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Just another thought about brake problems


CaptainBlue
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I've read all I can get my hands about Series 3 braking problems and one of the most common problems is excessive pedal travel and having to pump the pedal a few times in order to get good / fair braking. I've got a new set up, brake servo, master cylinder now a dual line system.

Does anyone know what sort of vacuum reading I should be getting from the pipe attaching to the brake servo ? i.e the manifold reading. I'm only wondering because if you have to pump the pedal a few times to get good pressure, does this mean you are not getting a decent servo assist by braking just once ? The pedal never hits the floor because it hits the front of the pedal box first. Looking at the old servo, seems there is about 3" of movement before you sort of bottom out.

All my brake shoes are adjusted spot on. No leaks in the system. I will clamp off front and rear brakes and test the pedal I will also adjust and lock up the brake shoes and feel the pedal, if hard, I've read there is no air in the system.

What do you think ? Do you have any vacuum readings to the servo ??

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The servo just makes the pedal feel lighter (or looking at it the other way- applies more force to the master cyclinder), if you're having to pump the pedal it will be air in the system, mal-adjusted or incorrectly fitted shoes.

Clamping the rubber pipes one at a time could indicate where the problem lies.

The twin leading shoes systems can be a sod to bleed, I clamp off the rubber pipes to all the wheels except the one I'm bleeding, open the nipple wide and push the pedal down quickly, the idea being to allow a rush of fluid to scoop the air out of the slave cylinde. Unfortunately the bleeding ports are on the centreline of the cylinders, not the highest point.

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I didn't have quite the same problem, my pedal felt fine but I just found the brakes to be awful, I had fitted a dual line system and a 90 brake servo to try and help improve things but they always felt terrible (compared to other lr's not comparing to cars)

I ended up buying an old peugeot vacuum pump and making up a bracket to hold it on the block (where the lifting eye bolts on) and connecting the vaccum pipe up to that, this had the advantage of ditching the butterfly valve which also had the advantage of stopping it from smoking as much.

The brakes are now spot on, and comparable to a normal car.

The only bit that's probably relevant to you here though is people told me to stop looking at the vacuum as the series 2's where fine without any vacuum at all, and they kept telling me that it would just be my drums out of adjustment or that they needed bleeding more, but I had checked, double checked and triple checked all adjustments (fitted new snail cams, new shoes, and just about everything else) and made sure it was all bled correctly.

As soon as the vacuum pump was fitted it was all solved. The pump cost me about £20 from ebay, the bracket was made out of scraps and I had to buy a new belt for about 3 quid. All worth it!

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Definitely have to clamp off rear and front brakes to see if there is any difference. Looks also like I need to bleed all the brakes individually clamping the wheel cylinders with G clamps, compressing them and hopefully limiting the space for trapped air.

You got no idea what the reading on a vacuum gauge should be from the manifold ?

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Definitely have to clamp off rear and front brakes to see if there is any difference. Looks also like I need to bleed all the brakes individually clamping the wheel cylinders with G clamps, compressing them and hopefully limiting the space for trapped air.

You got no idea what the reading on a vacuum gauge should be from the manifold ?

Should be in the range of 15-22" Hg.

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Right, solved it !

LH rear brake shoe spring was not attached properly. It was attached to both shoes. The trailing shoe is now free and when released from the spring the wheel cylinder pushed it out a fair bit. So my troubles was down to poorly adjusted shoes. :P

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