More ideas on cylinder repair seals.
I did not want to say anything to the forum.
I was not sure if it would last.
But now I can.
About 7 months a go my rear top cylinder lock leaked .I decided to do the repair my self.
I wanted fixed now and then. I dont like to wait,and have hydraulic lines open.
I looked in my garage and found some bike pump seals that convert the pump from either schrader or presta .The size was right.
The hight a little too tall , so I cut it with a blade.
I opened the cylinder and replaced the seal, with the bicyle frame hand pump seal.
7 months, and it is holding.
I will let you know when, and if it leaks.
Thanks for sharing aam! :-)
I'm starting to believe I could fix my cylinders by myself if I needed to. Provided I could find suitable seals and o-rings...
Could Mercedes really be so rotten and have designed the system (fluid) with the aim and intent of non-endurance?!? I'm not claiming anything but this gets my thoughts going...
I have read from this forum about the fluid (I would find it out and re-post for you) and seal material. Simply speaking, MB originally designed this soft top hydraulic system very concerning the SAFETY issue. They knew all hydraulic system leads to leak sometime, so they employed a kind of bio fluid that is “fire-proof” to prevent any future danger. But this kind of fluid is not good to the normal seal material like PU, NBR or EPDM, the “bad” material was conducted in all your R129 cylinders’ seal. So, no wonder you found the seals cracked seriously unlike another hydraulic system applications.
Why are the R129 cylinders’ seals so different that we are hardly to search out? (Dennis can prove the difficulty.) I think MB did not intend to make it special, but this kind of bio material seal DOSE come for special application and was specially designed for particular dimension, MB just took them into the r129 cylinders. How do you think?
Since the forum members are worldwide, we can search from each country, and share the result. I have been told somewhere in Holland can find what we want, but not proved.
"
I have some technical info on the seals used in the hydraulic pistons. We reverse engineered the material using FTIR methods and got a perfect match. MB used a polymer called polycaprolactone as the seal material. A quick google tells me this is a biodegradable material that melts at 140°F. It's mostly used in the biomedical industry.
Do you think maybe this material isn't stable enough for use? Plus, don't interior temperatures sometimes reach over 140°F? I can't imagine why MB would choose this for a seal material in automotive application!
"Seals for hydraulic systems made of conventional polyurethane elastomers, however, suffer a serious limitation which has become increasingly important in recent years. Because of the fire hazard which attends the use of mineral-oil hydraulic fluids, users and manufacturers of hydraulic systems often employ phosphate-ester hydraulic fluids in place of mineral oils. Phosphate esters, however, attack conventional polyurethane elastomeric materials, causing them to swell and lose strength. A conventional polyurethane-elastomer seal in contact with a phosphate-ester hydraulic fluid will weaken and have a substantially shortened useful life compared to the same seal in contact with a mineral-oil hydraulic fluid. In high-pressure hydraulic systems employing phosphate-ester hydraulic fluids, there is a significant risk that a seal made of a conventional polyurethane elastomer will fail catastrophically."
"
morriswu, many thanks for this insightful information it's so good to get this sort of feedback from a source that has such technical expertise.
Your comments about the formula of the seal material and temperature tolerances and the type hydraulic fluid would explain why the seals fail so regularly.
Perhaps changing over to the silicone based fluid would prevent the rapid deterioration of the seals?
MB's take on the fire hazard scenario seems a little strange, I would have thought that using a liquid that was more flammable but did not degrade the rubber seals would be preferable to a lesser flammable liquid that degrades the seals causing them to leak fluid everywhere which would in fact be a greater fire hazard.
"
I have some technical info on the seals used in the hydraulic pistons. We reverse engineered the material using FTIR methods and got a perfect match. MB used a polymer called polycaprolactone as the seal material. A quick google tells me this is a biodegradable material that melts at 140°F. It's mostly used in the biomedical industry.
Do you think maybe this material isn't stable enough for use? Plus, don't interior temperatures sometimes reach over 140°F? I can't imagine why MB would choose this for a seal material in automotive application!
"Seals for hydraulic systems made of conventional polyurethane elastomers, however, suffer a serious limitation which has become increasingly important in recent years. Because of the fire hazard which attends the use of mineral-oil hydraulic fluids, users and manufacturers of hydraulic systems often employ phosphate-ester hydraulic fluids in place of mineral oils. Phosphate esters, however, attack conventional polyurethane elastomeric materials, causing them to swell and lose strength. A conventional polyurethane-elastomer seal in contact with a phosphate-ester hydraulic fluid will weaken and have a substantially shortened useful life compared to the same seal in contact with a mineral-oil hydraulic fluid. In high-pressure hydraulic systems employing phosphate-ester hydraulic fluids, there is a significant risk that a seal made of a conventional polyurethane elastomer will fail catastrophically."
"
I'm glad we are back discussing the make up of the seals and hydraulic fluid. I believe this to be a very important topic in order to proactively maintain the system. We have discussed these issues in the past at-
Looking at the way the seals pictured have deteriorated really makes me think that the fluid used is the main culprit. I have rebuilt many hydraulic parts before and the seals were always worn, not deteriorated.
I would really like to know where to find the seals and o-rings so I would be able to repair these cylinders myself both inexpensively and immediately.
Another thought with regard to the fluid is that silicone hydraulic fluid might be great for this application. It is used in cars that aren't driven much (show cars)as it is good for their seals. The problem with silicone fluid is that it does not absorb water and this is bad for cars since the water pools in the system and easily boils at the high temperatures in brake systems. Regular fluid is designed to absorb the water to reduce this effect. Water contamination is pretty much unavoidable. I would think that the boiling issue is minor in this application.
if it was not for this post by dennis i would of not know that he was going out of town and (2) his number for we talked about the front hyd. and by talking to him I figure out that you most support the brass blocks that the hyd attach to. I used z ties and now i can lock my top and drive around intill i get my back. Lz
Also by typing large it is like yelling. why????
The Seal & O-ring dimension for cylinders are listed below, while "Diagram #" please refer to Lynns' post.
These dimensions are my measurment from the same seals&orings that I had used to repair my cylinders, and they have work fine for more than 1 month. Probably there is minor difference from the orginal MB parts, but they did work very well. If any friend knows the difference from MB's, please post to advise.
Also If any member is successful of obtaining the maker source, please kindly let us know.
I have to say, it is very easy to ask my friend to sell them to anyone who likes DIY, but I still think the "customer made" seals are not cheap and not recommended. (because of sharing the die cost)
Linear Mode
