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MGA MGA Master Cylinder rebuild problem

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Randy

Randy

Freshman Member
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Hi I've rebuilt my 59 MGA master cylinder, as well as replaced all wheel cylinders and also changing to dot 5. my problem is when I depress the brake pedel it doesnt return for a few minutes same condition on the bench any suggestions?

[ 12-13-2003: Message edited by: Randy ]</p>
 
Did you replace the hoses? An old hos emight collapse internally on the return.
Check the linkage on the pedal box. Did you overtighten the pivot bolt perhaps?
 
Hello Randy,

I take it that you mean if you push in the piston with the M|C on the bench it is very slow to return. If so what did you lubricate the seals with during assembly?, (I assume the internal spring is serviceable?)
If an unsuitable fluid is used to install the seals they may swell and be too tight, which will mean replacing them again.

Alec
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I take it that you are using silicone brake fluid? The same thing happened to me and I went back to Casterol LMA and raced with that. I never had any fading problems.

SB
 
From what I understand silicone brake fluid has a higher viscosity than other brake fluids.
When the brake pedal is released, the return spring within the master cylinder pushes the piston back to its normal position. However, for it to do that, the brake fluid needs to flow through several small holes that are drilled in the piston and then pass around the outside of the master rubber cup seal. There is a dished washer that fits between the master rubber cup and the piston. This pushes the piston away from the master cup seal slightly, which enables fluid to flow between the piston and the master cup when the pedal is released. Check to see if the seal and the dished washer are installed properly.
I guess if the dot5 fluid is the culprit, you can try installing a stiffer piston return spring (or stretch the spring out longer) and put a more pronounced curve in the dished washer. I don't know whether or not enlarging the small holes in the piston would really help. Besides, I think the pistons are hardened steel, and you would end up breaking drill bits anyway. Good luck!
 
Also, make sure the compensating port is fully open. This is the little tiny hole that lets the fluid in and out of the cylinder itself a s you stroke the pedal to build up pressure. Seen lots of them plugged on old nails. Sometimes corrosion, sometimes rubber bits. Poke some fine wire/ paper clip through the hole to make sure.
 
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