Air adjustable shock absorbers

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Growlerbearnz
Posts: 1929
Joined: Sat Jun 26, 2010 1:58 pm
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Vehicle: Delica P25W
Location: New Zealand

Air adjustable shock absorbers

Postby Growlerbearnz » Wed Jan 17, 2018 4:08 pm

The rear springs on my Delica have sagged (as they all do) to the point where they were sitting on the overload leaves, which makes the ride quite harsh.

I've tried adding a leaf (http://www.delica.ca/forum/viewtopic.php?f=10&t=18521&p=137471&hilit=add+a+leaf#p137471) which made the ride smooth again when loaded, but it also raised the rear too far when the van was empty. ("Too far" meaning it wouldn't fit through the garage door without letting all the air out of the tyres).

So I've removed the add-a-leafs and gone for an old-school solution- air adjustable shock absorbers.

Monroe MA708.
MA708.JPG
MA708.JPG (50.47 KiB) Viewed 984 times

(http://www.monroe.com/en-US/e-catalog/MA708/) US$70 from Amazon.

Allegedly the same compressed and extended length as my Pro-Comp 919520's (https://www.procompusa.com/eSearch.aspx?Ntk=primary&Ntt=919520) but I think they're measuring from different points, because these clearly have a *lot* more droop than the Pro-Comps. They're also slightly longer when compressed, presumably because they have internal bump stops, but by my measurements they shouldn't bottom out (and the internal bump stops should prevent any damage if they do).

MonroeMA708.JPG
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They require a touch of modification. Remove the upper pin mount:
MonroePin.jpg
MonroePin.jpg (70.07 KiB) Viewed 984 times


...and install the bush from your old shocks:
MonroeFixed.JPG
MonroeFixed.JPG (100.09 KiB) Viewed 984 times


Then you get excited and install them without taking any further photos. Sorry.

They work brilliantly so far. Just 30psi brings the rear end back up to standard height, lifting the tired springs off the overload leaves, and restores the smooth ride. With the caravan hitched up and a bunch of junk in the van it required 70psi to come back to standard ride height, and it tows without any wallow or pitching.

Monroe recommend 20-90psi continuously (so I'm well within the specs), or up to 150psi for short periods. Air shocks have a reputation for overloading the shock mount points when used on regular cars, but I figure our beefed-up 4WD mounts can handle it. (Or watch this space for a thread titled "Shock absorber mount point repair and strengthening".)

UPDATE: I've verified that these shocks are long enough with the standard bump stops.
Here's my van's measurements with the Monroe air shocks entirely deflated:
Measurements.JPG
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I estimated that the axle can move upwards by 30mm by measuring from the chassis rail to the clean, worn line on the bump stops, which is created when they deform from hitting the chassis rail. The actual measurement was closer to 25mm but I added 5mm for luck.
BumpStop.jpg
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I measured the length of the shock at rest between the lower edge of the dust shield, and the weld on the lower part. At rest this measurement was 95mm. I undid the lower mounting nut and, using a crowbar for leverage, pushed the shock closed as far as it would go (not pictured). The measurement reduced to 60mm. 95mm - 60mm = 35mm of upwards movement possible.
MEasureShocks.jpg
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So, from rest the axle can move upwards 30mm before the bump stop limits the movement. My shock absorber can move 35mm, which suggests that the shocks have 5mm more travel than I need. Not much margin for error, but good enough.

But wait, it gets better because the shocks are at an angle. 30mm of upwards movement at the axle doesn't mean they get 30mm shorter. Pythagoras to the rescue:
Math.JPG
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When the axle moves 30mm upwards, the shocks only need to get 26mm shorter. The shocks have 35mm travel between rest and their bump limit, which means I have not 5 but 9mm more travel than I need. Awesome.

9mm would normally still be a bit close for comfort- the bump stops could probably deform 9mm further than usual under an extreme load. Fortunately the Monroe shocks have an internal bump stop, so even if they reach the limit of their travel they shouldn't be damaged.

UPDATE: Added an on-board compressor for cheap: http://www.delica.ca/forum/viewtopic.php?f=10&t=18849
Nothing says "poor workmanship" more than wrinkles in the duct tape.

definingdigital
Posts: 37
Joined: Sat Dec 17, 2011 7:07 pm
Member's Photo Album: http://www.delica.ca/Photos/
Vehicle: Delica
Location: Victoria, BC

Air adjustable shock absorbers

Postby definingdigital » Sun Jan 28, 2018 4:56 pm

Hey There,
I'm kind of running into the same issue. I was gonna add another leaf or get new leaf springs built.. but I was wondering if there was an airbag or air shock option. What do you use to pump it up? just a air hose or do you have a compressor on the vehicle?

How's it working still?

User avatar
Growlerbearnz
Posts: 1929
Joined: Sat Jun 26, 2010 1:58 pm
Member's Photo Album: http://www.delica.ca/Photos/
Vehicle: Delica P25W
Location: New Zealand

Air adjustable shock absorbers

Postby Growlerbearnz » Sun Jan 28, 2018 10:10 pm

UPDATE: Of course I added an onboard compressor. Would you expect anything less? http://www.delica.ca/forum/viewtopic.php?f=10&t=18849

I just use an air hose. The shocks have an air line kit with a tee that ends in a regular Schrader (tyre) valve.

valve.JPG
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Tee.JPG
Tee.JPG (58.63 KiB) Viewed 896 times
RHS2.JPG
RHS2.JPG (63.75 KiB) Viewed 896 times
RHS.JPG
RHS.JPG (74.54 KiB) Viewed 896 times


I have a compressor in the van, but it's a tiny emergency one. I could use it to inflate the shocks if something went wrong, I guess.

So far so good. I've just finished 1200km driving towing the caravan and they've performed perfectly, with no squeaks or unexpected deflations. I left the pressure at 70psi when driving to the shops while camping (to avoid having to re-inflate the shocks later), and the van drove just fine, it just sits a little higher in the back than it should.
Nothing says "poor workmanship" more than wrinkles in the duct tape.

definingdigital
Posts: 37
Joined: Sat Dec 17, 2011 7:07 pm
Member's Photo Album: http://www.delica.ca/Photos/
Vehicle: Delica
Location: Victoria, BC

Air adjustable shock absorbers

Postby definingdigital » Sun Feb 04, 2018 2:46 pm

Looks great! Thanks for the updates! I'm gonna try it out.


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