900 wagon IPD lowering springs centre support spacing

How high should I lift the driveshaft centre support with these super-common springs?

I have:
  • Done some experiments with 0, 6mm, 10mm, 12mm
  • Asked IPD what they recommend

What do you recommend? What did you find works best?

I could also test 3mm, 8mm, 9mm and 14mm - but didn't yet.

Need to repeat the ones I did do with more gentle driving - not just hard first gear accel from stop to redline.

Thoughts?
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Old 11-23-2021, 08:50 AM   #2
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IPD article simply says -4mm to +12mm - and no more. But it's general advice for all lowering, not their particular kit.
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Old 11-23-2021, 09:17 AM   #3
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I lifted it about 10mm ballpark with my -40mm springs, which is not really enough in my case.

It still drones between 70-90kph but it's bearable with no load in the car.
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Old 11-25-2021, 10:17 PM   #4
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Interesting - I got zero above 60kph ie in 2nd gear or higher with no spacing. I feel like you might have a bad bearing or U joint or balance issue as well/instead?

But 0-60 with hard accel eg flooring it or pushing against hill or trailer was pretty bad and seeming to get worse as the rubber loosened up

Adding 10mm mostly solved it, no or not noticeable hard accel issues, but light accel first 10-20kph it did shake a little as I discovered later.

Adding 12mm seemed similar but I want to test for light accel see if it's cured

6mm was moderately bad under hard accel but a lot better than 0mm was.

I have modified the old centre support from the 960 by stuffing it full of window structural silicone and it's about half way through curing now. Probably good enough to install.

But before I do that I want to understand what the loose version does ie I want to get the geometry right first then stiffen it up.

after all the testing I just added the 10mm ones back in and then a few days later used it - that's when I noticed the shake under light accel - I had only tested under heavy accel, oops.

The thing with these old OEM supports is they're SO soft that ANY slight imbalance throws them into a low earth orbit AND they sag - so spacer is firstly offsetting the sag of say 4mm and then correcting after that. I need to measure the exact sag amount once I get the unmodified shaft back out again. But ball park, that's about right.

I'll use "successful spacing with loose/saggy support" minus "sag" = spacing I should run with the modified one.

Any other data points out there?

Cheers.
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Old 11-27-2021, 05:34 AM   #5
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Tried 13mm today with the soft 740 shaft and unmodified centre support and that was perfect as far as I could tell. There was some shake up around 140kph but I don't know if it was coming from the driveshaft and I don't usually go that fast anyway, just for testing. Sag in that shaft was 3mm so I'll be running 10mm with the modified/filled/reinforced support in the original shaft when it goes back in tomorrow or in a few days. IE, 13 - 3 = 10. 3 making up for the sag, 10 additional height.
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Old 11-27-2021, 12:28 PM   #6
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I would put it up on the drive-on lift and measure the u joint working angles.
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Old 11-28-2021, 02:23 AM   #7
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That's probably a good idea, and the right approach, but in practice might be tricky to get a base line for the transmission angle and/or diff angle to compare with the 2 shaft angles to find the joint angles in between? Any suggestions? If so I'm game to try.
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Old 11-28-2021, 06:36 PM   #8
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All seems to depend on the stiffness the center support. Loose original has many times proven to be superior to new stiff aftermarket.

I've gone as low as rear tires(225/45/17) on the same level as rear arches without any changes to center support height. And anything between that and stock ride height.
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Old 11-30-2021, 09:20 AM   #9
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Hmmmm, that's interesting. You have to wonder why IPD recommends it including the opposite if it's not needed. But you also have to wonder why a patented geometry that good fails with a lowring amount equivalent to a boot full of stuff on stock springs. Good data point - thanks.

What I can say is that the shaking roughly corresponded to the lowering and that the higher the soft/soggy centre support the less shake there is under accel which matches IPD advice and that there was no shake when not lowered.

I'll be installing the reinforced OEM one tomorrow with 10mm spacing to start with and hoping I didn't some how make it worse. I doubt it, but I wouldn't bet money on my gut feel this time.

I'll also try stock spacing at some point just to see what the score is with the reinforcement - I imagine the shaking will be present but less extreme.
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Old Yesterday, 05:46 AM   #10
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I've done some more experimenting and had a few emails back and forward with IPD and they reckon my engine has sagged rearward over time causing the issue. I've not tried to check that yet but it seems to make sense.

I got the modified one in and with no spacing it shook under accel, but a lot less than before and no thumping from bottoming out against the cross member/bracket. Under light throttle fine. At low speed (60kph or less) fine. Did not test that scenario at higher speeds which was a mistake and I need to revisit that.

Put in my 10mm spacer and around town it's good, shake is gone, feels fine. BUT I did high speed test this to about 120kph and anything above about 80 had a constant vibration, I assume from stupidly filling the centre support and coupling the natural U joint motion to the chassis when it's supposed to be isolated. Oops.

My guess is that zero spacer will also have that rumble at higher speeds and prove the glue-filling was a fail.

I've got a few more tests to do before I give up and order a new centre support and/or ask a pro driveline shop to help me sort out the issue. Will keep this updated as I go.
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