Violent EM disengagement slowing at 9 mph

szabi · 11-03-2009, 10:27 PM

Prius 2008, 17.5K miles. I am an engineer & have put 25K miles on 2 Priuses since 2007.

The car is completely warmed up, pavement is dry and clear, weather is mild, temp. 60F. I am coasting in Drive, beginning at 30mph, towards a stop sign with foot off the accelerator. I apply the brake at 20mph. As I pass through the transition from regenerative slow-down to brakes at 9 mph, there is a single violent shudder through the drive train, but no sudden slow-down. I am aware of what the normal transition is like; this is about 10 times more violent, really disturbing. There is no bang or other noise.

This has happened twice in 3 weeks, at 2 different locations. No indications from the monitor lights or other readouts.

Has anyone else experienced this? Any diagnosis or advice?

qbee42 · 11-03-2009, 10:31 PM

This sheds suspicion on the friction brakes. I can't see where the HSD would cause this, but it is easy to see how a friction brake problem could cause a shudder at the transition.

Tom

szabi · 11-03-2009, 10:45 PM

Quote:

Originally Posted by qbee42

This sheds suspicion on the friction brakes. I can't see where the HSD would cause this, but it is easy to see how a friction brake problem could cause a shudder at the transition.

Tom

Quite possibly. But why would it occur rarely and intermittently? If it IS a brake problem, I would suspect a problem with the brake boost actuators or their controls.

Shawn Clark · 11-04-2009, 12:57 AM

Have you tried making it do this at low speed in neutral? Since it is intermittent it would be hard to prove the negative, but if it did it while in neutral you could isolate the problem to the friction braking system.

Maybe there is some stickiness on the rails/mechanism of the friction brakes (sand/gravel/flash rust.) You might be able to clear this with some solid braking in neutral from moderate speeds.

szabi · 11-04-2009, 06:45 AM

[QUOTE=Shawn Clark;994973]Have you tried making it do this at low speed in neutral? Since it is intermittent it would be hard to prove the negative, but if it did it while in neutral you could isolate the problem to the friction braking system.

Thanks, I'll try this.

richard schumacher · 11-05-2009, 10:18 AM

Presumably you have experience with Prius brake grabbiness in damp weather? and this ain't that?

qbee42 · 11-05-2009, 10:45 AM

Quote:

Originally Posted by Shawn Clark

Have you tried making it do this at low speed in neutral? Since it is intermittent it would be hard to prove the negative, but if it did it while in neutral you could isolate the problem to the friction braking system.

Maybe there is some stickiness on the rails/mechanism of the friction brakes (sand/gravel/flash rust.) You might be able to clear this with some solid braking in neutral from moderate speeds.

These are my thoughts as well.

Tom

szabi · 11-08-2009, 11:18 PM

Quote:

Originally Posted by richard schumacher

Presumably you have experience with Prius brake grabbiness in damp weather? and this ain't that?

Definitely not. Tnx.

11-03-2009, 10:27 PM	#1
szabi I also have a 2007 Prius Join Date: Nov 2007 Location: 200 mi N of SF Bay area Posts: 16 My Car: 2008 Prius Model: Package: #4 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Violent EM disengagement slowing at 9 mph Prius 2008, 17.5K miles. I am an engineer & have put 25K miles on 2 Priuses since 2007. The car is completely warmed up, pavement is dry and clear, weather is mild, temp. 60F. I am coasting in Drive, beginning at 30mph, towards a stop sign with foot off the accelerator. I apply the brake at 20mph. As I pass through the transition from regenerative slow-down to brakes at 9 mph, there is a single violent shudder through the drive train, but no sudden slow-down. I am aware of what the normal transition is like; this is about 10 times more violent, really disturbing. There is no bang or other noise. This has happened twice in 3 weeks, at 2 different locations. No indications from the monitor lights or other readouts. Has anyone else experienced this? Any diagnosis or advice?

11-03-2009, 10:31 PM	#2
qbee42 Senior Member Join Date: Mar 2006 Location: Northern Michigan Posts: 10,474 My Car: 2006 Prius Model: Package: #7 Thanks: 94 Thanked 387 Times in 289 Posts Friends: 10	Re: Violent EM disengagement slowing at 9 mph This sheds suspicion on the friction brakes. I can't see where the HSD would cause this, but it is easy to see how a friction brake problem could cause a shudder at the transition. Tom

11-04-2009, 12:57 AM	#4
Shawn Clark Senior Member Join Date: Aug 2008 Location: Midwest Posts: 2,070 My Car: 2008 Prius Model: Package: #2 Thanks: 112 Thanked 103 Times in 85 Posts Friends: 0	Re: Violent EM disengagement slowing at 9 mph Have you tried making it do this at low speed in neutral? Since it is intermittent it would be hard to prove the negative, but if it did it while in neutral you could isolate the problem to the friction braking system. Maybe there is some stickiness on the rails/mechanism of the friction brakes (sand/gravel/flash rust.) You might be able to clear this with some solid braking in neutral from moderate speeds.

11-04-2009, 06:45 AM	#5
szabi I also have a 2007 Prius Join Date: Nov 2007 Location: 200 mi N of SF Bay area Posts: 16 My Car: 2008 Prius Model: Package: #4 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Re: Violent EM disengagement slowing at 9 mph [QUOTE=Shawn Clark;994973]Have you tried making it do this at low speed in neutral? Since it is intermittent it would be hard to prove the negative, but if it did it while in neutral you could isolate the problem to the friction braking system. Thanks, I'll try this.

11-05-2009, 10:18 AM	#6
richard schumacher Destination: Eschaton Join Date: Mar 2004 Location: United States Posts: 5,508 My Car: 2004 Prius Model: N/A Package: #6 Thanks: 99 Thanked 93 Times in 66 Posts Friends: 0	Re: Violent EM disengagement slowing at 9 mph Presumably you have experience with Prius brake grabbiness in damp weather? and this ain't that?

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