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Brakes Locked Up

Greggers

SAOCA Vice President
Platinum Level Sponsor
I had a brake master give out on me. Seals leaked, brake fluid everywhere. Cool.

So, per recommendations around here, as my S5 had its booster bypassed long ago, I ordered and installed a Series II master. Bench bled. Installed. After what seemed like too little bleeding, I had solid pedal feel, like almost zero movement (odd for SII master in an S5). The wife called me in for dinner, so I went to roll Miss Moneypenny into her parking spot and she wouldn’t budge, all four wheels locked. Long story short, the brakes aren’t releasing.

Here are some of the things I’ve done and their results:
1. Removed the drums - return springs are in place and fairly new.
2. Removed the master to bench - sprays fluid, springs back.
3. Reinstalled the master - locks up (albeit less so, as I didn’t rebleed)
4. Inspected the hard line to the pressure switch -no kinks.
5. Removed the hard line - sprays fluid, master springs back.
6. Hooked the hard line back up (master on but not installed, worked by hand) - fronts locked, rears not.
7. Reinstalled everything - four-wheel lock
8. Readjusted rears, rebled everything - everything locks except right rear.
9. Readjusted left rear - fronts lock.


Usual suspects:
1. Rod length - irrelevant, as it’s doing the same behavior on or off the firewall.
2. Collapsed brake hose - those were replaced with stainless braided five or so years ago.
3. Kinked hardline - nope.
4. A vengeful God punishing me for past indiscretions - repented, no change.

Any ideas?
 

sunalp

Diamond Level Sponsor
Greg,
I'd re bleed the brakes and the rod length does matter. You should have some free travel on the pedal.
It shouldn't be rock hard with no movement. There is a measurement of how much play you should have
and I'm sure it's in the WSM ( and I'm sure someone will chime in with it too) but it has to be there.

I know my SV is very sensitive to this as my brakes were locking up when I changed the brake light switch
to one that works off the pedal. There wasn't enough free play to allow the master to move the fluid so it
stayed locked. Think about the fluid, it works on pressure and when released, the fluid has to go somewhere
and in your case, and mine, it wasn't moving.

Hope that at least get's you in a better place.
Cheers!
Steve
 

Tom H

Platinum Level Sponsor
1. Rod length - irrelevant, as it’s doing the same behavior on or off the firewall.

Quite odd. You mean even with the MC unmounted, with no pedal connected to it, the brakes are locked? I assume you then released the brakes by opening one (or all) of the bleed screws, in order to remove the rear shoes. If so, it sounds to me like a messed up MC. Is it a new one ? Or a used one that you just rebuilt? Maybe the wrong piston? Clearly the MC is holding pressure even when released. Sounds like the "valve seal" on the end of the piston plunger is not releasing.

Don, in Greg's original post he says "bypassed booster"

Tom
 
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Greggers

SAOCA Vice President
Platinum Level Sponsor
Quite odd. You mean even with the MC unmounted, with no pedal connected to it, the brakes are locked? I assume you then released the brakes by opening one (or all) of the bleed screws, in order to remove the rear shoes. If so, it sounds to me like a messed up MC. Is it a new one ? Or a used one that you just rebuilt? Maybe the wrong piston? Clearly the MC is holding pressure even when released. Sounds like the "valve seal" on the end of the piston plunger is not releasing.

Tom

It’s a brand new SI/SII master from CS.

With the master unmounted, the hub spun freely, pump, less freely, pump, very less freely, pump, locked. Makes some sense, given that it needed bleeding when it was reconnected. Bled all three front to back. Fronts were locked. Cracked the driver’s side. It spun with some drag, front right less so. Cracked the front right, it spun with some drag. Front left, now locked. Rears now have some drag. Bled all three again, this time back to front.

There’s virtually zero pedal play unless I’ve bled off the residual pressure somewhere. But it builds right back up with a few pumps. Full travel of the pedal is maybe 2” (unless, of course, there’s a bleeder open).

I pretty much work on it for a while, crack a bleeder and roll it back to its parking spot.
 

Tom H

Platinum Level Sponsor
I'm 95% sure the problem is in the MC. Something is wrong inside it. It fails to release when the rod is un-pushed. I'm no brake expert, just a logical problem solver.


Tom
 

RootesRacer

Donation Time
Sounds very much like the MC piston is not letting the fluid back into the reservoir when the pedal is released. This usually is becuase the linkage is too short or the pedal set in the high position.
Also,SI/SII MCs used a spacer, omit it without mods to the pushrod length can cause exactly this issue.
 

Greggers

SAOCA Vice President
Platinum Level Sponsor
Sounds very much like the MC piston is not letting the fluid back into the reservoir when the pedal is released. This usually is becuase the linkage is too short or the pedal set in the high position.
Also,SI/SII MCs used a spacer, omit it without mods to the pushrod length can cause exactly this issue.

My SV had a spacer, so I swapped that over. The new master has an adjustable pushrod, which I set to the same distance from the spacer as on my previous master. The pedal starts out at about .5” above the clutch. After a few pumps, it lands and stays about .5” below.

Theoretically, I could pull the pedal up to reclaim that inch (and pull the pushrod out to its previous/more normal position). I cannot.

