What is the difference between the W126 master cylinder PN: 0044300901 and 0044302601?
Both the dealer and Pelican parts claim 0044300901 goes till Chassis 050789 and 0044302601 goes through 050790

I'm trying to order one to fit it to a salvaged 1983 300SD brake booster, and I just need to know which will fit, and if they both fit, which is better. I do not have the vin, and I know one of you bought a master cylinder for a W126 so please do me a grand favor and help explain this to me, because the Dealer gave me a vacant stare when asked the same question, and I hate blind firing.
as always thanks a million!

*I have a hunch the older vin and PN is for the W116 brake boster they put in early W126's.*
*is early 1981 to 1985? How early is early?*

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My experience is that back then any how, there was not much difference in any of the master cylinders.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Is there a brand on the master cylinder? I went through this recently on my Euro-Market 500SL and the brand on the MC and booster is what solved the mystery. In my case, both were branded ATE and made it easy to pick which was the correct part.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Its an ATE W126 '83 300SD Brake booster, and the corresponding fluid reservoir, but unfortunately I don't have the cylinder, for I knew I wanted a new one, and so I left it in the car I took the booster and reservoir from.
if it helps, the MC was black and had a Daimler Benz star on it.

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A junkyard is not for junk

I'd go poke around on the Pelican site and see if there's an ATE MC for one of the VIN runs and not for the other. If there is, that should answer your question. If ATE is listed for both, it can be a bit more complicated.

It might be a better idea to reverse-engineer the approach. See if there is a part number listed on the booster and see if there is a VIN split listed that you can find for it. Sometimes you have to think "backwards"

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

the 050789 PN: 0044300901 has an ATE master cylinder on pelican and not for the opposite. However, for the brake boosters, the Genuine mercedes part is PN: 002-430-68-30-64 and there is an ATE listed with the same number but there is ALSO an ATE with PN: 002-430-68-30 and the note: 9" diameter with threaded vacuum fitting.

When I get home ill check my booster PN

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Physically, either one will bolt to the booster.
The earlier one has a 15/16" front circuit bore, the later one a 1" front circuit bore. The change in bore results in a difference in pedal feel & stroke.

They are showing two different part numbers for 1984 300SD and a 1985 380SE. Was the change due to antilock systems being added to the w126 between those years?

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84 300SD
85 380SE
83 528e
95 318ic

Thats what im trying to figure out, I just want to buy an MC so I can get back to work, will either of those fit on this booster and is the 1" bore a better feel? I do not have ABS equipped fyi.

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I'm going to buy the later version FTE brand. Ill post pics once I get it.

According to post 45 of this page, I have some wiggle room as long as I don't buy one with ABS.
http://www.peachparts.com/shopforum/diesel-discussion/345503-can-sd-brake-booster-wedged-into-w123-3.html

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Ok so I actually bought the earlier VIN ATE Master Cylinder 0044300901 and it has no fitment problems as far as i can tell. I ran into a problem though. My brakes are gargantually heavy and require immense effort to stop the car. I get about 2 seconds of booster pressure then the pedal falls to the stiffest spot on earth before the metal, accompanied by a gas leak noise, and then if I try to bring the car to a complete stop, there is a loud clunk you can feel from behind. I beleived the Oring on the m/c was bad so i went to change it with a fresh spare i had on hand. 8 hrs after I drove i went to get to work and when I uncoupled the booster line the vacuum rushed to equalize, indicating the booster held vacuum, and a later test with a the new oring on and a mityvac in hand confirmed the boosters air tight. *I love that.*

I need to pick up another liter of Pentosin DOT4LV to rebleed the brakes, and I am wondering if I just messed up bleeding the new m/c and brake lines with my pressure bleeder. I heard that badly bled lines would be gummy not stiff though.

Could it possibly be the booster's pushrod? Can you adjust an 83 300SD booster pushrod & if so how do you do it properly?


Also the M/C I bought for this booster is the correct M/C as according to the snippet from the W126 FSM: see attatched

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The parts dept usually has no way of knowing what is different on a 34 year old car beyond asking for the VIN. Did you get a MC from the dealer?

There is more to it with a stepped bore MC. The front 15/16" will have slightly more front brake bias than the 1". The 1" will require a slightly more force to actuate the brakes.

This is all over the place and difficult to read all bunched up. From what I can make out:

Brake pedal travel is long and soft until it hits bottom then the brakes sort of work. This is usually a sign of either the front or rear brake circuit not working / holding pressure. It is likely the rear not working, if none of teh wheels are locking up. If the front stopped working, usually the rears will lock up when trying to stop the car. However see my last entry *

If the hiss is under dash, the brake booster has failed. The rear clunk can be a lot of things. ( like a caliper falling off. )

* It is possible to have a MC with a deeper push rod socket, this would lead to a long travel pedal because the booster isn't pushing against anything until late in the travel. Compare both MC / measure push rod on the booster.

M/C is off pelican and is the 15/16 bore. If the hiss is under the dash I am going to need a new booster, even if it holds vacuum? where would it leak from on the back of it?

Do I adjust the pushrod by grabbing the point where it connects to the master and rotating it in/out?

My calipers are for sure not falling off.

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Could the gasket where the booster meets the firewall cause a leak? Or is that just for insulation?

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So any Gen 1 (up to 1985) W126 booster will accept any M/C from a gen 1 W126 or even a W123, *without ABS*
The Gen 2 boosters like in the SDL will look drastically different and as far as i know, will not work with the gen1 equipment. As for the M/C VIN # split, the boosters are nearly identical even after the split. I have a booster from a 75,000 model and the pre 56,000 booster is identical. The only difference will be slight difference in pedal feel/ travel based on bore size for the M/C you choose, which beyond factory OEM, is really based on personal preference/ budget.

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