Brake system-Refreshed and No pressure

[mtnjag]

Problems-what else?

Sorry in advance for the long explanation.

Prior to refresh, brakes worked with worn front rotors and pads and long term Wilwood calipers, leaky front MC, and 1x stuck rear 1 3/4" piston. The system has been set up since restoration 20 years ago with a 3/4" MC for front brakes (a Girling clutch style alum that was leaking), and a replacement Girling 5/8" for the rear not leaking.

The refresh was, new pads and rotors on the front Wilwood Dynalites. Pistons compressed for the new pads with no leaks.
Professionally rebuilt original (front) dunlop 2 1/8" pots on rear calipers with new pads, rotors good.
Rebuilt front front MC since it was leaking and rebuilt rear MC cause it had been 20 years and the clutch mc/slave and front brake mc were all leaking and it seemed wise.

Observed the pistons on front and rear calipers moving upon bleeding and releasing and stopping wheels when checked by hand with car up.

But, despite bleeding the hell out of front and back with no air now being expelled I can't get the pedal off the floor and the brakes barely work, slightly slowing the car to a stop at 10mph. No leaks anywhere. Don't seem to be seeing a backflush to the reservoirs, although I don't know how obvious that would be. With pedal all the way down, piston rods are all the way into the MCs.

Pulled the top/rear 5/8" MC I rebuilt and bench tested it with my fingers and it didn't seem to have much pressure, either pull or push with perhaps a slight push back at the inlet so I ordered a new one from XKs which is here this weekend. Didn't see a problem with my rebuild when disassembled.

When I blocked the top balance linkage from compressing upon pedal press (MC removed entirely) with a block of wood and pressed the pedal the bottom cylinder rod went in about 2/3 and actuated the front brakes, seemed firm but car is on blocks and checked wheel by hand.

Without the top linkage blocked the bottom MC rod goes in maybe 1/4 to 1/3 with slight compression of the caliper but able to turn wheel by hand.

So:

-For sure replacing the top MC with the new one, don't know if I should pull and replace bottom or if I have normal performance out of it?
-does that behavior of the bottom MC seem normal?
-If one MC fails 100% should the other work normally and give full braking on that circuit or does the system not work like that?
-Don't know what it could be except I screwed up the rebuild of the MCs?
-Any other suggestions or comments, please?

Thank you
Layne

[mgcjag]

Hi Layne.....Hope you dont mind i moved your post here so you have a new post......Do you have a 3.8 setup with the Kelsey hays.....I dont have experiance working on the early brakes..so cant answer your questions....If you have no leaks then i would think you still have air in the system.....when bleeding on your final pedal stroke are you holding it down when you tighten the bleed valve....Steve

[mtnjag]

Yeas, an original early brake set up as far as configuration, other than the change to Wilwoods up front, 3/4” MC for front, and now the Dunlop 2 1/8” pots at the rear.

Bled the HELL out of the system front and rear, one pumping pedal, one opening and closing valve. Last time I bled input 2 reservoirs through the rear brakes with primed and filled hose (one man bleed technique) but with someone pumping and me watching hose, no air. Really don’t think there’s air in system but wouldn’t be the first time I was wrong!

[mgcjag]

Hi Layne..not trying to teach you how to bleed brakes but just to confirm starting at furthest point from master and moveing closer......open bleed valve...press pedal down....close valve...release pedal....and repeat....Steve

[mtnjag]

Yep, have done that tried and true technique multiple times, starting at furthest bleed valve. The last time i bled I used a method where a “head” of solid fluid is maintained in the clear bleeder tube with the exit end below fluid level in a catch can (clear beer bottle of which I have a few at this point) with the valve left open, and the pedal pumped never allowing air to re-enter the system. Usually done as a one man bleed, but I had someone pump while I watched the tube to see if any air was expelled, none was. Idea being to perhaps dislodge an air pocket with “continuous “ movement of fluid.

[abowie]

What may have happened is that with your bleeding you have got the MC pistons pushed all the way to the front of the cylinder and jammed.

Before you pull it all apart can I suggest you pressure bleed the system?

http://www.projectetype.com/index.php/t ... ringe.html

[mtnjag]

I do have the big syringe as in the link so may try that. But to be clear they are both pumping fluid so I don’t think pistons are stuck.

[mtnjag]

Can someone explain how the MCs should behave as per my Questions and description of their observed behavior in my first post?

[tinworm]

I assume all seals are the correct way around first. On pressing down on brake pedal the initial movement closes the small valve at the front of the master cylinder - this is a small rubber cup seal - if this leaks it sends fluid back to the reservoir and you can see this happening if you watch (or get someone to watch) the fluid level in the master cylinder as the brake pedal is pressed. No brake pressure can be felt if this happens.
The compensator linkage is there to give braking action on a working cylinder (front or back) if one or other circuit has failed. If you block one cylinder which is what I think you are saying above - all braking force is applied to the other cylinder and you say this still goes to full travel ? If this is the case either there is air still in circuit, there is a leak, or fluid is pushed back into the reservoir - there is nothing else.

