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  #1  
Old 12-27-2007, 01:21 PM
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W124 brake booster & master cylinder upgrade

Hi everyone,

As you may (or may not) recall, I installed early 500E brakes on my 1987 300D earlier this year (300mm front, 278mm rear). Afterwards, althought the pedal was high and firm... the pedal effort was a little more than it had been with the stock brakes. More than than I liked, anyway, although the setup has worked fine for the past 8 months.

So, I picked up a dual-diaphragm brake booster from the 400E/500E (which has more assist), along with the matching 400E/500E master cylinder (which has slightly larger internal pistons). A special thanks to Potomac Pat for helping out with getting the right parts! After installing both the V8 booster and V8 master cylinder, the pedal effort is SIGNIFICANTLY reduced. However, it was a bit too much (see later posts in this thread for details). The 124 "limo" booster ended up providing the amount of brake assist I was looking for, without the brakes being overly sensitive.

The V8 setup is a tight fit - there is minimal clearance to the engine firewall. And the brake lines require bending to fit, since the dual-diaphragm booster is 1.75" thicker. Anyway, if you have upgraded the brakes on any non-V8 W124 (300E, 300D, E320, etc), changin the booster and/or master cylinder to match can definitely reduce pedal effort.


Detailed photos of the installation are at this link:
http://www.w124performance.com/images/W124_brakes/boosters/

Photos of the stainless braded brake hoses from WRXtra.com are at this link:
http://www.w124performance.com/images/W124_brakes/hoses/




Before:



After:
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1997 E420 - 155kmi (Bugeyes)
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Last edited by gsxr; 07-10-2008 at 11:50 AM. Reason: Updated data after further experimentation
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  #2  
Old 12-29-2007, 06:07 PM
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SL600 MC Dimensions?

Dave, do you have the dimensions of the SL600 big brake master cylinder? I'd like to see if there is enough room for that item when I do the Silver Arrow brake installation.
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  #3  
Old 12-29-2007, 06:12 PM
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Originally Posted by need2speed View Post
Dave, do you have the dimensions of the SL600 big brake master cylinder? I'd like to see if there is enough room for that item when I do the Silver Arrow brake installation.
Dean, the SL600 master cylinder should be the same size externally, AFAIK. Only the internal pistons are different (larger diameter, longer travel). Just make sure you get the early SL600 M/C, which has the same line size and fittings as your 124. The late SL600 M/C (i.e., Silver Arrow M/C) has larger fittings. I think early is M10, late is M12, or something like that - can't remember exactly.

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Old 01-04-2008, 06:43 PM
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A NOS Ate 005 430 40 01 master cylinder from fleabay has arrived. Silver Arrow brakes go on in February, after a holiday in Argentina!
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Last edited by need2speed; 01-09-2008 at 11:48 PM.
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  #5  
Old 03-02-2008, 10:15 AM
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big brakes

thank you gsxr
i have all my parts ready to install e420 brakes on my 89 300e.
it is nice to see the job done and know it will work. thanks for the generosity of your time

mike
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Old 03-02-2008, 10:41 AM
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Originally Posted by mijo View Post
thank you gsxr. i have all my parts ready to install e420 brakes on my 89 300e. it is nice to see the job done and know it will work. thanks for the generosity of your time.
No problem, Mike. Just a warning, if you're installing the 294mm E420 front brake calipers, the rotor won't clear the ball joint unless you swap on either the E420 lower control arms (which have a different ball joint, for more clearance), or the E420 knuckle/spindle/hub assembly (which pushes the rotor out farther). You need about 6-7mm space between the back side of the rotor and the ball joint area (approx 3mm space on each side of the dust shield), same as stock. The only calipers that bolt on without mods are the 300mm units from the early SL500. The E420 rears work fine, but you'll need to cut the dust shield.

Side note - if you don't yet have stainless steel braided brake hoses, you can pick up a really nice set from WRXtra for about $90 including shipping. Photos of them installed on my car are at this link.

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  #7  
Old 03-02-2008, 12:17 PM
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A friend with a 300E bought a set of early 295MM brakes to install on his car.



