Brake pedal pressure

Mitchell Moore · **Joined:** Fri Aug 29, 2003 3:11 pm **Posts:** 197

My 325 BMW stops well but has always taken a lot of pedal pressure to get the ABS to activate. It takes at least 150 lbs of pressure to activate. I was talking with a guy with a 5 series BMW and he said that he had the same problem and a new master cylinder fixed it.

Has anyone had a problem like this and did a master cylinder fixed it?

DanDurusky · **Joined:** Sun Apr 10, 2005 7:31 pm **Posts:** 686

w/ the car off if you press and hold the brake pedal down it should press down a bit and then hold steady. pump it a few times and hold some more. does it hold hard or does it slowly sink down? thats the basic master cylinder check, it should hold steady and not sink at all.

how old is the brake fluid? air in the system will reduce teh transfer of pressure to the brakes.. lose enough pressure and the brakes wont lock up..

Mitchell Moore · **Joined:** Fri Aug 29, 2003 3:11 pm **Posts:** 197

DanDurusky wrote:

w/ the car off if you press and hold the brake pedal down it should press down a bit and then hold steady. pump it a few times and hold some more. does it hold hard or does it slowly sink down? thats the basic master cylinder check, it should hold steady and not sink at all.

up..

Pressing on the pedal as hard as I can, the pedal went half way to the floor. Pumping it 5 or 6 time did not change the distance it traveled. The pedal went half way to the floor and stayed there. Total pedal travel is 2 to 2 1/2 inches.

DanDurusky wrote:

how old is the brake fluid? air in the system will reduce teh transfer of pressure to the brakes.. lose enough pressure and the brakes wont lock up..

This is my track car so the fluid is changed often and the pedal pressure has alway been the same.

Wes Eargle · **Joined:** Mon Oct 27, 2003 9:47 am **Posts:** 3683

Are you using the stock brake lines?

Mitchell Moore · **Joined:** Fri Aug 29, 2003 3:11 pm **Posts:** 197

Wes Eargle wrote:

Are you using the stock brake lines?

I put in steel lines a while back to see if I could decrease the pedal travel.

No change.

Vincent Keene · **Posted:** Tue Sep 27, 2005 3:30 pm

Mitchell Moore wrote:

Wes Eargle wrote:

Are you using the stock brake lines?

I put in steel lines a while back to see if I could decrease the pedal travel.

No change.

The SS lines should not affect pedal travel, just pedal "feel". Too much travel most likely M/C related.

Mitchell Moore · **Joined:** Fri Aug 29, 2003 3:11 pm **Posts:** 197

Vincent Keene wrote:

Mitchell Moore wrote:

Wes Eargle wrote:

Are you using the stock brake lines?

I put in steel lines a while back to see if I could decrease the pedal travel.

No change.

The SS lines should not affect pedal travel, just pedal "feel". Too much travel most likely M/C related.

Found this on the net:

"Replacing the OE rubber hoses with Russell brake lines reduces brake pedal travel for more consistent braking. Featuring stainless steel braided hose with zinc-plated fittings, these brake lines are factory assembled for convenient installation."

Steel lines expand less under pressure so less fluid is moved thus less pedal travel. :wink:

I have to agree that my master cylinder is probably not working as it should.

DanDurusky · **Joined:** Sun Apr 10, 2005 7:31 pm **Posts:** 686

yeh, but unless your stock lines are balloons, i think the difference in travel is pretty negligable. its more of a feel thing

Mark Vitacco · **Posted:** Sun Oct 02, 2005 12:16 pm

Mitch:

When stock, the master cylinder in my Corvette did the same thing.
I could not activate ABS, even in the rain. Both BMW's & Corvetts use PBR brake componets.
At first I really thought it was the booster or vaccume leak but replacing the M/C fixed it. The pressure was low and needed high force to stop, pumping
the pedle did not make a difference. THOFF should have one in stock I
would try that first.

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Brake pedal pressure

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