FZR 400 Front Brakes Severely Binding?

[Woddy]

Hi all, thanks for taking the time out to try and help...

Right, i have 1990 fzr 400 sp race bike... I stripped both front calipers down as they where binding very badly when up on the front paddock stand (brakes being cold, havn't had chance to go out on the track with it yet), we started off by polishing the pistons on the lathe to a near like mirror finish but then only took the wiper seal out (as i was told this was all that was needed to be cleaned as the main seal rarely attracts the dirt :S) i also cleaned the seal groove on the caliper to (which was all pretty clean anyway!) After that i started poping all the pistons in which all slid back in very nicely having being very tight on removal which was good! Then bleed the brakes as much as i feel i could, and they where binding just as bad as before? less than 1 revolution spin, wheel seems to be very tight!

However, the brake leaver was very spongey before and are even worse now (fairly close to the handlebars!) so could they bind due to the amount of air trapped? Just wondering if i took it to my local bike garage to get them to bleed them up with the proper vacum pump and know how, is there a chance it would solve the problem...

I don't really want to strip them down again to be honest, the seals and pistons seem to be in good order in slid back into place very nicely but maybe i am wrong?

Front brake has Goodridge hoses on to if that helps...

Many thanks

[MarkT]

I just typed loads and my post disappeared!

Now in short, problem is with calipers or master cylinder.

Squeeze brake lever and check the brakes are binding, without touching lever again loosen the banjo bolt on caliper or master cylinder an catch fluid in rag.

If brakes are now free you have a problem with master cylinder!

If brakes are still on it's the callipers still !

Hope this helps left out a load of info as it is hard on my iPhone.

Mark
PS I tend to undo the banjo on master cylinder! If brakes are still binding loosen bleed scews one at a time as this will tell you which caliper is binding.

[Evilchicken0]

As long as you've got all the air out then I can't see that vacum bleeding will do anything else. When you took the seals out did you do both seals and clean behind them, did you rebuild them with some red rubber grease or run some fluid round the seals ??? With the calipers bled in take them off the forks and see if you can push them back if that's easy you could have a look at the master cylinder seals and check their condition but I'd probably look for a newer secondhand master before I'd replace them, you need to check the master cylinder ratio and then match it but I'd probably start with an R6 item.
With the lever coming back to the bar, have a check if the pads are low or if the discs are worn if they're in good condition then the 3TJ are quite good.

[Woddy]

Great info thanks guys,

Mark i will have to give that a try im pretty sure the pistons on both calipers go in and out fairly easy but with a obvious slight force... So maybe the master cylinder is the one that is giving the trouble???

Evilchicken, unfortunatly i only removed the wiper seals as i was told not to bother with the main seals, but now looking back i was a fool not to really!! But all seals where coated in brake fluid prior to fitting the pistons back in, as i say to Mark the pistons don't seem to be all that tight so the master cylinder could be the culprit which was something i over looked to be honest. Disks seem to be all good but i have to admit the brake pads don't have much meat left i would say around 1/4 on inch on each one but not critically low...

I am thinking it would be better to stop beating around the bush and go for the complete front R6 brake system change, but how much would i be looking to do this for they seem to go for good money? I already have Goodridge hoses on which i am hoping would fit onto the R6 set up and the original 3TJ disks? so then all i would need is the the calipers and master cylinder...

Many thanks

[MarkT]

Don't know about R6 even though I've had a few!! The test of calumets or master cylinder takes a couple mins and is worth doing just for piece of mind!

Mr E C is the main man so follow on the test with what he says!!

Hth Mark

[Evilchicken0]

The R6 calipers don't fit on the 3TJ forks.
Really it depends what you to end up with, I've got a 19x20 Brembo radial master cylinder on mine with braided hoses, standard calipers and HH pads. The bike stops hard but it's a bit on off.

[dobbslc]

I had something similar with my bike. It has a Brembo master cylinder & PFM discs on it and the brakes would bind a bit so I bled a very small amount of air into it. That solved the problem completely. This is a track only bike so is used very hard with no problems.
Also check your front wheel spindle is straight and that the forks aren't twisting when you tighten the nut,
are the correct spacers in place?
If you have 1/4" on all the pads it could be that the pistons can't retract far enough to clear the disc as they sound quite thick. What make are they?

Dobbs

[Morespeedvicar]

Id deffo give the calipers another rebuild and take put the main seals and give them a good clean and clean the grooves with a brass wire brush on a dremel if you can. then repack with loads a silicone or rubbergrease. I left the dust seals out of my calipers when i rebuilt mine, one less seal to stick.
Cheers
Ian

[Evilchicken0]

I wouldn't recommend leaving the dust seals out, not even on a trck bike. Dust isn't just road grime it's more likely to be brake pad dust and because your probably using sinterred pads that will contain metal which will lay on the scraper seal and can get inside on the piston face. The other thing would be the piston only has one point of contact so it isn't held square in the caliper running more of a risk of picking up.
Putting air in a system is ok as far as it goes but remember air will compress into the fuild softening the action and also causing the fluid to boil at a lower temp. On the one hand you improve the brakes then you make them worse ... Really it would better to get them working at their optimum

[Taggyd]

ivegot a '16' brembo m/c on mine and it works pretty well by all accounts, i might put it on the track bike but the standard ones with braided hoses have always done very well so long as they are kept clean. I would make sure the connection at the m/c is tight enough, i had this on a race bike and the banjo was only very slightly backed off, it was an almost impercievable (spelling!?) movement to tighten it, but it solved the problem! guess the vacuum wouldn't pull them back as the air was easier to move in!