Will these bolt on without modification?
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Old 03-02-2008, 12:32 PM
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Originally Posted by iwrock View Post
A friend with a 300E bought a set of early 295MM brakes to install on his car. Will these bolt on without modification?
Assuming your friend's 300E is a 1986-1992 model with the M103 engine... nope, he will have clearance problems with the ball joint on the LCA. BT, DT.

The 294mm, 295mm, 320mm, and 334mm rotors used on the 124 and 129 chassis all sit 6mm deeper than the 284mm and 300mm rotors. Note in the image below, the distance from the back of the mounting surface to the back side of the friction surface is approx 44mm. The 284/300 rotors are only 38mm deep. The air gap is only about 7mm, and if you push the rotor in 6mm, and have a 1mm thick dust shield... you get zero clearance. More specs are at this link. Stock 300E (M103) rotors are the 284mm, btw.

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  #9  
Old 03-02-2008, 07:10 PM
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gsxr , thanks again,
i swapped out the master and booster today ,
thanks for the heads up ,i will snap up the control arms and/or knuckles the car is in a upull it so cheap and available. i have the twin turbo set up so brakes are a good thing.
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  #10  
Old 03-02-2008, 07:36 PM
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gsxr
pls forgive my extra inquiry,are the rears going to need mods ,i do have the back plates.
the reason i ask is the u pull it yard has a ast turn around here .
the rear hubs are a bear to pull .i am patient and want to do this right.i have other cars
e320,300e ,chevy astro,so this can be in my garage once in a while
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  #11  
Old 03-02-2008, 08:34 PM
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Hes got the brakes from a car that used 295x22mm rotors.



He said he put the new rotor in place of his old rotor, and there is about a 3 or 4 mm gap between the rotor and the ball joint. You sure this will not fit?
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Old 03-02-2008, 08:54 PM
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Originally Posted by mijo View Post
are the rears going to need mods ,i do have the back plates. the reason i ask is the u pull it yard has a ast turn around here .
the rear hubs are a bear to pull .i am patient and want to do this right.
To do it "right", it would be nice to swap the backing plates. But as you said, pulling the hubs is a huge job, and not worth it unless you plan to replace wheel bearings too. So, what I did, was swap the entire rear wheel carrier+hub assembly from the donor car (E420, in this case). You would unbolt all 5 suspension links from the donor car, and remove the axle shaft, and take the whole thing, backing plates included. Then swap them on to your 300E. If you do this, make sure the bearings feel smooth, otherwise replace them before installing (they're usually OK though). The other option is to just cut your 300E dust shields.
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  #13  
Old 03-02-2008, 08:57 PM
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Originally Posted by iwrock View Post
Hes got the brakes from a car that used 295x22mm rotors. He said he put the new rotor in place of his old rotor, and there is about a 3 or 4 mm gap between the rotor and the ball joint. You sure this will not fit?
It's tight, and varies from car to car, but in general it's not a good idea. Used rotors may have an extra mm clearance compared to new rotors. Also, you need to check it with the car on the ground, as the ball joint will move as the control arm goes back to level with the spring compressed. That 3-4mm gap may drop to 1-2mm pretty quick. And if you want to retain the dust shield (which I'd recommend), that's another 1mm to allow for. I know some people have done this and driven the car with only a couple mm of clearance, but I would definitely not recommend it. That's why I put the 300x28 brakes on my car - no clearance issues.

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  #14  
Old 03-02-2008, 09:20 PM
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Originally Posted by gsxr View Post
It's tight, and varies from car to car, but in general it's not a good idea. Used rotors may have an extra mm clearance compared to new rotors. Also, you need to check it with the car on the ground, as the ball joint will move as the control arm goes back to level with the spring compressed. That 3-4mm gap may drop to 1-2mm pretty quick. And if you want to retain the dust shield (which I'd recommend), that's another 1mm to allow for. I know some people have done this and driven the car with only a couple mm of clearance, but I would definitely not recommend it. That's why I put the 300x28 brakes on my car - no clearance issues.


He has brand new Zimmerman rotors in boxes. New pads, and braided lines.


Ill tell him to put it all together, and make it settle out, and see how it lines up.
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  #15  
Old 03-03-2008, 09:37 AM
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I'll tell him to put it all together, and make it settle out, and see how it lines up.
Good idea. Make sure he checks clearance on both sides after the installation.
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