Hydraulic parking brake turns on while driving

[CHEESE_WAGON]

Originally Posted by s2mikon

CHEESE_WAGON, I like your idea, but what kind of liability would you be incurring if you got into a vehicle crash and injured or killed someone?

An interesting question. I'm no expert on that aspect, but I should think such a swap would be no different in terms of liability if done by a qualified shop that did it correctly with factory parts.

To fully CYA, an inspection by a (possibly DOT-cerftified) state trooper similar to what is required to re-title as RV, but in the interest of getting a certification that the system works as prescribed and has no deficiencies or defects. Seriously, if you think about it, it's more or less the same thing, just from a different aspect of functionality.

One thing that would be necessary in such a swap is to set up a low-air warning light, as the hydraulic system pressure warning would be a different warning light. This could be as simple as swapping clusters from the donor truck (which would have the correct low-air warning factory), but might require a bit of wiring to retain proper functionality. Not as big a deal as it sounds. But the serious part would be to update the bus' various electronics that could be spidered in so that they don't go apesh*t looking for something that isn't there anymore (probably the reason for the $5k dealer price tag).

After which OP would still be potentially shelling out more to fix a broken engine at some later date. As I said, in this case, I think they've already answered their own question in that regard. And I really think the money spent rebuilding / repairing a MaxxFarce failure would likely be better spent on a ruined motorhome donor for a gas engine repower with the following:

Modern FI engines: 8.1 Vortec, Dodge 8.0 V10, Ford 6.8 V10, Ford 5.4 V8 or Godzilla 7.3 V8. Any of which require PCM / harness / sensors from the donor vehicle.

Older, simpler engines: Mark IV (454 / 427 / 402 / 396) or tall-deck (366 / 427 big-block Chevy, 514 Super Duty or 385-series (370 / 429 / 460) Ford, Chrysler 400 / 440 / 426 Wedge.

Alternately, you could try to retain diesel power with a full older mechanical engine swap, but the legality of non-functioning emissions equipment is an even bigger problem than the potential issues of a gasoline repower.

Considering all this, unless OP has any kind of guarantee that their engine is not going to be one of the problem units, again, I think they've answered their own question. Personally, I would start over with another bus unless they can get a definitive answer on a clean bill of health for their existing engine.

One more thought, though. Option #5. Why not find a ruined gasser motorhome with either air brakes or at least a different hydraulic system, and simply swap your bus' body onto its chassis? Might be the best idea at this point -- Just my $0.02. Yes, it's a bit of work, but hear me out.

The chassis would likely need to be lengthened or cut to fit, but ultimately this would solve multiple issues - the diesel emissions equipment problems, and with them, the potentially looming MaxxFarce issues as well. This would also solve the brake system issue, and probably at not much more of a price tag than the air-brake swap alone, which would still leave OP with potential emissions and engine failure coming down the pike.

Plenty of candidates for this on CoPart, and you don't necessarily need a salvage or business license to buy, brokers are available to help with this, though transportation of your purchased donor is another consideration.

If done correctly, this should stop the current nickle-and-dime hemmorhage OP is currently experiencing, cold in its tracks. ol_trunt did exactly this with their older bus by setting its body on a newer GM Forward chassis (GM's version of the Isuzu NPR) with a 6.0 Vortec. Another member did this as well, dropping their 86 Ford Blue Bird onto an '07 Kenworth chassis with a modern Cummins ISC and 6-speed manual.

[joeblack5]

Why not go to scrapyard and get the same hydraulic module and replace it. See if you have the same problem.. Or get a simpler hydraulic braking system from a different brand truck and make it to work.
The key issue here is that with these older vehicles you need to spend a lot of time to learn how to do things your self. With $70 to $150/h shoprate every vehicle is a potential financial death trap.

That the guys with the laptop and software have no clues about what is happening means that they do not really know how the system is working in the first place.

Completely unrelated to you but my 40 year old unimog had no brake / dragging brake issues.
Could not understand it.. fortunately for me other people with more experience told me that after 10 years or so the rubber brake hoses could swell up on the inside restricting or closing the line.
Never seen this in other vehicles and everything I own is over 20 yrs old but the unimog had that problem.

If it is not locking up but dragging first then some residual pressure must be in the system. You can splice in a pressure gauge and monitor it.

