Leaky reproduction brake reservoir?

[wwheeler]

I purchased one of the newly reproduced dual reservoirs for the later cars a couple of years ago. I am just now installing it and discovered a molding flaw in the part. This area is where the float switch is inserted into the plastic shell. There is an O-ring that seals the switch body to the shell. Where the O-ring fits, this flaw is present. It is sort of a half circle shape. I discovered it when I was using my pressure bleeder and I could not get it to hold any pressure. Sure enough, it was leaking at that spot. O-ring is in good shape, BTW.

I had the angled Mercedes replacement reservoir on there prior and had no problems with pressure bleeding that. I only use 5 to 10 PSI when bleeding. Anybody run across this that pressure bleeds?       

[Tyler S]

I had a similar issue with a reproduction a year and a half ago. The opening was too big and the float assembly with o-ring was loose in the bottle. The cap also did not screw down correctly. I had to file the threads on the bottle to get the cap to fit. Used a thicker o-ring on the float switch.
Dont know if these issues have been fixed with the newer offerings.

[wwheeler]

That is good news, bad news I suppose. Being a rubber molder, I know that area is difficult and not surprised there are problems. My O-ring fit was actually very tight and I had to carefully chamfer edges to get the O-ring to fit w/o damage. I first thought I had cut the O-ring, but turns out it was the molding itself. There are many Metric O-ring cross sections and I will see if maybe a thicker one may help. I will also try to smooth the area to eliminate any excessive voids.

The threads on my cap/bottle weren't as good as the factory issue, but good enough.

Misery loves company....   

[Shvegel]

I bought one when they first came out.  It has sat in a drawer waiting for my body to come back ever since.  I pulled out out last night and I have the same mark in the same spot only less pronounced than yours.  I am pretty sure they are roto-molded as opposed to blow molding so it my be from some sort of blemish from ejecting the part from the mold.

[wwheeler]

Mine too were from the initial offering. Even before they came out with the correct screw caps. I noticed one side only has a slight indentation, whereas the other side is more pronounced. The indentations vary a bit from the two that I have. So could be from ejecting. The other bad thing is that the indentation is exactly where the point of the O-ring seals.

I am trying EPDM (must be that) 1/8" O-rings (.139") which are fatter than the 3mm (.118") O-rings that are normally used. I am also going to try 1/8" O-rings that have a smaller ID. My hope is that stretching the fat O-ring will thin out the cross section some and maybe make it easier to install. I am hoping the wider cross section will fill that gap and create a seal. Quad (X) rings and square rings are not available in EPDM in that size, or I sure can't find them.

If you do not fill the reservoir to the max line and do not pressure bleed, you may not ever see a leak. I hate to go back to the Mercedes replacement reservoir, but it never leaked. I have not heard from the seller to see if there has been a fix or how to remedy the issue. I will let you know what comes of the experiment.

[Shvegel]

Thanks.

[JPMOSE]

Is anyone aware of mfg. corrections since this posting?   I would be curious if the issue has been addressed before purchasing one.   Also, are there simple mods that can seal it from leaking out the sides of the reservoir?   I don't care about bleeding with a pressure unit, as I can do it the old fashion way.

[wwheeler]

I do not know if any changes have been done since my last post. Admittedly, I am a sealing engineer and am hyper-sensitive to leaks.

I still have the reproduction piece on my car and have no leaks. But, I ended up sanding areas with fine sandpaper to minimize the depressions in the plastic where the O-ring seats. I then added an 1/8" EPDM O-ring (actually measures .139") which is a bit fatter than the 3mm standard O-ring. All of this almost resolved all of the leaks when tested with air. The leaks were minimal enough now that I could pressure bleed @ 10 psi. 

So I doubt the reservoir would leak fluid during normal operation. Air is harder to seal than fluid. But given how caustic brake fluid is to paint, I still keep the fluid level low enough that it does not touch the O-ring when the car is at rest. My W111 mount has the reservoir at a slight angle towards the back. If I filled it to the max, the fluid would touch the O-ring in the back cavity. I just don't want to risk it.

[mdsalemi]

I then added an 1/8" EPDM O-ring (actually measures .139") which is a bit fatter than the 3mm standard O-ring.

Wouldn't you be more comfortable with a Viton O-Ring? I wouldn't trust a cheap O-Ring these days since who knows where they come from and what they are really made with, even if they say EPDM. I think Viton would be better?

[JPMOSE]

Thanks guys.....I hope you’ve been well!!

[wwheeler]

Wouldn't you be more comfortable with a Viton O-Ring? I wouldn't trust a cheap O-Ring these days since who knows where they come from and what they are really made with, even if they say EPDM. I think Viton would be better?

Most O-rings at the big box stores, I couldn't tell you what they are. Nitrile (NBR) is the most common and is great for oil and ok for water. Viton is generally known as a high temperature, chemically resistant material. However for brake fluid, it is NOT good. The best for brake fluid (dot 3 and 4) is EPDM.

When selecting rubber materials, the best source is on-line for compatibility charts. McMaster is a good source for O-rings (metric included) and having different materials. Yes, you have to buy 100 pieces. But generally are cheap and you know what you are getting. I would say that if an O-ring package spells out what the actual material is, there is probably a good chance it is what it is. When it says nothing, like at the big box stores, who knows.