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jim fl4

Help, Bedford OY brake problem

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Hi All,  I'm having lots of fun with the Bedford OY brakes.  Basically I am only getting a very low braking effect.  On a test drive on grass its impossible to lock any wheel and the braking effect it the same down a hill REGARDLESS of whether the engine is running or not.  The servo makes the engine surge slightly but has zero effect on the brakes.

All the brakes at each wheel have been thoroughly gone over, bisectors, adjustors, wheel  slave cylinders all 100% good.  All the shoes are in nearly new condition, no contamination, all the drums are like new as well.  All the pipework is copper, the flexi hoses are in good order and clear of any blockage.  Strangely, when bleeding the fronts the fluid would barely dribble out of the bleed nipple even though I was standing on the pedal, (which did not go to the floor but stayed in the usual position)! successfully bled nevertheless.

So, that now only leaves the master cylinder and/or the servo, unless you think different?

I shall be removing the combined servo/master cylinder tomorrow, I've never done this before so any tips would be appreciated.  I will strip then down, again never done that before so any advise welcomed.

Only 2 weeks to the YWE which I've promised the organiser I will attend so getting a bit worried now :).

Thanks for reading, Jim.

 

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Have you tried pressure /vacum bleeding the system to make sure there is no air trapped?

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2 hours ago, Tony B said:

Have you tried pressure /vacum bleeding the system to make sure there is no air trapped?

Hi Tony, thanks for your reply.  No I have not, but when checking all the cylinders to see if their pistons were free little or no fluid was lost.  I did open the bleed nipples after on those cylinders dismantled and bled the usual way.  What gets me is that when doing the bleeding on one of the fronts the pedal refused to go to the bottom or even any lower than the usual and the usual travel is minimal, ie a very good pedal you would say.  I will be out shortly to check if the linkage is all free at the master cylinder end and then remove the servo/master assembly. I will report my findings here, thanks again.

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13 hours ago, jim fl4 said:

 Strangely, when bleeding the fronts the fluid would barely dribble out of the bleed nipple even though I was standing on the pedal, (which did not go to the floor but stayed in the usual position)! successfully bled nevertheless.

 

 

Jim,

I note what you say about one bleed screw only dribbling. It is entirely possible it is blocked by dirt or rust. The only way to be sure is to remove it so you can check if the cross-drilling at inner end is clear. Not unusual to find this. Put a clamp on the hose so as not to lose fluid when removing the screw.

regards, Richard

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57 minutes ago, Richard Farrant said:

Jim,

I note what you say about one bleed screw only dribbling. It is entirely possible it is blocked by dirt or rust. The only way to be sure is to remove it so you can check if the cross-drilling at inner end is clear. Not unusual to find this. Put a clamp on the hose so as not to lose fluid when removing the screw.

regards, Richard

 

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Just now, jim fl4 said:

 

Hi Richard, thank you for your message.  I did remove the nipple completely which didn't make any difference.

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Jim, 

could be the hose has de laminated in side and acting like a valve shutting off the flow.

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18 minutes ago, Richard Farrant said:

Jim, 

could be the hose has de laminated in side and acting like a valve shutting off the flow.

Checked the hose, all clear no blockage, the problem is one of a poor/low brake effect to all 4 wheels with no difference whether the engine is running or not. No vacuum leak from the induction manifold to servo.  Just got this off, only have the army manual, a small A5 booklet with not much detail on striping the m/c or servo.  Does anyone have an advise on stripping etc these? thanks again, Jim.

PICT0957.JPG

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Hi again.  Decided to just have a go and removed the m/c and stripped it down.  All looks remarkably good, all the seals look quiet good, the outside gaiter is life new.  I cannot see a problem.  The only things ive not removed are the check valves for the front and rear outlets, do I need to remove them anyone? Would you recommend I fit new seals?

Next stripped the servo down. Not too bad a job and found a big problem.  The big piston had stuck in the bore and their was a lot on gunge in behind where the big spring goes.  So, no wonder the servo was not operating.  Could this be the sole problem?  The manual says the brakes are just as effective without servo assistance, just more pressure has to be applied by ones foot!  Any thoughts guys much appreciated as always.  Heres a few pics in the order of work, ie. the last is of the cleaned bore.

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Jim,

You can get a new leather piston seal and the little rubber valve discs from Bygone Bedford Bits.

regards, Richard

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