brakes don't "bite"

[chris davey]

mx83 cressida with RDA ba discs non slotted or drilled, r33 gtst calipers with unknown pads that have a fair bit of meat on them. The brakes just don't seem to pull up that hard at all. I was going to chuck some new pads on there but I thought I would just check if there is something else obvious that I am missing here?

Thanks

Chris

[twiztd]

i found with mine there's no 'bite' just a lil slow at the start then really start to firm up bout 1/3 to 1/2 way down. i've bled the brakes many times thinking it was to do with that, but i think its to do with the skyline calipers having a larger internal volume and needing more pedal travel before they start to really clamp down. i'm hoping that switching up to a jzx81 master cylinder will help, slightly larger bore, so should bite sooner. worth putting new pads in though if they were second handers to begin with.

Mike

[chris davey]

thanks mate.

also, forgot to mention that the pedal feels good as in doesn't need bleeding just doesn't seem to pull up that hard.

[MR22ZZ]

how old are the lines?

[chris davey]

nearly 20 years. stock ones.

[SuperDave]

Are the rotors brand new? They might need to be bedded in still.

[chris davey]

yep brand new.

[SuperDave]

Have you bed the pads to the rotors? Need to have a transfer of pad material into the rotor to give the pad something to bite.
Otherwise they haven't got oil on them?

[chris davey]

isn't that done when you put your brakes on?

[SuperDave]

The transfer happens when you apply the brakes, but can take some time driving normally. A couple of hard stops somewhere free of traffic will be able to see if that helps the cause (just make sure to not come to a stop during or soon afterwards).

[Ben12a]

Last time I purchased RDA rotors they came with bedding in instructions. They even went so far as to state the speeds you should stop from etc.

It was something like three or four hard stops from 60-80kph, and then a period of driving with no brake applications to cool them out. Maybe this was repeated, I can't quite remember.

The other thing I thought of: the pads are an unknown quantity. Maybe they are a performance/race compound and their operating range is too high for street use?

[bungs]

I've had mine for about a year, and I've got the same problem. I've bled them probably about 6 times and each time it's exactly the same. I mean, for the first 1/2 of the pedal travel there's nothing, and then when it bites it bites hard. Surely there can't still be air in the lines.

I need to replace my pads soon so I'll bleed it once again and see if there's any difference. Good odds it'll be exactly the same though.

[ecko]

id say its more master cylinder related...
to try to explain incase u dont know(u probly do so sorry if u do)

basically say standard front calipers may require say 150ml of fluid in them to work
so when you press the pedal the master cylinder sends that much to the calipers which may be at say 100mm of pedal travel..
now if u upgrade to 4 piston nissan calipers they may require say 300 ml so when u press the pedal 100mm in its not pressing enough fluid so u need to press another say 200mm...

i realise this is a very basic explaination and that the fluid should be measured in pressure not ml... but its very basic explanation...

also as someone else said brakes will feel dull when brand new get them bedded in asap then see how they feel, then maybe look at upgrading the master cylinder

[mark_vdh]

mine act exactly like Bungs, replaced pads no diff.
I'm thinking because there is like two spaces between the pads & pistons, thats why the brakes don't bite until about 1/2 of the pedal travel

like this pic

[af300e]

id say its more master cylinder related...
to try to explain incase u dont know(u probly do so sorry if u do)

basically say standard front calipers may require say 150ml of fluid in them to work
so when you press the pedal the master cylinder sends that much to the calipers which may be at say 100mm of pedal travel..
now if u upgrade to 4 piston nissan calipers they may require say 300 ml so when u press the pedal 100mm in its not pressing enough fluid so u need to press another say 200mm...

i realise this is a very basic explaination and that the fluid should be measured in pressure not ml... but its very basic explanation...

also as someone else said brakes will feel dull when brand new get them bedded in asap then see how they feel, then maybe look at upgrading the master cylinder

Hmm, it could be the ratios (as you say) but the effect is actually the opposite to what you describe. If the master is too small, the pedal feels soft and has more travel but the bite/power is good (like using a long lever). If the master is too big, the pedal feels firm and there is less/no bite.

The pads don't sound new, have you de-glazed them? It sounds as though the pads are the issue (providing the system is totally bled). Are the calipers on the right way up? The bleed screws should be towards the top.

Being from a R33, the chances that the previous owner was a sikunt is quite high and therefore so are the chances that he/she has fitted super hard race style pads that don't work until they are nice and hot. Or, they may just be shit pads.
For street use try some lucas/trw pads. They are cheap at around $60 and have great power/feel.

Putting old pads on new discs is usually a bit of a mistake as they can cause funky disc wear. I'd be getting rid of the oldies asap.