Front brake callipers binding

[fireblade]

Both front brake callipers are binding on my 69 Elan S4 after driving for a distance of say 5 miles. From starting off from cold the brakes are fine and then gradually the brake pedal feels solid with no free travel. The car has the original Girling callipers which I overhauled approx 3000 miles ago with new pistons and seals and have been fine up to now, The pads are Greenstuff and are hardly worn. I have noticed if I leave the car for and hour the brakes cool and the front wheels spin freely. I find it odd that both front wheels are affected at the same time. The rears seem perfectly fine. I have removed the pads and cleaned them and the pistons appear to move freely. The brake master cylinder was replaced at the same time I did the callipers. Your advice would be appreciated.

[richardcox_lotus]

Do you have a servo ?

[LI-599]

Hi, same happened to my S4 and my moden car, it turned out that the fluid had not been changed for many years. The fluid is hygroscopic and absorbs moisture so should be changed from 2-4 years depending on climate.
Ian

[nmauduit]

do you have a dual circuit (re. problem at the front and not at the rear)? if so one thing to consider is the travel of the piston of the corresponding circuit inside the master cylinder, which may not properlly clear the return circuit hole hence getting fluid pressure accumulated into the corresponding closed circuit (if just renewed I would check pedal travel and free play, proper assembly and internal travel stop etc.)

[vxah]

Assuming single circuit brake system I would drive it until the issue occurs then pull over somewhere safe. I’m guessing with the issue live you can’t easily push the car on the flat? If not I would firstly give the brake pedal a pull upward in case it’s sticking and not allowing heat expanded fluid back into the reservoir? If that doesn’t work I would crack open a brake pipe fitting momentarily and see if the fluid pressure is released freeing off the brakes? If it does then you need to determine if it is the servo or master cylinder? So did you open the circuit before or after the servo?
A small amount of pressure in a single system might well apply the front brakes but not the rears due to the larger piston area in the fronts. Common when using a pressure bleeder at 20 psi that you can’t turn the front wheels but you can the rears!

[fireblade]

Thank you all for responding so quickly and I value all of your comments and good advice. I do have a Girling servo but I had to decommission it some while ago because again it caused the brakes to bind and I was worried it might cause the brakes to lock solid.Incidentally I had the servo refurbished (£250) and it worked for about a year! So I bridged the brake line. The brakes have been perfectly fine until now. The car has single circuit system. Concerning the brake fluid when I think about it this has not been changed for at least four years and on looking in the reservoir the fluid looks a dirty grey in colour so always looking for the easy way out I think I will bleed the whole system and lets see what happens. I will also try your suggestion of driving the car until the brakes start binding and then loosen a brake pipe and see if this releases the pressure. If it does as you suggest it could point to the brake reservoir being the culprit despite me renewing it not that long ago.

Roger.

[2cams70]

A common problem causing caliper binding is rust buildup in the cylinder bore just under the rubber dust boot in the area above the main seal. Moisture gets under the boot and into this area causing rust and piston binding. The dust boot is never a 100% moisture seal.

Whenever you rebuild a cylinder it is essential to remove any rust in this area with emery paper or it will cause you problems down the track. It exacerbates the problem if you use brake fluid as a lubricant during caliper assembly rather than rubber grease. The brake fluid used for assembly will sit in this area, absorb moisture from the atmosphere and promote rusting. I always pack this area with rubber grease on reassembly. It seems to prevent any further issues.

[pharriso]

A common problem causing caliper binding is rust buildup in the cylinder bore just under the rubber dust boot in the area above the main seal. Moisture gets under the boot and into this area causing rust and piston binding. The dust boot is never a 100% moisture seal.

Whenever you rebuild a cylinder it is essential to remove any rust in this area with emery paper or it will cause you problems down the track. It exacerbates the problem if you use brake fluid as a lubricant during caliper assembly rather than rubber grease. The brake fluid used for assembly will sit in this area, absorb moisture from the atmosphere and promote rusting. I always pack this area with rubber grease on reassembly. It seems to prevent any further issues.

True, but the OP said " The car has the original Girling callipers which I overhauled approx 3000 miles ago with new pistons and seals and have been fine up to now, "...................

[2cams70]

True, but the OP said " The car has the original Girling callipers which I overhauled approx 3000 miles ago with new pistons and seals and have been fine up to now, "...

My experience is that 3,000 miles after rebuild is around the time the issue occurs if during the rebuild process you haven't done what I've just described. That's about how long the corrosion if not completely removed during rebuild takes to re-establish itself - accelerated of course if brake fluid has been used as a caliper assembly lubricant

[oldelanman]

Roger,
Do you have free play on the master cylinder pushrod ?
As I recall replacement master cylinder pushrods are not the correct length for the Elan and you need to reuse the original or fit an adjustable one. If there is no free play the piston may not return fully and that could be what's causing the brakes to bind after a few applications.

[Foxie]

Roger,
Do you have free play on the master cylinder pushrod ?
As I recall replacement master cylinder pushrods are not the correct length for the Elan and you need to reuse the original or fit an adjustable one. If there is no free play the piston may not return fully and that could be what's causing the brakes to bind after a few applications.

I had that problem many years ago.

An adjustable pushrod, adjusted through a hatch in the top of the brakebox fixed it.

[2cams70]

Dodgy pattern brake seals swelling over time could also be a problem.

Suggest you jack the car up when the brakes are binding. If you find a wheel is binding whilst the car is in the air crack open the bleeder valve on the offending caliper to bleed off any hydraulic pressure.

If the wheel then turns freely you know you have a problem with hydraulic pressure caused by a faulty master cylinder or wrong pushrod length. If the wheel still binds you know you have a mechanical resistance problem probably caused by corrosion in the caliper cylinder or a swollen caliper piston seal.

[fireblade]

Thanks again for all the input so far. The fact that BOTH front callipers are binding at the same time must point to a clue somewhere. I have checked the pushrod and there is some movement but I plan to give the car a run this afternoon and will check the freeplay movement on return home. Plus I will raise the car and slacken off the bleeder valve. Concerning the suggestion of rust surely the new pistons are stainless steel so as to eliminate this problem. It is looking like the master cylinder could be the problem despite me replacing it not so long ago.Will keep you all posted.

Roger.

[pharriso]

Suggest you jack the car up when the brakes are binding. If you find a wheel is binding whilst the car is in the air crack open the bleeder valve on the offending caliper to bleed off any hydraulic pressure.

If the wheel then turns freely you know you have a problem with hydraulic pressure caused by a faulty master cylinder or wrong pushrod length. If the wheel still binds you know you have a mechanical resistance problem probably caused by corrosion in the caliper cylinder or a swollen caliper piston seal.

That sounds like a good quick(ish) test.

[2cams70]

Concerning the suggestion of rust surely the new pistons are stainless steel so as to eliminate this problem

Makes no difference whether the piston is new, old, stainless steel or some other material. The main issue is the cast iron cylinder. That is what corrodes. When rust forms on the cylinder surface in the small clearance area above the seal between the piston and caliper wall it expands and creates friction and binding. Trust me - ALWAYS remove all rust from the cylinder in that area whenever you do a caliper overall. Rust in this area of the cylinder is more critical than any rust that may be in the cylinder below the seal.

Stainless steel as a piston material probably even hastens rust in the cylinder in this area. Stainless steel will likely cause the cast iron cylinder to corrode more sacrificially compared to a conventional steel piston. Nice shiny pistons but more corroded cylinders in other words! The main reason stainless steel pistons are promoted in the aftermarket is probably because they are cheaper to manufacture - steel pistons have to undergo an expensive non-environmentally friendly chrome plating process.