Master cylinder

[cellaway]

I've just changed the standard rear calipers and discs for PNM. The front have hispec 4 pots and bigger discs. Bleeding the traditional way doesn't appear to give me enough pressure. The brakes work fine but do feel "soft" , I'm going to bleed the system yet again but if the pressure doesn't improve I feel I should be looking at the master cylinder. So the question is should I go for a standard or the brake "upgrade" one ?
From reading the "cheapest way to upgrade brakes" thread, I'm concerned about the amount of pedal travel and fluid that the upgrade cylinder will require.

[simonbuk]

Isn't the upgrade cylinder slightly small in diameter ? So would require less fluid ?

I recently drove one with the Hispecs on the front and wouldn't have thought that you need any extea help by uograding the cylinder - lucky i didn't have dentures in or wearing glasses !! It quite surprised me when i stomped on the brakes !!

[dapinky]

Isn't the upgrade cylinder slightly small in diameter ? So would require less fluid ?

Wrong way round, Simon.....

The diameter is smaller, so to shift the same volume of fluid, needs to travel further.

The maths is all in the original thread, but the question is whether the narrower master cylinder will have enough travel to shift the 'extra' fluid for the Hi-Specs.

IIRC, the numbers showed that it *should* be okay, as the total moved fluid is minimal difference - but I have never tried it myself, so can't give the definative answer asked for.

[cellaway]

I suppose the buy one and try it might be the best solution. The seals in the original are 25 years old so might be on their way out. As an aside I've got a couple of vented slotted front discs, standard size and the original rear callipers and discs, does any body want them ?

[alan e]

Buy a easy bleed it makes bleeding the brakes easy works off the tyre pressure and makes it a one man or woman job, I have the same brake set up as you and have no problem but it did take a lot of bleeding before it was right.

[simonbuk]

Update your profile with you location - there are many scavengers around these parts.......... !!

[Brit-Car-Nut]

His email address suggests France...

[cellaway]

Yes France it is south west near Royan. 8 hours sailing from La Rochelle. I'm starting to wonder if we could enter a Lotus Crew for one of the local regattas. I've got a Sunrise 34. Oldie but a goodie and quick enough to win on handicap. How many sailors have we got ?

[Fredjohn]

Yes France it is south west near Royan. 8 hours sailing from La Rochelle. I'm starting to wonder if we could enter a Lotus Crew for one of the local regattas. I've got a Sunrise 34. Oldie but a goodie and quick enough to win on handicap. How many sailors have we got ?

Yep I'm up for that. Done several flotillas and several deliveries for Neilson, with RYA dayskipper too. Mostly on 34-38 footers. Nice location though..... Rochefort is close by and was there in 2012 for the launch of L'Hermione.

[FunElan]

I've just changed the standard rear calipers and discs for PNM. The front have hispec 4 pots and bigger discs. Bleeding the traditional way doesn't appear to give me enough pressure. The brakes work fine but do feel "soft" , I'm going to bleed the system yet again but if the pressure doesn't improve I feel I should be looking at the master cylinder. So the question is should I go for a standard or the brake "upgrade" one ?
From reading the "cheapest way to upgrade brakes" thread, I'm concerned about the amount of pedal travel and fluid that the upgrade cylinder will require.

Hi Cellaway - did you ever solve this? Just spent hours bleeding my PNM front and rear - pedal feels just a tad soft even tho brakes function well. It’s almost like the pedal requires a lot less input too

[cellaway]

Yes I did. I put the car on an angle. Front up on stands, easy bleed connected and it bled through after two attempts.

[FunElan]

Yes I did. I put the car on an angle. Front up on stands, easy bleed connected and it bled through after two attempts.

Maybe I need an easy bleed. We're doing it the old fashioned way: pump the pedal, while one person cracks the bleed screw/closes it. I have had every single corner up in the air while doing this though...that's why I'd hope we'd have done a good enough job bleeding!

