Front Caliper drag

[Shipper]

I have run my '75 rebuild up[ and down the street multiple times now and I'm really happy with the way it pulls. Just a couple of nagging problems before I'm road worthy.

Thanks to Twins and others I have a direction on the oil blow by from the breather head.

The last problem I'm dealing with is drag on the front calliper. I had to go to Mike's for a front calliper (single disc) because the original was so badly rusted out. Problem is, I can't seem to get the inner piston to release all the way when I release the brake lever. Real piss off. Have bled the lines till I'm dizzy on fluid absorption and it refuses to release clear of the disc. The wheel is locked with brakes on but turns stiff when released. Any ideas?

 

[Gcraay]

I know they're new, but could there be a bad seal? Rolling instead of letting the piston slide? You said you bled your brakes a lot, but could you be sucking air? Did you have to bleed them or did you just do It? Put the caliper hose end in a clear cup of brake fluid, pump the brake look for bubbles.

 

[retiredgentleman]

You should take the caliper piston out and inspect the piston seal ring.

 

[XSLeo]

If you crack open the bleeder on the caliper, will the clapper release? If so perhaps the master cylinder needs looking at.
Leo

 

[Shipper]

If you crack open the bleeder on the caliper, will the clapper release? If so perhaps the master cylinder needs looking at.
Leo

Doesn't release still drags. But thanks for the idea.

 

[Shipper]

You should take the caliper piston out and inspect the piston seal ring.

Will do but first, I'm thinking that the disc isn't being centred properly with the wheel bolted in place. Has anyone ever needed a spacer ring between the disc and hub piece that the disc bolts to? I'm thinking this will centre the disc more appropriately and allow better clearance from the inside brake pad.

Idea's?

 

[gggGary]

You shouldn't need spacers on a stock set up...
But as an experiment wouldn't a couple of washers on the fork tube to space the caliper towards the wheel be simpler?
Perhaps do some comparing of distances between the mount and slot on the stock caliper and the replacement. Maybe someone was having a bad day at the people's co-operative caliper and dog food can recycling plant?

 

[gggGary]

Wouldn't hurt to post some pics.

 

[Shipper]

You shouldn't need spacers on a stock set up...
But as an experiment wouldn't a couple of washers on the fork tube to space the caliper towards the wheel be simpler?
Perhaps do some comparing of distances between the mount and slot on the stock caliper and the replacement. Maybe someone was having a bad day at the people's co-operative caliper and dog food can recycling plant?

The PCC&DFCRP is famous for poor production, I agree. Don't know why I didn't think of comparison measurements prior to tearing the wheel apart but didn't. Did try to use washers to compensate but that brings the inner caliper housing too close to the spokes. What's needed is space between the caliper and inner wheel hub. Will experiment with washers on the disc mount first to try my theory as a machined stainless steel ring will likely be pricey.

Thanks G's. will let you know.

Sure enough G's, Mikes caliper are almost a full mm narrower than stock. That's more than I would need to make that crap work.

 

[gggGary]

Couple more possibilities;
Thin up the rotor a bit, tell em to take more from the inner surface. dang things are mighty fat anyways.
Machine spacers tend to be a bit thinner than washers. SS washers are often thinner than steel washers
Use an aftermarket rotor or an FZR600 rotor not sure how the offset works with the early calipers. I'll look next time i'm near the rotor pile.
1mm <> 1/32" inch
MM, prox Fraction, Decimal Inches
1mm, 1/32 inch, 0.039
you could cut a spacer out of aluminum sheet with tin snips and drill holes using the rotor as a guide. Both hub and rotor center are aluminum, the spacer can be too.
File a bit off the back corner of the caliper.
Use a slightly used pad on the inside. or grind one down a bit. (dust protection)
Use a machine spacer on the axle.

 

[Shipper]

Couple more possibilities;
Thin up the rotor a bit, tell em to take more from the inner surface. dang things are mighty fat anyways.
Machine spacers tend to be a bit thinner than washers. SS washers are often thinner than steel washers
Use an aftermarket rotor or an FZR600 rotor not sure how the offset works with the early calipers. I'll look next time i'm near the rotor pile.
1mm <> 1/32" inch
MM, prox Fraction, Decimal Inches
1mm, 1/32 inch, 0.039
you could cut a spacer out of aluminum sheet with tin snips and drill holes using the rotor as a guide. Both hub and rotor center are aluminum, the spacer can be too.
File a bit off the back corner of the caliper.
Use a slightly used pad on the inside. or grind one down a bit. (dust protection)
Use a machine spacer on the axle.

