Triple

I just completed a full front/back brake job on my 89 2WD 22r pickup: new master cylinder, calipers, rotors, wheel cylinders, drums, shoes, and rear brake hardware.


Bleeding took a few hours, but I'm not getting any bubbles at any of the four wheels or the MC. The pedal will build pressure after a few pumps with the engine off, but as soon as I start it up and build some vacuum, the pedal drops to the floor. Surely there is air in the system somewhere, and the only component with a bleeder that I haven't addressed is the proportioning valve.


The service manual makes no mention of the LSPV in its bleeding procedure, and all it says about servicing the LSPV is to take it to a qualified shop.


I've read that these trucks are very prone to proportioning valve failure, but the most common symptoms do not match mine. Fluid is passing through the valve and creating pressure in the rear brakes, just not enough.


So, should the LSPV be bled during a full brake system flush, or is it better left alone? What else could cause the lack of pressure in my system, even after putting multiple bottles of bubble-free fluid through the lines?


ALSO, just a note for those considering a one-man power bleeder... this thing is absolutely, utterly useless:


http://www.harborfreight.com/brake-f...der-92924.html


Damn its positive reviews and its surprisingly decent build quality. It does not work. I've never had any success with the smaller hand-held pumps (Mity-Vac, etc), either. I may try one of these next:


http://www.motiveproducts.com/

scope103

Why do you think that?

The usual symptom of air in the system is "spongy" pedal. A pedal that goes to the floor (particularly vacuum-assisted) doesn't sound "spongy" to me. Instead, pedal-sinking-to-the-floor usually means a bad master cylinder, which is just not holding pressure. (I'm assuming you don't have a puddle of brake fluid on the floor.)

I've always managed to draft a neighbor, girlfriend, etc. to sit in the driver's seat and follow instructions. I have had less than stellar success with vacuum systems; they require a very tight seal at the bleeder screw or the bubbles you see are just air leaking in there.

But if you want to do it single-handed, consider an auto-bleeder like http://www.speedbleeder.com/ . While I've never tried one, I've heard good reports on this site, and they don't cost too much to try.

Terrys87

iTrader: (1)

Did you get your master cylinder or slave cylinder at the parts store? Compare your old parts to the new parts and see if they are the correct ones. I ran into an issue with a slave cylinder and helped a member with a similar problem a few weeks ago and he had the wrong master cylinder from the parts strore.

RustBucket

iTrader: (1)

I just went through this pain this past weekend.

You MUST bleed the LSPV. Start with driver's rear, passenger rear, passenger front, driver front, then LSPV. Repeat.

It never hurts to bleed the master cylinder fittings too. Just like you would an actual bleeder valve -- have someone pump up the brakes and hold them, then crack the fitting til a bit of fluid runs out (and hopefully the bubble along with it).

You can also use a tube going straight into a bottle and into a couple of inches of brake fluid. The fluid level prevents air from coming back in on the upstroke of the pedal. I used this method with good success when I needed to flush 25+ pumps through each bleeder. I do feel it is best to end with a 2-person bleed to make extra sure the last little bit of air is out.

Triple

The master cylinder was not replaced at the same time as the other parts. The MC went on about 3000 miles ago and worked fine until I replaced everything else this past weekend.


How do I confirm that the MC has failed? I really don't want to replace it again so soon if I'm not absolutely certain it is the problem...



Yes, this method duplicates the operation of Speed Bleeders for virtually zero cost. It also helps to wrap a film of teflon plumbers tape around the threads of your bleeder screws. I use this method on my motorcycles but it works on cars/trucks as well.


I had a helper sit in the cab of the truck to help me bleed this system, however.

wyoming9

iTrader: (1)

This is one of those things.To each do there own thing

I gotta ask with all these new brake parts did you change the rubber hoses as well??

Living in the great Salt belt my one attempt to bleed the LSPV resulted in great expense.

That was back in 2000 since then I have never bled one the ones that leak get removed and thrown away .

Learning to drive without any such devices I don`t miss them and I doubt any really worked like they should being 20 plus years old or so.

I have had good luck with Vacuum bleeders But then mine was around $100.00 which might make a difference.

I always finish with a good pedal if anything I am real picky when it comes to brakes and tires.

Triple

No, still running the original hoses. The only symptom (of which I'm aware) of failing hoses are too MUCH pressure in the system; fluid flows through the hose and into the caliper or wheel cylinder, the interior lining of the hose collapses (preventing the fluid from flowing back out), and the brakes lock in place.


A member of another forum referenced his factory service manual and bleeding the LSPV is indeed part of the procedure (in the order RustBucket listed above). My crappy Haynes says to leave it alone, but I'll give it a try.

nothingbetter

as mentioned above, your rubber flex hoses might need to be replaced as well. over time they begin to soften and it takes more brake pedal travel for them to expand before the pressure is put to the calipers. Braided steel lines will fix this.

Hose your lspv down with the penetrating lube of choice and let it sit before trying to open the bleed valve. If it breaks anyways just throw it away and run your front and rear brake systems seperately off different holes in the MC.

