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Brakes locked solid - help needed please!


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Hi All.

 

My beautiful wife of nearly 40 years helped me bleed up the clutch and brake systems this afternoon after having had both master cylinders apart and re-kitted (plus clutch slave) as per previous posts. I decided to use Dot 5 silicon in the clutch circuit to reduce the risk of paint damage, but stayed with Dot 4 for the brakes at this stage as to change I will need to clean out the entire hydraulic system - that's for another day.

 

Anyway, when refitting the front wheels I thought it a little odd that they didn't spin freely. It was as if the handbrake was applied to the front wheels. There was also some drag on the back wheels, but this was because the handbrake was partially applied. I realised at that point that I should have released it fully before bleeding, but after checking the parts diagram decided that this should have had no real effect on the process.

 

Started and warmed the engine (its starts instantly on all 6 cylinders and runs like a Swiss watch after the throttle body balance and installation of a new choke cable) to take it for a test drive, then nearly stalled the engine as I went to back out of the shed - oops. The brake pedal has no travel whatsoever!

 

Ok, so the fronts really are locked up :(:( . Turned the engine off (didn't really want to cos she was sounding so sweet just idling away there), and broke the vacuum at the booster non-return valve seal, but no change, still a full hard pedal.

 

The brakes were fine before I started apart from the leaking master cylinder, so something has changed since then :unsure::unsure: .

 

Any thoughts from members as to what I may have done wrong and/or what may be causing this? I should mention that the entire brake system was overhauled 7,000km ago and the front pads are like new.

 

Oh, and the clutch works fine....

 

Gavin

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Further to my query, I've since removed the master cylinder from the booster to take make sure there isn't any pressure from a mis-adjusted push rod (although I haven't changed the adjuster) and the front brakes remain locked solid. I'm now starting think that the issue is the master cylinder which I sent off for rebuilding after I found it was leaking. Grrrrrrrrr... :angry::angry:

 

I'll open the bleeds on the calipers next to see what happens.

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Since both are locked, it is reasonalble to assume you're right with the master cylinder. Although I have no idea how.

At first I thought of an internally collapsed hose. But two at the same time? No.

I had this with the clutch of my 3A when I first bought it. The internals were so brittle. Fluid was allowed to pass to the clutch, but the debris blocked the return. As said: not likely that it happens with two at the same time AND if it would happen at the same time, the chance that it's equally firmly locked at both sides is too small.

 

Back to the cylinder would be my guess

Edited by Menno van Rij 2
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As Menno says it does sound like a Master Cylinder issue but unsure why the rear brakes also are not binding so much.

 

It is easy to assume it has something to do with the new/recon parts but may not be. You might find that where you have pressurised the pedal several times quite hard the pads are now binding in the front calipers. It would be an idea to see if you can return the pistons in the caliper bore with moderate leverage, remove the pads and ensure that they move freely in the housing. Clean off and apply a little copper slip on the edges which touch the caliper if necessary. Refit and pump up the pedal before starting of driving.

 

When pushing the pistons back, ensure you watch for spillage from the master cylinder cap and clean off straight away.

 

Kevin

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It will be the tipping valve :angry: remove cap and press the pedal does the fluid move?

 

Thanks Neil. I've got the master cylinder in pieces and think I have found the problem - a combination of factors perhaps.

 

First question though. Is the tipping valve in the photo below the correct part for this MC? It doesn't seem to tip much at all, which may be either because it's not the correct type, or (more likely) because the stainless sleeve is limiting its movement (see the second photo).

 

In addition, after taking some measurements it appears the actuating rod is holding the piston in by 0.5 -1.0 mm even though its adjusted correctly according to the Haynes (yeah, I know :D) manual.

 

So assuming the tipping valve is correct, then an adjustment to to the pushrod to get the correct clearance and grinding of the port in the stainless sleeve are both required.

 

Comments welcome as usual.

 

post-14246-0-41696300-1490083101_thumb.jpgpost-14246-0-51475400-1490083138_thumb.jpg

 

Gavin

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Problem solved!



Filed away the edge of the stainless sleeve protruding into the tipping valve opening, cleaned up the inside lip of the cut with my Dremel using a small grinding wheel and reassembled all.



Re-checked clearance to the pushrod end which measured up OK, but also cut a gasket to fit between the MC flange and booster to give me another 0.5mm clearance without having to adjust the rod end. Figured I can easily remove it later if deemed necessary.



Bled the system up again and carried out some short road tests and everything seems to be back to normal - thanks again Neil :D:D



Regards to all.


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