Variable brake feel (again/still)

[kherseth]

Hi folks,

Need some help on getting this brake problem straightened....

Finally the snow have gone from the roads and been able to try out the brakes a little. I feel like i cant trust the brakes, they seem to be very good in one moment and rubbish in the next.

I have checked the wheel bearings and found no slack. All calipers where replaced this winter with factory refurbished ones, braided lines were fitted this autumn, carbotech AX6 pads all around accompanied with brand new discs also fitted this winter. Master cylinder refurbished last spring.

Basically the whole system have been refurbished the last 12 months. The only thing that have not been touched is the brake balance valve, but i dont think this is a part that normally fails? The system have also been bleed multiple times following the manual.

An example from just a couple of hours ago, I drove to work, last 500 meters i gave it some gas and revved up to ~70mph, brakes down to work and the brakes did bite better than ever. Drove slowly across the parking lot and left the car for about 5minutes before driving to the shop. On the return to work i did exactly the same thing, breaking from 60-70mph and entering the parking lot, but now the brakes felt like they were fading or glaced over. On my way home just now, they were somewhere in between, but feeling better before reaching home

The only thing I feel could be a problem is that the pads have not had a proper bedding yet, but i would think they should not be this variable even with that in mind. Any carbotech daily drivers who could comment on that?

Thanks for reading,
Kim

[michaeljapp]

I have Carbotech pads on mine, they do take a bit of effort to warm up, the cold performance isn't great.

When bleeding are you sure there isn't air in the system, a good trick I was shown was to gently tap the calliper to help dislodge any air.

Also as a thought check for leaks around the master cylinder unions.

I'm not a great or even good mechanic but I'm sure one will be along soon to answer your question.

[kherseth]

Hi Michael,

Thanks for the reply.

Ok so some of the trouble might be explained by the lack of heat, thats good to know.

I did incidentally check the area around the MC this weekend when bleeding the cooling system, could not find any sign of leaks. I know there was a leak before I refurbished the MC. Maybe i should lap the unions to make sure. Hmm, maybe there is a slight bubble in the MC still

Maybe try to bleed the brakes yet again, might be as you said that some air have been stuck.

Cheers,

[coanda]

Isn't there an issue where if you depress the brake pedal too far when bleeding the brakes, you can push the piston too far and the master cylinder internals can be damaged/dislodged and give a variable pedal feel?

Someone like Paul Woods or Lauren will probably know the details...

[PW@Woodsport]

That happens on some Vauxhalls but never had it happen on an Mr2, must be the design of the MC. The older Vauxhall MC used to flip the seals when bleeding.

[kherseth]

Sounds like I should just try a good bleeding again then, start with the MC and then do the calipers. If that does not help (and not being too optimistic) I`m stuck.

Starting to get that love/hate thingy about these cars, still more love than hate tough I do have a strong dislike for the previous owner, but that is another story.

[PW@Woodsport]

Hang in there, the good times outweigh the bad

[kherseth]

Oh absolutely, although I feel otherwise after driving 500km to get on a track just to find out that the brakes are good for only 5 laps in a weekend

Happened twice already, NOT going to happen again!