[Simon_P]

pedal feels just a tad soft even tho brakes function well. It’s almost like the pedal requires a lot less input too

what are the piston sizes in the old calipers Vs the new?

[FunElan]

pedal feels just a tad soft even tho brakes function well. It’s almost like the pedal requires a lot less input too

what are the piston sizes in the old calipers Vs the new?

Stock -> PNM front and rear. Great question, I didn't measure.

Spent another hour bleeding each corner, and even tried a pressure bleeder. At 13 psi the seal on the cap failed and got brake fluid all over the LHS suspension

So we pressurized the cap to 3-5 psi and left it, while I pumped the pedal and dad cracked each bleed nipple. Kept getting so much air. But once we didn't get air, we thought things would be fine, the pedal was nice and firm before I started the car. Once I started it, suuuuuuper soft pedal.

I think I'll be buying a master cylinder just to have on the shelf in the case that I don't see any leakage at the caliper ends. Didn't see any leaks this last time.

[lotusflasherman]

pedal feels just a tad soft even tho brakes function well. It’s almost like the pedal requires a lot less input too

what are the piston sizes in the old calipers Vs the new?

Stock -> PNM front and rear. Great question, I didn't measure.

Spent another hour bleeding each corner, and even tried a pressure bleeder. At 13 psi the seal on the cap failed and got brake fluid all over the LHS suspension

So we pressurized the cap to 3-5 psi and left it, while I pumped the pedal and dad cracked each bleed nipple. Kept getting so much air. But once we didn't get air, we thought things would be fine, the pedal was nice and firm before I started the car. Once I started it, suuuuuuper soft pedal.

I think I'll be buying a master cylinder just to have on the shelf in the case that I don't see any leakage at the caliper ends. Didn't see any leaks this last time.

I had problems on my Lotus Eclat Riviera that brakes were firm until engine started - tried driving and the exhaust emitted smoke after I'd braked and traced it to a fluid leak into the servo. New seals in master cylinder and servo sorted it. .. just something to consider..

[FunElan]

I think I'll be buying a master cylinder just to have on the shelf in the case that I don't see any leakage at the caliper ends. Didn't see any leaks this last time.

I had problems on my Lotus Eclat Riviera that brakes were firm until engine started - tried driving and the exhaust emitted smoke after I'd braked and traced it to a fluid leak into the servo. New seals in master cylinder and servo sorted it. .. just something to consider..[/quote]

yep....going to pull master cylinder this weekend and hopefully have it rebuilt. Weirdly, I don't see any GM part numbers that are readily available in the US.

[dapinky]

I have no idea which MC is used in the FED car (cross-reference wise!) - but I do know that the internals are nothing special and standard(ish) sizes to get the thing re-built with new seals.

There are undoubtedly lots of other MC's which will fit on the same servo mounting, but they will have different output ports, so will mean making up new pipes to fit their exact locations. For a UK car I can tell you what you'd need to replace, reseal or change for a different bore unit - but I haven't ever had to do such things for a USA car.

[FunElan]

I have no idea which MC is used in the FED car (cross-reference wise!) - but I do know that the internals are nothing special and standard(ish) sizes to get the thing re-built with new seals.

There are undoubtedly lots of other MC's which will fit on the same servo mounting, but they will have different output ports, so will mean making up new pipes to fit their exact locations. For a UK car I can tell you what you'd need to replace, reseal or change for a different bore unit - but I haven't ever had to do such things for a USA car.

I'm investigating a rebuild, but thinking of perhaps ordering a 4 port from the UK. Does anyone know the thread pitch or what plug would be suitable?

[Simon_P]

Stock -> PNM front and rear. Great question, I didn't measure.

The point being that the diameter is likely to be larger which will give you less pedal pressure and greater travel.

[FunElan]

Stock -> PNM front and rear. Great question, I didn't measure.

The point being that the diameter is likely to be larger which will give you less pedal pressure and greater travel.

So it stands to reason that a different sized master cylinder will offer a firmer pedal...