front brake question

Hi all, I am installing my brakes, I have 1985 lotus esprit turbo brakes all round
fronts are single piston 2¼ inch (57mm) and rears are single piston 1¾ inch (45mm) with integrated handbrake mechanism
Balance bar mechanism replaced (for testing) with a solid shaft so I can connect front or rear for testing and to check pedal travel , pedal ratio is 5 to 1 floor mounted.
Connecting the Rear mc only with both 0.625 and 0.7 mc gives a nice “feel” with a solid stop (no flexing) no too much travel and not too much pushing from my leg
However connecting the fronts only I feel a lot of flex, not a real solid stop in pedal movement but pedal travel is almost 5-6 inch (tested with 0.625/ 0.7 /0.75 without much difference)
Calipers have new piston seals and sliding pins have new seals and grease and no leak
Is it possible that the calipers go back too much after releasing the brake pedal? And because of this need too much pedal travel? (sticking piston seals)
How much of a gap (feeler gauge between disc and pad) is normal / ok for sliding pistons so I can test if they go back too much ?
Thanks, Rick

Your front piston requires 65% more volume than the rear, so there is going to be some degree of a "softer" feel to the front ones vs the rears. Considering the subjective description, have you considered re-bleeding the fronts to ensure all air is out of them? Given both use a single O-ring, on a floating design, I would think the pull-back would be minimal as compared with fix caliper designs. Assuming hoses for both front and rear are the same design/material.
Understanding the Esprit's configuration, I'm still going to ask; Have you considered or evaluated a more balanced set of calipers F-to-R? The reason I ask, is a nice mid-engine rear design will generally bring the delta between the front to rear down quite a bit. Using a program to determine my needs, I found that identical setups front and rear was very close to neutral balance, which has been born out by track testing. I believe I've had to input about 1 turn on the balance bar to bias the front after it was all said and done.

Do you have residual check valves front and rear and are they working as they should? are the pads new on the front vs used on the rear? master cylinder inside diameters ? Air, well how does one ensure 100% there is none. Some calipers may have to be removed and angled just right to be sure. Just my 5 cents worth.

hi Yes bleeding was done with and without taking the calipers of (bleedvalve hole straight up) on the esprit I have the same set, never have to take them of and they are mounted the same as well, (I did it as an extra check without any difference) I do not have a residual check valves because the brake fluid reservoir is 30 cm above the calipers and 40-45 above the mc. but maybe I can put a low pressure one inline. can I take just one directly after the mc before the T-joint? and yes hose is the same on all corners (nylon/stainless) checked the padel travel today, on a 0.75 mc I have about 4 inch. pads are all new (f and r) maybe I need to leave as is and just test first before doing anything else. is brake line pressure a good indication? if yes how much pressure is wanted for a road car?

thanks, Rick

Yes, 2psi as close to mc as pos. New pads will feel a bit soft till run in.

thanks

Rick, the stock Esprit brakes really are a weak point of the car. As I recall, they're Toyota calipers from a Corolla. There are some excellent kits to upgrade the calipers/rotors to two and four piston, with larger vented rotors. The kits aren't too expensive. Let me know if you want a reference to where to buy.

Hi Cliff, the brakes are fine for the esprit in NA form, it is just the turbo esprit that struggles. for the esprit I have a nice 4 pot upgrade (nissan 300zx calipers mount directly on the toyota uprights with peugeot 406 disks they are 285mm x 26mm, more then enough for my NA s3 ) but for the baby gt40 (banks europa 62, some 300-400kg less then a esprit,) I need some oem looking brakes thats why I put the esprit brakes on (they were laying around anyway) as the layout of the esprit is more or less the same.... after I got my registration they will be replaced by 4 pots as well. if I can get the brakes to work right they will end up on a friends gt40 replica for testing and oem look (for the same reason) I got myself a little residual valves, all I need now is some time to mount them. thanks