Brakes to the floor

Sir Sam · **Posted:** Thu May 28, 2009 3:07 pm

chrispitude wrote:

I wonder if it has something to do with the brake boosting mechanism since diesel engines don't pull a vacuum at idle?

- Chris

FYI we have a timing belt driven vacuum pump that provides the vacuum source for everything on the vehicle.

chrispitude · **Posted:** Thu May 28, 2009 7:28 pm

Sir Sam wrote:

FYI we have a timing belt driven vacuum pump that provides the vacuum source for everything on the vehicle.

Thanks Sam. That's why I asked it as a question instead of giving it as an answer (I figured someone would know if brake booster differences between the CRD/gasser was a factor or not).

- Chris

tjkj2002 · **Posted:** Thu May 28, 2009 7:42 pm

chrispitude wrote:

Sir Sam wrote:

FYI we have a timing belt driven vacuum pump that provides the vacuum source for everything on the vehicle.

Thanks Sam. That's why I asked it as a question instead of giving it as an answer (I figured someone would know if brake booster differences between the CRD/gasser was a factor or not).

- Chris

Having a vacuum pump does not matter,your brakes still should not fall under steady brake pressure.

Easy way to tell if the vacuum supply is okay.................

Get in vehicle,leave engine off and pump the brake pedal a few times to deplete any vacuum in the system.Then hold the brake pedal down with steady pressure(not standing on them,just steady pressure),then start the vehicle.The pedal should fall about 1"-2" and hold steady.If it does this the power booster and vacuum supply is good.If the pedal goes to the floor you got a vacuum leak,if the pedal falls then holds and then slowly sinks you got a brake fluid leak in the system.

mngoat01 · **Joined:** Wed Aug 06, 2008 11:25 am **Posts:** 67

Replaced my master cylinder when i had a fading pedal and all is better now. Have a stiff pedal now and much better brakes esp. when hauling.

ribbon · **Posted:** Sat Jun 06, 2009 10:43 pm

i test drove 3 cars today and all of them did it. Jeep and 2 chevys. Not buying anything though. I guess its with all abs cars

retmil46 · **Posted:** Sun Jun 07, 2009 1:55 pm

My '87 MB 300D Turbo diesel, with MB's then-current version of ABS, passes the startup test - with everything properly set up, pedal stays nice and firm.

Tried my CRD 2 days ago - upon startup, the pedal sinks slowly to the floor. But after pulling out of the parking space, it has a nice solid pedal. On a couple of occasions, I've had to do near-panic stops with it, and the pedal was solid on those occasions.

I know of a couple people who replaced their MC, and had to order 2 or 3 replacement MC's because of the poor quality before they got one that performed properly. That might be part of the problem - cheap stupid bean counter parts once again. One gent noted that the MC on his 02 gasser KJ was made from steel, the MC on his 05 CRD from aluminum - never had to touch the MC on the 02, the MC on the 05 CRD has already required replacement - and the steel MC for the 02 was notably more expensive than the aluminum one for the CRD.

grywlfbg · **Posted:** Mon Jun 08, 2009 9:28 pm

Wife's CRD does this - though the fluid level hasn't dropped (except for a tiny amount from pad wear). Never noticed it on my TJ or my Vette - rock hard pedals both. I figured it was a diesel thing. I'll try the startup test this wkend.

e_poirier2004 · **Posted:** Tue Jun 09, 2009 9:54 pm

Just changed MC and flush the whole system: NO CHANGE at all. I noticed that the vacuum is not holding long. If I drive and pump the brake, at the 3rd pump, there's no vacuum left at all and the pedal get stiff with not so much booster assist. During normal braking, the pedal still sinks to the floor. Where's the ghost? Did anybody was successful trouble shooting this problem?

