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Hey folks!
Great site and my first post. Irecentlypurchaseda 1980 GL1100 with 69,000 miles. I had my local mechanic (Orlando, FL) change both timing belts, rebulid the front calipers, adding braided lines and pads, flush the radiator, adjust the valvesand change all fluids.

Problem: When coming to a stop, the front brakes grip and then slip. This causes the front end to pump up and down until full stop. My mechanic said I have a slightly warped rotor, but there is NO pump in the lever and no pull to either side.

I have just relocated to Columbus, NC and will have to address this myself. Could this be fluid on the pads? A sticking caliper? The caliper leaked when I bought it, but is dry now.



Thanks for any input!

Motorhead
 

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First off, Welcome to the boards!

Take the bike and put it on the center stand, and get the front wheel off the ground with a small jack under the front of the motor. Spin the wheel and lightly press the front brake and you should be able to hear if you have a warped rotor or not. It may be able to be seen, but it may be to slight to see.

Also, check all 4 sides of the front rotors and see if you see any spots that are shinier or duller than normal.

Raymond
 

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Sounds like a warped rotor to me, but, you can try cleaning the rotor with brake cleaner and a Scotchbrite pad to see what happens.

I would imagine that you would be able to see any changes in color consistency on the rotor if you looked at it with a light.

If the fluid was on the pads only it would not create a pulsation because the contamination would be spread evenly around the rotor as it turned.

Vic
 

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If the caliper was leaking then you might have air in the the line which would cause you to have to pump the brake. Make sure you are not leaking now. Check you fluid lever and re bleed your brakes.
 

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It may just be a dirty rotor... mine does it sometimes. I just spray the whole thing with brake cleaner and it goes away. Most effective if you unmount the calipers and also spray the pad surfaces.

A bike isn't going to pull one way or another with a warped rotor (because there's only one wheel up front), and you might not feel it in the lever.
 

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motorhead wrote:
Hey folks!
Great site and my first post. Irecentlypurchaseda 1980 GL1100 with 69,000 miles. I had my local mechanic (Orlando, FL) change both timing belts, rebulid the front calipers, adding braided lines and pads, flush the radiator, adjust the valvesand change all fluids.

Problem: When coming to a stop, the front brakes grip and then slip. This causes the front end to pump up and down until full stop. My mechanic said I have a slightly warped rotor, but there is NO pump in the lever and no pull to either side.

I have just relocated to Columbus, NC and will have to address this myself. Could this be fluid on the pads? A sticking caliper? The caliper leaked when I bought it, but is dry now.
Motorhead, your problem has all the earmarks of a front rotor problem.

There are about 3 basic problems with a brake rotor..

1)- They warp,, as long as the warpage isn't too great & the gain in out-of-plain isn't too close together the brake will act somewhat normal as the caliper can float & follow the rotor run-out. You might feel a slight pulsation but no feed back into the hand lever. The more the warpage or the closer together the bends the more you will feel it.

2)-A rotor that varies in thickness,, eitherdue to heat damage or rust in then metal pores. Depending on how much thickness variation, it can cause a severe brake pulsation & a definite pulsation back up through the hand lever as the caliper pads are actually being moved apart form each other as the thick place goes between them. That is a nasty brake pulsation & can cause a lock up as the thick place comes between the brake pads.

3)- Oxidation on one or more places on the rotor,, (usually caused from parking with wet brake parts that has metallic pads). What you get there is a gain & loss in friction coefficient as the oxidized place passes through the brake pads & that will not only cause a brake pulsation but usually also a brake shudder. Sometimes it will feed back up through the hand lever if the pads are moved back into the calipers as the high friction areas draw the pads along.

Twsity
 

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unfortunately, if it is a rotor about the only option is to replace it. I did know a machine chop in collinsville IL (or was it caseyville) that would grind them down, and had that done on my 1000 and 500, and so you might find a shop that can do that. they do not "turn" like car rotos so that is out
 

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motorhead wrote:
Problem: When coming to a stop, the front brakes grip and then slip. This causes the front end to pump up and down until full stop. My mechanic said I have a slightly warped rotor, but there is NO pump in the lever and no pull to either side. Motorhead
You might want to check that the wheel itself is true. A cheap dial indicator from Harbor Freight (if they have the in your area) would be a worthwhile investment to check the wheel and rotors. You won't feel much feedback in the brake lever usually unless the warpage is pretty bad. You will never feel any pull to either side unless your are riding a bike with more than two wheels.
 

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Thanks Paul,

The mere mention of Harbor Frieght fills my heart with joy!
 

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Me too. Their stuff isn't first drawer, but I do buy a good bit of stuff from them. Most of my mechanics handtools are Craftsman, SK Wayne, and the like, but there's a lot of handy things that don't have to be first quality if you aren't running a commerical shop. I got a sliding compound miter saw from them for $90 that's been a gem.
 

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Welcome to the boardd Motorhead. This does really sound like a warped disc, but you can eliminate pads by pulling them and giving them a rub with sandpaper and thinners to get rid of any fluid. A test run will then give you a better idea.
 

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It was in fact a warped rotor. Turnedboth of themthis weekend at the local auto shop and it seems to be fine.

Thanks to all for the help!



Motorhead
 

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Matt,



I read your reply that you can't turn these rotors, but figured we had nothing to lose. They seem to be fine, but the metal came off like curly fries instead of dust. So far they seem ok. It has started quite a debate amoung the locals. Any more input?

Thanks!

Motorhead
 

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motorhead wrote:
Matt,



I read your reply that you can't turn these rotors, but figured we had nothing to lose. They seem to be fine, but the metal came off like curly fries instead of dust. So far they seem ok. It has started quite a debate amoung the locals. Any more input?
Motorhead, watch your brake pad wear. I have seen cases of turned (thinner) rotors allowing the caliper pistons to extend too far & either leaking or cocking & jamming. Not saying they will just saying to keep an eye on that aspect.

Twisty
 

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There's a limit to howthin they can be, might want to look it up.
 

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Anyone know a vendor for rotors on the '80 GL1100. The day will come either way.
 

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I have a pair of rotors from an '81. They measure 4.90 mm. No ridges on them, so I feel that is close to stock thickness.

Raymond
 

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Have you set a dial gauge to them for trueness? And what do you want for them?

Thanks!

Motorhead
 
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