Brake bleeding issues (Edit: see bottom)

[dremu]

Symptom is waaaay mushy brake pedal, push it and it sinks to the floor something fierce, truck barely stops. One would suspect, then, air in the lines.

The vast majority of the parts are new, as I've converted to dually in the front and disc in the rear. Details on request, but I don't think they're relevant. Pretty sure I know how to bench bleed, etc, as I've done this on my K5's without this kind of hassle.

I've bypassed the combo valve, both by gutting it per the article, and even bypassing it entirely (line from the master goes directly to the rear line.) Pedal was mushy before, even with the stock combo in place.

If I pressure bleed with the garden sprayer, the front hardly moves, like the combo valve is preventing flow or something. The back seems okay when I pressure bleed it, but the pedal is still insanely mushy.

If I reverse-bleed it with the garden sprayer at the calipers, the front fills up right away, and the rear does too, but still craps out.

If I use my hand-made vacuum bleeder, concocted from a Harbor Freight air-powered vacuum pump and a Mity-Vac bleed bottle, the front seems to bleed okay ... but the back gets crazy bubbles and froths the fluid into a frenzy. Like, forever ... not just bubbles, but BUBBLES, on and on and on... serious cavitation.

Now, it IS a crewcab, so the brake likes are long ... but they're not THAT long, and I've vacuumed that thing for 5+ minutes at a time, so solid fluid should come out eventually.

I am suspicious that one of the hardlines has sprung a leak. Is there an easy way to test for this? I've visually gone over everything I can get to and checked all the connections, and they're all tight and look okay.

The vacuum bleeder may be sucking, as it were, too much... develops maybe 10-13" vacuum, so that's not much more, if any, than a hand pump.

Other than that, I can only presume that my truck has been possessed by air demons, and will never ever brake properly. Which is a shame, as it would otherwise be a nice truck.

Any ideas? Suggestions? Perhaps I should buy somebody's SK and shoot holes in the thing?

-- A

 

[1-ton]

The only two things I can think of is that the master cylinder is no good (regardless of how new it may be), or the rear brake shoes are not adjusted up tight enough.

Uhhhmmm. forget the last sentence.

 

[1-ton]

You are [sic] "like" the second person (on this site) currently having problems getting your brakes sytem to work, after modifying it to rear disk. This is making me afraid to to modify my truck to rear disk. I think the people that are manufacturing the rear disk brake kits for 14-bolts need to do a liitle investagation into this, in order to have their customers be happy with the purchase they made.

 

[dremu]

You are [sic] "like" the second person (on this site) currently having problems getting your brakes sytem to work, after modifying it to rear disk. This is making me afraid to to modify my truck to rear disk. I think the people that are manufacturing the rear disk brake kits for 14-bolts need to do a liitle investagation into this, in order to have their customers be happy with the purchase they made.

Well, I've had the same issues with the drums, actually, and rather tan spend any time or $$ on them since I was gonna do the disc thing anyway ... I went ahead and did it.

I've also done the discs on my K5 (also 14BFF, but with Caddy calipers and SRW) without a hitch. That truck will stop on a dime and give you change, so I'd say it's well worth it. On that truck I tweaked less than I have on this one, but this one is decidedly custom (i.e. DRW, etc) so I can't use any off-the-shelf stuff.

-- A

 

[MattK]

im currently kinda in the same spot as far as a disgustingly soft pedal and no stopping power. ive had several MC's on there(couple remans now a new 1 ton). switching from 3/4ton to 1/2ton calipers in the rear gave me back some pedal but still no real power.

at one point i was getting foamy fluid and it turned out being the flare at the master cylinder looked like it had been over tightened. it was real sharp on teh edges and letting air in.

at this point ive also got a disc/disc prop valve from black widow that didnt do anything for pedal feel. my next step is to replace the rear hardlines on the axle, then ill do new front calipers, then new lines throughout. between all that i should be able to nail my problem i hope lol.

 

[dremu]

im currently kinda in the same spot as far as a disgustingly soft pedal and no stopping power. ive had several MC's on there(couple remans now a new 1 ton). switching from 3/4ton to 1/2ton calipers in the rear gave me back some pedal but still no real power.

at one point i was getting foamy fluid and it turned out being the flare at the master cylinder looked like it had been over tightened. it was real sharp on teh edges and letting air in.

at this point ive also got a disc/disc prop valve from black widow that didnt do anything for pedal feel. my next step is to replace the rear hardlines on the axle, then ill do new front calipers, then new lines throughout. between all that i should be able to nail my problem i hope lol.

The flare on the rear hardline to the master had been ... well, badly done, it seems, by a PO... single-flared, and even that not very well, so I was glad to replace it. Didn't change anything, but I am now contemplating checking the mating surfaces on both hardlines very carefully.

Anybody got any bright ideas on pressure-testing the systems? I'd like to sort out whether it's front or rear that's leaky, try and narrow the issue down some... Suppose I could use the pressure bleeder at the master, see if it leaks down any... donno how to check backwards though.

-- A

 

[R77K10]

if the pedal sinks while holding the brake pedal down- and if there were no known leaks then we would say faulty m/c

but..

good luck

 

[dremu]

Hey, you're not R72K5 any more ... yeah, I know, you've not had a K5 since forever.

On three different masters though? All of which were brand new? I think there are leaks. Grrr.

