Escape Posted March 30, 2021 Share Posted March 30, 2021 I hinted at the problems we're having with our Discovery 2, Dirty Daisy, in @Jon W for sale topic. As the replacement parts brought us no closer to a solution, it's time a start a thread to call on your collective knowledge. We got Daisy as a running project. When driving her home my mate discovered she had little or no brakes. I found a VERY worn wheel bearing that seems like a likely culprit. Bearing replaced, all calipers bled as per Rave, but no difference. We got little or no flow from the primary circuit (left front and right rear), secondary seemed fine. Working back we looked at the modulator and removed the pipes coming from the master. Good flow on the secondary but very limited on the primary. With a strong tendency to suck back the fluid, so you can't really 'pump up' the brakes. New master was ordered (not without difficulty as it was my first order post Brexit and nobody seemed to know just how to handle it!) and installed, but no difference. Still no strong flow in the primary circuit when disconnected from the modulator. And no flow coming out of the modulator left front and right rear. I then got a spare modulator from Jon. It arrived yesterday and was immediately installed, with fingers crossed. Again, no difference?! We first pumped the brakes with the modulator outputs disconnected to get it filled again, then bled the modulator and pump with Rovacom but still the pedal went to the bottom, unable to pump up. We bled the brakes again and while that improved pedal feel a bit (no longer going to the bottom but unable to pump up) we still only got flow from the secondary circuit. We're at wits end, there are no signs of leaks anywhere, master and modulator have been replaced with no effect, the only thing left is the brake booster. But I can't see how this could cause the problems. Happy to be corrected though! Greetz, Filip Quote Link to comment Share on other sites More sharing options...
elbekko Posted March 30, 2021 Share Posted March 30, 2021 Could it just be the ECU not operating the secondary shuttle valve properly? Quote Link to comment Share on other sites More sharing options...
Escape Posted March 30, 2021 Author Share Posted March 30, 2021 This is all without ignition on, the basic hydraulic system, so the ECU is out of the loop. As far as I can tell, both shuttle valves are hydraulicaly operated from the master and the only connection to the ECU is via the shuttle valve switches to tell the brakes are on. Quote Link to comment Share on other sites More sharing options...
Pawl12 Posted March 30, 2021 Share Posted March 30, 2021 (edited) If you can't get flow out of 1 of the mastercylinder circuits, you won't get braking on that circuit. Are you confident the replacement mastercylinder was good ? Did you check the output from each circuit with the other circuit locked off / sealed ? Edited March 30, 2021 by Pawl12 Quote Link to comment Share on other sites More sharing options...
Escape Posted March 31, 2021 Author Share Posted March 31, 2021 The mastercylinder is new and didn't come in a blue box, so no real reason to doubt it. I agree it seems the likely suspect, but I find it strange the symptoms are exactly the same as with the old master. Only thing I can think of is it was pushed in too far and the seals got damaged while bleeding. Maybe related to the booster, though I don't think the booster pin can be adjusted as on some other cars. The primary circuit that seems at fault is the one closest to the booster. Wouldn't the secondary be more prone to damage when pushed too far? We checked the output circuits one by one with the other connected to the modulator, so not actually sealed off. Filip Quote Link to comment Share on other sites More sharing options...
Pawl12 Posted April 3, 2021 Share Posted April 3, 2021 The secondary circuit piston doesn't move as far as the primary piston - I can't remember exactly for the D2, but 15~18mm on the secondary & 30~36mm on the primary - so that the displacement of each piston / circuit is the same at full stroke. Neither set of seals should be damaged by being pushed to full stroke if the mastercylinder was new (its designed to cope with full stroke during bleeding). If the original mastercylinder was very old, its theoretically possible the pistons have created a worn area in the bore due to repeated "normal" braking & moving the seal past this point during bleeding might cause seal damage - although I've never seen it on old / worn units ( I used to work for TRW / Girling). You're correct, the servo outputrod is not designed to be adjusted. The servo shouldn't influence the problem, but if something was trapped inside the mastercylinder primary piston (where the booster outputrod should contact), it could hold the mastercylinder forward of where it should be and prevent the primary circuit bleeding properly Each mastercylinder circuit ought to dispace approx 5.5cm3 of brake fluid at full stroke . From your description, I would focus on output from the mastercylinder & ignore the ABS as a very (very) unlikely cause of the problem. 2 Quote Link to comment Share on other sites More sharing options...
Escape Posted April 4, 2021 Author Share Posted April 4, 2021 Thank you very much for the detailed description! Just the info we need to investigate further. I'll take the master off to check the booster output rod to make sure nothing is trapped. And then check the displaced volume with a syringe. I didn't realize the primary and secondary have a different stroke, that does make sense for the D2 layout. Will post our progress, but probably wont find the time tomorrow to look at it. Filip Quote Link to comment Share on other sites More sharing options...
Escape Posted April 12, 2021 Author Share Posted April 12, 2021 As expected, didn't find much time (or motivation...) to take another look at the brake problem last week. I did take off the master and checked the booster outputrod. Nothing seemed out of place, no items trapped. I did notice the rod can be adjusted. As I know some work was done to the car, but no idea what exactly let alone to what standard, it is quite possible somebody had a go at adjusting it. And made things worse. The car came in with a very worn wheel bearing, that would of course have caused a delay in braking power, and could have let to overadjustement. @Pawl12 you wouldn't happen to know what the correct setting for the pushrod is? Otherwise I'll put the master back with a thin washer to the booster, so it sits a bit further. Just to see if that makes a difference, and easily reversed without having to mess with the adjustement. Filip Quote Link to comment Share on other sites More sharing options...
Pawl12 Posted April 12, 2021 Share Posted April 12, 2021 Escape, unfortunately I have no memory of what the booster output rod setting should be. Good luck ! Quote Link to comment Share on other sites More sharing options...
Escape Posted April 15, 2021 Author Share Posted April 15, 2021 We had another go at the brakes. Refitted the master, double checking that the booster pushrod was properly engaged. Then put on the nuts to the booster but only tightened by hand. Gave the pedal a (careful) try and with the second pump I got a nice and firm pedal. so that seemed to confirm the theory of the master being held forward. I tightened the nuts further, checking the pedal in between. All seemed fine even when fully tightened, much to my surprise. Then we did the bleeding, both with the Rovacom and manually following the sequence in Rave. Out for a testdrive and after a few applications the brakes are working properly. Even if the stroke seems a bit long before the brakes really bite. But that could be down to pads and discs needing to bed in again. We'll try an MOT after I've had a look at the oil leak that has appeared... Looks like it's from the ACE, which could explain the noisy pump as well. Thanks again for the help! Filip 1 Quote Link to comment Share on other sites More sharing options...
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