Sud brake problem?

[Mika]

I have a twin carb Sud that i have brought back into good condition over the last couple of years. In relation to the brakes i have replaced the brake master cylinder, re conditioned the front calipers fitted new front rotors and EBC green pads. As they are meant to, it brakes very well (for a car of its era) most of the time. The issue is that there seems to be an intermittent problem where sometimes when you brake it feels like there is little or no power assistance. Light pressure braking is okay but when you increase pressure there is little increase in stopping power. As i said this is intermittent sometimes they work as they should and when you increase brake pressure you get an equal increase in retardation. Note: it is not a heat issue, it can happen when they are cold or when up to operating temparature.

Has anyone come across this before or have any suggestions?

[colcol]

I don't know what green EBC pads are, they may be a higher temperature than standard, i think the standard EBC pads are black, but i may be wrong, after you recced the  hydraulics did you bleed the system?, with suds you have to bleed the system all at once, all bleed nipples open at once, one for the back brakes and one on each caliper, if you do it like you do a normal car, that is bleed the one the most furthest from the master cylinder and work towards the closest, it doesn't seem to work in a sud, and you end up with one line working and the other not, you may also have a vacumn servo on the way out too, if it only works sometimes, it may have a leak in it, if it has a leak in it you may note an erratic idle as it is leaking air into the manifold, upsetting the idle mixture, Colin.

[Mika]

thanks Colin, i'll try your bleeding method but i suspect the problem may reside with the booster. If bleeding (which has already been done but not as you suggested) doesn't fix it i might try replacing the vacum hose and then finally the booster. The EBC green are meant to be "higher" performance than their standard black series. They seem to work quite well but fade still sets in after hard use - probably more a Sud issue than a pad issue though.

Mika

[colcol]

The EBC green higher performance usually mean higher temperature, not good for day to day driving, where you need good brakes from the minute you get in the car, not after they warm up, the vacumn hoses can leak after about 20 years, but if the leak is significant you will notice a rough idle due to the mixture being too lean, just go to Repco and get a new length of hose, if it has gone hard and cracked and is over 10 years old, just replace it, Colin.

[Sportscar Nut]

Mika

Agree with your thoughts that the booster could be the problem and wise to replace hose prior. Can't fit a bigger booster (ie 33) unfortunately due to clearance but I did fit a stepped master cylinder to the Sud which improved the balance & front brake pressure considerably (not expensive either).

Sud brakes should be fine for road use with good pads & fluid.

All the best.

Paul

[Frank Musco]

Do you have inboard brakes? If so, you might be getting some oil fouling the disks. There are a few ways this can happen.

I agree with the booster failing, that will cause that feeling that the pad is fading and the harder you press on the pedal, seems to make no difference.

As far as the ebc greens being an issue, I believe they require SLIGHTLY more pedal force first stop in the morning and after long periods of driving like coming off the freeway, and in constant stop start traffic they bite so well I find I use less pedal pressure than the factory original pads. If your getting fade you have an issue with calipers 'dragging' the pad on the rotor causing the pad to overheat. If the calipers are in good condition and the pistons return as they should the ebc green pads should not fade. I use the greens in my race and daily driver sud and I can't even get them to fade at the the end of Conrod straight!

Is the stepped master cylinder the same type fitted to xr6 falcon, also known as a 'quick take up' master? and is the main bore the same diameter as the original sud master cylinder?

[colcol]

Sometimes the calipers can stick and the brakes are rubbing, which is why they are fading, make sure the gaps between the pads and the rotors are about .004 inch or ,1 mm, or you remove the pad clip and you can 'rattle' the pads with your hand, these calipers are renown for sticking and the pads having different wear rates, so as they wear unevenly, you can work out which pad is doing all the braking and which one isn't, and you can move them around accordingly, Colin.

[Sportscar Nut]

Frank

The stepped master cylinder is a Mercedes part from memory. Beninca's fitted over ten years ago so memory is hazy but believe is the same diameter as the original Sud master cylinder.

As you probably know, the Ti QV came with a fluid rear proportioning valve that is very similar to the 33 S1's but different so not inter changeable. These valves are no longer available so fitted an adjustable  proportioning valve in the engine bay and the stepped m/c to get the brake balance right.

I think all other Sud's came with the mechanical/ arm rear proportioning valve so QV is unique! Think it was probably due to the stiffer springs Alfa fitted.

All the best
Paul

[Mika]

thanks for your feedback Frank, i do have inboard discs. Your comments are interesting regarding the EBC green pads.

It seems like the most likely cause of my problem might be the servo unit - has anyone had one fail ?

[colcol]

Check the one way check valve on the vacumn hose, they have been known to fail, put a vacumn gauge in the vacumn line and see what you come up with, THEN, isolate the servo assistance and see if the vacumn readings are the same, if the vacumn is lower with the servo connected, then it might be leaking, Colin.