Brake issue (a real adreneline rush)

[Lanskpr]

Not really. Although when it happened yesterday my heart was a pounding pert good.

Here is what is happening: about a year ago I went to apply the brakes. The pedal wouldn't budge. The truck pulled hard to the left, but really wouldn't slow down. I took my foot off the brake and applied the brakes again. Normal braking ensued. I immediatly called my mechanic and had him look at it. He recommended starting with replacing the front pads since they were pretty worn. He also noticed some seepage at the Hydroboost. He also said the Power Steering Fluid looked dirty and since the PS is integrated with the brakes he recommended a flush and new fluid. I had him do the pads. Since the Hydroboost was like $800.00 and the flush was like $80.00 I opted for the flush. That and since he was less than 100%confident that the Hydroboost was the culprit.

During the next few months of daily driving, this hard pedal/no brakes would rear it's ugly head occasionally. (I really have increased my following distance and am the most defensive driver in Virginia). Always the same. Hit the brakes. Pedal doesnt budge. Release and reapply brakes are fine. Happens maybe once every two thee weeks.

Last week it did it at a time that I really needed the brakes to work. Nothing bad happened but I said enough. Took it back to my mechanic and told him the problem again. He recommended the new Hydroboost. Had him install it. After 3 days of driving it did it again. With a abrupt pull to the left to boot. I called him to let him know and he said bring it in.

This is why I am here with this awe inspiring story. Can anyone come up with an idea of whats causing this so I can relate it to my mechanic?

One more thing. The ABS light has been on intermittently now for about a week. He put his reader on it and said "left wheel sensor" somethingorother. Didnt make a big deal out of it. He did say to replace both rear sensors when its time to tackle that issue

I am grateful for any insight anyone can offer.

[Robyn]

My take on this is that the ABS Unit is taking a leave on you.

There is really nothing other than the ABS system that can cause a hard pedal and a pull to one side or other that is intermitent.

I will say this, you are not goin g to like the cost of the R&R on the ABS.

My 3500 truck has a gremlin in the ABS although not a functionality issue, it is however anoying (light on at times then off)

Dealer quoted me $1000 to replace the thing and bleed the brakes.

The brake system (without the ABS) is simple. The hydroboost provides the extra power to the brakes, the master cylinder supplies fluid to the brakes themselves.

A failing master cylinder will not cause the symptoms you are having.

A failing or failed hydroboost can make a hard pedal but not a pulling issue.

Individual brake calipers or drums brake assemblies either work or they don't.

The issue you are having is most likely directly related to the ABS system.

A failed/failing sensor should not cause the rig to pull but you never know.

A failing ABS unit can cause many issues.


Good luck and keep us posted.


Robyn

[DmaxMaverick]

Is this a C3500, or 3500HD? Very different animals. The HD is a 15,000 GVWR chassis, usually used for wreckers, ambulance, utilities, etc, and the front axle is unique among GM Pickup chassis. The C3500 is the regular 1 ton truck. The brake and ABS systems are different.

[Lanskpr]

My take on this is that the ABS Unit is taking a leave on you.

There is really nothing other than the ABS system that can cause a hard pedal and a pull to one side or other that is intermitent.

I will say this, you are not goin g to like the cost of the R&R on the ABS.

My 3500 truck has a gremlin in the ABS although not a functionality issue, it is however anoying (light on at times then off)

Dealer quoted me $1000 to replace the thing and bleed the brakes.

The brake system (without the ABS) is simple. The hydroboost provides the extra power to the brakes, the master cylinder supplies fluid to the brakes themselves.

A failing master cylinder will not cause the symptoms you are having.

A failing or failed hydroboost can make a hard pedal but not a pulling issue.

Individual brake calipers or drums brake assemblies either work or they don't.

The issue you are having is most likely directly related to the ABS system.

A failed/failing sensor should not cause the rig to pull but you never know.

A failing ABS unit can cause many issues.


Good luck and keep us posted.


Robyn

Thanks for your imput. Every thing with this truck is expensive.

Do you know if there is a proportioner on this system? Could that be an issue?

Andrew

[Lanskpr]

Is this a C3500, or 3500HD? Very different animals. The HD is a 15,000 GVWR chassis, usually used for wreckers, ambulance, utilities, etc, and the front axle is unique among GM Pickup chassis. The C3500 is the regular 1 ton truck. The brake and ABS systems are different.

DmaxMaverick,

It is a 3500HD. I have a dump body on it so I can haul 3 tons or so in a safer manner. Safer than the 1 ton Ford I used to drive.

Andrew

[DmaxMaverick]

Thanks for your imput. Every thing with this truck is expensive.

Do you know if there is a proportioner on this system? Could that be an issue?

Andrew

Yes. It has a bias proportioning valve, and a good place to start. Sometimes, they don't reset after being shuttled, leaving the "bias" favored to one side. It could effect pedal feel, due to one side requiring less fluid volume. In most cases, it is best to replace them, rather than attempt a (usually unsuccessful) cleaning/repair.

The 3500HD ABS system is almost entirely passive, unlike the C3500. Unless it's full of air (which causes havoc in any ABS system), I would not suspect the module it at this time. It doesn't seem like air is the problem, as you are able to get a hard pedal. Verify you have cleared and remedied the sensor error code. If not, I'd suspect the reluctor or sensor harness issue.

