Master cylinder removal question?

[AlaskanJack]

I am replacing my master cylinder today on my 91 Sport. After removing the master cylinder I started thinking hmmm....I didn't have to plug anything off. Very little brake fluid came out during the removal and the two brakelines didn't need plugging. Shouldn't this system be pressurized? Could the (Damn forget the name) you know the valve going to rear brakes, be bad?

I will check my manual and search some posts, just in case my master cylinder does not need replacing. I will wait to bench bleed the master cylinder just in case.

 

[AlaskanJack]

well according to some other posts I should need to use baggies and rubber bands around the brake lines to catch fluid as it comes out. Should I worry if no measureable fluid came out? I'm pressing on with bench bleeding as soon as I go pick up some bolts or fittings. I had nothing that fit the holes....

 

[dogfriend]

Its only pressurized when you push the pedal, i.e. the plunger in the master cylinder is what provides the pressure which is in turn transferred to the calipers (and wheel cylinders if you have rear drums). I don't think that you would lose a whole lot of fluid because gravity will hold it in the lines since the lines are below the level of the master cylinder.

I would just make sure to bleed after everything is back together to get rid of old fluid and make sure all of the air is bled out.

 

[AlaskanJack]

According to the instructions that came with the master cylinder it should only take 4-5 pumps to clear the air from the master cylinder. I purchased a master cylinder bleeder kit which runs hoses into the resevoir. Problem is I have pumped it more than 15 times and I am still getting air bubbles. I think one of the plastic inserts is letting air suck back in when I release the plunger. Can I just use a bolt and bleed that one by tightening the bolt before releasing the plunger?

 

[dogfriend]

This is what my service manual says:


Master Cylinder Bleeding

When the brake master cylinder has been replaced, or the system emptied or partially emptied, it should be primed to prevent air from getting into the system.

1. Disconnect the master cylinder brake tube nuts.

2. Install short brake tubes with ends submerged in the brake master cylinder reservoir and fill the brake master cylinder reservoir with High Performance DOT 3 Brake Fluid C6AZ-19542-AB or DOT 3 equivalent meeting Ford specification ESA-M6C25-A, DOT 3.

3. Have an assistant pump the brake pedal until clear, bubble-free brake fluid flows from both brake tubes.

4. Remove the short brake tubes and install the brake outlet tubes.

5. Bleed each brake tube at the brake master cylinder as follows:

1 Have an assistant pump the brake pedal 10 times and then hold firm pressure on the brake pedal.

2 Loosen the rearmost brake tube fittings until a stream of brake fluid comes out. Have an assistant maintain pressure on the brake pedal while tightening the brake tube fitting.

3 Repeat this operation until clear, bubble-free fluid comes out.

4 Refill the brake master cylinder reservoir as necessary. Repeat the bleeding operation at the front brake tube.

6. Tighten the brake master cylinder tube nuts.



If I understand your description correctly, if you have a plastic insert in the port where the brake line will attach, then yes I think that you could be sucking air back into the master cylinder when you let off the plunger.

 

[AlaskanJack]

Are Corona's good after being in the fridge for 6 months?

Well I found 3 Corona's in my fridge so I decided good time to take a break and see what gets posted here.

I tastes allright to me!!!! hahaha

Step up I'm serving

 

[AlaskanJack]

Thanks I was so busy drinking and looking for that gif file that you posted before I was done.

Well I will chug the beer and go work on my truck.

 

[AlaskanJack]

Ok now, I'm pissed!! I followed Dog's directions on bench bleeding the master cylinder. I then bled each wheel until no more bubble came out in jar.

Surprise my pedal still goes to the floor. Here's my question. We bled the brake lines with the vehicle off and the brakes are hard. Then when I start the car and put my foot on the brake it goes to the floor. Turn car off and it firms up again. I even pumped the brakes while the vehicle was running and nothing.

So what's this I have read about an ABS valve under the vehicle?

 

[dogfriend]

Doh!

Does your truck have 4 wheel ABS? or just rear ABS?

If you have 4 wheel ABS, read this thread because Mommix had the same problem:

Dead Link Removed

 

[AlaskanJack]

Just rear ABS. I had already read that thread on the 4 wheel ABS hoping it could shed some light.

 

[dogfriend]

Did you figure this out yet?

I read though both the Chilton's and the Haynes manuals and I have no clue what your problem is.

Chilton has a sentence which says "It will be necessary to centralize the pressure differential value(sic) after a brake system failure has been corrected and the hydraulic system has been bled". No other info is given on this, no diagrams showing a pressure differential valve. Some pickups use a valve to control front to rear brake pressure to avoid locking the brakes with no load in the pickup bed; I don't think the Explorer has this, especially with Rear ABS which would do the same thing.

The only other thing I see is that there is an adjustment for the brake booster pushrod length. I suppose if it were way off it might cause a problem, but otherwise I don't have a clue.

If you suspect the RABS module, you could unplug the electrical connector. Its supposed to be on the left frame rail.

 

[AlaskanJack]

I started a new post on this.

I checked the booster push rod before installing the master cylinder.

Can I just disconnect the wiring at the RABS proportioning valve and it will remain open? What does disconnecting it accomplish? Also where does the wiring go? If it goes to the rear axle sensor that sensor is already disconnected from axle regearing.

 

[dogfriend]

According to Haynes, the RABS module is located in the center of the dash. The system consists of the RABS module, the RABS electrohydraulic valve (on LH frame rail near the front), the rear axle sensor and the exciter ring which is inside the rear axle housing.

Haynes has a decent picture (page 9-2) if you have a copy.