Also worth noting, with the pedal unhooked and by simply pressing the pushrod by hand, I can make the brakes fairly locked (and the no release situation keeps them that way).
 

Tom H

Platinum Level Sponsor
Sounds very much like the MC piston is not letting the fluid back into the reservoir when the pedal is released

Agreed. Again I say I am 95% sure the problem is inside the MC. I ma betting that when the MC was assembled someone messed up and something is messed up. Disassemble the MC and compare it to the drawing and description in the WSM.124. Or call SS and see what they say.

Does your MC have a cast in reservoir, like Fig 8 section K of WSM24? Or like the LHD insert on Fig 8 ? Or like Fig 18 , a Rapoer MC?
 
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Greggers

SAOCA Vice President
Platinum Level Sponsor
Agreed. Again I say I am 95% sure the problem is inside the MC. I ma betting that when the MC was assembled someone messed up and something is messed up. Disassemble the MC and compare it to the drawing and description in the WSM.124. Or call SS and see what they say.

Does your MC have a cast in reservoir, like Fig 8 section K of WSM24? Or like the LHD insert on Fig 8 ? Or like Fig 18 , a Rapoer MC?

The new MC, being for Series II, was intended for an MC-mounted reservoir. Mine, being a dual Strom SV, is set up for a remote mount. I had to change the fitting inside the reservoir to my old one. The new one was set crudely cut off, presumably to clear something inside your typical SII MC, and the fitting hit the shoulder before the bubble flare on the hardline hit anything. My old remote hardline (connected to new MC and reservoir) had to be pretty tight at both ends to... um... minimize leaks.
 

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Tim R

Silver Level Sponsor
I had a similar problem, it was the rod length. A new MC was fitted that required the re-use of the original rod but with it cut down to remove the 'bulge'. It was cut ⅛" too long and as a result the brakes would go on but not release, this totally locked the system. I would release the pressure by undoing a fitting and things would be good, apply the brakes and everything was solid again. When I got the rod the correct length it all worked correctly again.

Tim R
 

Tom H

Platinum Level Sponsor
Tim, Greg says he has the problem even with the MC unmounted, no pedal connected. There must be a problem inside the MC. Something is wrong regarding parts 3,4,5,6,or 7 shown in Fig 8 in the WSM124.

From the WSM "With the final movement of the plunger the seal is lifted from its seat allowing free flow of fluid between the muter cylinder reservoir and wheel cylinder." This action is apparently not happening. Return spring (#6) too short? Valve stem ( #7) too long? Something is wrong. Looking at Fig 8 again, you can see that if something prevents the plunger from coming all the way back it will not be able to pull on the Valve stem, which would then not open the seal and let the pressure on the line be relieved. Could be something as simple as the dished washer (#13) installed backwards, or maybe the clip on the end of the plunger is loose and not able to pull the valve stem.

Tom
 
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mikephillips

Donation Time
Look at the back end of the piston of the original and the replacement. Bet what you'll see is that the piston in the original has a deeper "dish" to it than the replacement. Which means that the original pushrod is slightly longer past the bulge for the retaining washer. So with a shallower dish to the piston which an earlier one has installing the later pushrod will move the resting position of the piston slightly further forward which will cause the hole for bleeding fluid back at rest to remain sealed. So I'd say you either need and early pushrod or to take an original and cut to end off until when installed you have a slight amount of play before you feel it push the piston.
 

Tom H

Platinum Level Sponsor
Mike, Does your explanation assume that the new MC does not include a new pushrod and the user needs to use his old pushrod ? Or are you simply noting an error in the new MC.
Greg, if you are using your old pushrod on the new MC, I think Mike's explanation may be correct. But if not, then there is something wrong in the MC you bought, as I noted above.
 

Greggers

SAOCA Vice President
Platinum Level Sponsor
Attached are some images. Shiny and new are what I’m using. Dirty and old (with parts missing) is on its way to the bin (I know, keep it, sleeve it, White Post Apple Hydraulics). Fun aside, they clearly show the difference in size between the stock SV compared to the SII.

After disassembly, I shot some air in either side (and blocked the opposite), and it came out the plunger end. After reassembly, I shot air in the reservoir side and it came out the brakes side. I shot air in the brakes side and it didn’t go anywhere. So I pushed in on the pushrod, and the air forced it right back out.
 

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Bill Blue

Platinum Level Sponsor
Greg, Tom H has it nailed. There is something inside the MC that is keeping the piston from returning all the way, causing fluid to be retained in the lines. Over the years, I've had the same issue. Can't recall the details, but for some reason the piston was not returning properly.

Bill
 

Tom H

Platinum Level Sponsor
I shot air in the brakes side and it didn’t go anywhere. So I pushed in on the pushrod, and the air forced it right back out.
Unless I misunderstand something, this means you can see why the brakes do not release. If it were working properly, it seems that once the piston got pushed back far enough, it would release the pressure back into the reservoir. See the description in the WSM. Call SS and see what they say.

Your photo does not show the push rod retaining washer on the new assembly. What does it look like? Is it dished like the original? or is it on backwards?
 
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