BodhiBenz1987 · **Posted:** Tue Jun 09, 2009 11:32 pm

To echo retmil, my 1987 Mercedes 300D and my 78 240D both perform as desired in that test on startup. When the engine is running, neither ever sinks to the floor. My CRD does, and it is something that started about two months ago. I have had this car since June 2005 and definitely would have noticed this before ... something has changed. It also had bad rear rotors and tore through a whole pad on the rear left for some reason ... no stuck calipers so I replaced the rotors and pads and it stops just fine. However, it doesn't seem to be bedding into the new rotors very well, and the pedal definitely sinks. I'm going to do a flush/bleed but I'm starting to think it's a bad MC. I don't see how it could be normal if the car didn't do it for the first 20,000 miles. It's very noticeable even though the cars stops fine ... I have short legs and as the pedal sinks it gets a little far for me to reach!

e_poirier2004 · **Posted:** Wed Jun 10, 2009 5:07 am

The bad rotors at the back just happened to me. It's cause by pads getting stuck in the holder. At the front, just removed the caliper pin with the rubber and replace it by the another pin like the one that doesn't have the rubber sleeve. Did that last year with no problem whatsoever. As for the pedal, try pumping your pedal with the engine off and if it gets hard, don't waste your time and money changing your mc like I did. The problem is somewhere else. Where? We have to dig deeper!!! I suspect something with the ABS (leaking block of pump) or the booster.

chrispitude · **Posted:** Wed Jun 10, 2009 7:17 am

BodhiBenz1987 wrote:

...so I replaced the rotors and pads and it stops just fine. However, it doesn't seem to be bedding into the new rotors very well, and the pedal definitely sinks. I'm going to do a flush/bleed but I'm starting to think it's a bad MC. I don't see how it could be normal if the car didn't do it for the first 20,000 miles. It's very noticeable even though the cars stops fine ... I have short legs and as the pedal sinks it gets a little far for me to reach!

Before I sold my CRD, I put a new set of pads/rotors on all around. They were one of the discount slotted/crossdrilled pad/rotor combos from Ebay built using Chinese blanks. I bled the brakes with my wife using the classic two-person system. After bedding in the pads, it stopped but it didn't feel grippy like the factory pads did. When Fred came over to buy it, I told him my no-name brakes weren't very good and I was unhappy with them. After asking how I bled the brakes, he suggested we re-bleed with the engine running.

What a dramatic difference! Noticeable air bubbles came out on the first pump at the two rear calipers. I think it was a combination of time allowing the remaining air to collect into bubbles, plus having the engine running. Either way, the thing stops fantastically now.

- Chris

bigugly · **Posted:** Wed Jun 10, 2009 10:58 am

My brakes stay firm when stopping and stays firm. The only time the pedal starts to fall is if I am at a stop and stand on the pedal. I only did that to see what you guys were talking about.

e_poirier2004 · **Posted:** Thu Jun 11, 2009 10:01 am

New observation: this morning when I went to work (40km) I checked my wheels and find out that rear wheels were warm when front wheels were cold. The internal leak seems to only be acting on front wheels.

BodhiBenz1987 · **Posted:** Sat Jun 13, 2009 10:33 pm

e_poirier2004 wrote:

The bad rotors at the back just happened to me. It's cause by pads getting stuck in the holder. At the front, just removed the caliper pin with the rubber and replace it by the another pin like the one that doesn't have the rubber sleeve. Did that last year with no problem whatsoever. As for the pedal, try pumping your pedal with the engine off and if it gets hard, don't waste your time and money changing your mc like I did. The problem is somewhere else. Where? We have to dig deeper!!! I suspect something with the ABS (leaking block of pump) or the booster.

I believe that is exactly what happened, the pads were wedged in the holder so I could barely remove the caliper. Indeed the pedal does not sink with the engine off ... it sinks a bit, as it should, when the engine is started. Then it sinks too much. I checked the vacuum at the lines on the booster, but couldn't figure out how to get the check valve off to test it. Didn't want to just rip it off and make a bigger problem for myself.

Brakes to the floor

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