[Lanskpr]

Yes. It has a bias proportioning valve, and a good place to start. Sometimes, they don't reset after being shuttled, leaving the "bias" favored to one side. It could effect pedal feel, due to one side requiring less fluid volume. In most cases, it is best to replace them, rather than attempt a (usually unsuccessful) cleaning/repair.

The 3500HD ABS system is almost entirely passive, unlike the C3500. Unless it's full of air (which causes havoc in any ABS system), I would not suspect the module it at this time. It doesn't seem like air is the problem, as you are able to get a hard pedal. Verify you have cleared and remedied the sensor error code. If not, I'd suspect the reluctor or sensor harness issue.\

When they scanned it(when I took it in last week) they wrote: " We found code 23 Erratic right front wheel speed sensor stored in the ABS Module. We cleared the code." My question is, could this sensor thing cause the irregular braking. I didn't get the impression they thought it was the cause as they never said that it had to be replaced to alleveate the funky braking. They did'nt have one avalable that Friday afternoon and also said they should be replaced in pairs? Hence, it was not changed.

These folks I take it to are sound mechanics. However, I don't think they see many GMC that year, that weight class. I am hoping for some possibilities to suggest. Or at least be able to have a discussion with them.

[DmaxMaverick]

If you have a city/county/state or utility yard near you, give them a visit. I'll bet their mechanics see this more often than auto shops. There are/were a LOT of 3500HD's in service for city and road services, and utilities.

[Lanskpr]

If you have a city/county/state or utility yard near you, give them a visit. I'll bet their mechanics see this more often than auto shops. There are/were a LOT of 3500HD's in service for city and road services, and utilities.

Good thought. Those trucks were everywhere. I am heading up there now, keep you up to date.

Thanks
Andrew

[Lanskpr]

They are looking at the rotors/wheel speed sensors. The are saying the rotors are bad(can't be resurfaced) and that the portion of the right rotor that works in concert with the wheel speed sensor (they described as like gear teeth) is corroded,etc.. Therefore they are going to start by installing new rotors.

They will, if this doesn't fix it, consider the PS pump next.

[DmaxMaverick]

Thanks for the update.

So far, the issues points to the wheel(s) components. NOT the power steering pump--no mention of loss of steering, and if you have steering power, the pump is working (at least well enough to not effect the brakes, and it WILL NOT cause a braking bias). If you have good power steering, and issues with the brake, the hydroboost unit or MC can be suspect, but not the pump. The ABS module and system operates passively. If it's causing a brake bias, it must be receiving bad input information (such as a sensor not performing accurately or connection/wire issue).

If your rotors are used up (as in, can't resurface), corroded, and you have ABS sensor code(s), you MUST get that addressed before anything else. I suggest looking for nothing else until that issue is put to bed.

[Robyn]

A wheel speed sensor thats feeding false info to the Computer can certainly make for all sorts of wierd conditions.

My bet is that once the problem with the rotors and reluctors are fixed that the gremlin will go away.

Sadly there is not a quick guess work plan with this stuff. Codes must be looked at before any real work can begin.

At least that gives an idea of what is not happy.


Missy

[Lanskpr]

Thanks for the update.

So far, the issues points to the wheel(s) components. NOT the power steering pump--no mention of loss of steering, and if you have steering power, the pump is working (at least well enough to not effect the brakes, and it WILL NOT cause a braking bias). If you have good power steering, and issues with the brake, the hydroboost unit or MC can be suspect, but not the pump. The ABS module and system operates passively. If it's causing a brake bias, it must be receiving bad input information (such as a sensor not performing accurately or connection/wire issue).

If your rotors are used up (as in, can't resurface), corroded, and you have ABS sensor code(s), you MUST get that addressed before anything else. I suggest looking for nothing else until that issue is put to bed.

No loss of power steering. Sounds like Monday morning I will give them the go ahead to put on new rotors and wheel sensors.

I appreciate your imput. Thanks again.

[Lanskpr]

A wheel speed sensor thats feeding false info to the Computer can certainly make for all sorts of wierd conditions.

My bet is that once the problem with the rotors and reluctors are fixed that the gremlin will go away.

Sadly there is not a quick guess work plan with this stuff. Codes must be looked at before any real work can begin.

At least that gives an idea of what is not happy.


Missy

Going to have the rotors/wheel sensors replaced on monday.

I understand that its a complicated issue. Certainly what wasn't helping was that it wouldn't act up when they drove it.

Thanks for your help.

[Robyn]

Oh of course not, they are always perfect little angels when ya drag it over to the shop. :eek:

Whatever it is the likelyhood that its electronic is pretty high.

If there is a wheel sensor going hen house or an internal circuit in the ABS Unit going by by it can act intermitently for a long time before a total failure happens.

The wheels sensors are over $100 each just to buy them.

I priced sensors for DaHooooley a week or so ago when My ABS light came on.

Unfortunately the code I have relates to the ABS pump unit and not sensors. So mine is gonna just have to burn the stinking light.

Good luck with the gremlin.

Robyn

[rustyk]

Oh of course not, they are always perfect little angels when ya drag it over to the shop. :eek:

Robyn

This is "Wort's Law": No device will work closer to design specs than the instant the technician starts diagnosis.

[Lanskpr]

Three days of driving and no brake problems.