-- A

 

[dremu]

Followup: On the advice of the guy at the local speed shop / parts store, I installed a residual valve in the rear line. Wilwood, 2psi for discs.

Not a WORLD of difference, but better pedal feel. I'm gonna go get another one and put it in the front line as well.

I have both gutted the factory combo valve and just removed the damn thing, which is my current configuration, and plumbed around it.

Note that my rear calipers are stock fronts, i.e. do NOT have a parking brake, and I'm having all sorts of hydraulic issues. On my K5, I used Caddy calipers (i.e. WITH parking brake) and had no issues 'tall, so I wonder if the parking brake somehow changes the hydraulic behaviour, and/or the combo valve is different for disc/disc setups, i.e. has different residual functions built in.

After the 457th bleed, I'll post up more results. (Then I gotta wait for my custom DIY4X wheel spacers to show up to realy drive the thing ... fear not, they're just ~1/4" shims to make the rear disc stuff fit inside the dually wheels )

-- A

 

[readymix]

I have a 1 ton K10 with disks on the rear. I used 1975 3/4 ton 4x4 front calipers on the rear. Only thing I had to do was install a Wilwood adj. prop. valve in the rear to turn the rear pressure down a little bit

 

[goldwing2000]

If you had a line leaking bad enough for the pedal to hit the floor, you would definitely have a puddle somewhere.

Here's something to try: completely block off the line to the rear and see if the pedal picks up. At least that would tell you which end the problem was on.

 

[dremu]

I have a 1 ton K10 with disks on the rear. I used 1975 3/4 ton 4x4 front calipers on the rear. Only thing I had to do was install a Wilwood adj. prop. valve in the rear to turn the rear pressure down a little bit

Huh. I assume that's a D60 front and a 14BFF rear?

What master did you use? I'm currently running Camsk5's suggestion of the Raybestos 39030 or whatever it is from a P30 van. (Mind you, I had crappy brakes with a 'correct' one too... but I like the larger reservoirs on this one, plus I paid enough for it that dammit, I'm gonna use it! )

I'm eyeing the proportioning valve, but so far I've not had too MUCH brake on either end ... once I drive it on the street I may do that as well, we'll see how the ass end goes. This is a dually crew-cab, so the weight distribution is different from a K5 or your K10.

-- A

 

[dremu]

If you had a line leaking bad enough for the pedal to hit the floor, you would definitely have a puddle somewhere.

I kept thinking that, and I've inspected the entirety of that truck for leaks. Though I s'pose it's possible that the master could leak internally, but three masters, not so likely.

Here's something to try: completely block off the line to the rear and see if the pedal picks up. At least that would tell you which end the problem was on.

Ah yes, did that, and found that the rear line was largely at fault. Though both ends are pretty simple, just hardline from the master to the wheels, then rubber lines to the calipers. Apparently the master wants the residual pressure, 'cuz it's better with the valve in the rear line. If/when this weather clears I'll plumb the front with a valve too and see how she goes.

-- A

 

[readymix]

60 and 14FF with the stock K10 MC and stock, un-modded prop valve

 

[dremu]

Hokay... pedal is decidedly better after the installation of residual valves front and rear (pic attached.) This afforded me the chance to swap the front and rear lines *back*, as the P30 master has them reversed.

I am also suspicious of the booster, after Pauly383K10 described his failure, and to note that I had a leaky master which was putting brake fluid at least *onto* the pushrod to the booster. Whether it went IN or not is another matter, donno how impervious to brake fluid the booster is.

Anyway, the truck is driveable now, and I know WAAAY too much about flare fittings and plumbing than I wanted to.

Thanks all; as always, CK5 is a tremendous resource. Once I get all four rear wheels on, I'll take her for a test drive and see how the front/rear balance is.

-- A

 

[muddybuddy]

so are those blue things the valves? do you have the part numbers? ive got 60/14 w/ discs and my brakes feel the same way yours did.

 

[dremu]

so are those blue things the valves? do you have the part numbers? ive got 60/14 w/ discs and my brakes feel the same way yours did.

Yup. Wilwood #260-1874:

http://www.wilwood.com/Products/006-MasterCylinders/010-RPV/index.asp

Mind you, it's not a VAST improvement ... I'm suspicious of the booster, if only 'cuz it's the only piece I've not replaced

When I have time I'm gonna swap boosters with my K5, which is better behaved, and see if it changes anything.

-- A

 

[muddybuddy]

alright thanks. well ive got new calipers front and rear, new lines front and rear, so i guess i just need to bleed 10,000 times, if that doesnt fix it, then ill go with the valves, then maybe the p30 master.

 

[dremu]

On the premise that if a little reduction to the back makes the pedal feel good, that more would be better, I've added the adjustable proportioning valve. The guys at the local speedshop think I'm nuts now =))

Pedal feel is decent, but I've not been able to get the rear wheels on to road test the thing until today, so I'll have actual experience with braking the thing shortly.

Those who are now scared to do rear disc conversions on their K5, note that I'm doing this on my longbed crew-cab and I'm anal about brakes, so this is an entirely different animal than a K5. (I should know -- my K5 went like a charm!)

-- A

 

[dremu]

alright thanks. well ive got new calipers front and rear, new lines front and rear, so i guess i just need to bleed 10,000 times, if that doesnt fix it, then ill go with the valves, then maybe the p30 master.

Might be better off with the adjustable proportioning valve, as your combo valve should act as a residual valve to some degree.

-- A