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Front Brakes - Help


Richard Grove

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Hi,

 

I need some help / advice on brakes. I am completely stumped, have tried everything and spent hours researching possible solutions but just can't figure out what is wrong.

 

We are building a Robin Hood 2B with 2L pinto for my son and its almost ready for IVA. We can't get even close to a good brake pedal feel. With the engine off the brakes feel very spongy, with the engine running and the servo working the pedal just goes to the floor.

 

Our set up is standard RH 2B i.e Sierra pedal box with Servo fitted, 22mm Master cylinder and Teves style calipers. The calipers and the master cylinder are new.

 

With 3 bleed screws blocking outlets from the master cylinder the pedal is solid so we have concluded the master cylinder is OK.

 

With 2 bleed screws blocking the front outlets from the master cylinder and the rear brakes connected and bled the brake pedal is solid so we have concluded the rear brakes are fine and the problem must be with the front calipers.

 

On the front we have 240mm vented discs with new pads. We have bled the brakes to death and are convinced there is no air in the system and the calipers are fitted the right way round with bleed nipple at the top.

 

We have lubricated the caliper pistons to ensure the seals are not sticking to the piston. We have checked the entire system for leaks and found none.

 

To test the servo I start the engine while foot is on brake pedal and feed the brake pedal move down as the servo vacuum is created so the servo is working OK.

 

We have been pulling our hair out for two weeks trying to work out why the brake pedal is so soft. When we press the brake pedal there is no bulging in the flexi hoses and the calipers can be seen moving on the guide pins as they clamp on the disc and then release.

 

Only thing I can think of is perhaps we have the wrong size caliper? Our Teves calipers have 50mm diameter pistons. Did they make calipers with smaller piston?

 

Couple of pictures attached. Why can't we get a firm pedal?

 

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Thanks

 

Richard

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Difficult one. The pic shows the right front calliper. Common problem is having them on the wrong sides which puts the bleed nipple at the bottom so fails to bleed air out of part of the calliper. However the right front is correct. Check the left front also has the bleed nipple uppermost and you haven't by chance got two right callipers on there.

Fitting the dust boots can be awkward and increase retraction of the pistons. This can give a long pedal that suddenly firms at the end of the stroke.

 

Nigel

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Going to remove the calipers again tomorrow and measure the piston properly. Been researching and there are 54mm and 60mm versions so need to check this.

 

Also going to try pushing the pistons back into the caliper and then putting a spacer between the disc and pad so that the piston does not have to move out as much before clamping. Will see if this gives a better feel to the brake pedal.

 

Thanks

 

Richard

Edited by Richard Grove
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is the pinto injection just a thought but the servo needs vacuum i think, not sure how the injection system works my cossy needs a pump for the vacuum.

are the front callipers running out of travel. have you checked the pipework and it all goes were its supposed to ie you havent got a back and one of the front ones crossed.

cant remember but does the back on have a bigger connection.

Paul

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Ahh, spring on the carrier not the pads as they should be

Other thing to check is that the pads slide easily in the carrier

You have painted the carriers black and may be the pad is scraping the paint on the sliding surfaces, I have these bare metal and use a thin wipe of copper grease

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Mitch, I think you might be right - when brakes are applied there does seem to be too much movement of the caliper but I can't figure out how the spring is supposed to go. Anyone got a picture of the correct fitment.

 

Thanks

 

Richard

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What can happen if one pad is jammed in the carrier is the slack is taken by the loose pad then when the slack is taken up it forces the other to drag in slowly giving a soft feel

With all you have done to check I can only see it being a pad sliding in the carrier problem

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Just checked on mine and the springs seem exactly as you have then. The mid loop of the spring does not rest on the pad on mine. Its about a 3mm gap. I would clean the contact parts of calliper and slider where the pad ends slide and add a touch of brake grease. Contacts in white.

 

Nigel

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Guest mower man

Cat among the pigeons time !!!!! throw the bloody awfull sliding calipers in the skip and go to Hi-Spec brakes ,light weieght 4 pot calipers and pads and apair of vented discs around £300 fit and be happy mower man :crazy:

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Well I now know the problem must be the calipers themselves. We clamped the flexi hoses just before they enter the caliper and brake pedal is solid. We have scraped all the paint off the carriers etc and copper greased so the pads are sliding freely. Retaining springs are correctly fitted.

 

Back to the garage after lunch but I am starting to think new light weight 4 pots is the way to go.

 

Richard

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Bob,

 

The servo & master cylinder are mounted in the standard position for a 2B. There just seems to be far to much movement within the caliper itself. They are new re-manufactured calipers so we plan to strip them down on the work bench this afternoon to see if we can find any problems inside.

 

Richard

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