Brake Pedal Pressure

[fireblade]

I have recently overhauled my brake callipers on my Elan 69 S4 SE. I have cleaned the calliper bodies and fitted new pistons, seals (inner and outer) pads and bleeder valves. I have filled the system with new brake ( DOT4 Synthetic) fluid and have bled 4 or 5 times. On initially applying pressure to the brake pedal it goes flat to the floor but regains correct pressure from the second stroke onwards.I have checked the movement of the pistons and they are moving in and out correctly. Wheels turn freely when jacked up with very slight resistance on the rears.
I have paid particular attention in keeping everything clean when reassembling. Any advice would be much appreciated.

[Chris]

I don't mean to be rude, but have you fitted them on the correct side of the car, as they will fit either side. The only difference is the bleed nipple, is it at the top. You wouldn't be the first to fit them wrong way up.
Chris

[fireblade]

Hi Chris. I overhauled them one at a time so as to ensure they went back exactly as I found them.
Roger.

[tonyr27]

Looks as though there is still some air in the system.

I would start again at the rear and make sure you get plenty of fluid through.
TonyR

[fireblade]

I agree it has all the symptoms of air in the system but I must have put about one and a half litres of brake fluid through the system. The brake fluid exiting in turn from each of the bleed nipples is completely clear with no sign of air bubbles. I am now wondering if its a brake master cylinder problem although it was functioning correctly before.

[Europatc]

Good evening Roger, why did you overhaul them, did you have a problem? or was it just routine maintenance?
Do you have a servo or has that been bypassed. In the foot well have you checked to see if there is any sign of leakage where the m/c comes through tho connect to the pedal?
all the best
Stuart

[frogeyesimon]

Roger,

I had exactly these symptoms on my +2. It turned out to be a perished rubber seal in the master cylinder. The one at the end of the piston assembly which seals against the fluid reservoir when the pedal is depressed.

Simon

[nigelrbfurness]

Roger
I agree with Simon. Classic symptoms of impending master cylinder failure, probably brought on by the number of operations needed to bleed the brakes.

Nigel F.

[fireblade]

Hi Stuart Simon and Nigel F

I decided to overhaul the braking system even though it was functioning correctly because it was last done some 22 years ago. On dismantling the pistons there was some rust and corrosion and the seals were looking past their sell by date. The Girling servo is still connected and there is no sign of leakage from the system including the master cylinder. In hindsight I feel I should have flushed the system through to clean out any dirt before refilling with fresh brake fluid. My suspicions are dirt behind the seals in the m/c and your comments Simon and Nigel F seem to reaffirm this to me. Do I replace the m/c with a new unit or should I go down the route and replace all the seals instead as the cheaper option? Either way it looks like I will be calling on the services of Sue Miller.
Your help is much appreciated.

Roger.

[frogeyesimon]

Roger,

I dismantled my master cylinder. There appeared to be no detectable wear in the bore nor piston so I fitted a new seal kit from SJ Sportscars. All is now well.

Simon

[Europatc]

Good evening Roger,
apparently master cylinder castings are out of production at the moment so the m/c's are in or becoming short in supply. I managed to get one from S J Sportscars. Power Track are also excellent I have a servo, clutch master and slave on route from them as we speak
all the best
Stuart

[PeterK]

Could this symptom could also be caused by the new dust seals holding the caliper pistons too far away from the disc. Initial predal pressure moves the pistons a bigger distance, so long pedal travel. For subsequent presses of the pedal, the pistons are close enough to the disc to give short pedal travel. Leave for a while and the piston dust seals pull the pistons far away again.

Peter

[oldchieft]

I would have thought you would have noticed other problems as well, but long pedal travel can be caused by wheel bearing failure.

The wobble of the wheel pushes the piston back into the calliper.

A check that might show something is shake the wheel top and bottom and side to side while jacked up.

(put stands under the car don't do any work on the jack alone.)

If you have any play get someone to put the brake on, if the play reduces that is the total play less the wheel bearing play.

After checking all corners this way, shake all the wheels again with the brakes off.

Then try the pedal to see if you have reproduced the problem.

Jon the Chief