AMGDave

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 it worked fine like that 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. I still have a high, firm pedal... but now I don't need to use much muscle to obtain decent braking power.

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), this upgrade can improve the pedal feel and/or reduce pedal effort. I am also replacing my old, cruddy Bekkers stainless brake hoses with new, vinyl-protected hoses from WRXtra.com (which actually have the correct 17mm front hose fitting!).

Note that if you are planning to install either 320f/300r, or 334f/300r, brake setups on your car... there is an even larger master cylinder that should be installed at the same time (from the early SL600, with M10 lines). The "medium" size MC that I used (from the 400E/500E) is properly matched for my setup, but is too small for the really big brakes. This results in excess pedal travel, which feels like a slightly soft/spongy pedal. You need to properly match the front & rear caliper size with the correct master cylinder to get the right pedal feel.


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


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





Before:



After:

AMGDave

UPDATE:

After driving with the V8 MC & booster for a number of months, I decided it was a tad too sensitive (pedal effort was TOO light). I re-installed the stock MC (on the V8 booster) and it helped slightly, but the effort is still a bit light. Interestingly, my brake pedal felt perfect when I had 4 people in the car and a trunk full of luggage. But with only 1 or 2 people and no cargo, it was a bit touchy. The V8 setup is probably perfect for a wagon (which weighs abou the same as a 500E), it's just a hair much - IMO - for a lightweight early 124 sedan (86-89 260E, 300E, 300D). This is all pretty subjective stuff, so your opinion may vary. Reid is happy with the stock booster & MC, and we have identical brakes, including the same brake pads, on the exact same car! Anyway, some additional research turned up a different booster which was used on the 124 LWB (limo version, only sold in Europe) that has more power assist than the standard 124 booster, but less than the V8 setup:


Stock 6-cyl 124 has a single-diaphragm 10" booster with a boost factor of 3.85
The 124 "limo" has a dual diaphragm 8"/9" booster with a factor of 4.50
The 400E/500E has a dual diaphragm 8"/9" booster with a factor of 5.60


The "limo" booster was also used on the USA 201.029 and 201.034. The .029 (190E 2.6) is quite common, so I was able to pick one up at a local salvage yard. I installed the "limo" booster last weekend. It works GREAT. The 500E booster was just a bit overkill on a 6-cyl sedan. The pedal feel with the "limo" booster is just about perfect, no more sensitive brake pedal, and no more difficulty trail braking. What's interesting is that although the pedal travel did not change, it FEELS like it changed. The 500E booster, with more assist, made the pedal move more with less effort... so it seemed like the pedal was moving farther.


CONCLUSION:

For anyone contemplating brake uprades on a 124, I would recommend leaving the brake booster (and master cylinder) stock at first. Drive the car for a while. If the pedal effort is too high, move up to the "limo" booster on a sedan, or the 500E booster on a wagon. If you use front brake calipers with larger pistons (320mm or 334mm front brakes), the pedal travel may be slightly more than before. Using the 500E master cylinder, which has a slightly larger piston for the front brake circuit, should improve the travel. Finally, remember that brake pad compound will also affect the pedal feel... it would be a good idea to settle on the pads you want, and get the pedal feel to match your choice of pads.

All of this stuff is pretty subjective, and what one person considers good feel or acceptable pedal travel, another person may not. You'll need to experiment and decide what works best for you. Part numbers, and brake specifications, are in my brake spreadsheet at this link. Additional photos of brake components are here. Hopefully this information will help you decide what to try out!

RHW

Dave,

With your help, the 500E brakes on my Sportline are fantastic. I would describe my braking ability as far more nimble than original, so safer than stock.

As you said, this is subjective, but I find the pedal position and effort to be very comfortable without having changed the booster. This was probably my single favorite mod I've done to the Sportline, maybe the lights compete for top honors at night.

Your time in documenting this kind of work is greatly appreciated.

XJguy

What is recommended for stock brake system on a 94 E320 coupe?

I have no leaks, Porterfield pads, braided stainless brake lines. Brembo rotors (not drilled not slotted). Fresh Motul fluid, everything properly bled. With all this, I think braking sucks. Takes a lot of pressure to get it to really bite down. My brother a high performance driving instructor also feels the braking is horrible.

I dont swap out the calipers to larger just yet because I use the stock 15" wheels for winter tires.

QVHK

I upgraded my front brakes to E320's a few years ago, and, at the same time, replaced the brake master cylinder, renewed the calipers with new seals (repair kit available), and drained and replaced system with a higher grade brake fluid. The 320 brakes has a larger rotor (hence greater brake force due to larger frictional surface), and four pistons instead of two on stock set-up. I left the booster untouched, and all has been well. Car stops more confidently, and there is a little less (not much, but a little) effort needed to step on the brake pedal. I have driven other cars, Japanese and Italian, but found my W124 braking character unique - the braking feel is more progressive than linear. Over the years, I have mastered this character well, and love it that way. IN the earlier post n this thread, AMGDave has shared with us his experience of possible overkill in brake upgrades, and also offered an middle-of-the-road solution. Perhaps doing the upgrades one step at a time would be the way to go.

GSbeto

So, replace BB first? My Cabrio needs effort/assist to do the job. I would like to make it more touchy to the pedal (stock brakes all around)

Thanks.

QVHK

It depends what previous repairs have been done to the brake system. If it has not been touched before, or you are not sure, I would try replacing the brake master cylinder first. It is a cheaper and an easier fix than the brake booster. Pelican Parts has a very useful step by step guide on the web, ditto for the brake booster.

GSbeto

Thank you for you reply QVHK, my car has the stock two piston calipers and I think replacing the MC will help my stopping power more.

Lou.

QVHK

If I am not mistaken, E320 stock calipers are 4-piston ATE? Older W124s, like mine, have stock two-piston calipers. Anyway, the brake master cylinder typically wears out with age and mileage, so is the best investment in restoring gripping power on the brakes. If this does not bring much improvement, and you do not have any noticeable drop in brake fluid level, the prime suspect would be the brake booster.

yungcuan25

May I know what's the part number for the brake booster and master cylinder can be fitted in w124?

QVHK

Try Pelican Part's on-line catalogue, here is an example,
http://www.pelicanparts.com/catalog/...284-Brakes.htm
then input your model year to enhance accuracy.