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MG MGA - Disc Brakes with MGA Master Cylinder
|I have an MGTD with an MGA master cylinder, MGB disc brakes in the front and MGB drums in the rear. |
First of all, the pedal is very hard and secondly, the drum brakes grab before the front discs. Does this mean I need a residual valve, or are there other issues. I have seen articles about putting MGB disc brakes on an MGA, which is almost identical to my situation, except the body is a TD. The master is of course below the front calipers. I wanted to get some feedback before I go ahead with putting in a residual valve.
The car has complete MGB running gear, rack and pinion steering, engine and tranny and it is a great car with plenty of performance. It just requires a LOT of brake pedal pressure, and there is no room for a booster.
|Maybe you have a sticking caliper piston(s) or a delaminating hose(s)?|
the fact that the rear brakes grab first and yet you still have a hard pedal seems strange to me. Is the brake point high on the pedal? Or does it need pushing almost to the floor?
|Are you sure it's an MGA master-cylinder? The MC for the MGA 1600 has two pistons and an enlarged reservoir on the top. Would be difficult fitting that peddle box of a TD.|
|This sounds like you may have no front brakes, or something very wrong up front that is reducing braking force. There is no way the rear brakes should ever lock up before the fronts.|
A casual suggestion (and be very careful doing this). Put a clamp on the rear brake hose to disable rear hydraulic brakes. Be sure the hand brake works, and take it easy on the first test drive. Let us know how the front brakes work without the rears.
An MGA master cylinder properly built and functional has a residual pressure valve included in the brake side cylinder. This retains about 8-psi residual pressure, which is plenty to handle the low position of the master cylinder in the TD. No additional RP valve is (or should be) required.
That said, recent issue Lucal/TRW master cylinders for MGA have a faulty non-return valve that holds too much residual pressure (about 12-psi), and that makes front disc brakes drag badly.
|I don't see the suggestion here (sorry if I'm repeating), but maybe you should try backing off on the rear brake adjuster a couple of notches, and then see if the front brakes start to work....Of course, carefully test drive in a safe area (as previously suggested)....|
You are running a different system for the car, and have mis-matching parts, (with an MGA m/c, MGB brakes, so some experimenting is probably necessary.
|Edward Wesson 52TD|
|Thanks for the feedback. |
It has new calipers and new hoses. I added a supplemental MC reservoir in the tool box that feeds into the two cylinder (clutch and brake) MGA MC below the floor board, which should provide enough fluid.
The pedal is very hard and depresses only about 1/4 inch. The idea of backing off the rear brakes is simple and makes sense.
I had heard that sometimes if the MC is below the calipers that fluid runs back into the master, hence the thought of the residual valve which keeps is supposed to keep just enough pressure on the cylinders to keep the calipers close to the rotor, but so much as to keep the brakes on. I will try the adjustment thing, and the residual valve if that is unsuccessful. I'll let you know..
|I do not have a 1600 MGA master cylinder that is designed for disc brakes, I am wondering if mine has the residual valve built into it as mentioned by Mr. Gaylord? The generic residual valve I am going to use has only about 2 PSI residual pressure. |
If the 1600 master has the residual valve, then I suppose that's what I ought to be using.
|I have MGB front disk brakes with the standard 1500 master cylinder|
It works great.
|The only difference between the 1500 and 1600 master cylinder is the top cover. The 1600 is "domed" to hold more fluid to compensate for wear in the front disk pads. The body is interchangeable between the two, so I don't think you would have gotten one without the internal return valve.|
There are some folks using the 1500 master cylinder successfully with disk brakes on the front, but they are diligent about checking the fluid level.
|A couple of other thoughts about the original post ...|
Are the rear drums perfectly round? There are many slightly oval drums around.
I know little of TDs, but I wonder if the weight balance between front and rear wheels is similar to the MGA? Less weight on the rear wheels perhaps?
This thread was discussed between 16/08/2013 and 18/08/2013
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