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Moss Motors front brake calipers [BJ7 to early BJ8]

pschauss

Freshman Member
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Has anyone used these (Moss part numbers (021-155/021-154)? I just installed these and, after several attempts at bleeding the system, the brake pedal still goes half way to the floor before it gets firm. I am wondering if there is a mismatch between my master cylinder and the new calipers.

Everything was working properly before I started this process but I could see that the rubber seals on the old calipers were starting to deteriorate.

thanks,
Peter Schauss
1963 BJ7
 

steveg

Yoda
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You may still have air in the system.

There shouldn't be such a thing as a mismatch. I'm sucessfully running a Fiat dual-circuit master cylinder with Toyota calipers on the front and Jag calipers rear - with silicone brake fluid. Bleeding was the only problem until I adapted a version of Randy's recirculating bleeder tube to get the final air out of my master cyl. That's discussed in another thread - see:

https://www.britishcarforum.com/bcf/showthread.php?104910-Bleeding-Brakes!&highlight=bench+bleed
 

Joe A

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I purchased my front calipers and rear brake cylinders from Moss and found the bleeding process pretty simple with the use of a Gunson Eezibleed system.

Steady air-pressure prevents the sucking in of air that may be experienced when a second person pumps the brake pedal.

I too use silicone brake fluid.

~ Joe
 

healeyblue

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Are your bleeders on the top? I know it is a silly question but I have seen it many times on forums with people not noticing and have the right and left side swapped with the bleeder facing down and it traps air that can not be bled out.
 
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Filling up new/rebuilt empty calipers has always__in my experience__been a multi attempt process. You get the bulk of the air out the first couple of times, but due to high surface tension, can be a bear to get some of those last few bubbles out during successive bleedings.

If you have a pressure bleeder (it does not take a lot of pressure, 12-15 psi is plenty) open the bleeder just a small amount so that the fluid is just trickling out, and tap around the caliper with a small hammer. I can often see the tiny pockets of air surface.

Assuming that you have a decent, if not great pedal, put some test miles on the car and repeat those last steps again.

You just have to keep telling yourself that you're smarter than the car, even if at times you don't believe it yourself! ;)
 
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pschauss

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The guy at the Moss Motors hot line said that the problem might be that the pistons were stuck to the rubber seals. They have been having this problem with some of the calipers (for multiple makes - presumably from the same supplier). The solution he suggested was to remove the calipers from the car, insert a piece of plywood about half the thickness of the disk, and have someone step on the brake pedal. This, he said, should free up the pistons since they would now have more room to travel.

I tried a variation of this leaving the calipers mounted and replacing disk pads with a piece of cedar shake. The pedal went right to the floor at first but then came back up as the pistons freed themselves and compressed the cedar shake fragment against the disk. I still had to remove the calipers so that I could use a C-clamp to push the pistons back in, far enough to get the pads into place.

Thanks for all of the suggestions.

Peter Schauss
1963 BJ7
1980 MGB
 

Jack T

Jedi Hopeful
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The guy at the Moss Motors hot line said that the problem might be that the pistons were stuck to the rubber seals. They have been having this problem with some of the calipers (for multiple makes - presumably from the same supplier). The solution he suggested was to remove the calipers from the car, insert a piece of plywood about half the thickness of the disk, and have someone step on the brake pedal. This, he said, should free up the pistons since they would now have more room to travel.

I tried a variation of this leaving the calipers mounted and replacing disk pads with a piece of cedar shake. The pedal went right to the floor at first but then came back up as the pistons freed themselves and compressed the cedar shake fragment against the disk. I still had to remove the calipers so that I could use a C-clamp to push the pistons back in, far enough to get the pads into place.

Thanks for all of the suggestions.

Peter Schauss
1963 BJ7
1980 MGB

Wow. That wouldn't give me much confidence that it wouldn't happen again if the car sits for any length of time. Sounds like there is an issue with the tolerances of the pistons and seals that needs to be addressed.
 
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