brakes gone then back then gone
11-20-2015, 02:12 PM
#31
Patdaly - thanks. I'm easily confused, it seems - misidentified valves are littering my previous posts. I sure need to find a '97 FSM vs the '96 I've limped along with so far.
Per the last drawing you posted:
part 15 = 52007312 = "brake pressure limit valve", AKA "RWAL valve" from earlier drawing
part 16 = 52008784 = "proportioning valve", AKA "combination valve" from earlier drawing.
You're saying I probably need a boneyard-sourced or new part 15 (which may not be available), right?
I've not read exhaustively other posts about this, but one had numerous references to people finding that they couldn't even bleed their rear brakes, perhaps due to this valve being stuck closed, though I'm again unsure of whether it's part 15 or something else that they were describing. If the rain ever stops here, it would be simple enough for me to crack a bleed-screw and see if I can get a jet of nasty dark fluid out of it when I step on the brakes, but I'm sure that's not the ultimate diagnostic.
BTW - I think I do have a "load-sensing" valve, but can't recall for sure. Anything to poke at there? Some seem to have bypassed this with a simple hose...
Per the last drawing you posted:
part 15 = 52007312 = "brake pressure limit valve", AKA "RWAL valve" from earlier drawing
part 16 = 52008784 = "proportioning valve", AKA "combination valve" from earlier drawing.
You're saying I probably need a boneyard-sourced or new part 15 (which may not be available), right?
I've not read exhaustively other posts about this, but one had numerous references to people finding that they couldn't even bleed their rear brakes, perhaps due to this valve being stuck closed, though I'm again unsure of whether it's part 15 or something else that they were describing. If the rain ever stops here, it would be simple enough for me to crack a bleed-screw and see if I can get a jet of nasty dark fluid out of it when I step on the brakes, but I'm sure that's not the ultimate diagnostic.
BTW - I think I do have a "load-sensing" valve, but can't recall for sure. Anything to poke at there? Some seem to have bypassed this with a simple hose...
11-20-2015, 03:11 PM
#32
Administrator
Yes, you are looking at part 15, which is not available new, but used to be available remanned.
The proportioning valve only changes the metering from the front to the back, and isn't a dynamic item, so it isn't that for a variable issue like you have.
The load sensing valve is back by the rear end, the valve is controlled by a rod attached to the rear end, and varies rear fluid flow to the brakes via. load height. It is somewhat a dynamic function, but here again, not one that would vary randomly like you describe.
The proportioning valve only changes the metering from the front to the back, and isn't a dynamic item, so it isn't that for a variable issue like you have.
The load sensing valve is back by the rear end, the valve is controlled by a rod attached to the rear end, and varies rear fluid flow to the brakes via. load height. It is somewhat a dynamic function, but here again, not one that would vary randomly like you describe.
11-20-2015, 07:49 PM
#33
You know, I had two occasions to slam on the brakes today, and both times, I heard the right rear tires (at least) lock up and skid.
Both the ABS and 'brake' warning lights are chronically on - except this morning when I first drove out and made a point of seeing if I could feel any give in the pedal, when they all went out, as if to tell me the problem had magically self-corrected (but they came back on a minute or two later after I started driving). And it's actually been a long time since I had one of those sudden "loss of power-assist" episodes.
What does it mean? Really an ABS failure?
At minimum, I need to replace front pads. Anything new/different I should go after, considering the above?
Both the ABS and 'brake' warning lights are chronically on - except this morning when I first drove out and made a point of seeing if I could feel any give in the pedal, when they all went out, as if to tell me the problem had magically self-corrected (but they came back on a minute or two later after I started driving). And it's actually been a long time since I had one of those sudden "loss of power-assist" episodes.
What does it mean? Really an ABS failure?
At minimum, I need to replace front pads. Anything new/different I should go after, considering the above?
11-22-2015, 01:41 PM
#34
Administrator
Hmm, almost makes me think you need to scan it for ABS codes. Mine only had the ABS/Brake light on after an issue with the pedal going to the floor, when it was working right, the next time you started it,m lights were off until another issue.
Could be your rear wheel sensor.
Could be your rear wheel sensor.