Good luck,
Johan

[joeblack5]

Is this your problem as described on school bus fleet?
https://www.schoolbusfleet.com/forum...TOPIC_ID=18459


Posted - 05/06/2008 : 03:41:42 AM A SAHR cannister is a "spring applied hydraulic released" cylinder which mounts on the left rear frame rail and applies the driveline park brake via a short cable on IC buses with full power hydraulic brakes. Loosely, it operates like an air brake chamber...the spring applies the brake and hydraulic pressure from the system releases it. It is also tied in to the ABS system and if it is applied in an emergency situation, it brings the bus to a safe controlled stop using the ABS. We had a good bit of problems with SAHR's when they were first released, but following the recall which changed the way they where wired, have been fairly reliable. We have 32 of these buses with only limited problems with the SAHR cannisters. We have never had one leak yet. Our biggest problem with the system is the pumps in the main HCU unit on buses built prior to Sept. 06. The toughest failure for us to work through though is when a pump MOTOR fails in the HCU on one of these earlier units. If it is the front pump motor that quits on a run, there is no pressure supplied to the SAHR and therefore the bus can't be moved. Then, after towing it to the dealer, getting Wabco to cough one of these HCU units up is like pulling teeth. They send the dealer through a bunch of extra steps and lengthy phone call holds to ensure that it really is the HCU unit (they are expensive). The best news is that on these earlier units, Wabco has extended the warranty on the pumps and the HCU units from 3 to 5 years due to some early design glitches. Take some time to play with this brake system on a slippery parking sometime. You will really be amazed at the function of the traction control feature and the anti-lock functions. It is no longer possible to have any fun at all spinning or sliding these units in the snow! They work beautifully.Bassman
Top Member


USA
558 Posts



maybe replace the parking cable with a more convential manual parking brake lever?

Good luck Johan

[Seb1]

Thanks Johan for that research. Yes, I came across that thread too last year. It is the same system with the SAHR, which we got replaced. I usually fix things on my own, but I am not confident working on the brakes system and prefer a profesional to work on it for safety reasons, but indeed it means accepting the dealership hourly rate on top of the parts.

[joeblack5]

Sorry about my rambling in my earlier post. Should have done some reading first.

Further in that article they mention a cause being coil packs that are swollen by salt, I guess you have checked that.
If it only is the parking brake and the anti lock and traction control is working and now warning lights are on then I would pull that parking brake cable and make another kind of parking actuation.


I think you have a very nice braking system, advanced as it should be.
the parking brake although very important is really only a parking brake in this case. because your hydraulic system is split a total failure is unlikely and with that an automatic self applying parking brake is not a high priority, especially if you can manually still apply the parking brake.


good luck,
Johan

[ISAF2009]

You will be facing 10k plus keeping that maxxforce on the road. That being said keep the bus and convert to air brakes if it’s only 5k. 5k is cheap I know 6.0 and 6.4 powerstroke (International) customers who have to spend that yearly to keep their pickup trucks running. You bought a Commercial vehicle typically not owned by an individual. When it breaks it costs a lot of money. It doesn’t matter moving forward what you have already spent, You will never get your money back out, it is a sunk cost. Try not to throw any more money away by starting over.

[jazty]

I see that the idea that first popped into my head has already been discussed, but I'll reiterate it.


If it were my bus I would start with the easy things. The parking brake seems to be crap. Fine. The next thing I would do is to chock the wheels and unplug the actuator to see if the rest of the braking system will work without it (It might need to be "caged" or whatever.. not sure how this unit works). If there is a safe, empty, flat parking lot it could be taken for a drive to see how it does. It would be important to have two people for this. One to hold the brakes and the other to pull and place the wheel chocks.


If things otherwise work, then I would go find a manually actuated drive-line parking brake and slap that in. Even if it required you to go to a shop for fitment and fabrication it would cost a good deal less than the $4000 already invested in the faulty parking brake.

[CHEESE_WAGON]

BTW, just an FYI, Wabco is a dirty word to professional truckers, and strikes fear in the hearts of most. I won't even touch a vehicle with Wabco components of any type.

Reason being that I once drove a Freightliner Cascadia with the infamous OnGuard system, the collision mitigation / preemptive brake control that hallucinates and can actually contribute to losing control of and/or crashing the truck. That system gave me quite a few gray hairs and mini heart attacks while driving, as there is ZERO modulation (application pressure is either 0 or 100+ psi) and it has shown me several times that it is anything but safe.