Terrys87

iTrader: (1)

On your firewall, there is a white check valve in the brake hose. Is it by chance leaking or not functioning?, as far as you MC issue may be.

RustBucket

iTrader: (1)

OP, I had similar symptoms to you after replacing rear brake hardware.

-> Bleed system really really well, including LSPV
-> Make sure rear brakes are adjusted well. If the adjusters are not pulled up tight enough your pedal travel will be too far
-> Check your brake pedal pushrod slack. Spec is 3-6mm. Mine was 10mm. I adjusted it down closer to 3 and it helped pedal feel.

buickid

Definitely bleed the LSPV. When I serviced my brakes, replacing lines, etc, I couldn't get a firm pedal until I bled the LSPV. When I bled it, some REALLY nasty looking brake fluid came out.

Could be a cause of failure. People ignore it, moisture and other gunk collects there, rusts it out, failure results.

bugs1961

Read the section on bleeding the master cylinder. It's usually necessary to bleed it before starting at any of the wheels when the cylinder is drained empty or is replaced. That's the first place I'd start. The FSM has the procedure for bleeding it but here it is:

Disconnect the two fluid pipes leaving the MC.
Put your fingers over the holes in the MC to prevent fluid from draining out.
Fill the reservoir.
Have a buddy push the brake pedal and hold it to the floor while you let fluid past your fingers into a cup.
Plug the holes again with your fingers and have the buddy slowly release the pedal.
Repeat several times and all the air will be out of the MC.
Reconnect the fluid pipes
Go to the wheels and bleed normally.
I have never (dozens of brake fluid changes and system rebuilds) bled the LSPV and have had great luck so far, but I think I will next time and see what comes out.

daved5150

iTrader: (1)

Remove it and scrape it....did it to my 88 4Runner and it's done to my 94 4Runner which is still on stands (to my wife's dismay)....

Basically, you add a manual proportioning valve (the one I used) at the master cylinder and you need an adapter for the metric brake fitting to go into the valve (unless you make a custom line with a standard fitting at valve and metric fitting for the master).

Then you essentially eliminate the rear return line and plug it off at the tee by the right front tire. Not hard to do and works great. Then you don't have to worry anymore about bleeding the LSPV, tying up the LSPV rod or adding lift to the rod mount on axle when you lift the truck, etc....

Here's some links for ya....

Pirate 4x4....

Yotatech...

4x4spot...

There are more if you search harder than I just did. Good luck...

Krazy Ken

Best thing you can do. I fought bleeding my brakes any time I did any sort of brake maintenance. I would bleed it 100,000 times and they always felt spongy/not right afterwards. Finally I bit the bullet and put in an adjustable wilwood proportioning valve. Best thing I ever did. Makes bleeding the brakes a cinch because there is no where for air to hide at. The brakes on my first 1988 are incredible compared to my second 88 in my signature. The very first time I have to do any sort of brake work on it you can bet I will be installing a wilwood and ˟˟˟˟- canning the LSPV.

Triple

I don't see how this is any different than just loosening the fittings and letting the fluid seep out with the lines still attached (which I did). I don't understand why most master cylinders lack true bleeder valves. Doesn't make sense.


I bought the Motive bleeder (http://www.motiveproducts.com/) and it works as advertised. I bled every fitting in the appropriate sequence, including the master cylinder and proportioning valve. Some slightly mucky fluid came out of the LSPV, but no bubbles. No bubbles at any of the four wheels, either. Went through two more bottles of fluid and still no pedal.


I suppose I'll replace the master cylinder AGAIN, but I'm not convinced it is the issue. Honestly, I've never bled a brake system without encountering some kind of mysterious, physics-defying problem. It's like black magic. Voodoo. A simple job that should take 30 minutes ends up lasting days... weeks... months...

Triple

I finally have a good, firm pedal, but now I have insufficient brake pressure to the rear wheels. Even with the shoes adjusted out far enough to prevent the drums from turning by hand, the wheels will spin with the brakes applied. There is some resistance, but not nearly enough to effectively brake the truck in motion.


I tried tying off the LSPV's adjustment rod in its highest position, but that made no difference. The truck is drivable, but the front discs are providing nearly 100% of the braking force. Not particularly safe and guaranteed to burn up my pads/rotors in short order.


Hard to believe the LSPV has failed considering the truck's condition and relatively low mileage. The rod moves smoothly up and down and there is no visible corrosion anywhere on the truck.


ANYTHING else that could cause lack of pressure to the rear brakes, despite good fluid-flow while bleeding and despite a firm brake pedal? I don't want to replace the LSPV unless I'm certain it's the problem. The fab work associated with installing a manual proportioning valve looks like a pain in the ass.

RustBucket

iTrader: (1)

How does the hand brake do? Does it hold the back wheels tight?

First thought is the drums need to be adjusted tighter still, but if you have a firm pedal too then that may not be the case.

Not sure what else could cause that other than a clog in a line (unlikely) or the LSPV.