Hi there, I recently changed the cylinders on the front wheels of my A7, which has the 1960s Morris hydraulic conversion two of them were a bit rusty one being seized. So whilst I was there, I bought new shoes and had the Girling drums cleaned up and take out the ridges. The problem that I have after a good bleed is that with the car jacked up and my wife applying the brake pedal I can turn the front wheels with a bit of effort by hand. Could it be the master cylinder not effective? although it's not leaking. I have checked the wheel cylinders which move in and out by about 1/8 is that good or bad. The snail adjusters are fully turned out.
The minimal bight that I do have is at the end of the travel on the foot brake
I would appreciate any help.
Regards RPM
26-04-2021, 06:25 PM (This post was last modified: 26-04-2021, 06:28 PM by Duncan Grimmond.)
You may find that the master cylinder is not large enough for the work it expects of the slave (brake) cylinders. I had this problem, all air bled out and only minimal bite at the limit of travel on the pedal. A larger diameter maser cylinder cured it. Can't promise this will work for you...
The diameter of the cylinder is usually stamped on the outside
(5/8, 3/4, 7/8")
I second Duncan’s diagnosis. Exactly the same problem on my old special. I ended up with a 7/8” master cylinder.
However I don’t like the idea that the cams are full out and with 1/8” slave cylinder travel. It gives no room for bedding in or wear. Have you cleaned up the drums a bit too much? I would check the drum diameter. What thickness are the linings?
There are two types of brake cam (see photo) check you have the correct one, also check the drums have not been over skimmed your cyl pistons should not have to move 1/8" the cam adjusters should lock the brake before they reach their limit then back off one click with worn linings and over skimmed drums they will go over the top of the cam. Terry.
Did it ever work with this master cylinder/wheel cylinder set up?
Does the pedal rise with pumping? - as many have found bleeding the front can be a challenge
Have you chalked the linings to see how much contact you have between the lining and the drum? Won't be much if the drums are well worn/have been skimmed a few times. If there's very little contact area it won't be difficult to turn the wheels with the pedal pressed.
You can shim the flat bottom of the cam where it seats against the wheel cylinder. A strip of ali can be wrapped around each end of the cam base to keep it secure in use.
HI RPM,
This is a common Problem when you purchase standard shoes they have been sized to fit standard drums allowing for small amount of wear to the drum.
In my opinion the correct way is to measure drum inside Dia and if there is enough thickness have the drums skimmed all to the same size,
Then have the shoes relined with a thicker material and reground to the new drum Dia
you will find when fitted the adjusters will have returned to standard allowing for full adjustment
PS
Any machining of the drum will increase dia so the lining has to be Radiused to the same dia otherwise you will not get at least
90 percent contact between drum ad lining