Once, it nearly caused me to lay a fully-loaded semi on its side at 65 mph. I was going downhill, changing lanes to pass another rig and to clear the right lane for traffic merging from an on-ramp. It locked up all five axles mid-lane change -- I was over 600 feet from the truck ahead and merging to go around it! Random full air-brake engagement changing lanes at 65 mph with 44k behind you is not something you want. I thought that truck was going over and do not know to this day how it didn't. When the OnGuard finally failed, I had no cruise control. I'll never knowingly own a vehicle that has Wabco anything on it, nor will I drive another.

So if this system has Wabco components in it, that is likely the entire problem, and there is no getting around it other than doing an air brake swap (still leaves the potential for engine / emissions control issues) or doing a body swap to another chassis (personally the option I would favor, as it would solve all these problems across the board). We all know about the MaxxFarce and we all know about the parking brake issues with these models. If wifey is still on board for now, a bit more to do a body swap will very likely save you tens of thousands down the line. Just my $0.02.

[Seb1]

Hi Cheese Wagon, your suggestion is quite extreme in my view, but it has the merit to be "out of the box". Regarding the Maxxforce DT engine, between US07 and until US10 emissions, I believe that it is no worse than other NA OEMs engines which all had EGR and DPF to meet EPA standards in regards to Particulate Matter and NOx to some extend. Where things got really sour for Navistar and all their engines is when their CEO pushed for trying to meet US10 EPA regulation only by using HEAVY Exhaust Gas Recirculation (+DPF), despite the engineering impossibility to meet the regulation while at the same time keeping temperatures under control, resulting in large EGR coolers and other complexities... and failures until class action suite and Navistar abandoning the design and manufacture of diesel engines. All other NA OEMs switched to adding SCR to meet the more stringent NOx limits, resulting indeed in also complicated systems, but at least that met teh regulation and with better reliability. Indeed US07 engines after treatment systems are more complicated than if there was none, and an EGR and a DPF costs around $2000 each, but I believe that replacing an EGR and a DPF should be possible by the average DIY guy/gal (although I have never done it myself yet, but I very likely experience it sooner or later...). I will not be living in my skoolie, but instead taking week end and vacation trips, so very likely less than 5000 miles/year. I would be driving 30 to 40000 miles a year with possibly 1 replacement of each per year, it would start to be costly indeed.

[Booyah45828]

What you should do depends on your skillset and how much labor you have into the conversion. If you're just starting out, cut your losses and start over. If it's maxxforce powered, this brake issue is only the beginning of your problems.

Converting to air brakes is an option, but I would hate to pay a shop to convert your bus over to air brakes, even if you have a donor vehicle. I think it'd be cheaper to buy a bus with air brakes, and sell yours at a loss, then to convert yours to air brakes.

To be brutally honest, I wouldn't have bought a maxxforce powered bus anyways. That name alone has bankrupted more small/regional fleets then I care to count.

[CHEESE_WAGON]

Originally Posted by Seb1

Hi Cheese Wagon, your suggestion is quite extreme in my view, but it has the merit to be "out of the box". Regarding the Maxxforce DT engine, between US07 and until US10 emissions, I believe that it is no worse than other NA OEMs engines which all had EGR and DPF to meet EPA standards in regards to Particulate Matter and NOx to some extend. .... I will not be living in my skoolie, but instead taking week end and vacation trips, so very likely less than 5000 miles/year. I would be driving 30 to 40000 miles a year with possibly 1 replacement of each per year, it would start to be costly indeed.

Don't believe the BS spewed by those who say MaxxFarces aren't that bad. Point blank, as an OTR trucker, I was sacked with 7 Class 8 tractors in 7 months that were equipped with the POS MaxxFarce, and every one of them stayed in the shop. These did not have engine failures so much as electrical and sensor failures in the control system, but either one can leave you sitting on the side of the road waiting for an expensive tow truck. Believe me, I know this better than most from bitter experience.

During that 7 months, most of my paychecks were more layover / breakdown pay than actual mileage pay. And yes, I realize the MaxxFarce 7 in a skoolie is not the same engine, but that doesn't make it any better than the Class 8 engines. The 7 was, in fact, included in a list of engines that Navistar was sued for, and it nearly bankrupted them with a $135M settlement. The MaxxFarce technology was cited as faulty.

A body swap to another frame with different mechanicals may seem extreme, but I believe you will be kicking yourself later if you don't. It's a cheaper alternative to scrapping / selling and starting over. Let's face it, you can still find a decent bus with far more reliable mechanicals, but they aren't on every corner like they used to be. Sure, this approach might cost upwards of $10k to do right, but it will likely save you twice that in the long run. You'll likely spend that much chasing the parking brake issue even before the potential (and likely) engine issues.

