Okay, here's the problem with my brakes. They work - sortof. They bring you to ALMOST a complete stop with normal pedal pressure. but you have to stand on them to come to a COMPLETE stop.

First thought was booster, so I checked it. Pumped the pedal with the engine off to relieve any vacuum in the booster and held the pedal while I started the engine - pedal went down a little over an inch. This is correct behavior, right? Next, I checked the vacuum - it was fine and the valve only works one way when blowing through the hose

Next I checked the front brake pads - still have about 1/4" of pad left and the rotors are slightly glazed.

Then I checked the back. The rear pads were a little less than 1/8" and the rotors were glazed and had a decent outer ridge. I pulled it apart, had the rotors turned and put new pads on them. Didn't help the problem, but needed to be done. I'll do the fronts once I get the main problem fixed.

I just bought this truck last week at auction. It has 145,000 on it. I have some other problems I am working on, so it isn't on the road yet. I am going to replace the master cylinder anyway bc I am adding the factory TBC to the truck. Just looking for a good used one to get the iTBC switch off of bc a new one is over $100 (for a SWITCH!)! So, does it sound like the booster is bad or the M/C? I thought if the booster was bad, the pedal wouldn't move when it gets vacuum from the engine? But it seems logical that if you don't have power assist that you would have to stand on the brakes to stop it.

Thanks for any advice you can provide,
Matt

 

Sounds like a failing MC or air in the system---try bleeding the entire system to make sure that's not the issue.

 

Thanks for the reply JWA - I'll try that before I order a new one. Any idea where I can buy a used TBC switch? I can't seem to locate a M/C with the switch for a gas truck and no one wants to sell just the switch. Kindof makes me want to puke thinking about buying a new one for $100. I'm thinking about buying a used M/C off a diesel truck for the switch and a replacement M/C made for a gas truck with the brake controller port if I can't locate a good used M/C.

Thanks again,
Matt

 

Forgive my ignorance but what is the TBC? Not the secondary cruise control canceling switch on the M/C ?

 

Sorry, that is an abbreviation for Trailer Brake Controller switch. It's not really a switch, but I forgot what they called it - a trans..... something or another.

 

Not sure what the part is Will----I've run out of expertise when it comes to anything towing related.

 

No problem. I've come to the conclusion I will have to buy a used master cylinder to get the transponder at an affordable price! I already ordered a new master cylinder from Rock Auto. The plan for this week off will be to machine the front rotors, replace the pads, install the new m/c and bleed them. I also ordered a vct solenoid as a last ditch effort to solve my other problems. If that doesn't work, at least I'll be able to get in there while it's opened up to rule out the lifters and rockers and check the phaser and chain looseness.

 

I received my new MC and my eBay MC with the iTBC switch last week (the day I went back to work!). I installed the brake switches and bench bled the new MC today. I plan on installing it after the New Years trip to Pittsburgh. The weather is supposed to be clear, but colder next week. Will report back if that solves the brake problem . I also plan on turning the rotors and replacing the pads on the front before I put it on the road.

 

Quick review ....

• Air in hydraulics would be long pedal but normal stopping.
• Bad cups in master cylinder would be a dropping pedal and poor stopping ability.
• Frozen slide pins or caliper piston would be normal pedal but poor stopping.
• Blocked brake hose would be poor stopping with a pull if it was an individual wheel hose, poor stopping if the rear axle drop line was an issue, both would have normal to higher pedal travel.
• Poor stopping especially at end of stop could be poor quality bake pads or thin pads that are overheating/fading, or rusted slide pins.
• Hard pedal during stopping would be lack of boost assistance: low PS pump pressure if hydro boost; with a vacuum booster either low vacuum from source, booster partially filled with brake fluid from leaking master cylinder, or poor choice of brake pad material for the application.
• Pulling to one side could be frozen caliper piston, frozen slide pin, blocked brake hose, or frozen brake pad in bracket due to rust.

 

Thanks for the down and dirty brake troubleshooting guide Jack! Looking at your list, it looks like I might need to check the slide pins. I never even thought about them being corroded! I pulled the wheels off and checked the pads but didn't pull the calipers off. Good thing is that I haven't wasted any money on the brakes yet (been troubleshooting the misses I have first) - all I have done is what was needed that I have found so far. I turned the rear rotors and replaced the pads, and I have purchased (but not installed yet) a m/c with iTBC switch. I will pull and check the front calipers and pins when I replace the m/c. I might go ahead and turn the rotors and replace the pads while I am working on them.

 

The first thing I always check on these trucks are the slide pins. If the vehicle has set for some time it is really easy to freeze the pads in the bracket due to rust. I once had to hammer out pads in an Excursion that sat on a parking lot for three months. They were not moving!

