Hello all,

It looks like the brake master cylinder on my 1997 SL600 is dying, and I need a replacement. The original part 0054307101 is NLA from MB. I have been unable to find any aftermarket sources for this part. Some online sellers list a TRW master cylinder as fitting the 1997 SL600, but this seems to be wrong because it is a replacement for a different master cylinder, part 0054308901. The main difference seems to be that mine has a flange on the right side (as seen from front of car) for mounting a brass-colored metal cube with a 2-pin electrical connector, that MB calls a brake valve. The other part, and the TRW one, don't seem to have this flange. There is a eBay seller from Germany selling what he calls a good used one for around USD$650. Is that really my best (or only) option?

Has anybody else been down this path and found a solution? Of course I searched the R129 forum (and the internet) on this topic but came up empty.

Tom

 

You are most likely going to have to rebuild the one you have.

The extra valve is probably associated with the BAS function.

Flushing the brake system regularly has never been more important.

 

I think I may have found one, possibly the last new one on the planet. The valve isn't for BAS because the car doesn't have it. BAS was introduced in the following model year, 1998. I agree frequent brake fluid changes are cheap insurance. I do it every two years as per Mercedes advice, with Mercedes DOT 4+ brake fluid..

Am I right in thinking that to rebuild a master cylinder, you have to get a rebuild kit with new seals for it? So far I haven't seen any rebuild kits for these master cylinders offered anywhere.

Thanks for your reply,
Tom

 

BAS was introduced model year 1997, but you are right, the valve has nothing to do with it.

 

Interesting. My top-of-the-line 1997 SL600 came pretty loaded, it even has the optional xenon headlights. But it doesn't have BAS. Strange.

Tom

 

It was not exact model year 1997. Starting with december 1996, BAS was build in, not as an option. So yes, if your car was build from september to november 1996, it is a year 1997 build car with no BAS.

 

Andreas, that must be the explanation then, because the car's datacard says it was built in 1996-06, so in June 1996, well before the rollout of BAS in 1997 according to your post.

Cheers
Tom

 

Well what's that little valve for then?

 

Good question, mahunt. Maybe Andreas knows. For the future, I think it's important for R129 SL600 owners to know if/how they can delete this valve so they can replace the master cylinder with a regular non-SL600 master cylinder.

Tom

 

We own one V12 release date 1996-12-11, with BAS <pheuuuu>

I read something about the function in the past, but forgot about it. I think it has something to do with the ESP. The functionality is probably explained in the Mercedes WIS. BTW: Ebay 235730277950

 

Yes I am familiar with that eBay listing in English as item 286047008961. The master cylinder is the correct part and looks rebuilt in the photos, but the listing simply says it is used and in good condition. The seller is asking for a lot of money for a used part. I am spending a bit more but supposedly getting a new OEM part.

Cheers
Tom

 

If rebuilding is in the cards, it's usually the aluminum bore that's at issue.

They can be sleeved with stainless, reusing the original seals.

BAS (circa 199X, not today's BAS) senses the difference between your regular stopping brake pressure and when you panic stop. The idea of BAS is when in a panic situation the driver doesn't hit the brakes hard enough for a good short stop early enough. BAS provides extra braking pressure and the car stops quicker.

 

Only to be clear: The valve on the brake cylinder has nothing to do with the BAS, it is only available on the V12.

Fun fact: There is a service instruction from Mercedes to deactivate BAS on vehicles without ESP during inspection permantly. Since the 600 was always delivered with ESP, it is not listed as an optional extra. This sometimes leads to Mercedes workshops deactivating BAS on the V12 by mistake.

 

More than that, my understanding is the master cylinder with the valve isn't even used on the S600, the SL600 is its only application, which just makes it even stranger to me.

Mahunt, regarding rebuilding the master cylinder, I would have thought it's much like rebuilding a brake caliper in that you replace all the seals but the piston and bore usually good. So I'm surprised to read from you that this is not the case, that it's the cylinder bore that goes bad. But I'm certainly not an expert on this.

Cheers
Tom

 

Master cylinders do wear and get honed during rebuild. I, in fact, do have a small bore master cylinder hone. I have rebuilt (honed and new seals) master cylinders, brake calipers and wheel cylinders, some to no avail. Some still leaked.

Aluminum, like cast iron does react to the water absorbed in the brake fluid and can pit the bore surface. Both types of cylinders are also susceptible to galvanic corrosion due to dissimilar metals in the brake system just like the cooling system.

I think it might be easier to hone and rebuild a cast iron master cylinder, but that's why some folks rebuild with stainless steel and are done with it. It's just a final option to consider.

Good luck with your search and repair.

 

Mahunt, thanks for the information and the good wishes. I will hope I never have to rebuild a master cylinder!

Cheers
Tom