Master Cylinder

[Longtooth]

I have a 2nd or 3rd version tandem Master Brake Cylinder on my '67 250SL.  I removed it and the Brake Booster to identify the cause(s) for increased rpm at idle when pressing on the brakes (rpm increases by 500) ... previously isolated to a vacuum leak in the booster or between booster and Master Cylinder (MC) via the o-ring.

My questions are:

1) Has anybody rebuilt the Master Cylinder moving parts (piston seals, springs, etc) or IF I remove the two piston asm's, can the vacuum seals (2 each) on the rear piston (push rod circuit piston) be replaced?.

2) Is the O-Ring (between MC and Booster) a purchasable item from MB?

3) Is the rubber Plug fitting for the Reservior to MC housing joint (at the rear opening from reservior into MC) available and purchasable from MB?  

The reason for my question #1 is discussed below (Q's #2 & #3 I can probably find out on my own, but if there are any caveats involved let me know).
 
On removing the MC I note that the o-ring (in the groove on the MC) is flat as a pancake... i.e. I can't see how it can provide much of a seal at this point, so assume this has been slowly letting fluid leak into the Booster... and low and behold, there's a considerable puddle of brake fluid in the booster to confirm.  

I now assume the cause for the vacuum leak in the booster is due to slow deterioration of the rubber in the booster due to the accumulation over time of the brake fluid leaking past the 0-Ring 'seal'.

Now for the hard part... the MC's Leak Hole (tiny exit hole at the bottom rear of the MC near the MC flange) is clogged... so any fluid leaking by the vacuum seals (internally on the piston) has nowhere to go and if the 0-ring seal between MC and booster is weak, then any fluid getting by the internal vacuum seals will not be able to leak out the Leak Hole, rather be forced in varying degrees past the O-ring and into the Booster.

But, even if the Leak Hole weren't clogged, the fluid leaking by the vacuum seals on the piston would be leaking out the Leak Hole anyway.... saving my Booster, but still necessitating replacing the brake piston seals.  

Hence my question about replacing critical parts on the rear piston --- namely the vacuum seals which are the primary means by which fluid can get by them ---- and which would otherwise be forced out the Leak Hole --- but which get's into the Booster past the poor seal being provided by the current state of my O-Ring.

Longtooth
67 250SL US #113-043-10-002163
95 SL500

[n/a]

Personally, I wouldn't think of rebuilding a master brake cylinder. I'm sure others will disagree. W113 owners are the most "Let's rebuild it" owners I have ever seen. It's just too critical a component to compromise on. Of course, some may think that one rebuilt with care and patience can be as good or better than new.
I guess it's possible, but I wouldn't bet my life on it.

Rudy
Los Angeles
1971 280 SL

[Longtooth]

rudy, I've rebuilt Master Cylinders on a Porshe ('66), VW's ('64 & '70), and my old '65 Chevy 3/4 ton.  My friend kept and drove the '66 Porshe for ~10 years after I rebuilt the MC... I kept and drove the '64 for ~6 years before selling it after I rebuilt the MC, and I've been driving my ol' Chevy PU since '80 after rebuilding the MC.  These versions weren't that hard to rebuild with care.

The reason I do this when the need or opportunity exists is that my '63 Volvo's MC went clunk in '64 when I was driving back from Italy over the Alps... on the way back home (at that time) in Germany.  I drove the fully loaded Volvo with my passanger friend down the Alps (Brenner Pass as I recall) and all the way across Germany with ZERO brakes --- just the 4 gears, a good clutch, strong transmission, and the emergency brake  It's a good thing I was only 18 at that time, cause otherwise I wouldn't have made it (ha!).  

Since then I've been wary of MC's, though I'll admit that there's always a risk.  My Service Manual has the details for rebuilding them (per factory), so I'm not too worried, but would like to know if there are any caveat's experienced by others that aren't stated in the Service manual.  Besides, for all I know a 'new' one is just another old one rebuilt by some OEM anyway.  Besides that, if I run into problems I can always buy one of the 'new' ones I suppose.

Longtooth
67 250SL US #113-043-10-002163
95 SL500

[n/a]

Well, that's different. I was thinking I was addressing someone who didn't know what he was getting into. If you're comfortable with it, nothing I said earlier applies. You obviously have rebuilt the cylinders correctly because here you are writing about them. You're a braver man than am I.

Rudy
Los Angeles
1971 280 SL

[ja17]

Hello Longtooth,
These master cylinders are fairly inexpensive new. As I recall the kits are fairly expensive. Years ago it was more common to rebuild these. However as labor rates increased, rebuilding one was not economical and just not worth the risk. If you shop around you should be able to find  a new one for around $100.00. A  kit will probably cost over $50.00 by itself.  I rebuilt many years ago with no problems, but these days probably not. Making the special fixture showed in the manual helps. The most difficult part is the installation of the last two seals, spacer etc. This is where the fixture helps.
 Dealers and aftermarket suppliers usually can obtain the rebuild kits or new units.


