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MG Midget and Sprite Technical - Frogeye brakes

I recently completed the rebuild of my frogeye. I kept the original braking set up of drum brakes.
I adjust up the shoes to correct clearance and then go out for a run but after around 5 miles performance dips and the brakes are hot to the extent that the brakes sieze on and the car cannot be pushed. I left the car for around 20 minutes and rechecked and the brakes had freed up and I was able to start again and limp home.
On arriving home I took off the hubs cleaned out the worn brake dust and readjusted but with less turn on the snail cam but the same thing happened even when the adjustment is turned right off.
It seems to me that when the brake pressure is applied it is not releasing so then when you again press the brake pedal more pressure goes on and eventually the brakes sieze solid.
The only modification from original is that I have fitted Aeroquip flexible hoses. master cylinder is new and all lines brake shoes, drums, cylinders etc are new.
For such a simple system this has got me baffled, any ideas??
Dave
DW Rochford

I had this on an IMP (drums all round)
the push rod between the pedal and the MC piston didn't have enough free play. When it got warm the fluid expanded and dragged the brakes on (which made it worse then they locked). You really notice dragging brakes in an IMP!

The instant roadside fix was to release the bleed screw, when it would split a little fluid out, and return to normal.

My fix was to make an adjustable MC push rod, this needed at least 1mm of 'slack' to (I'm guessing) ensure that the piston was far enough back to uncover the return hole to the resovoir.

HTH

Rob
robnrrugby

Dave,
My Frogeye did the same thing when I first rebuilt it. The cause was the length of the pushrod in the master cylinder. Inside the bore of the cylinder is what I would call a breather hole. This releases pressure to allow the piston the move in the cylinder. If the pushrod isn't adjusted correctly, the hole in the bore doesn't release the pressure and brakes stay on. It requires a simple adjustment of the adjuster nuts on the end of the push rod where it attaches to the pedal. There is a measurement that provides the ideal position but I did mine by trial and error.
Neil
Neil (K series)

Rob / Neil
Thanks for the quick response. It certainly sounds like that is my problem and it doesn't sound too difficult a fix.
Thanks for that i will let you know how i get on
Rgds
Dave
DW Rochford

Thanks to all,
I checked the pushrod to master cylinder and immediately saw that the pedal adjuster with the lock nut had been left loose and had jammed under pedal link and was keeping pedal on.
All is now tightened up and hopefully after adjusting brake shoes again we should be OK.
Thats a job for the weekend!
Thanks again
Dave

DW Rochford

Good news Dave. Glad you are working towards the solution.
Neil
Neil (K series)

This thread was discussed between 08/06/2010 and 09/06/2010

MG Midget and Sprite Technical index

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