Leaking Brake Master Cylinder On Discovery Series II

hywy61

Well-known member
May 25, 2004
725
0
atlanta, ga
The cold weather has caused my Master Brake cylinder to start leaking alot more. So i guess I need to either replace the whole thing or just buy a repair kit. Its leaking right under the reservoir pretty badly.

Watched a few videos on the repair but was wondering if anyone had tips, things to watch for etc?

Use an OEM part or aftermarket?

AB has one for $165

http://www.roverparts.com/Parts/SJC100432

Thanks
 
Last edited:

hywy61

Well-known member
May 25, 2004
725
0
atlanta, ga
I have a strong break pedal still so should i just do the repair kit or replace the whole Master Cylinder ?
 
Last edited:

K-rover

Well-known member
Jan 15, 2010
2,163
62
Raleigh, NC
Is it leaking from just below the res tank? There are two O-rings that tend to go bad and leak. Just get the repair kit. If its leaking from somewhere else, then I would get a new MC
 

Dangeruss

Well-known member
Mar 28, 2007
104
1
Ontario, Canada
Pretty straight forward, but you can't buy the seals separately, you have to get the whole reservoir. IIRC it took a surprising amount of pressure on the reservoir to compress the new seals enough to get the retaining clip back in.
 

hywy61

Well-known member
May 25, 2004
725
0
atlanta, ga
Thanks. The repair kit is only $65 cheaper so probably pays just to replace the whole thing.

I have bled the regular brake lines before but never the master cylinder. How do i do this? The AB site says it hard to bench bleed it so i need another method.

Anyone know the size of the brake line nuts connecting to the master cylinder?
 
Last edited:

hywy61

Well-known member
May 25, 2004
725
0
atlanta, ga
Thanks but I don't have one and was told it could be done with out it. I have done the rest of the lines without it many times and no issues but never the master.
 

K-rover

Well-known member
Jan 15, 2010
2,163
62
Raleigh, NC
Thanks but I don't have one and was told it could be done with out it. I have done the rest of the lines without it many times and no issues but never the master.

Ive heard of people driving on a gravel road to activate the ABS system.. I guess that will push the air through, then you would bleed it at each wheel? But I wouldnt trust that. The proper way is to have it down with the Testbook.

You can bleed the lines without it no problem, but if you replace the MC or the ABS block you really need the book to make sure you get all the air out.
 

ezzzzzzz

Well-known member
Apr 22, 2010
604
7
SE Va
Bench bleed the MC. Perform a manual bleed on all four corners. Use a Testbook or Hawkeye (with D2 download) to perform the final bleed. There may be other LR code readers that will perform this task too.
 

hywy61

Well-known member
May 25, 2004
725
0
atlanta, ga
i have heard you can also put on the traction control and go down a hill to activate the abs. Then bleed the four wheels.
 

JohnB

Well-known member
Oct 18, 2007
2,292
12
Oregon
You can put 12 volts to the modulator plug and run it and bleed. Warning it pushes fluid pretty quickly.

It's overkill though I'd just bleed at the wheels and be done.
 

JohnB

Well-known member
Oct 18, 2007
2,292
12
Oregon
Have heard that its almost easier to open all four calipers and let gravity work for you if you keep it dripping all night long.
 

toadermcgee

Well-known member
Sep 26, 2007
689
4
Newburgh, IN
I just replaced the master cylinder on my D2 a few weeks ago. Once I had the master cylinder bolted to the booster I filled the reservoir and let gravity work. Once I say some fluid seeping out I final tighten the lines from the cylinder. While I had the system opened I replaced both rear calipers. Let each bleeder valve open until fluid was coming out then closed. I did one side at a time. I then bleed the brakes per the rave order. Brakes where a soft but worked. There was snow and ice on the driveway so I used that to make the traction control / anti lock hit. Went back and forth a dozen times or so. Re bleed all four corners and got some more air out of the the LF and LR calipers. I total I went through about 2 liters of brake fluid. Brakes feel just a good as when I first got it. Stops like a D2, it is not a Ferrari.
 

Dave03S

Well-known member
Jun 22, 2012
62
2
Seattle, Wa
You don't need a gravel road or hill to do the final bleed without a Testbook.

The procedure once the calipers are bled is to put it in LOW range then drive slowly with the Hill Descent Control on. Get up to say 20mph, activate HDC and allow it to slow the vehicle down. Speed up and repeat a few times.

If your pedal is still not right, bleed calipers one more time.
 

JohnB

Well-known member
Oct 18, 2007
2,292
12
Oregon
Can't see how operating the ABS can do anything if air is still trapped in the lines somewhere.
 

hywy61

Well-known member
May 25, 2004
725
0
atlanta, ga
I am guessing once you run the ABS and then bleed again it would get any remaining air out.

I finished the job and my pedal is pretty decent.

1. I swapped out the master cylinder and filled with fluid.
2. Waited for it to start seeping out before reconnecting the brake lines. Just snugged them in a little.
3. Had my son pump the brakes and loosened one line at the master at a time until fluid came out. then fully tightened both lines.
4. Then bled all four wheels in this order. Pass rear, Driver rear, Pass front, Driver font. Most of the air bubbles came out during the Pass rear bleed - probably since it was the first one i did.
5. Test drove and went down a big hill with Traction Control engaged to cycle the fluid.
<b>6. Haven't re-bled all four lines again yet but the brakes seem fine.</b> I still have another quart of fresh brake fluid.

So one question I have is once i swap the master out and then bleed, is that bypassing the ABS channels so to speak? I know the lines go thorough the unit but could air go through the lines from the master and get trapped in the ABS ?

The air would have been in the MC and those lines before it hit the ABS unit right? So when i bled, the air bubbles would have been removed via the normal bleed method or could some get trapped in the ABS and then release when i activated the ABS unit via the downhill decent?