Front Brake Upgrade Makes Soft Pedal

[BroncoHauler]

Personally, with your family onboard, I would not head out for Indiana until you get this beast slayed. There's too much at stake.


Herb

[jage]

Originally Posted by Gooseberry

This is going to sound strange but take it to a dirt road and activate the abs a few times to see if it changes anything.

Not strange at all. It was one of the first things I did, back when there was still ice. Hit a solid sheet of ice at 45 mph about 6 times and then had shop #1 bleed it again, zero changes before or after the bleed. I got the ABS vibration but it didn't force any air out or firm anything up.

Good thought though.

Originally Posted by BroncoHauler

Personally, with your family onboard, I would not head out for Indiana until you get this beast slayed. There's too much at stake.

True even though the kids won't be riding with me on the way out I do need to be there to bring them back. It's going to be interesting heading back too, and probably worthy of a new thread- first time with just me and the girls, no "mommy" to jump between the seats and serve snacks, pick up dropped tablets etc. I feel like it's going to be an every single exit kind of trip...

[boywonder]

....sounds like vacuum booster needs to be added to the list of suspects as well.....at this point, it's clearly not the master cyl...

As far as calipers being upside down, just stick your head under there.....the bleeders need to be on the topside.

[karma]

Originally Posted by MadScience

Jage: Good luck!!



Some pads can be squishy until they bed. I think that's been ruled out in this case though.

May be or may be not in my case. My pedal was soft and it will sink to the floor. I had to pump it to get it hard.

[bcaine]

I have this exact problem at the exact same time as you. I'll post elsewhere if this comes across as a hijack. Hoping doubling our efforts may be more effective thinking we may have the same root cause.

What I did: Pulled rear axle and replace all brake hardware including wheel cylinders.

Reassembly 1: I reassembled with a bleed of all wheels, even upstream at the front calipers. The symptom was a very firm pedal with key off, but almost no resistance with van running.

Reassembly 2: Thinking perhaps I let the master get too low, I pulled that and bench bled. Reassembled everything bleeding all wheels and the abs unit of the frame rail. Still no improvement.

Troubleshooting along the way (most of which does not even logically connect to the problem): jacked up axle and adjusted star until shoes rub just slightly, doubled checked to be sure shoes and all hardware are on correctly, probably other things...

Detail that's different: i don't have a front axle and the calipers are just connected. I have two pieces of 1inch square tube serving as an artificial rotor to give a surface for the pistons to push against rather than popping out of the cylinders.

Question: I'd been wondering about the booster, but was under the impression that a failed booster would give a hard pedal since the boost assist is no longer functioning.

Happy to be a second set of hands on the problem, especially if it saves Jage a trip to the dealer since I'll be working at my place.

[bcaine]

Having someone to commiserate with has pushed me to figure this out.

Please chime in and address my logic.

If I disable the booster and get a firm brake pedal, my assumption is that the problem is not likely the abs.

So, I put a pair of vise grip pliers on the vacuum line going to the booster to disable the booster. With the booster disabled, I get a firm pedal with the car running. Exactly as firm as when the car is not running.

I'll throw parts at the problem in order of cost. So first up is booster check valve, then the entire booster.

Any other ideas?

[MountainBikeRoamer]

Hey bcaine,

You say you get a firm pedal when the van isn't running, and also when you cut off vacuums to the brake booster --- but how firm are we talking? And have you driven it with the brake booster vacuum line pinched off to see how it stops?

Curious if (when enabled), the brake booster's additional "pedal force magnification" effect is creating sufficiently more force at the master cylinder than you have been generating with un-assisted foot power alone, and is thus allowing an leak elsewhere to show itself / cause the drooping pedal.

(As in....the booster may be fine, but it's additional brake-force power has to be present in order for the leak/issue elsewhere to be present. Maybe your foot power alone isn't sufficient to cause the presumed leak (or compressing air in the line) elsewhere to happen. Just a thought.

[bcaine]

I quickly pulled the checkvalve and just blew through it to see if the valve was sealing properly. The first time I got a hissing sound, like when you blow across a reed of grass between your thumbs, but after that it sealed fine. Hoping that maybe the diaphragm had seated due to my breathing through the valve I put the valve back in. No luck. Still a soft pedal when running.

Mountainbikeroamer... That's a great idea that I need to file. I can't drive the van at present as there is no front end. Having bled the thing twice, the second time with a friend who is a professional, I'm hoping it doesn't come down to your proposal. I won't say it's impossible though. Thanks.

Because the van isn't going anywhere quickly, I'll try a booster.

[MadScience]

I don't see any confirmation that this has been done:

Originally Posted by mgmetalworks

another thing... if you have an ABS module and it hasn't been run through the service bleed process, you should try that too. There is a routine in the IDS software that puts the ABS module into the service bleed mode then follow the procedure in the service manual.

At this point at the latest, I'd make sure someone went through that procedure.

In fact I'm trying to get my head around what it takes to get a working IDS setup at home for myself right now. The knock off interfaces seem a little sketchy, but potentially workable for DIYers that are dealing with a single vehicle.

[jage]

Dropped at dealer yesterday.

After a whole day they called and said yeah the tech hadn't found anything but would look tomorrow (today). I didn't post because I know everybody wants to hear the answer. I did make a point of asking, "but the tech DOES agree there is a problem right?" Because of course the one thing I don't want is...

Just now they called and said the tech drove it and it drives like a "normal diesel"and that he even had another tech drive it and it drives like a "normal diesel" and said how long have I owned it?

I admitted I am kind of green, I have only had it for ten years and I only know about 200 of you all who also own them, so it's probably just me not understanding how a "normal diesel" drives.

I really need to take the tech to Imogene pass or somewhere and come down in low range trying to hold it with the "normal diesel" breaking and see if they still think it's oh just fine.

So I asked and the tech doesn't think it's the booster so doesn't want to mess with that and they didn't even bleed the HCU (or bleed it at all apparently). I did spin Erics dune buggy theory (slightly mismatched booster for whatever reason) but by that point I felt like I was trying to convince my kids that broccoli is something they've always eaten.

Apparently they didn't want to bleed it without customer input and now I just feel like we've been at cross purposes this whole time. Like do anything, but don't treat me like some idiot who doesn't know the brakes have nothing to do with the fuel type.