12-05-2015, 10:23 PM
#35
So one Rock Auto order, delivered with box 'zip-stripped' open, and then taped shut, with notes from USPS to the effect that it had opened in shipment, came without brake pads...probably under that back conveyor belt at the San Francisco processing facility...Rock has what seems to be a no-humans-involved series of questions to get through under these circumstances, and seemed to just cyber-shrug it off. They sent me another box with just the pads, and at last, I was able to take Step 1: pad replacement.
Pad replacement was easy and reassured me that many improvements have ensued in automotive engineering since the Brits built the cars I cut my teeth on back in my 20s. No frozen fasteners, nothing stripped, no cracked seals...and it's almost a 20-year-old truck. Nice.
All I'd really expected from the pad replacement was peace of mind and a better starting-place, since my pads were WAY thin. And that looked like all I was going to get, too; I got in the driver's seat, fired it up and pumped the pedal a bit to set the calipers & take up the slack, and the ABS/Brake lights remained on. I eased it down the steep scary gravel & dirt driveway, not alarmed but not stunned with any sudden improvement, either, and figured, "yeah, I didn't really expect this to fix things, anyway." Backed up the driveway, hooked up a tube to my RR brake bleeder, started the engine, and observed great flow of fluid through the tube - no crazy obstructions getting to the rear brakes. A mere touch of the pedal, in fact is all it takes to set the fluid flowing through the clear tubing - seems as if it's TOO free-flowing to the rear, if anything, certainly not restricted, as some report.
And there's simply no "payload-weight" compensating valve in existence on mine. Did 3500s maybe not have those? I don't see any evidence of one having been there, either. All looks factory, with a rubber hose leading from steel tubing inside frame, down to a block on the top of the diff that combines a breather for the diff with two outlets for the L/R brake cylinders.
I went inside to refresh my memory of OBD connector pinout, location, flashes, etc, then went back out, located the connector, and was about to jumper across pins 9 & 13, so I switched the ignition on to get started. ABS light came on...but then went OUT. Huh? I started the engine, whereupon it came on again, and then...went OUT again. What about the red "brake" light? OK, I release the handbrake. BOTH of them out now. ***? All I did was change my pads, then bleed maybe 4 oz of fluid through the RR wheel-cylinder, and both lights are out?
I repeated the above keyswitch/start check - same behavior - both lights out under "normal" driving conditions, though I have yet to actually drive it anywhere.
I kinda can't believe it's "fixed," especially because the braking action isn't any better than it was before I replaced the pads.
Any thoughts now? Sell it immediately?
Pad replacement was easy and reassured me that many improvements have ensued in automotive engineering since the Brits built the cars I cut my teeth on back in my 20s. No frozen fasteners, nothing stripped, no cracked seals...and it's almost a 20-year-old truck. Nice.
All I'd really expected from the pad replacement was peace of mind and a better starting-place, since my pads were WAY thin. And that looked like all I was going to get, too; I got in the driver's seat, fired it up and pumped the pedal a bit to set the calipers & take up the slack, and the ABS/Brake lights remained on. I eased it down the steep scary gravel & dirt driveway, not alarmed but not stunned with any sudden improvement, either, and figured, "yeah, I didn't really expect this to fix things, anyway." Backed up the driveway, hooked up a tube to my RR brake bleeder, started the engine, and observed great flow of fluid through the tube - no crazy obstructions getting to the rear brakes. A mere touch of the pedal, in fact is all it takes to set the fluid flowing through the clear tubing - seems as if it's TOO free-flowing to the rear, if anything, certainly not restricted, as some report.
And there's simply no "payload-weight" compensating valve in existence on mine. Did 3500s maybe not have those? I don't see any evidence of one having been there, either. All looks factory, with a rubber hose leading from steel tubing inside frame, down to a block on the top of the diff that combines a breather for the diff with two outlets for the L/R brake cylinders.
I went inside to refresh my memory of OBD connector pinout, location, flashes, etc, then went back out, located the connector, and was about to jumper across pins 9 & 13, so I switched the ignition on to get started. ABS light came on...but then went OUT. Huh? I started the engine, whereupon it came on again, and then...went OUT again. What about the red "brake" light? OK, I release the handbrake. BOTH of them out now. ***? All I did was change my pads, then bleed maybe 4 oz of fluid through the RR wheel-cylinder, and both lights are out?
