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MG MGA - Where did I go wrong?

Some time ago I installed a new powertune servo under the front right hand mudguard on my A. Many of you guys on this forum would know this because I wrote a few posts on this subject in the past. I don't wish to annoy you again, but I am hoping to get some advise from guys who have a servo installed and are fully satisfied with its functioning.

With this servo installed, the brakes seemed to function OK but the foot pedal travel was excessively low. To activate the brakes I only had to lightly push on the pedal and when it reached full force, it went down to a position at about 2 inches from the floor. I found this very scary as I'm driving along, thinking the pedal will, all of a sudden, slam right down to the floor resulting in no brakes at all.

I checked all hydraulic lines connections for any leaks, but found none. The entire braking system was bled thoroughly twice. I removed each brake drum to inspect the wheel cylinders. No problems here. So, if anything, where did I go wrong? I have now disconnected the pipes from their connections and installed a bi-pass tubing between the two connectors where the lines
from the servo were connected. My braking system is now as per factory original.

I will be very grateful for any help I get on this unfortunate mishap.

Frank






F. Camilleri

Frank, I had just this problem after I fitted a Delphi replacement Servo to my BV8. It was frighteningly underivable until I blanked off the vacuum pipe. The servo went back to the supplier and my old unit was sleeved and I re-built it. No problems since. I put the Delphi down as more aftermarket rubbish!! The air valve piston, which activates the air valve and thus the slave cylinder, should only do so when there is reasonable pressure put into the system, thus ensuring "progressive" braking. Light braking often doesn't involve the servo at all. Like you mine stood on it's nose as soon as you touched the pedal, then the pedal pushed my foot up!! Scarey!!
Allan Reeling

Thanks Allan. My servo is still installed under the front right fender. It's completely hidden and does not bother me at all. If I can find the details of the guy whom I bought it from, I will send the unit back to him. It is a Powertune make and I bought it from the UK. Where in Shropshire are you? I spent 2 and a half years in your area. I was serving in the Royal Air Force & was stationed at RAF Shawbury.

At the moment I am running the car with brake drums on all four wheels. The braking efficiency is excellent, cannot be better. As before I now have to push harder on the pedal, but the car stops at any speed, the faster I drive the harder the push.

I was hoping that some members here who have servos fitted and the project was 100% successful, would barge in telling me how to fit a servo the proper way, and indicate where or what went wrong in my case.

Frank
F. Camilleri

Frank, Just down the road fro Shawbury on the outskirts of Telford.
The difficulty many people have, at least with B's and the V8 servo installation is that the air valve is uppermost, making bleeding the air valve piston very difficult. Air trapped under the small piston I fancy leads to a premature opening of the air valve. The general advice is to rotate the slave so that the air valve is between 5 o'clock and 8 o'clock, which helps when bleeding that part of the circuit. "Nose up" definitely helps but I used a double banjo, then installed a bleed nipple, as the washer reservoir prevents rotating the servo, see photo. (The nipple is partially hidden by a brake line!) This works well.


Allan Reeling

Thanks Alan. My servo is still installed under the front right fender. If I find the details of the guy whom I bought it from I will contact him and send him back the unit. I have a feeling that dot5 brake fluid is not compatible with the Powertune servo, making it useless in operation.

Frank

F. Camilleri

Hi Frank,
Dot 5 is silicone fluid. Lockheed didn't favour it, and I seem to remember, refused to honour guarantees if it was used, Mostly, I fancy, down to the rubber/neoprene they used for seals, but there may have been reasons than that!
Allan Reeling

hello again Frank, Here is the link to a note in the V8 Register regarding silicone fluid.
Al http://www.v8register.net/subpages/V8NOTE228.htm
Allan Reeling

This thread was discussed between 11/05/2018 and 15/05/2018

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