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Swapping Master Cylinders - Is It Possible/Necessary?

704 Views 7 Replies 3 Participants Last post by  Zeitgeist
Hi all,

I recently have been experiencing brake firmness problems and I need to ask a few questions regarding this.

When I brake, sometimes the brake feels perfect, like new, and it has only been 10 months since I replaced the pads, rotors, sensors etc. But sometimes three stops later, I feel the pedal loosen up, sometimes to the point where I worry it is not gonna stop. Then randomly it will firm up, all in the same trip. I can't tell when it is gonna cooperate.

So after reading a few posts it seems as though the master cylinder might be the culprit or the vacuum hose. All in all, if it is the cylinder, I was wondering if anyone had put in a stronger m/c? If it needs changing I might as well go "all out" :thumbsup:

I am also looking to get bigger brakes for my 400E and was looking at the 500E 320mm and possibly the 334mm setup. But if I do go bigger, do I really need to put in a bigger m/c? Will the one for mine suffice? I would like to know so when the time comes, I can do it right the first time! hehe

I was looking online and it seems that some of the 400E's have the same or close to the same m/c as the 500E and 500SL. I have a chart that shows all the m/c part numbers and which cars they were applied to, but I am still a little confused.

So if I do go with the 320mm or even the 334mm "big brakes" will I need to get different lines/booster/pins/etc. or is it just direct bolt on?

I have found almost no posts on this subject so any feedback will be greatly appreciated. Thanks!


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When I upgraded to 334mm/300mm SL600 brakes, I opted to install a 500E MC. I've heard that this may not be necessary, though there has been some discussion about stepping up to either the Limo or 500E vacuum booster as well.
Hi Zeitgeist, thanks for the response.

When you changed to the 500E m/c was it a clean swap or did you have to "make" it fit? lol

Also, if I change the booster will I have to get new lines or can I use my old ones?
Well here what I really want to know:

Can I put the 1999 SL500/600 master cylinder on my 400E/500E brake booster? Or would I need to get a new booster?

If I can, would I really need to?

99-02 SL500/600 M/C - 005 430 89 01 ~$345

99-02 SL500/600 Booster - 005 430 09 30 ~$554

93 400E/500E M/C - 004 430 75 01 ~$161

93 400E/500E Booster - 004 430 65 30 ~$305

Prices from
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I did the same 600sl set up and used the booster and m/c from a w140 - s320
Hi joef,

was this a direct bolt on swap or did you need to play around with it to make it fit?

I saw your old thread with the SA brakes on the CE and that is exactly what I am trying to do to my 400E. I'm being told that my 400E master cylinder is good enough to handle the brakes. I currently have the same one that is used in the 500E. What do you think from driving with your setup?
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