90 Lego brake pedal will not move .... solid like a rock

[mikeamondo]

My son and his 95 Legacy 2.2 auto wagon, AWD, are in New Hampshire.  The car sat for a few weeks and battery is now dead.  But worse, the brake pedal will not depress.  He says when he steps on the pedal, it will wiggle side to side with a little play, like you'd expect, but as for pushing down.... it's like if you put a brick on the floor and stepped on it... it does not push down at all.

 

This happened once before, when a tow truck driver dropped off the car... he ended up leaving it in neutral, because the brake pedal was stuck and he could not shift the car into park.  When my son got in later, the pedal moved as normal.  In both occurrences, the outside temperature was warm to hot... so nothing is freezing due to cold, as indicated in other threads.

 

Is this a failure of the master cylinder?  I can't think of anything else that would mechanically stop the pedal from moving. 

 

Ideas?  We are going up this weekend, and I should be able to do some repairs.....

 

Thanks!

Mike

[Fairtax4me]

Probably not the MC. Much more likely for it to be rust or some obstruction in the booster servo.

The pedal pushrod doesn't actuate the MC directly. It pushes a cylinder inside the booster, the booster pushes the MC pushrod. The boosters on these are known to get moisture in them which freezes in winter weather. Moisture also means rust.

[mikeamondo]

Makes sense.... can you see the rust, or is it hidden from view.... in other words, can you visually confirm that's the issue, or do you just guess....

 

And.... is the booster something a guy could change with an afternoon's worth of time in a parking lot?  I've bled brake lines, and done calipers, rotors and pads... never touched the MC or the booster.

 

Thanks

[Fairtax4me]

It's not something you can just poke your head under the dash and look at.

The rust happens inside the booster. You may be able to see some by removing the dust boot around the pedal pushrod, but you probably won't be able to tell if that's definitely the problem.

 

The best test is probably to unbolt the master cylinder from the booster. Loosen the bolts or nuts and pull the MC out away from the booster about 1/2". Then try to push the pedal again and see if it moves that 1/2" or so.

 

Typically the booster can be removed without having to remove any brake lines from the MC. Just unbolt the MC and pull it forward a few inches. Then unbolt the booster from the firewall (usually bolted from the inside) and pull it up and out. It may help to remove the pedal pushrod from the booster if possible. Sometimes it just pulls out, other times there is a snap ring or circlip that needs to be prised out, and it's not worth fudging with.

[mikeamondo]

Advance Auto shows two parts... a single diaphragm booster with 2 bolts thru the firewall and a dual diaphragm with 4 bolts.  I'm not at the car..... any idea which one it should be?