Barrie

[mgcjag]

Hi Layne...do you have a Jaguar service manual..there are diagrams and descriptions of how the Kelsey hays and master cylinders operate....we also have copies of all the service manuals in the Knowledge base Technicaln.nfo section...Steve

[christopher storey]

I suspect the bleeding technique is the problem. Even if you get fluid through to the end of the bleed tube, and keep the open end under fluid in the jar, if you do not shut off the bleed screw before each return of the brake pedal then in some - not every - cases all you are doing is alternately blowing and sucking the same fluid up and down the bleed tube . This means that any air trapped further up the system is not being expelled. Before you go any further, I should adopt the approved method of bleeding ( which unforthunately does require two people ) and shut off the bleed screw before the pedal is released on each stroke

[mtnjag]

Sorry I wasn’t clear. I have bled repeatedly using the standard two person method. One with a pedal pump up And hold with valve closed, another then opening the valve, pedal stroke down to bottom, hold, close valve,repeat. Bled many cars with this standard technique with success. Only used the “one person” technique to see if the pumping action would dislodge an air pocket.

Please see my orig post with my verbose explanation for a full picture.

Still hoping someone can explain:

Should the two MC circuits supply full braking to their independent circuits regardless of the others failure.
I explain some tests I did and the results which in my case indicate they don’t?

Thanks.

[christopher storey]

Right - I misunderstood all you had done . Have you tried just opening the bleed screw on the farthest cylinder and letting it flow by gravity - or possibly on both rear cylinders simultaneously ? Sometimes this will dislodge a bolus of air , which sounds to be possibly the problem. I am not familiar with the Kelsey system so cannot comment specifically on any hydraulic idiosyncracies of it , but I always thought it was just 2 separate masters operated in parallel, and thus ( unlike the 4.2 system ) there is no common hydraulic connection between the front and rear circuits . perhaps if all else fails you could detach each cylinder at the clevis connection to the pedal , and operate the m/c pushrod by hand so as to bleed each separately , and see whether that improves things

[mgcjag]

Hi Layne..Just to try to help until somone else comes along....im not familiar with the 3.8 setup...however I just read the brake section...there is nothing to say they are not two totaly independant hydraulic systems front/rear..you should be able to confirm this by looking at you pipe work......each MC has 2 ports one connected to its reservoir and the other to the pipework.....hope this helps.....Steve

[mtnjag]

Seem to have lost my last post so I’ll say again, may get redundant.

Have not done gravity bleed but can try on fronts since rear MC is removed now with tests results posted. I have bled assiduously so I have my doubts but can give it a try.

They are absolutely two separate systems. That’s where my head scratching comes in. No interconnect hydraulically. Only connection is a balance linkage between the two MCs and actuated by the pedal with help from vacuum. What’s funny, and not ha ha at this point, is what my test results are.

I have family in town for next couple of days so need to lay off, and perhaps the light bulb or someone else’s light bulb will pop on and figure out what’s up.

I know there’s someone that can explain how proper operation of the system relates to my results.

Really at this point I can think of nothing but somehow I screwed up a simple MC rebuild and need to replace them. Still want to understand how the failure mode of one MC effects the other.

Thanks for continued responses.
Layne

[Gerry]

Hi Layne,are you on Jag Lovers?If not I suggest you join,there are knowledgeable E type owners on there that live in your area.

Regards Gerry 62 Ots.

[mtnjag]

I’m on Jaguarforums.com but not jaglovers.
I haven’t posted anywhere else yet but you’re right, I guess I should spread the wealth. I’ll post my original and see what comes in.
But I have faith in the resources here!

[Gerry]

Tha'ts for sure Layne, both forums are great,most enthusiasts are quick to help others I am sure a couple of fellas in Santa Cruz would come round and point you in the right direction.
Regards Gerry 62 Ots.

[Tom W]

Hopefully this answers some of your questions.

The circuits are totally hydraulically independent. If one circuit were to fail, you should still have full braking available on the 2nd circuit. This would require the pedal pressing a lot further though, as the compensator has to move the actuator rod for the failed circuit all the way to the end of the master cylinder before it can transfer any force into the remaining working circuit. If the pedal reaches the floor before the 2nd circuit generates full braking pressure, then I would suggest there’s either an internal fault in the 2nd circuit, air in the system, the compensator is assembled wrong, or a miss match of master cylinder and slave cylinder sizes.

The latter is possibly the case if you have larger rear wheel cylinders but a standard size rear master cylinder. You’ll require more travel on the master cylinder to move the wheel cylinders onto the disks. Maybe you’re running out of pedal travel? If this is the case, this isn’t good. If you were to loose the front circuit on the road, you’ll have no brakes, somewhat negating the purpose of a split braking system!

[mtnjag]

Thanks, that’s what I thought but wanted to confirm.

So have seen here in other posts that you can move front 2 1/8” front pistons to the rear without changing the master since it too uses a 5/8” MC in original configuration. I have a replacement MC and they all seem to have the longer travel piston set up which was original to the system on the front brakes. Using a 3/4” master on the front Wilwoods.

All worked well before but during the refresh put rebuilt 2 1/8” at the rear and rebuilt MCs.

When I push after bleeding the pedal goes to the floor with some effort, both MCs show full rod travel, and the braking is barely enough to stop the car from 10mph.

Removed top/rear MC, blocked top linkage from moving, pressed pedal and it won’t go to floor and front brakes seem to be applying more pressure to wheel, but car is up on blocks.

This was a working system with no disassembly of the linkage other than MC RR.