Triumph Repair: Spitfire brakes, piston seals, pist

Question
QUESTION: Hi,

  Carrying on from the other question, I had someone sit in the car and press on the brake pedal and I watched the pistons. The caliper on the drivers side only one piston was moving forcing the disk to one side. On the passengers side both were moving but one was a little faster.
I put the piston seals and pistons in a little while ago and there was a period were the car wasn't worked on for 3 months, also it was a very cold winter. Hope this helps to understand the cause.

Jason

ANSWER: Jason, do this, remove the brake pads from both calipers and put in place of the pads anything about half as thick as the pads. (It don't matter what you put in as you are not going to drive the car yet) (old worn out pads work well) Then pump up the brakes and after you have done that, remove what ever you put in there. (the reason you need to put something in there is so you don't have a piston pop all the way out of it's cylinder.) Now, carefully pry one piston at a time in just enough to have to force your new pad in. If you pry it in too far and the pad slips in freely you need to remove the pad and put the thinner item in and pump the brakes again to get the piston out. The objective it to have to force each and every pad in place. NO pad should slide in freely.
If you did it correctly all the pads will be very tight and you should not be able to rotate the disk very freely by hand. Now, go pump up the brake pedal to see if you have a good pedal.

If you do, don't drive the car on the highway but drive it either in a parking lot near by and drive hard in circles in both directions or if there is no close parking lot drive it down the street in hard "S" turns for at least a city block and jack up the front of the car and see if you can hand spin the front wheel. If you can and you still have fair pedal you are finished.

The reason for all of this is that the piston seals are the piston retraction system meaning when you step on the brakes you force the piston against the brake pad and the seal does not slid on the piston but the seal flexes and when you release the brakes the seal pulls the piston away from the pad and that displaces so much fluid that it sometimes takes two pumps of the pedal to force it against the pad again. The process I covered flexes the seal the wrong way making the seal hold pressure against the pad at all times which you should not drive far like that or it would burn up the brakes. Then when you drive in circles hard or make hard "S" turns makes the disk force the pistons back just a slight bit to a neutral position where it belongs.

let me know how it works (don't short cut any part of the process)

Howard

---------- FOLLOW-UP ----------

QUESTION: I've tired the method you've said above and I'm still getting the same problem. I've placed re-conditioned calipers on and bleed both sides which are still the same. I've separated each caliper and only used one pipeline directly to the flexible hose to the caliper and get better resistance but not solid (the same on both sides). Put both calipers together and the pedal goods softer then when they are separated.


The only thing I haven't changed on the brakes is the front manifold. I'm running out of ideas to locate the fault.

Jason

Answer
Jason, there is a simple fact and that is that fluid does not compress. Air does. If all the air is out of the system and you have a soft pedal then you have too much movement somewhere.

First test the master cylinder by removing the lines and putting in place bleeder valves (most auto parts stores have an assortment)
Pump the pedal up and bleed at the bleeder/s. You should get a rock hard pedal. If you have that, the master is ok and now move to the joint in the line that runs the lines to the other brakes and block off all but one wheel by using the bleeder valves. Now you can test just one wheel at a time with this method. If you did what I said you will have NO movement of either piston so you should have a hard pedal since NO fluid compresses. ONLY air compresses or something is moving. Also have some one pump hard on the pedal while you hold the flex line to see that they are not expanding any.

It is impossible to fail to find a problem if you follow this procedure exactly and not skip any part.

Howard