But even continuously operated vehicles can have this issue. I'm attaching a photo of rear pads that were just changed on an MDX which was driven practically everyday. The inner pad rusted in the bracket at one tab (right side) causing a slightly higher running temp, but the pad contact to the rotor continued to wear the pad during brake-off conditions. Therefore the pad had tapered wear, the slight twisting of the caliper caused the outer pad to also have some taper, and the vehicle had a longer pedal due to the caliper movement. No noise, no braking issues except "pedal feels like it moves longer".

Careful on the rotor turning. The common belief is due to thinner rotors they heat warp. A few decades of engineering study shows that is rarely true, and certainly not on this platform. The real issue is either the rotors are bench turned with a high runout, or they already have hard spots that cannot be turned out. Either way in 5k to 15k miles the owner complains about brake pulsation. While on-vehicle lathes solve the issue of runout fairly well, they still cannot address the hard spotting issue that ends up with rotor DTV, disc thickness variation, or non-parallel rubbing surfaces.

 

That would make sense - I bought this truck off of Govdeals.com. It was a Dept. of Natural Resourses truck. I didn't ask how long that they had it in their possession or if they knew how long it sat before they got it. It could've been sitting for months for all I know. The last registration in the glove box was in March.

So, one these trucks, would putting the disk brake grease (or anti squeal) on the ears of the pads be helpful? Or would it not stop the rusting? Putting it on the pins without a doubt.

 

Yes, I put grease on all the problem points and have never had a rust in place problem. Brake silicone grease is the industry recommended product as any petroleum based product has a swelling effect on any of the brake related rubber products, brake hose outer layer the exception. So caliper boots or slide pin boots can loose their sealing abilities if a petroleum product is in contact.

Now I deviate from what my past life would have officially designated. For the last few years I've been trying Permatex Countermans anti seize as a very light coat on the slide pins and that has been working fine.

On the brackets these trucks use stainless steel "slippers" as we called them to provide an anti-wear surface for the pads to rub against. If you've done brake work on older vehicles where the pad ends rode against the bare bracket you would have seen wear grooves that when deep can catch the pad. Stainless slippers provide a very hard surface and are rust free. But the ends of the pads can still rust as so can the bracket material under the stainless. So my way of handling that is to use a silicone moly grease that Honda and many of the Asian manufacturers use for lubrication and noise suppression. They use it on the back of the noise insulators attacked to the pads steel back to interrupt noise vibration transmission to the caliper. It is a thick, black compound that I believe you can get at the parts stores. I never had to as I have a tub of Dow's Molykote M- 77, which is the product that these manufactures use. In tub size, it's very expensive so I'd look for packets if you want to try it. Molydelubium disulfide is a great product for lubricating sliding surfaces like the brake pad tabs and the silicone carrier grease is a very high viscosity so it stays put. I've tried it on the pins but the viscosity is too high and the slide pin movement is inhibited with it.

 

A lot of good information there - thanks for the input! I will have to take the back pads back off because I did NOT put anything on the pad ends. Now that I know how to R&R them, it won't take half the time - better safe than sorry! I am planning on replacing the MC and (at least) checking and lubing the pins tomorrow since it is the last decently warm (45deg) day that I will have to work on the truck this week. I want to have the brakes working correctly when I haul it to the shop to fix my engine miss - I'm about to give up on that one!

 

Just an update - still stuff left to do:

I made it outside to work on the truck today, despite it being in the 30's and still a little muddy! First up was to switch out the original M/C with the new one with the iTBC switch. That was fairly straight forward once I figured out what had to be removed/moved to be able to get it out of there. That fluid sensor was a pain - ended up waiting to disconnect it AFTER I got the M/C loose because I couldn't figure out how to release it.

Next, I pulled the driver front wheel, caliper and pads. The pads were glazed (the rotors are also), the inner pad was worn more on the bottom than the top, and the ss sliders showed some rust. The pins were greased and moved freely.

So, one of the problems you stated WAS a problem. The caliper bracket slots were NOT greased, so they rusted and the brake pad ears bound in the slot. I don't know why the pads and rotors were glazed like they were unless the calipers were sticking at some point. Just for *****s and giggles, I deglazed the pads with a file and the rotors with an angle grinder and flap disk. I wire brushed the caliper bracket slots and greased them and the pad ears. I assembled everything, making sure the pads moved freely. I jumped in the truck and pumped the brakes until I had a good pedal, started up and tried them out. Same result - have to push hard to come to a complete stop.

NOTE: I did NOT bleed the brakes after installing the new M/C (nobody to help and I don't have a pressure bleeder). I also ran out of time - had to pick my daughter up at school. I know I will have to bleed the brakes before I will know if the problem is solved because there is definitely going to be air in the system because I opened the system up. I also know that I will have to replace the pads and turn/possibly replace the rotors because they might have hard spots.