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*Premium Member
1998 SLK230
Joined
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65 Posts
Discussion Starter · #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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*Premium Member
2005 SLK55 AMG /2005 SLK350
Joined
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7,051 Posts
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.
 

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*Premium Member
1998 SLK230
Joined
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65 Posts
Discussion Starter · #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
 

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*Premium Member
1998 SLK230
Joined
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65 Posts
Discussion Starter · #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.
 

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*Premium Member
1998 SLK230
Joined
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65 Posts
Discussion Starter · #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.


Blue Font Material property Screenshot Electric blue
 

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*Premium Member
1998 SLK230
Joined
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65 Posts
Discussion Starter · #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.

Hand Automotive tire Gesture Finger Thumb

Hand Finger Wood Tool Thumb

Hood Motor vehicle Automotive tire Bumper Crankset
 

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*Premium Member
1998 SLK230
Joined
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65 Posts
Discussion Starter · #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 ..

Tire Automotive tire Synthetic rubber Font Rim

Automotive tire Rim Font Bicycle part Automotive wheel system
 
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