And it's not just me telling you about the MaxxFarce and its issues. Another member has said keeping the MaxxFarce could cost you that much to keep on the road. Take heed. There are 135,000,000 reasons Navistar doesn't build the MaxxFarce anymore. Today, the ProStar has been redesignated the LH series, offering only Cummins power.

As for the suggestion of salvaging used replacements from a donor truck and attempting to fix the problem yourself -- well, I really don't think that's going to fix the problem. The parts that fail won't be any different on a truck vs a skoolie -- reason being that skoolies are nothing more than a bus body built on the same frame with the same mechancials. Forgive the indelicacy, but you can't make chicken salad out of chicken sh*t.

The only issue I see with the body swap is that your factory tach is for a diesel, but I'm sure the cluster from the donor frame/vehicle can be transplanted. After all, the harness will have to transplanted anyway so that the engine will run properly. You'll likely have to make your own mounting pod to adapt it to the Navistar dashboard, or swap the donor vehicle's dashboard, but you'll still be money ahead if it's done right. No one said it would be easy, but it will be better.

[joeblack5]

Here is another link to possible solutions.


https://www.schoolbusfleet.com/forum...TOPIC_ID=37575


No doubt it is something simple as a bad connection. It is very sad that the culture nowaday is to throw away instead of repair, I guess to ome here that even applies to the whole bus.

That same bus in Mexico will run for another 20 years because it has to.



A lot of noise around this brake problem how this bus should not have been bought while it is already owned,



Removing the bus body and mounting it on somethings else while the engine is not even broken yet and maybe never will.


For myself I would like to keep these problem solving threads clean because other can be helped by it and not get lost in unrelated chatter.



Lets solve the actual problem on hand so that everybody can learn from it.


Johan

[Jolly Roger bus 223]

i cant remember if i have said this in this thread but just north of you off of I85/40 is a huge bus barn in the GRAHAM/MEBANE area.
maybe stop by there and talk to them and see if they have any solutions to try?

[Seb1]

Hi Jolly Roger, yes, I read your suggestion about the bus barn between Graham and Mebane. I have not located it yet. Is it the Alamance-Burlington School System Bus Yard, on Prison camp road, along I85 ? Thanks for your tip !

[CHEESE_WAGON]

Originally Posted by joeblack5

Here is another link to possible solutions.

https://www.schoolbusfleet.com/forum...TOPIC_ID=37575

No doubt it is something simple as a bad connection. It is very sad that the culture nowaday is to throw away instead of repair, I guess to ome here that even applies to the whole bus.

That same bus in Mexico will run for another 20 years because it has to.

With broken pistons and random stopping due to power loss from unpredictable derating? I'd like to see that... There's a reason the Chevy Nova (both original and Toyota-cloned) didn't sell well south of the border. Supposedly, 'nova' means 'no-go' in Spanish. An unreliable bus is not likely to be welcome or tolerated there either.

Originally Posted by joeblack5

A lot of noise around this brake problem how this bus should not have been bought while it is already owned,

Removing the bus body and mounting it on somethings else while the engine is not even broken yet and maybe never will.

MAYBE a MaxxForce 7 will not have problems? That's a DAMNED BIG maybe. And everyone here knows it.

Originally Posted by joeblack5

For myself I would like to keep these problem solving threads clean because other can be helped by it and not get lost in unrelated chatter.

Lets solve the actual problem on hand so that everybody can learn from it.

The actual, bigger problem, is the steady hemorrhage of money going into chasing problems on this bus. Yes, the immediate problem is the parking brake, but you really have to look at the bigger picture. Is it smarter to spend $5k swapping for air brakes on a bus with a moderate-to-high probability of randomly derating while driving and/or future castastrophic engine failure? Or to completely replace the current known-to-be-troublesome mechanicals with a proven platform whose donor could also possibly yield some nice upgrades and other goodies for the conversion?

Don't take that as a personal attack, I'm just trying to point out that the parking brake is the IMMEDIATE issue, but not the REAL issue. The REAL issue is that OP is tired of dumping money into this bus, and I can't say I blame them. A body swap to a chassis with better, more reliable and proven mechanicals is a good alternative to starting over from scratch with another bus.

Also, as I have stated in another post, if this system has Wabco components, that is likely the problem, and there really is no fixing it. Wabco components have consistently proven themselves to be junk in my experience.