I repeated the above keyswitch/start check - same behavior - both lights out under "normal" driving conditions, though I have yet to actually drive it anywhere.
I kinda can't believe it's "fixed," especially because the braking action isn't any better than it was before I replaced the pads.
Any thoughts now? Sell it immediately?
12-07-2015, 11:50 AM
#36
Administrator
Good lord, don't sell her.
Lets go back to square one.
When you say braking action, do you mean pedal feel, pedal effort, or excessive pedal travel.
The brakes on the pre-2000 ones aren't anything to write home about, but they do stop you, if you are patient.
Lets go back to square one.
When you say braking action, do you mean pedal feel, pedal effort, or excessive pedal travel.
The brakes on the pre-2000 ones aren't anything to write home about, but they do stop you, if you are patient.
12-07-2015, 12:04 PM
#37
Nah, I wasn't serious about selling. My vehicles generally end up disappearing into piles of rust-flakes before they'd get sold.
I was referring to pedal /effort/, at least, and maybe "feel," too. It's been a while since this happened, but there are brief flashes of "wow, my brakes just grabbed like maybe I remember they're SUPPOSED to" that happen. I don't get a sense of excessive travel, either.
Other probably unrelated stopping concern: I've mentioned my extreme steep-slope dirt/gravel driveway. 4WD is a requirement to back up this slope, and backing up is the "natural" way to approach it. But on leaving, I often find myself in awkward struggle to get it OUT of 4WD at the bottom of the driveway, not wanting to scrape up my tread any more than necessary once I'm on solid pavement. And since I don't need that 4WD "drive traction" to help me roll DOWN the driveway, I will sometimes (but rarely) shift out of 4WD before beginning to roll down. I don't do it always because it nags at me a little that I might need 4WD to get me back up, say if I need to yield to an unexpected passing car, etc. So I did this - pre-shifted to 2WD - last week at one point, and I then found that I seemed to have no positive braking control at ALL, just a slow ploughing action, as my front wheels (still "curbed") seemed to just scrape their way straight down the driveway. It wasn't particularly panic-inducing because I knew gravity wouldn't keep me moving into the street proper, and for some reason the fronts were not trying to steer me into the hillside even though that's where they were pointed. But it baffled me that, apparently only because I was no longer in 4WD, I was unable to stop my slide. Does this make any sense or add anything to the braking issues I've been describing?
I'm about to go on a 40 mile round-trip, so I will see how she performs.
I was referring to pedal /effort/, at least, and maybe "feel," too. It's been a while since this happened, but there are brief flashes of "wow, my brakes just grabbed like maybe I remember they're SUPPOSED to" that happen. I don't get a sense of excessive travel, either.
Other probably unrelated stopping concern: I've mentioned my extreme steep-slope dirt/gravel driveway. 4WD is a requirement to back up this slope, and backing up is the "natural" way to approach it. But on leaving, I often find myself in awkward struggle to get it OUT of 4WD at the bottom of the driveway, not wanting to scrape up my tread any more than necessary once I'm on solid pavement. And since I don't need that 4WD "drive traction" to help me roll DOWN the driveway, I will sometimes (but rarely) shift out of 4WD before beginning to roll down. I don't do it always because it nags at me a little that I might need 4WD to get me back up, say if I need to yield to an unexpected passing car, etc. So I did this - pre-shifted to 2WD - last week at one point, and I then found that I seemed to have no positive braking control at ALL, just a slow ploughing action, as my front wheels (still "curbed") seemed to just scrape their way straight down the driveway. It wasn't particularly panic-inducing because I knew gravity wouldn't keep me moving into the street proper, and for some reason the fronts were not trying to steer me into the hillside even though that's where they were pointed. But it baffled me that, apparently only because I was no longer in 4WD, I was unable to stop my slide. Does this make any sense or add anything to the braking issues I've been describing?
I'm about to go on a 40 mile round-trip, so I will see how she performs.
12-08-2015, 07:57 AM
#38
Administrator
Don't want to send you down a wrong road, but that sounds more like a Hydraboost getting flaky than anything with the ABS system.
