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MG MGA - Bleeding Clutch and Brakes
|As mentioned in another thread I recently bought an MGA that's been off the road for 14 years. One of the reasons it was never put back on the road was the hydraulic system. I don't want to start it until I know I have brakes and a clutch.|
I rebuilt my master cylinder and I'm now trying to bleed the system (I'm using silicone brake fluid if that matters). I'm working with my wife and I think she understands what "pump" and "hold" mean...but we're not getting anywhere fast.
Right now the brake pedal will go to the floor on the initial press, then pumps up and seems to stay pumped up as long as you have pressure on it. I have been around the car three times bleeding them one at a time, left rear, right rear, left front, right front, and don't see any bubbles coming out anymore.
I've bled the clutch slave cylinder several times and even removed it to press the piston up with a screwdriver and bleed it that way. When my wife pumps the pedal the piston moves the rod a bit less than a 1/2" but I don't know if that's enough.
Is it just a matter of going over and over the bleeding or should I assume the master cylinder needs replacement?
(I've replaced both rear brake cylinders, both front calipers and the slave cylinder).
|Need to adjust all brake shoes up close to the drums. Hang brake cable must be slack when you do it. Also check to be sure you have the proper 7/8" bore master cylinder, not the 3/4" bore unit. Is it front drum brakes or disc brakes?|
It's got front disk brakes (brand new calipers and bleed screws are on top)...rear brake shoes are adjusted up close and emergency brake cable is slack.
Any other suggestions? Have I just not bled them enough times?
|Check to be sure you have the proper 7/8" bore master cylinder. Sometimes a 3/4" bore unit form 1098cc Spridget may find its way into an MGA. The smaller bore master cylinder makes for long pedal travel, stuff the brake pedal in the carpet on the first stroke, and less than 1/2 inch of travel on the clutch slave. The master cylinder should have "7/8" cast on the side, but you may have to extract it from the mounting bracket to read it. Otherwise remove two screws to remove the end plate from the master cylinder, and measure the piston or the bore. Occasionally a 3/4" unit gets re-bored to 7/8". More rarely a 7/8" unit might be sleeved down to 3/4". Fore some special applications it may have one 3/4" bore and one 7/8" bore (never a factory style).|
If it is 7/8" bore master cylinder, and brake shoes are adjusted close to drums, then there must be air in the system. I have never had any problem bleeding hydraulics on the MGA, but it is a matter of technique. In essence, you need to move fluid through the lines quickly enough to carry any air along with it to the bleeder. If you have a short spurt of fluid followed by a long pause, air may bubble back up the line and never be ejected.
My favorite technique (with two people) is to open the bleeder one turn and put your finger over it to serve as a check valve. Then have your helper pump the pedal multiple strokes to flush the entire length of the line, then hold the pedal down while you secure the bleed nipple. Very quick, and you only need to open he bleeder once. Don't let the reservoir run empty.
This technique may result in fluid spraying about. You might connect a hose to the bleeder, put your finger over end of hose and hold it in a catch pan. You might otherwise put the hose in a bottle with the outlet and of the hose below fluid level.
If all else fails you can reverse bleed the system. Use a MityVac or a trigger pump oil can to push fluid into the bleed nipple to force flow and air back up line to the reservoir.
If you have a long hose you can connect it between the clutch slave bleeder and one of the brake bleeders, open both bleeders, and use the clutch to pump fluid to reverse bleed the brake circuit. This works the other way to reverse bleed the clutch as well. It is really slick in the MGA with the common fluid reservoir, as you don't lose fluid, and the reservoir never runs over or goes empty.
Double checked rear brakes and readjusted them tighter. Bled them several more times along with the clutch. Much better now. While still on jack stands I started the car and tried shifting into gear...no go....clutch disk stuck to the flywheel. Tried the tricks on Barney's site, especially letting the car warm up well and it finally came free.
Tomorrow the car will be back on the road for the first time in 14 years!
This thread was discussed between 16/11/2012 and 17/11/2012
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