Joe Alexander
Blacklick, Ohio

[Longtooth]

ja17 - thanks for the feedback... you're right about the kits being relatively expensive as I began to search around on the net... in most cases ~75% the price of 'new', though I haven't yet determined what 'new' really means.  I'm guessing with the difference being as small as it is the 'new' ones are rebuilds marked up for the cost of rebuilding + some profit.

Longtooth
67 250SL US #113-043-10-002163
95 SL500

[W14]

Hi Longtooth,

I replaced my '65 (first generation?)MC new for $107,- from an aftermarket supplier - it was identical to the stock unit.
The O-ring betw. MC and booster actually has a square cross-section, so it might appear more worn than it actually is.  My new MC came with O-ring, but i'm sure it's avail. at M-B, or a generic O-ring might work as well.  I used a bit of silicone sealer on it as well.
The rubber plug between the reservoir and the MC was part of a "mounting kit", along with some "wavy" washers and a hollow bolt for the front mount (kit #000-586-01-43  $11.50).  The plug was actually too small for my '65, so it might fit your 2nd generation MC.
I believe brake fluid is actually a rubber conditioner, so I would do another vacuum test on the booster itself before writing it off as unusable.

Will W14
1965 230SL 4spd
Victoria,BC

[Longtooth]

Got my Booster back, repaired to original factory fresh condition.  Took it in yesterday at noon, picked it up today at noon. $170 + tax.

The shop ran a vacuum test on the unit before pulling it apart... it was leaking (not as badly yet as some do apparently, but in the upper half of leakiness.... they said it won't hold the vacuum).  The technician who did the repairs said inside was rusted... they take the rust off inside (& out), give insides a thin layer of primer, then proceed to replace the rubber and seals.... and then put it all back together.  If I squint real hard and look real carefully I can see some of the re-tool marks in the deepest portion of the crimped joints... though not on all of them, so other than these miniscule marks at the base of some crimps the rebuild can't be distinguished in any way from an original unit.  

BTW, the puddle of brake fluid inside the booster is a no-no and was primary cause for the booster rubber and seals leaking when compressed (pushing on brakes).  The tech said this is the most common reason why these ATE units need to be rebuilt.

FYI, PowerBrake Exchange is a large shop in the old industrial area of SJ... literally thousands of boosters in production line manual type facility to re-manufacture... Most of these visible thousands are of 3 or 4 types but there are shelves lined with other types too.... the tech immediately recognized my booster from 20 feet away and referred to it as 'mercedes'.   They can rebuild literally any booster (they said). It's apparent from the freshly packaged boxes of boosters they are for retail and shop esale 'Remanufactured' "[insert brand-names]" Booster) on the boxes.

If you need a 113 booster rebuilt before spending $480 on a 'dealer' provided one... you might want to give these guys a call.  I'll hazard a guess that the $480 variety you purchase is remanufactured anyway... since ATE doesn't produce this model anymore.  The $480 price sounds about right for a remanufactured one... $180 plus shipping both ways = ~$200, plus 20% for distributor = ~ $240, and thus the retail markup at 2x =~$480.

Oh, the 'walk-in' price listed for this is $211 + tax... I got the 'garage' price because of my friend the restorer I think.

BTW, you have to specify using your 'cans' (i.e. the sheetmetal case) or they'll just use another set of "can's" that have already been readied for new guts.  Similarly with any labels on the part you send or bring to them... make sure they save it (or save it yourself before sending it)... the tech had mine apart within 5 minutes of my leaving it, and I was still discussing with the front desk when I could pick it up when I mentioned to him to make sure the orig. ATE label was safe-guarded.... he had to pick it out of his trash already.  They're efficient that's for sure.  If the tech that does the work on this type booster hadn't needed to leave work that pm for P.B., he said it would be ready by 4pm same day (I dropped it off at ~12:30.

I asked if they have any 'problem' returns... of course he said not yet (20 years doing these types of boosters).  But I asked my restorer friend (who's the one who recommended I take mine in for rebuild) if he's had any problems from his customers who spend several hundred grand for his restorations (mostly 300SL's and the like), and he said there've been no problems ... and he's been  restoring the sports and high priced classic MB's for 30 years.... you've got to trust somebody.

Longtooth
67 250SL US #113-043-10-002163
95 SL500

[Longtooth]

Will W14 (Victoria BC)

Thanks for info on the Master Cylinder. I've called around and can't find a 'new' one for less than $200+ in my area --- retail.  But the rebuild kits are near $100 anyway.  I have a lead on a $115 price for 'new' Master Cylinder thru the restorer friend I have... + shipping/handling, so it might run $150 by the time's all said and done.  The difference in that and a rebuild kit is probably ~ $60 or so and with my spending 3-4 hrs direct time on rebuilding mine (and that may not work if my barrel's are shot... rusted), it works out that I'd be working for only $20/hr max... in this case I think I'll pass on rebuilding my MC... I can reap far better return on my time doing other things to the car... or satisfying honey-do's (which cost a lot more than $60 when the wife decides to go shopping out of frustration that I'm not getting the honey-do's done fast enough).

I was told that the rubber plugs come with the new unit, as does the O-ring (between MC and booster).... we'll see.

Longtooth
67 250SL US #113-043-10-002163
95 SL500