Another 1st gen brake problem

[PEIslander]

When using the linked brake on my 84 Venture after a few seconds of normal braking it begins to pulse similar to a warped rotor. I have replaced the pads and bled the front and rear and the Antidive and the problem continues. I have checked the runout on the rotors and it is less than 1/2 a millimeter on the front and almost none on the rear.

 

Any suggestions? Is it possible that the rear master cylinder return hole is partially plugged ? My next step is disconnecting the front caliper to see if the rear alone is OK.

 

Rick

[Squeeze]

Sound like Heat causing a Rotor to warp. A partially plugged return Hole wouldn't let you feel any Pulse while braking.

[PEIslander]

Squeeze,

 

I guess I'll disconnect the left front caliper to determine which rotor.

 

Hmmmm - I have a silly question, Can the front wheel be put on backwards? This would exchange the front rotors with minimal work and I would know if its a front rotor this way. What do you think?

[Squeeze]

Only temporary and without any extra Weight or Load, this would work. But you won't have the Speedo connected. No big Deal, but thats the Way it is.

[KingSizer]

I'm having the same problem and I look forward to hearing some ideas.

I think I have warped rotors or a high spot that rubs the pads on each rotation through the calipers. It sort of feels like it's one particular spot that gets tight and then releases, even though I'm not pumping the pedal and am applying the same constant amount of pressure.

I put new pads on it recently, but I remember it sort of doing this before with the old pads.

 

btw, what is runout?

[PEIslander]

Squeeze, I was only thinking of reversing the front wheel to check the rotors, certainly not for more than a short test run. I might try that tonight.

 

KingSizer, Runout is a measurement of the deflection in the rotor as the wheel is rotated. There are dial guages available to measure this. I don't know the specs for these brakes but a small amount of runout is normal. In my case the pulsing starts after the brakes are applied for a few seconds so the rotor may be warping as it heats up.

[Squeeze]

Squeeze, I was only thinking of reversing the front wheel to check the rotors, certainly not for more than a short test run. I might try that tonight.

 

KingSizer, Runout is a measurement of the deflection in the rotor as the wheel is rotated. There are dial guages available to measure this. I don't know the specs for these brakes but a small amount of runout is normal. In my case the pulsing starts after the brakes are applied for a few seconds so the rotor may be warping as it heats up.

 

Rick, i sure understood what you plan, but i wrote my Statement for the Guys who might read this in the Future. It's not good to use the Wheels in reverse Direction. It may not be a Problem with our Bikes, but there certainly are Problems ahead when you do that with nowerdays Rims which are as thin as they can cast it. They probably can't hold up the Brake Forces when used the wrong Way.

[PEIslander]

I understand your comment Squeeze. and for everyone else.

" Don't try this at home. "

[Squeeze]

I understand your comment Squeeze. and for everyone else.

 

" Don't try this at home. "

 

 

 

 

And don't forget to mention the Subtitle ..

 

"recorded with a professional Rider on a closed Circuit"

 

 

:big-grin-emoticon::big-grin-emoticon:

[skydoc_17]

Hi PEIslander,

According to the Yammer Service Manual, (page 6-4) Max runout on the front brake rotors can be .15mm (.006 ins.) You said in your post you were seeing .5mm (.020 ins) runout. This would be more than 3 times the allowable runout according to the service manual. Sounds to me that you have a pair of warped front rotors. The Mark 1 VR used the unvented rotors (no slots) and like a regular car were suseptable to warping. Plus if you use the front brake lever more than the foot pedal you would be stopping your 850 lb. scoot with just the right rotor. If you are seeing more runout on the left side, it is one of two things, you brake a lot with the foot pedal or you have a caliper draging on the left side. Either way, If you decide to replace the rotors I would take a REAL CLOSE LOOK at both of the front calipers to make Darn Sure you don't smoke those new rotors. (Don't ask me how I know this!)

Just my 2 cents,

Ride safe,

Earl

[bobcat]

When using the linked brake on my 84 Venture after a few seconds of normal braking it begins to pulse similar to a warped rotor. I have replaced the pads and bled the front and rear and the Antidive and the problem continues. I have checked the runout on the rotors and it is less than 1/2 a millimeter on the front and almost none on the rear.

 

Any suggestions? Is it possible that the rear master cylinder return hole is partially plugged ? My next step is disconnecting the front caliper to see if the rear alone is OK.

 

Rick

 

I had the same problem on my 86VR....Pulsing when I used the foot pedal..I wasn't sure if it was the rear or Lt front rotor..Several members plus a couple of parts people told me that a vast majority wound up being the rear rotor..Bottom line is they were right..it was the rear rotor

[bongobobny]

You may have a "hard spot" on your rotor. This is different than runout. Hard spots are usually caused by the rotor being in the same place for extended periods in the weather (Not being used for months and months) and as the surface rust that is on the rotor everywhere BUT where the calipers are gets eroded off, the clean spot gives extra "Grab", or possibly less grab, with every revolution. Also impurities in the metal can cause these hard spots to occur. This is usually fixed with resurfacing the rotor but in the case of motorcycle rotors, they should not be turned down. They can be lightly resurfaced though, but not really recommended.

[PEIslander]

Well, I decided not to reverse the front wheel so I removed the front caliper from the fork tube put a couple of old brake pads in place of the rotor and secured the whole thing with the brake lines attached and then went for a short ride. It turns out that my left front rotor is bad. The runout on this rotor was .5mm and as skydoc_17 says the limit is .15mm. With this rotor not used the rear braking is smooth as silk. So the good news is I found the cause of the pulsing brake but the bad news is I need a left front rotor.

 

 

Guess I need to start a new thread " Left Front Rotor needed for 84 XVZ12L ":hurts:

 

Rick

[shighley]

PEIslander; I've had good luck with straightening rotors and have done it a couple of times. I bought rotors off EBay and they were warped. I used a travel dial indicator and a magnetic stand to tell me where the low and high spots were. I then used a large adjustable wrench to coax the rotor back to where it belongs. Amazingly, the heat cycles don't seem to make the metal go back to it's bent position. Call me a crazy shade tree mechanic, but the process worked for me. Ride safe, Steve

[PEIslander]

Just an update for anyone watching this thread.

 

Bought a pair of front rotors on ebay for about $70.00 including shipping. They measure 8.8mm and 8.9mm. My old rotors were closer to 8.3mm so I changed both. My bike has 101,000km on it. So To make a long story short I rode about 100 miles last night and both rotors are true and my pulsing is gone.

 

YAHOOO!

[GeorgeS]

Its just Amazing, what US Back Yard Mechanics can Achieve !!!

 

Thumbs UP !!

[george0fthejungle]

Its just Amazing, what US Back Yard Mechanics can Achieve !!!

 

Thumbs UP !!

 

And as I get braver, Im going to try some of these maintenance and repair items myself. I've really been impressed with some of the step by step instructions with photos that members have posted on this site. They may just give me the confidence to attempt this stuff myself!