FJ 80 Brake Grab. (1 Viewer)

[onomo]

Hello everyone. I have trolled routinely with great insights from IH8MUD. I thank you very much and that was long overdue. I first Yota'd purchasing a coworkers 96 4Runner unlimited. 200K of loved performance for a project which began and ended with and FJ set of wheels and tires that thing is flat awesome. I quickly moved to a 95 FJ with half the mileage and none of the appreciation. Originally owned by a foreign (no disrespect just insight into the issues) GP who likely never realized he'd need to wash road salt out from underneath of it. Kentucky is unpredictable on the need for that but it shows overall the needless neglect for such a machine.
I've replaced all of the front brakes assembly with no improvement to this issue. Discs, rotors, brake lines. I would like some insight please before I purchase anything else needlessly.
Front brakes begin to grab, vibrating the front end/ steering after about 10 miles of driving. Like they're loosing the vacuum that holds the discs off their rotors. When I go to brake terrible vibration from the front. Starts out slow and increases to a violent level sometimes.
But if I'm able to tap them occasional going down the road, sometimes difficult to do in going to work traffic the vibration will lighten up sometimes even cease. Actual braking (at least when this clears up) is perfect.
Could this be the vacuum booster or the master cylinder? If not does anyone know of a common place it could be leaking off? Does anyone know the vacuum spec that comes off of the intake to the vacuum booster. Didn't see it in the FSM but I'm sure it will be in there somewhere. