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Revisiting hydraulic roof repair

2K views 20 replies 6 participants last post by  Stonemull 
#1 ·
So my rear left boot opening ram leaks a little and needs sorting.

I just read the entire 18 page thread on repairing the cylinders, that thread is not open for reply’s though and I had a couple of questions.

There are still “kits’ available on Amazon which show images of 5 o-rings, 2 are larger. This has me wondering as I thought ALL 5 piston seals are the same size, specifically the 15 x 5 x 22 u cups.They obviously don’t mention sizing so they can sell a few 50c o-rings for $30US plus $25 postage. Is the picture correct or a red herring ?

I was considering trying to get u cups instead of o rings but can only find 16 x 5 x 22 here in oz and I think lack of posts here lately about leaking pistons lends me to believe that the o ring solution works just fine even long term. Given it appears somebody stuffed up and the original seal material and hydraulic fluid were incompatible, I would imagine a non leaking o ring is a long term solution as it doesn’t deteriorate

So I am wondering if anyone has experienced leaks with the o rings ? Are they all the same ?
Some people reckon the "correct" o-ring is 15 x 4.5 but others say the 15 x 5 works fine. I can get either. Looking at the u cup dimensions then (22-15)/2 = 3.5mm is the actual rod to cylinder clearance. So 4.5 or 5mm, or some other size like 4.8mm ? I’ll probably buy a few sizes anyway and spares given they are like 50c each.

another advantage of o rings is it looks like in at least a few instances the o ring can be stretched over the piston without removing the clevis from the ram, though the rams I want to do first have a lock nut anyway and should be simple enough.

I will probably tackle the 2 rear cylinders first and the latch cylinder as I currently have the boot lining and headliner off.
 
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#2 · (Edited)
The seal sizes do vary. I was never able to rebuild the boot lid cylinders successfully, despite trying twice. The process of disassembly is different for these two. If you can, post DIY on it.

These cylinders can leak onto the muffler in the right circumstances, and cause a fire - I've seen the aftermath first-hand (not my car, but one for sale).

If you have the cylinder out, you can clamp the rod in a vise using two pieces of hardwood - quarter-sawn is best - and remove the yokes.
 
#3 ·
Any idea what size these use ? I have not seen mention of any size other than 15mm by 4.5 to 5mm

I thought the boot lid cylinders have a lock nut or do you still need to clamp firmly to get the yoke unscrewed even after removing the lock nut ?

‘these cylinders leak directly behind the wheel, are you mixing them up with the main lift cylinders next to the roll bar, they need heavy clamping.

best and clearest resource i have found is SLK Top Cylinder Rebuild Guide with Cut-Away Diagrams
 
#4 ·
Ram is removed from boot but still attached by the hydraulic lines, the clevis was easily removed from the piston rod by unscrewing the lock nut with a 13mm spanner with a large screwdriver inserted through the holes. 10.5 to 11 turns to remove my particular bracket. Need to count as it’s adjustable obviously.
I have unscrewed the pressure release screw about 2 turns but it’s still hard to move the ram, impossible by hand, I may yet remove line 21 and 22 from the pump and have cleaned the area with brake cleaner in preparation but I will avoid it if possible, at least wait till I have drilled the dimples.
 
#7 ·
The 15 x 5 x 22 u cup seals seem an odd size and have had no luck finding them locally.
The eBay sellers selling overpriced o rings and calling them “my upgraded seal kit” are annoying me, they are not an upgrade, they are a hack imo. There are also none in Australia and cost around $40 from the UK and $50 from the US. If I am going international I might as well go to china.

Looking into it PU seals are rated to 5000psi (30MPA) and have all the required property’s, I have ordered a 5 pack from china for a couple of bucks. I expect if it doesn’t leak straight away it won’t leak in the next century or 3 as it simply will not degrade. I’ll report back when they get here.


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#10 · (Edited)
Removed the steel stop. I used a $2 hobby vice backwards (I attempted to it to split the timing chain last week lol) and drilled 4mm holes checking with the depth gauge on vernier callipers till they hit at least 3.5mm. Probably a little overkill but I couldn't see the point in being to worried.
Knocked the end stop partially out using an automatic centre punch then used vice grips and twisted it out.
Next job is remove the ram but I have an idea to use a piece of angle iron with some nuts welded to it and some threaded rod, if it proves difficult that is.
I’ll wait for the seals for this part.

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#12 ·
When I ordered it did say delivery by Nov 22 which o thought was ludicrous but just in case it was accurate I ordered nitrile rubber ones from 2 other suppliers.
I had trouble finding the correct size still and one is a double lip design but 7mm tall instead of 5. Not sure if it will fit but if it does I will probably use that one first.
They use PU seals in a lot of heavy duty applications like excavators etc and they are usually pretty good. However I saw mention somewhere that the Benz fluid contains some naphtha and PU only has a B rating for chemical resistance to that.

also ordered ..

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#13 · (Edited)
Well it was instantly obvious that the 15 x 5 x 22 seals were completely incorrect for the boot cylinder. I have zero idea why I did not measure the damn thing. It’s more like 7 x 5 x 15 needed. I still have not seen anyone mentioning the correct size. These guys (used to?) manufacture them on a CNC mill so maybe off the shelf they will be tricky to find, I am yet to find u cup seals under 8mm interior. SLK R170

edit: found a few suppliers down to 4mm ID. Many have minimum qty of 20 tho. I’ll get a more accurate measurement tomorrow, calipers were tricky to get a good measurement with the ram all the way in. From memory it was like 7.5mm for the rod and 15.5 for the ram. Height is not so important as you can soon turn a bit of the plug off on a lathe. One of the more promising suppliers looks like a manufacturer so I might see if they can do custom sizes.
 
#16 ·
My only leak currently is the cylinder for the boot, so the ones by the tail lights. I intend to do all 5 tho, especially the roof one as it doesn’t look too hard and is catastrophic if it leaks, plus I have the lining off atm. I have on hand 3 orders for the 15 x 22 x 5 in PU and “black” which I assume are nitrile. Pretty sure they will fit at least one of the cylinders, possibly the roof latch. Happy to post ‘em later to anyone who wants some.

‘this store seems the most promising,low qty, cheap postage and large range.
GBT-Hardware Store
 
#17 · (Edited)
Only just restarted work on this, actually put it back on the road and have been driving it.

So a quick update to all this, I was never able to find the correct size u cup seals, I ended up buying a bunch of different size nitrile o rings locally and jammed 2 in out of frustration. These were too large and left the end stop hanging out by a mm or so. I ended up making a clamp arrangement out of 2 pieces of theaded rod and some steel brackets to fit through the clevis's and by doing up the nuts could apply a lot of force to compress the o rings sufficient to get the end bracket locked in. I ended up straighening old some big paper clips as clamp wire to feed through the holes. I figured if it leaked its easy to work on now. I have cycled the roof maybe a hundred times since and not a drop of oil has leaked.

Yesterday the other side boot lift failed though. Working on it now. I will try and identify what O rings I used this time.

Edit: a few mneasurements while its in bits, rod dia 8.00mm, ram inner 14.0mm. End (seal) stop depth 14mm, internal depth to end of inner pinned end stop 20.3mm. So effectively 2 x O rings of 8mm ID and 14mm OD would just fill the internal space, be a poor seal though, imperial sizes are the solution.

Looks like 2 x #203 standard size o-ring is what I used, chart reckons 7.52mm ID 14.58mm OD and 3.53mm cross section, they are a tight fit and need tooling to compress 2 in there.

edit2: fail, oil everywhere trying to bleed the ram. I didnt get the same compression this time, used MIG wire to tie the cap in and it backed off maybe 0.5mm or so. I think compressed it would work so I might revisit the clamp methodology.
 
#19 ·
So it turned out that it sheared the mig wire stitching and completely blew out the end stop and one of the o rings. Explains why it went with quite a loud pop followed by a hydraulic squelching sound. So I guess even without the compression I wanted the o rings were sealing originally. It's damaged at least one of the o rings so I'll get some more tomorrow. Next idea is to drill between 2 pairs of the 5 holes and fit 2 or 2.5mm roll pins, then tap a 4mm roll pin onto the 5th hole for good measure.

Actually I don't like that the holes in the cylinder wall are already 4mm so I might do some engineering further down from the holes or tap them and add set screws.

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#21 ·
If it had 6 holes around the perimeter I would have gone with the roll pins, ended up tapping the holes and fitting 5mm grub screws though. Thorough clean up of the interior with sandpaper to remove swarf from the threading so as not to damage the o rings on install then simply screwed it up. Thought I might need to get a blind tap due to proximity of the rod but a standard 5mm did the job. I did mark the rod with the tap end but if you fully insert it into the cylinder is no big deal as it's above the seals. Cleaned it out with throttle body cleaner (upside down!) and lubed the rings but it's damn tight now, I can't even move it by hand. Car seems to have no issue with it though it might be a bit slower but battery needs a good charge ATM.

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