My 2003 S2 Discovery has developed a brake problem. initially the brake warning light came on and on investigation the fluid was low. I topped her up but today after leaving her for a week, the fluid had all drained away and the pedal went to the floor. There is no sign whatsoever of fluid leakage, either at the wheel calipers, the brake lines, around the master cylinder or servo.
Therefore I suspect the master cylinder has failed depositing fluid into the servo. Is this possible and if the servo has fluid leaked into it, then what is the effect? I have read somewhere that the servo would need changing?
Also what is the process for bleeding the brakes on a S2 ABS equipped Discovery. I have a NanoCom Evolution which I believe has a Power Bleed facility, but have never used it for the purpose.
Your comments would be most welcome please.
Steve

 

Yes, if you see no visible leaks...the brake booster is a likely source for the volume loss. Master cylinder is probably leaking into the booster. Normally, there will be a telltale sign of leakage right where the master bolts to the booster.

Brian.

 

X1 ........... sounds more like the problem. ABS power bleed requires the system to be bled with a diag: tool capable of activating the ABS module. It may take more than one power bleed to expel all of the air in the system, possibly 2 or 3 bleeds.

 

Thanks for the reply Brian and OffroadFrance. Sounds like the master cylinder is the culprit, I will sort a replacement. However I am still unsure regarding the condition of the Booster if fluid has leaked inside. Is this an automatic failure for the booster and it will need replacing, if so I am unsure why. Or can the fluid be drained from the booster and a new Master cylinder fitted?
Regarding the bleeding of the brake system, whilst I am OK on bleeding conventional non ABS systems, I am wondering the process for for the S2 Discovery here, fitted with ABS. I have a NanoCom Evolution which I believe has the facility to do this. Is it a matter of doing a manual conventional bleed at each wheel then running the NanoCom Power bleed, then the modulator bleed after?
Thanks for your assistance
Steve

 

My guess would be you can empty the booster and reuse, but I’m guessing.

for the bleed-

manual bleed at the ABS modulator the 2 lines coming from the MC.

then power bleed the modulator.

then power bleed the wheels in the sequence indicated by the nanocom.

 

If the master cylinder hasn't been leaking long, the booster may be fine. Also, the vacuum being drawn from the booster, during non-braking situations (while engine is running), would somewhat clear (suck) the minimal amount of fluid entering the booster chamber out. You may even notice rough idle shortly after starting engine, sometimes, if it is drawing enough fluid through the vacuum line.

However, if it has seen alot of fluid, over a long period of time and has been sitting with said fluid inside for a length of time...in my opinion...replace. The rubber diaphragm inside the booster can become soft/mushy and can be a potential issue somewhere down the line.

Brian.

 

As far as bleeding goes...

Both of the master cylinders have been replaced on our 01 and 03, and I did a manual bleed on both with satisfactory results. Both were never extremely low, where air would have entered the system.

Most ABS units remain closed (in hold position), if key is off or an ABS event is not in progress...so bleeding the system can be done the old fashion way (pumping until firm, open bleeder and hold until pedal is against the floor). Now, if you've been extremely low on fluid and have had any type of ABS event...then this is a different story and other devices must be use to help assist the bleeding process. Most ABS units will cycle the module through its operating positions...once the key is turned on...so do your initial bleed with the key off. Once you have constant fluid coming out of each bleeder, then you can start the engine to help assist the "pedal pusher" for better bleeding results.

Brian.

 

Thanks guys for the info so far.
Well, I pulled the MC and servo off the car this morning, bit easier than i expected, especially the brake pedal retaining clip. The MC was wet around the fixing holes, but seemed dry towards the rear where it is inside the servo. The servo had no fluid apparent in the bottom and looked perfectly dry and serviceable, so thats gone back on the car. If the MC was leaking then it would seem at this stage the fluid entering the booster was being pulled straight into vacuum line and hence the engine as you advised Brian.
The car is now up on axle stands with the wheels off ready for bleeding when the new MC comes. I have had a good look around the lines and wheel cylinders/calipers and all seems to be dry. However as I jacked the back of the car up a dribble of fluid exited from the near side chassis member drain hole roughly mid way down the car opposite the rear of the front passenger door. Nothing unusual I thought, she stands outside. But it looked a bit like brake fluid and tasted very bitter. The two rear brake lines run along the top of this chassis members and again I can see no obvious leakage.
Maybe I am leading myself down a rabbit hole here?

 

Not doing too well here.
Put new MC on this afternoon, manually bled through to the modulator and the four wheel cylinders, then power bled the modulator with the Nanocom. Fine accept from the fact that with the foot hard on the pedal now it starts nice and hard and now slowly goes down to the floor. So it wasn't the MC after all.
Guess its under the car again tomorrow, for there must be a visible leak somewhere. Unfortunately the car has to stand on a mechanics nightmare: Flint gravel. Horrible stuff and no chance whatsoever of finding a leak on the ground, never mind a dropped nut!

 

It may be your booster. I went thru this about 3 months ago. The booster is pretty easy. a couple of things:
1) easier with an extra set of hands
2) you will need to reset the switch that activates the lights. Take it out pull on it till it pops out. Don't be afraid it must fully extend to get reset.
3) I do not recommend a rebuilt booster. I bought a Cardone rebuilt. One of the threads holding the MC in placed stripped when I hit the brakes real hard to avoid adding a Bambi hood ornament to my D2. I know the OEM is a big ticket, but I'm not going to risk my life for a difference of $275.00 between rebuilt and new.