Choosing correct master cylinder

Update:

Bike finally hit the road. The brakes seem solid!! However, there is a bit of a pulsing feeling to them. A sort of jerkiness. Not at the lever. Just seems like they grab harder at certain parts of the disc than others. And more pronounced at low speed than high.

I was doing some hard stops and it seems to be getting better so for now I'm going to assume it is just the brand new pads still bedding onto these beat up used rotors. *shrug*

I was doing some hard hits from 50mph enough to get the front tire to squeal. It felt great and the cheap Shinko 705 tire seemed to perform better than I expected.

Of course, it was a hot day and 100% dry for this sort of thing.

Moral of the story: the 5/8" MC seems like a perfectly fine match for these GSXR calipers and 320mm rotors.

Resized_20200905_110409_953.jpeg


Thanks to everyone for the helpful advice!!! Much obliged!
 
Thats awesome, glad to see you are on the road.

If the rotors are used its very possible they are warped. Disk lateral tolerance is usually pretty small like 0.003" (0.08mm) so any warpage and you will feel the pulsing. I have to deal with this on a bike of mine. I will have Truedisk to grind a new face.
 
Thats awesome, glad to see you are on the road.

If the rotors are used its very possible they are warped. Disk lateral tolerance is usually pretty small like 0.003" (0.08mm) so any warpage and you will feel the pulsing. I have to deal with this on a bike of mine. I will have Truedisk to grind a new face.

I looked at the GSXR service manual and it says that the rotor runout max is 0.3mm .... which is generous. And my rotors are well within that limit.

However, it would appear that the rotors have a bit of thickness variance when I measure with a micrometer. Probably as the previous owner used some crap quality pads or something.

At this point I'm not sure what I'm going to. I have the winter to think about it, because I dont have a budget for new rotors. And if I go with ebay again, I might end up with rotors I'm not happy with again.

I also figured with warpage I should feel pulsing at the lever. That is what most people report as well. My lever, however, does not pulse at all.
 
I looked at the GSXR service manual and it says that the rotor runout max is 0.3mm .... which is generous. And my rotors are well within that limit.

However, it would appear that the rotors have a bit of thickness variance when I measure with a micrometer. Probably as the previous owner used some crap quality pads or something.

At this point I'm not sure what I'm going to. I have the winter to think about it, because I dont have a budget for new rotors. And if I go with ebay again, I might end up with rotors I'm not happy with again.

I also figured with warpage I should feel pulsing at the lever. That is what most people report as well. My lever, however, does not pulse at all.

If it’s not that bad ride it until you can afford to fix. True disk charges 60 per rotor to Grind. It’s a good deal for basically a new disk. Also check the rotor bobbins to make sure they are seized. they should move freely.
 
If it’s not that bad ride it until you can afford to fix. True disk charges 60 per rotor to Grind. It’s a good deal for basically a new disk. Also check the rotor bobbins to make sure they are seized. they should move freely.

They seem ok. On one of the rotors someone had cut se of the wave washers out so that side moves more than the other. An attempt to turn semi-floating rotors into full floating? For some reason?

I will likely just replace them next year.

However, I noticed something else .... that this metal plate that goes on the back of the caliper has some pad Marks on it. Is this supposed to contact the pads? I thought maybe there to stop the pads from rattling and such, but then I thought wouldnt these divots prevent the pads from moving properly??

Might take this off and do a run without to compare.
 

Attachments

  • 20200906_201829.jpg
    20200906_201829.jpg
    556.4 KB · Views: 183
  • 20200906_201814.jpg
    20200906_201814.jpg
    777.8 KB · Views: 187
You might try just cleaning the rotors carefully with brake cleaner. It doesn't take much to produce that sensation. I find that just a couple day's setting undriven would make a fairly drastic braking pulse on my old Suzuki SX4 until a few stops had cleaned the corrosion off of the Chinese steel. I've also experienced it on several vehicles after working in the area, and probably leaving greasy hand prints on the disk. The grease tends to take longer to go away.
 
You might try just cleaning the rotors carefully with brake cleaner. It doesn't take much to produce that sensation. I find that just a couple day's setting undriven would make a fairly drastic braking pulse on my old Suzuki SX4 until a few stops had cleaned the corrosion off of the Chinese steel. I've also experienced it on several vehicles after working in the area, and probably leaving greasy hand prints on the disk. The grease tends to take longer to go away.

Yup, I did that. Brake cleaner, then I scuffed them with some 400 grit in a criss cross pattern, then cleaned with brake cleaner again.

I think it was getting a bit better but still there. I think if rotor was bent it would be more noticeable at higher speed not less. And the important thing is, the bike does stop well!

In any case. My riding season is pretty much done as hunting season starts in 2 days :D :D so I will keep an eye out for deals on ebay over winter.
 
If it’s not that bad ride it until you can afford to fix. True disk charges 60 per rotor to Grind. It’s a good deal for basically a new disk. Also check the rotor bobbins to make sure they are seized. they should move freely.
After some rides and trying to bed the pads, I think the variance in thickness is a problem. The rotors dont shake under braking. But when you clamp down you definitely feel the brakes doing an on/off as if they're only grabbing one (thicker?) Section of the rotor.

What's your opinion on the Arashi ebay rotors? I'm a little paranoid of another set of used ones coming in just like what I already have.
 
Having the same thing happen on my KLR. Bastard thing's rare as hen's teeth so finding any part for it is a headache, let alone a front brake rotor. But a front brake rotor is what I need alright - definite pulsing at slow speeds. Rotor's crooked as a dog's back leg
 
Having the same thing happen on my KLR. Bastard thing's rare as hen's teeth so finding any part for it is a headache, let alone a front brake rotor. But a front brake rotor is what I need alright - definite pulsing at slow speeds. Rotor's crooked as a dog's back leg

Did ya measure run out to confirm? I measured mine, and it wasnt as bad as I thought. But somehow its thickness varies more than I'd like which isnt helping. Not sure how that develops even.

One last thing im oing to do is unbolt one caliper, stick a 3/16" shim between the pads and tie the caliper to the fork leg. And see if one side is significantly better behaved than the other.
 
Back
Top Bottom