Brake Booster Advice

[KO KO]

Update:

Vacuum was around 18 in
Check valve still good

Time for a new booster.

Thanks for all your help.

 

[TomH]

Thought I would pile on in this thread since we're on the booster topic.

Yesterday I finished renewing my brake system. Rebuilt calipers, new pads, rotors all the way around. All new Toyota hoses. Cleaned up the parking brake parts and new shoes there. New Advics master and a new Seiken booster. Get it all bled out and take it for a drive and brakes are hard. By the third pump they are hard as a rock. This points to the booster to me.

I didn't adjust the booster push rod on assembly so I did my best at getting it set the same as the parts that came off. It may not be zero clearance but I think its close. Going to have my son 3D print a gage later today.

Booster passes all the tests in the FSM. I swapped out the check valve this morning from my old booster (that was still working). The new booster was still holding vacuum when I pulled the check valve. Both check valves were functional. Of course no difference in the hard pedal.

I'm kind of at a loss at this point. Hard pedal usually indicates a booster problem. If it was the master or bleeding I would expect a more spongy feel.

Any insight is appreciated.

 

[TomH]

My son 3D printed a booster measuring tool frame and I added a pin.

Measured the master on the truck.

Measured the booster.

Think I got it close enough with may crude measuring yesterday. I don't think this adjustment is the problem so next step is to pull the booster and swap it with the known good one.

 

[pedwards]

This is very cool.
props to your son.

 

[TomH]

Well, it's not the booster. Same results with the old booster. Not sure where to go next, master or bleed. Not sure what would make the brakes hard besides the booster.

This is very cool.
props to your son.

Let's not give him too much credit. He pulled the file from Thingyverse and scaled it to fit the Land Cruiser master cylinder. Having the tool is a big help.

 

[pedwards]

Well, it's not the booster. Same results with the old booster. Not sure where to go next, master or bleed. Not sure what would make the brakes hard besides the booster.


Let's not give him too much credit. He pulled the file from Thingyverse and scaled it to fit the Land Cruiser master cylinder. Having the tool is a big help.

I think you underestimate how much engineering work involves modifying a copy of someone else’s work.
He seems to have already mastered the basics.

 

[SNLC]

FYI if you get the rod adjustment wrong it will lock up the brakes all around.

Cheers

 

[TomH]

I think you underestimate how much engineering work involves modifying a copy of someone else’s work.
He seems to have already mastered the basics.

You're right, he does things so easily I just take it for granted.

 

[TomH]

FYI if you get the rod adjustment wrong it will lock up the brakes all around.

Cheers

I think the rod adjustment is good. I get one pump of decent braking, one pump of a little braking, and by the third pump I could stand on the pedal with all I got and get almost nothing.

 

[SNLC]

When the rod is adjusted wrong it doesn’t allow the fluid to release pressure when you let off the brakes. The pressure will build each time you brake until the brakes are completely locked up. You will only be able to unlock the brakes by opening a bleeder and letting of the pressure.

Not saying it is anyone’s problem here in this thread, just providing info.

Cheers

 

[TomH]

Keep striking out here. Pulled all the wheels and did a visual, found one caliper with some fluid around it but I couldn't tell where it was coming from. I did find two of the rings that hold the piston boots on the caliper were loose so I put them back on. I did rebuild the calipers myself, they came off my LX450 and were working when removed. I swapped the old master cylinder in and bled everything. Brakes are still hard as a rock by the third pump. Guess I swap out the calipers next. Eventually I'll have all my old brake parts back on the truck.

 

[Dave 2000]

When I have encountered the brake lock up after X amount of brake applications or period of time scenario, I loosen the master cylinder nuts holding it to the booster and space the master away from the booster with a couple of washers with a slot cut in them. Drop them between the master and booster and re-tighten the nuts.

This allows you to see how far out of adjustment the push rod is, simply add/subtract until you get a good pedal, then measure your washer stack and subtract the dimensions from the push rod length.

Regards

Dave

 

[sogafarm]

Does anyone know how the booster check valve can be removed for testing? It looks like it is held in place by a rubber grommet. Can it be pulled straight out or some other method?

It's the last thing left to check before I plunk down for a new booster. My '94 just started the hard pedal/no brake situation, happening more frequently. I've got good vaccuum coming from the rubber hose so next to check is the one-way check valve.

Thanks for any advice.
J.

 

[mudgudgeon]

Check valve is a push fit into a rubber grommet, but looks like it has a pin to lock it in place?

Good chance the rubber grommet will be rock hard and won't survive you pulling the check valve out.

I'm about to refresh my brakes and was gonna change both these out.

Anyone sourced either of these? Partsouq has no stock of either.

I've had the opposite trouble with a spongey soft brake pedal that has persisted after re-bleeding, but think mine is master cylinder related.

 

[Dirt Ferguson]

80 Series 1FZ Brake Vacuum kit

80 Series 1FZ Brake Vacuum kit (BVK-1)

absolute-wits-end.com

 

[LandLocked93]

Wits' End @NLXTACY has the kit with valve, grommet, and hose. Believe that's where I got mine.
The pin is for alignment of something IIRC, not fastening or attachment.

 

[bicycleagent003]

Is there a generic or Gates hose which will work for the brake booster? I like Japanese rubber, too, but $60 is pretty spendy for such a short hose.

 

[LandCrusher'70]

I have seen plenty of boosters fail that give intermittent hard brakes before they finally fail completely. My last 80 had that issue until I put in a new booster, it also got progressively worse over 2-3 months until it finally failed.

Cheers

100%!
My booster followed this path. The check valve was working as it should. I replaced the whole unit Monday, and now it’s working as it should.

 

[sogafarm]

100%!
My booster followed this path. The check valve was working as it should. I replaced the whole unit Monday, and now it’s working as it should.

I replaced mine last week for the same reason. Works good now.

 

[Kernal]

Ditto, a couple months ago started getting an intermittant hard brake pedal which worsened over a week or two until complete failure. New booster fixed it.

The valve can be worked out by rocking it back forth, in and out, then some gentle prying with a plastic tool or large screwdriver.

Someone above asked about the rollpin on the valve. It's there for a small flat arm or bracket that runs from the top US driver's side nut on the master cylinder (top stud on the booster) to the valve. It's purpose is to "clock" or hold the valve in the correct position (doesn't rotate) so the nipple or pipe of the valve points in the correct direction allowing the OEM vacuum hose to fit in the correct orientation.

Click on the image below then click again to magnify the area where the vacuum hose attaches to the booster valve to see the correct orientation
of the valve/hose.