Early 1967 250SL - Master Cylinder Replacement Questions

[NoEcm]

Master Cylinder appears to be frozen and leaking:






Early chassis (below #02980) so it appears that I'll need the more expensive Master Cylinder p/n  001-430-89-01


Questions:

1. Does a new master cylinder include the grommets for the fluid reservoir?

2. Does a new master cylinder include the O-Ring that fits between the master cylinder and brake booster?

3. How difficult is it to move the brake fluid reservoir between the old master cylinder and the new one?

4. When I just barely touched the little rubber plug on the brake fluid reservoir nipple it fell apart, any suggestions on how to make or secure a replacement?

5. Any other tips or suggestions?

Thanks!

[Jonny B]

Authentic classics has the reservoir and their part includes the little black rubber piece - reuse the clamp you have on yours.
Buds Benz has the picture (and it includes the black rubber piece) but their's is listed as NLA

[Pawel66]

I am not 100% sure, but this plug, I think A 000 987 03 45 (?), may be available at MB (it is here in Europe, if it is this part - you do not see it in the picture in the EPC, but it is there together with the clamp on the parts list, it may be this one you ask about). It is $ 3-4 here.

Keep the original small clamp, I think it is quite rare.

I am not sure if the fluid reservoir you have is available in its exact original shape. I would keep it (I think this is what you are planning to do). It has been discussed in another post that a good wash with soap water or washing powder may significantly improve its look (yours does not look that bad, actually).

The sealing ring between the master and booster is available in MB, ca $5 (A 004 997 32 45).

I do not know if master cylinder kits include the reservoir grommets.

What I see is that the grommet appears as a separate spare part "As of ident. no.: 043 002980" and it has a part number A 000 431 09 35. This chassis number marks also the change of master cylinder types or PN. Could be the earlier one had grommets built in the later one - separate - but I am not sure, you would need to confirm.

There are also some repair kits in MB, but do not know if applicable in your case.

[NoEcm]

I found a temporary solution to that little black plug on the master cylinder reservoir:

"Dorman Help! 47396 Vacuum Cap". I paid less than $4.00 for the assortment of 8. Perfect fit and I was able to use the original clamp.




Keep in mind that this is only a temporary solution as I do not know how compatible this rubber is with brake fluid.

[mauro12]

I have a 250sl early chassis too and I’m starting to think that would be a great idea to buy the new master cylinder and save it. I read somewhere that this pieces will be not longer available shortly or maybe the price will be near 400/500 dollars. What do you think could be the best way to prevent brake fluid failure? Try to use more often the car and so the brakes?

[NoEcm]

I have no opinion of buying a master cylinder and saving it for future use. $500 is a lot of money and there are other places I can spend that now. By not buying one and setting it aside for future use I hope I don't kick myself down the road.

But as an FYI the leak that I had was from between the reservoir and the master cylinder. Simple and cheap fix (under $25). Google "ATE 390001" and you'll find the repair/reseal kit.

[thelews]

If you drive your car and bleed your brakes regularly to remove moisture, your MC should last just fine.  Worn seals can be replaced.  I would also think there are generic solutions that would not look original.

[inci]

take a look at rockauto.  remanufactured/tested. $45
CARDONE 111919

[mauro12]

Hi guys , I would like to know if the old style brake fluid reservoir ( the one from ate NLA)
Has the float level sensor and where is located . Since I’m going to replace the master cylinder, I would like to know if I have to disconnect some wires or remove some sensors inside the reservoir itself .
I have never seen wires in the old style reservoir like for the later one ( 280sl ).
In case I decide to replace with a new reservoir ( reproduction unfortunately) , what I have to do ? Put  back some sensors ? Thank you

[Jonny B]

The early style reservoirs do not have the brake level sensors.

[mauro12]

So there is not any problem about low brake fluid and activation of the fuel pump while doors are opened ?
Considering that there is not any floating sensor , there should be not any warning light on in case of low fluid , right ?

[Jonny B]

Correct, the door open , car run is for the "creative" wiring MB did with the new type reservoir and sensors.

[mauro12]

hello guys, i know it's been discussed in the past but i would like to know if it's possible to re use the old brake fluid reservoir with the new master cylinder. Is there a risk to damage the old one during the removal? Also i guess there is for sale a kit to mount the reservoir to the master cylinder. What do you suggest to buy? I dont want to be in the situation to not have all available parts to complete the job. Thank you.

