My Dad Has 2008 E350 4matic trying to replace front brakes. Don't have a long Allen wrench to remove caliper. Anyone know what size so I can buy and remove? Thanks Curtis

Allen wrenches usually come in a set, try 3/8.

I'm not sure of the size. I have an allen socket made for GM brake calipers!! But i would guess it is a metric size, maybe a 12 mm. Call an auto parts store and they can pull the tool and tell you with a phone call. Good luck.

Allen wrench size to remove brake caliper on my 2008 mercury mariner

For front brake pads replacement you only need usually wrench set, inclusive 7 mm allen key also. But for rear brake pads replacement you need obligatory a special caliper piston pressing tool, in order to press back rear caliper piston with parking brake automatic adjustment!!!
Instructions for front brake pads replacement.
For change front brake pads you must raise vehicle, remove wheels, extract the retaining spring of the caliper, and remove the caliper as follow:
1. Do not disconnect the brake hose from the caliper, and do not allow the caliper to hang by the brake hose!
2. Remove top and bottom caps (on back side of the caliper) for access to guide pins, then unbolt and remove them from the brake carrier. Remove the caliper.
3. Now you must thoroughly clean the brake calipers (free of grease).
4. Remove outer brake pad from brake carrier.
5. Pull inner brake pad out of brake caliper piston.
6. Check up the brake fluid level on the reservor, and emptying if neccessary!
7. Push piston back into brake caliper housing.
8. Install inner brake pad (with expanding spring) in brake caliper piston. (Arrow marked on pad - if exist, must point in direction of brake disc rotation when vehicle is moving forward).
9. Install outer brake pad into brake carrier.
10. Bolt brake caliper housing to brake carrier using two guide pins. Tightening torque is 25 Nm.
11. Install both caps.
12. Insert retaining spring into brake caliper housing.
Important note: Depress the brake pedal firmly several times while the car is stationary so that the brake pads adjust to their normal operating positions!!!
Check brake fluid level and top up as neccessary!

You will need a 7mm allen to remove the front brake caliper.

i just changed my front rotors and pads on my 2001 escape, 6 cylinder. everyone was wrong on the wrench sizes, including the idiots at my local ford dealer. to get the brake calipers off I needed a 7mm hex bit. to get the caliper bracket off I needed an 18mm socket, it was a very easy job but check your wrench sizes first, it seems that every year and model uses different sizes.

You'll need the Allen or Torz wrench that fits the locking bolts on the caliper so you can remove the calipers and you will need a caliper compressor to compress the caliper cylinders to install the new brake pads once you replace the rotors. I would have the Rotors checked to verify they need to be replaced before replacing them. It is possible you can save money by simply having them turned instead. $25 for each rotor is better than the normal $150 to $250 to get new ones.

it's metric i think get a set, . It doesn't look that big in the manual perhaps 8mm thread so anything from 6-8mm driver depending on who made the thing. cant you measure across the flats?

it is a 3/8 allen wrench

So this is what it takes to replace rear brake rotors on a 2003 Mercedes E320;
1) open the bonnet (hood) of the car and loosen/remove the cap off of the brake fluid resevior.
2) remove outer spring clamp from brake assembly (it clips in to the iner edge of the holes of the caliper).
3)using a 7 MM allen wrench, remove the brake caliper.
4) using 18 MM box wrench, remove the caliper housing assembly off of the wheel hub.
5) using a star wrench, unscrew the rotor locking screw from the rotor
6) squirt some liquid wrench on the rotor hub and knock the rotor with a hammer to work the liquid wrench in.
7) using the same hammer, knock the rotor off the hub.
8) using a metal file, lightly file old residue off of the hub and place the new rotor on the hub.
9) set the hub by screwing in the lug nuts and then screw in the hub locking screw using the star wrench, then remove the lug nuts.
10) reinstall the caliper housing assembly onto the wheel hub using the 18 MM box wrench.
11) push back the brake claiper piston to its home position and install the inner brake pad (the one with the snap clips)
12) insert the outer brake pad in the claper housing assembly.
13) slide on the caliper housing with the inner brake pad in place (over the outer brake pad) and screw in the caliper screw rods using the 7 MM allen wrench
14) on the right wheel brakes, DO NOT FORGET to slide in the brake sensor (the one with the black connector) and connect it to the connector on the caliper housing.
15) be sure to reinsert the spring clamp onto the outer brake assembly to set the assembly squarely onto the wheel (there should be no wiggle in the brake assembly after the spring clamps are installed).
16) finally mount the wheels.
17) you can bleed the brakes at this point to release any trapped air (which is unlikely) but be sure to pump the brakes after starting the car BUT BEFORE MOVING IT to re-preassurize the brake system before driving the car.
17) ONE WEEK LATER - recheck brake assembly to ensure all is okay and brake fluid.

This proposed solution is for a 2003 Mercedes Benz E320 and NOT a 2005 model as stated by the limited option selection provided by FIXYA.com when initially describing the problem.