[AlfistiSA]

Do both front wheels lock or just one ?? One is a problem on that corner, two lead back to a common denominator the master cylinder

As Alfaloco said, when things heat up they expand, an easy way to check is to momentarily crack a bleed nipple and see if you get a spurt from both calipers, that'll instantly release them. Just crack & lock so you don't suck air.
As dbest says - how far can you drive from cold without applying brakes. In this scenario your MC is heating up from the exhaust on a LHD car.

Take a decent shop trolley jack with you on your next test and jack up each front wheel - check for drag/lock on each wheel BEFORE you crack a bleed nipple, that way you know if both or just one is dragging. can test the rears as well - take your soft wood block to lift on the diff pumpkin. if it's both fronts & rears --> it's the MC

I had this with my GTJ and it was braided hoses that were failing internally, the rubber had perished and was acting like a 1 way valve, fluid simply could not return. In my case it was easy, cracking the nipple produced a thunk from the MC as the piston returned, so I knew something was blocking the return. Bleeding the 4 corners produced clean fluid, pulling the MC revealed lots of rusty syrup, despite clean fluid being returned out the bleeders. Pushing a length of brazing rod down the flexible revealed ribbons of internal rubber being extruded out the other end.

Are your braided hoses NEW or New Old Stock (NOS) ??

You can do a crude test on hoses using a length of brazing rod - round the blunt end edges first and gently wiggle it through a loose hose.

It's going to be simple - when you find it... Ahh the joys of brakes

Ciao
Geig

 

[AlfistiSA]

Well Don tonight I timed it I drove for 14 mins very mellow hardly used the brakes. Then the pedal gets really hard and within a min or so they completely lock up. Brake light stays on then goes off when they cool.

My 0.02 Lira's worth is your master cylinder is being boiled by the exhaust & the fluid is expanding internally & the piston is blocking the fluid return hole - you have the MC pushrod too tight (yet you said you backed it off 3 turns...)

I can here something at the caliper almost a tick tick....tick tick its weird.

Internal pressure is bleeding slowly back through the MC as it cools down, with each drop in fluid pressure the calipers un-clamp just a fraction & that's your noise

2 Simple things - do you have a loose sheet of aluminium, old license plate, neighbour's license plate etc & can you fabricate a quick & dirty cover over your MC & just wire it into place - better still if you have some heat resistant material to stick on it & then test again - if your test drive goes over your 14/15 mins to say 25 then your MC is running cooler

It's a quick & dirty test, but won't cost you any $$ except for gas & hey a drive is a drive

Crack a bleed nipple to release pressure & get home

I'd strip & re-check the MC, easy enough to do with a standing pedal car

Ciao
Greig

 

[AlfistiSA]

Brake light stays on then goes off when they cool.

Internal fluid pressure between MC & calipers will do this, fluid expansion is 100% normal with brakes & heat, but if the bleed hole in the MC is exposed internally like it should be, then the heated fluid expansion simply pushes the excess expansion up the feed pipe into the reservoir bottle like it should, if the MC piston isn't in the correct position, then the bleed hole is closed off & the hot fluid expansion has no where to go but push backwards & that's into the calipers & their pistons.

The rears are not affected as they work via a different bleed hole, that's why there are 2 nipples on the side of the MC, one to front & one to rear. Your internal piston has 2 washers & two out-feed ports but one feeder port. Split circuit brakes, the forerunner of dual or X circuit brakes. My 750/101 cars are single circuit.

Yeah my Lira is on the MC push rod adjustment as others have noted.

Ciao
Greig

 

[AlfistiSA]

If the push rod that connects the pedal mechanism to the master cylinder is too long the piston will not retract far enough to open the inlet port of the master cylinder. This will prevent bleed-back to the reservoir, holding pressure in the system
Don

My Lira is on this ☝

 

[AlfistiSA]

After bleeding the calipers yes they stop fine....release and stop again.

Yes once the pressure is released, the calipers free up & the MC piston is free to move again, but the fluid will heat up & expand just like it did before as it has no return

So adjustment of the rod. Ok so how far back do I have to turn this in to get to the bleeder hole..

Impossible for me to tell from here, plus my 105's are RHD. My guess is anywhere from 1 to 2.5 turns - it's one of those things that you are going to have to do by feel, also remember that shortening the push rod = a longer free play on the pedal. I always take mine 1/2 a turn more after I've got the system to work just to cater for expansion

not sure mine has any bleeder screws on the Mc itself.. but it has been 7 months since I install the brake system

IIRC only the last of the dual circuit M/C's had the cast reservoir pot on top of the MC with the bleed nipple in the side - OK, again this is my experience of RHD & my 105 cars

 

[AlfistiSA]

Fluid leak past the washers in the master cylinder - you are loosing pressure in the main hydraulic pump, which is the M/C. You said you got a new master cylinder - did you just fit it, or did you first strip, clean, check, re-assemble & then fit ?? Reason I ask is because a friend got a new reconditioned (stainless sleeved) twin cylinder for his Austin Healey Sprite and had bad brakes, I went over to help, 2 hours of bleeding later I pulled the newly rebuilt M/C off and washed out the most incredible amount of machining swarf from the innards.... sold as fully assembled & ready to fit. Needless to say I fitted new washers as the supplied new ones had been running in grinding paste

We've identified the source of your issue as the MC where the piston isn't returning far enough to uncover the feed hole from the reservoir which is also the bleed-back return for excess fluid from heat expansion. In your shoes I'd take the MC off and strip it on the bench, then check carefully. You said new, but is it reconditioned with a stainless sleeve or a brand new cast iron unit. Check that the fluid feed holes have been drilled through correctly and that there are no sharp edges or burrs protruding into the smooth bore.

Brake Cleaner spray is a good start to getting things clean, Remember that the ONLY other cleaning fluid compatible with brake fluid is Methylated Spirits or White Spirit, nothing else. Use 3 clean ice cream tubs in a row, wash and clean using an old tooth brush is the first one, again in the second tub and a final rinse off in the third one. Stand to dry on clean paper towel. A dollar to a dime you will have muck in the bottom of the first two tubs. Now you need new washers as if there's swarf in the tubs the washer edges will have sustained damage.

I'm a bit of a pedant with brakes, but the alternative is dire & price of bodywork & chrome is heavy

Aye
Greig

 

[AlfistiSA]

Great news on the calipers

If the MC rod adjustment doesn't yield any change then you've probably got a little bit of aeration in the fluid from pumping & bleeding as well - let it stand till the weekend & give it another bleed - whoever pushes the pedal must just go slowly & positively to prevent aeration - enthusiastic pumping makes problems.

Ciao
Greig