[Duncan200]

Hello Mauro,

Absolutely no problem in reusing your old reservoir on a new master cylinder.

I purchased the fitting kit from Authentic Classics (AUTH-007783) and it is a genuine ATE part.

I’ve attached some pics of the box for the reservoir mounting kit and the box my master cylinder came in as it shows the original ATE numbers so you may search for that and possibly find it cheaper. Also the master cylinder came with the seal for the booster.

I also ordered a new reservoir from Authentic Classics and whilst it’s not an ATE part, it’s much cleaner than my old original one. See pics. My reservoir is different as it’s a late 66 230 and doesn’t have that fitting on the front with the clamp. I fitted my original cap and I think it looks ok. Only purists would spot it’s not original and I do keep a look out for an original one to fit if one is reasonably priced in the future.

Just remember there will be two rubber fittings in the fitting kit, the thinner/longer one is used on our masters and it’s fitted with the fatter end going in to the master on the rear brake portion of the master. Happy to send you more pics if you need clarification.

Hope this helps.

Doug

[mauro12]

Hi, thank you for your clear explanation. Basically is not needed to buy a new reservoir unless yours Is damaged . Mine looks dirty and yellow like yours but is original . I believe that the mounting kit is essential right ? If you have more pictures of the fitting between the reservoir and master cylinder would be helpful.
It takes only 500ml of dot 4 the entire sistem right  ? Thank you
Mauro

[Ed Riefstahl]

Greetings,

I replaced the master cylinder on my 230SL about a year ago, including the fluid reservoir, both from Authentic. I decided to remove the booster and paint it and much to my surprise, the booster had several ounces of brake fluid in it. The master cylinder had been leaking fluid from the rear seal, into the booster. I wasn't sure what to use to remove the brake fluid, but wanted to clean it with something. I ended up rinsing the booster out with WD-40. I figured it would be less harmful to the booster than brake fluid.

Anyway, for what it's worth, something to check for when you have the master cylinder off.


Ed Riefstahl
Erie, PA

1966 230SL (Ms Magoo) Horizon Blue
1970 280S (Miss Daisy)
1999 BMW Z3 5 speed
1991 BMW 318I 5 Speed
1997 Toyota Paseo Convertible - One of 1000, (have you ever seen one?)
1997 Ford Ranger step side (Mater)
2023 Mazda CX 5

[Duncan200]

The fitting kit is definitely needed.

I’ve attached some pics, it’s difficult to see once it’s fitted, but essentially the o ring in the kit goes around the front hole of the reservoir and the larger mushroom shaped grommet fitting it pushed in to the rear hole of the master cylinder large end first. In one of the pics I’ve attached, it shows the larger mushroom shaped grommet which comes in the kit, but that is only used on the 280’s. I’ve used it to illustrate how it goes together.

The reservoir is then pushed on to the rear grommet fitting and the 17mm bolt and wave washer are fitted inside the reservoir to hold it in place.

I used just over 500ml of brake fluid in my system, but it was completely dry as I had fitted all new lines, wheel cylinders, hoses and calipers.

Brake fluid is cheap so I would buy 2 bottles to be sure I had enough.

[mauro12]

Thank you all. I've read also that the master cylinder differes according to vin and model. Mine is a 250sl early model , last vin number 001533 , so it should have the second type of MC. Honestly i've never had any problems with brakes until 3 days ago. I had the so called vapour lock during 35 km of downhill braking , so its time to replace fluid and mc.

[Duncan200]

If it was me, I would bleed the brakes to ensure fresh fluid in the system before replacing anything.

Doug

[mauro12]

You are right but since my master cylinder is the original from 1967, i'm scared that by flushing with new oil it could damage the internal seals. The price for a new mc is high but reasonable so far . How about the cluch slave and master cylinder ? do you need to bleed those too since they share the same oil ?

[Duncan200]

Any fluids other than engine oil need to be replaced every two years, regardless of mileage.

Engine oil more often, I would recommend every 6 months, once before the spring/summer driving season and once before autumn (fall)/winter season where less driving is normally done.

Easy enough to hook a clear piece of tube between your left front caliper and bleeder on the clutch slave cylinder, loosen both (ensuring you prime the length of hose with fluid to minimise air in the clutch system) and flush your clutch fluid backwards through the system, utilising your brake pedal to pump the fluid through the clutch system and a syringe to suck the old fluid out through the clutch reservoir until it’s filled with fresh fluid.