[Booyah45828]

I'm with cheesewagon.

This brake issue is the immediate problem, but IMO there are a whole host of others just over the horizon with this bus. You put this fire out, and a new one will pop up elsewhere, guaranteed. If it's not in the brakes, it will be in the CAN multiplex, or the engine, or any other system here.

Truth be told, this bus is 12 years old. Now, I'm not certain how this specific district is ran, but If we got rid of a 12 year old bus, it's because it was a problem child. The average age of retirement for buses we maintain is 15+ years old. Some are closer to 20. If one was retired and it was only 12, I'd be way suspect, especially if there are older buses then that in the fleet yet.

Sorry OP, this will be my last post on this thread. I wish I could help you, or wave some magic wand and this be fixed. But the reality is, is that I can't help you, and nobody on here can, because there isn't a cheap common failure point to lead you to. And without being there in person and looking at the data that the abs ecm is seeing, anything I suggest to replace would be spitballing.

Corrosion in the powers and grounds could cause this, an alternator putting out ac voltage could cause this, a poor connection at a speed sensor or solenoid could cause this, frayed wiring could cause this. Heck, even a loose bolt holding the hcm could cause this.

There's no cheap solution here. Fortunately you seem to have an understanding wife, don't ruin that.

Good luck!

[TJones]

Given that the computer diagnostics have not uncovered any problems I would suspect an intermittent short or open wire in the harness either between switches / sensors and the controller or between the controller and actuator. The only way to diagnose this would be to have a wiring diagram that showed the state (on or off) or voltage range for each wire in the system when operating correctly. Then one would have to test each circuit at multiple points to determine where or if the problem is in the wiring. This would tell you if the controller is bad if it is getting all the correct input and not outputting the correct signals.

The other diagnostic would be to time how long the brakes operate correctly from taking parking brake off to failure. If this time is consistent when starting with a "cold" system and the time decreases after repeated on off cycles when the system is "warm" I would suspect a bad solenoid, relay, breaker or other component that would fail after warming up. Again a detailed wiring diagram would be needed to understand what to test.

I would assume that in this system a lack of power to an actuator would cause the parking brake to be applied.

On the mechanical side maybe a bad pressure sender or check valve?

Ted

[Zork]

Originally Posted by CHEESE_WAGON

There's a reason the Chevy Nova (both original and Toyota-cloned) didn't sell well south of the border. Supposedly, 'nova' means 'no-go' in Spanish.

Hard to believe this hilarious myth is still being repeated these days. Nova means the same thing in Spanish or English. Putting the space between the syllables makes for something totally different. Same thing happens in English, where "everyday" is an adjective that means commonplace, ordinary, or normal, but "every day" means "each day."

The Nova sold VERY well in Mexico and other Central and South American countries. In Argentina it was manufactured locally for 16 years (1962-197 and was a very popular, reliable car.

[Seb1]

Sooo... 8 months later, problem is fixed. Dealership proceeded step by step, trial and error : brake lines, font rotors and calipers that were in bad shape, parking brake hydraulic control module, parking brake valve on dash, brakes hydraulic control unit valves module, and then finally the big kahuna : the complete hydraulic control unit @$4000 ish a pop. Took 4 Wabco technician consulting to attempt troubleshooting. Had brakes lock 7 or 8 times during test drives. This has tested my patience. Because the HCU module had a core return value, I did not keep the defective one, so I was not able to perform an autopsy on it. But presumed failure : The HCU module handles all hydraulics for both service brakes and parking brake. Parking brake circuit is always under pressure except when applied. Seems that there was a leak (thru a crack ?) between the parking brake circuit and the service brakes circuit. So while driving 10 min, the leak was enough to pressurize the service brakes circuit and pressurize calipers/pads on the rotors, bring the bus to a halt. At that point, applying the parking brake was releasing the pressure in the parking brake circuit, as well as in the service brakes circuit, allowing the bus to roll again.
An after thought : this issue did cost more than the bus itself (I was expecting this to happen to the EGR or DPF instead - will come later). When I purchased the bus, there was a second identical one also for sale. I should have bought it for spare parts. Seriously.
Anyway, went for a day trip last weekend, it was great. Took my daughter to her high school graduation with it, she had a blast. Priceless.

[joeblack5]

He seb1, I was curious what happened with you. Glad that you found the issue and got it resolved. For sure smells like a manufacturing defect.
Johan