Like the option of thinning up the rotor. Only really need about .06mm and agree that they are real fat. If you don't mind though, before I shave an OEM rotor I'll wait to hear from you on the FZR600 when you're near the pile next. Have noted the pad alterations as well.

Thanks G's

Sorry .6mm not .06, but you probably knew that.

 

[Shipper]

Couple more possibilities;
Thin up the rotor a bit, tell em to take more from the inner surface. dang things are mighty fat anyways.
Machine spacers tend to be a bit thinner than washers. SS washers are often thinner than steel washers
Use an aftermarket rotor or an FZR600 rotor not sure how the offset works with the early calipers. I'll look next time i'm near the rotor pile.
1mm <> 1/32" inch
MM, prox Fraction, Decimal Inches
1mm, 1/32 inch, 0.039
you could cut a spacer out of aluminum sheet with tin snips and drill holes using the rotor as a guide. Both hub and rotor center are aluminum, the spacer can be too.
File a bit off the back corner of the caliper.
Use a slightly used pad on the inside. or grind one down a bit. (dust protection)
Use a machine spacer on the axle.

So prior to thinning out the rotor (which I think will work) I took the front hub apart to make sure All parts were present and therefore not hindering the alignment problem im having between the bake calipers and the disc. I really am mystified by this. Anyhow, after removing the cap from the left side, I find six bolt holes but only three on the cap. (see pics) This appears to be a hub for double front discs and mine is only single. Is this a part of my alignment problem?

Thanks for the continued advice/suggestions.

 

[gggGary]

Those are both correct, as factory installed You do have the two piece "early" rotor, not the later one piece rotor, right? Show us a pic of the fork and caliper? the 73- 75 has the caliper in front of the RH fork tube. 76 had it in back of the RH tube. Axle is set up with nut on the RH side?

 

[Shipper]

Yep, caliper in front of the legs and two piece rotor. See pics. '75-650B. Grasping at straws before I shave the rotor. Book says minimum thickness should be 6.5mm. Gives me just enough room I think.

Thanks G's.

 

[Shipper]

Those are both correct, as factory installed You do have the two piece "early" rotor, not the later one piece rotor, right? Show us a pic of the fork and caliper? the 73- 75 has the caliper in front of the RH fork tube. 76 had it in back of the RH tube. Axle is set up with nut on the RH side?

 

[5twins]

I would put a couple washers on the caliper mounting studs, space it in a little more. I would use stainless washers and sand them as thin as need be if they were too thick to begin with. That looks to me to be the easiest and cheapest solution. Shimming the disc out a little is a good one too but harder.

 

[XSLeo]

Can you get a pic of it all bolted together and showing how centered the rotor is in the caliper?
Leo

 

[XSLeo]

My 75 sat for a couple years without much riding, poor health, feeling much better now, I just got a working master cylinder on it and the brakes acted as yours do now. My 75 has the later 35 mm tube front end with the later style calipers, dual disc, any way they front wheel was hard to spin at first. It would lock solid when pressing brake lever but had a lot of drag while tring to snip by hand.
I was eager to ride so I just rode it, expecting some brake issues. After a short test ride they worked just fine.
Have you rode the bike with this issue to see if the bike is ok with it?
Leo

 

[5twins]

Yes, sometimes these minor issues just sort themselves. I noticed on my buddy's bike recently that his rear wheel was spinning hard. He just rode it and all that stuff went away. I guess the clutch was hanging or something, dragging a bit even in neutral. We don't know for sure what it was, but it's "fixed" now. Glad you're feeling better Leo and good to have you back.

 

[gggGary]

I did that on a CB1100F that was new to me, I didn't realize the rear brake had a plugged port in the MC, couldn't figure out why it didn't have much power until it finally came to a halt. After a wait I poured a can of diet soda on it, and nursed it home. Would suggest very short slow trips trying to "ride out" a brake issue.