Author Topic: Bouncing rear while braking  (Read 747 times)

Offline csj992

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Bouncing rear while braking
« on: August 16, 2018, 08:14:42 AM »
Got a question guys, can a front rotor with a lateral run out of .007 (on front left only) cause the rear end of the truck to hop  while braking. Everything from master cylinder to rear pads has been replaced. It seems to do it more after getting warmed up and severity depends on how much brake pressure is applied. Thanks, Charlie
1984 K2500
1995 Samurai
1998 Road King
1990 Goldwing trike

Offline VileZambonie

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Re: Bouncing rear while braking
« Reply #1 on: August 16, 2018, 11:12:51 AM »
No.

check your springs and shocks. Are you sure it's hopping and not pulsating? If it's the rear, remove the drums and inspect.
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Offline csj992

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Re: Bouncing rear while braking
« Reply #2 on: August 16, 2018, 07:21:34 PM »
Thanks for the reply. Shocks are new, all suspension bUshings replace with poly bushings. Rear drums were turned at a machine shop and all internals are new. When braking easy, I can feel a slight catch and release.
1984 K2500
1995 Samurai
1998 Road King
1990 Goldwing trike

Online zieg85

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Re: Bouncing rear while braking
« Reply #3 on: August 16, 2018, 07:24:42 PM »
are you certain the primary shoe(smaller) is towards the front?
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Offline csj992

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Re: Bouncing rear while braking
« Reply #4 on: August 17, 2018, 08:23:11 AM »
Thanks zieg85, I read that suggestion before and I made sure it was as you said. Thanks, Charlie
1984 K2500
1995 Samurai
1998 Road King
1990 Goldwing trike

Offline VileZambonie

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Re: Bouncing rear while braking
« Reply #5 on: August 18, 2018, 06:06:09 PM »
Well it sure sounds like you need to reinspect.
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Offline Henry

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Re: Bouncing rear while braking
« Reply #6 on: August 20, 2018, 01:36:40 PM »
Hi CSJ992:
Does your year service manual say that .007" disc lateral runout is acceptable?...my 76 service manual says max lateral runout is .005". Also, my book states that a disc thickness variation greater than .0005" will cause brake pedal pulsation.

When you get the rear wheel hop, do you know if it is because of an initial rear brake lock-up?...if you are not sure, maybe you can have an assistant stand on the side of a deserted road and observe what happens when you drive by and brake. Do you have any other anomalys? like noise or pulling to one side?

If rear suspension parts are all tight and all brake parts are new except for discs and drums, I would guess that the pulsation you feel in the pedal at low speed is causing the lock up at high speed. Another thing to look at is the tightness of your front wheel bearings...they have to be adjusted very carefully ...too loose can possibly exacerbate a excessive runout condition on the discs.

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Henry

Offline csj992

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Re: Bouncing rear while braking
« Reply #7 on: August 27, 2018, 01:17:54 PM »
Hey Henry, Thanks for the reply. I read somewhere that .004 was unacceptable. Right side is 0. I was thinking it might be the compensator valve, but I did use the bleeding tool when bleeding the brakes. It is strange. After driving the truck for a while it gets worse than when cold. The only thing that wasn't done was to have the rotors turned. Guess I will have them turned and see if anything improves. Thanks, Charlie   P.S. bearings were tightened to factory specs.
1984 K2500
1995 Samurai
1998 Road King
1990 Goldwing trike

Offline Henry

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Re: Bouncing rear while braking
« Reply #8 on: August 28, 2018, 10:10:37 AM »
Hi Charlie:
Yeah, I think it would be a good idea to have your rotors inspected and turned...I always do it when I replace a lot of brake components for good measure...especially if you have not had them turned for a few thousand miles. Let us know how this affects your braking when you are done. There seem to be fewer and fewer shops that do rotor turning anymore, but O'Reillys does it for the best price in my town.
Regards,
Henry

Offline VileZambonie

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Re: Bouncing rear while braking
« Reply #9 on: August 28, 2018, 06:13:12 PM »
So I'm not following your logic here. You are saying the rear end is hopping and are going down the path of .007" of an inch of runout in the front rotor potentially being the cause? We are talking less than two sheets of paper in thickness variation so clearly this is not the problem that's causing your rear end to bounce or hop as you describe. Have you reinspected the rear brakes yet? check the shoes, hardware, adjustment and drum for out of round.
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Offline csj992

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Re: Bouncing rear while braking
« Reply #10 on: October 10, 2018, 06:04:14 PM »
Update. I did reinspect the rear drums and sure enough one was a little out of round. I finally found a rear disc brake conversion for a K2500. Parts should be here tomorrow. Hopefully this will eliminate my bouncing rear end.
1984 K2500
1995 Samurai
1998 Road King
1990 Goldwing trike