Hopefully someone who has had one go bad will chime in here.
Hopefully someone who has had one go bad will chime in here.
12-08-2015, 10:36 AM
#39
I'll believe anything at this point.
Data from yesterday's drive: ABS/brake lites out still, as I drove down widowmaker, my killer-driveway, but this was short-lived; both lites came on by the time I was driving out our tiny road onto suburban streets. When next I noticed, they were out, and I was on the freeway...then on again at some point later.
As to brake action, they wavered, from being very-effective to moderately-effective, but never felt like they were utterly without power-assist. And I didn't notice a direct correlation between warning-lites being on and brakes being marginal.
Anyone?
Data from yesterday's drive: ABS/brake lites out still, as I drove down widowmaker, my killer-driveway, but this was short-lived; both lites came on by the time I was driving out our tiny road onto suburban streets. When next I noticed, they were out, and I was on the freeway...then on again at some point later.
As to brake action, they wavered, from being very-effective to moderately-effective, but never felt like they were utterly without power-assist. And I didn't notice a direct correlation between warning-lites being on and brakes being marginal.
Anyone?
12-09-2015, 04:53 PM
#42
Administrator
Ok, now when you have the funky brake feeling, have you noticed that the steering has less assist?
The reason I ask is both the brakes and steering is dependent on the PS pump pressure, and if it is varying you could get the sensation that you describe.
The reason I ask is both the brakes and steering is dependent on the PS pump pressure, and if it is varying you could get the sensation that you describe.
12-09-2015, 06:21 PM
#43
Good thought, Pat...I did have that combination at one point, (maybe 1-2 years ago) but it was quickly attributed to low PS reservoir, though I'd been excited to think I might fix everything by just replacing my PS pump. Seems as if when parked, if I curb the wheels to the extreme on my scary driveway, it can somehow, on a sometimes-only basis, cause a fluid leak.
Today's 40-mile round-trip didn't seem as peppered with the twin warning lights - only noticed them when I was leaving home, and not afterwards - but they're both in a position where I kind have to move around to see if they're on, which doesn't help log the problem.
Today's 40-mile round-trip didn't seem as peppered with the twin warning lights - only noticed them when I was leaving home, and not afterwards - but they're both in a position where I kind have to move around to see if they're on, which doesn't help log the problem.
12-15-2015, 05:46 PM
#44
This keeps morphing.
Mostly lights are OFF now. But not to make me feel /too/ OK about things, I noticed twice during driving yesterday, coming to a gradual stop, the pedal sank smoothly, in a second or two, from a nice high position, to a midway position, but not to the floor. That's something I've only noticed at idle, when coming to a smooth stop. Seems not associated with loss of PS (I try cranking the wheel side-to-side as soon as I realize, but don't notice a loss of assist.)
Mostly lights are OFF now. But not to make me feel /too/ OK about things, I noticed twice during driving yesterday, coming to a gradual stop, the pedal sank smoothly, in a second or two, from a nice high position, to a midway position, but not to the floor. That's something I've only noticed at idle, when coming to a smooth stop. Seems not associated with loss of PS (I try cranking the wheel side-to-side as soon as I realize, but don't notice a loss of assist.)
12-16-2015, 08:07 AM
#45
Administrator
This keeps morphing.
Mostly lights are OFF now. But not to make me feel /too/ OK about things, I noticed twice during driving yesterday, coming to a gradual stop, the pedal sank smoothly, in a second or two, from a nice high position, to a midway position, but not to the floor. That's something I've only noticed at idle, when coming to a smooth stop. Seems not associated with loss of PS (I try cranking the wheel side-to-side as soon as I realize, but don't notice a loss of assist.)
Mostly lights are OFF now. But not to make me feel /too/ OK about things, I noticed twice during driving yesterday, coming to a gradual stop, the pedal sank smoothly, in a second or two, from a nice high position, to a midway position, but not to the floor. That's something I've only noticed at idle, when coming to a smooth stop. Seems not associated with loss of PS (I try cranking the wheel side-to-side as soon as I realize, but don't notice a loss of assist.)
I hope someone who has actually had Hydraboost problems will chime in.
Mine just keeps stopping........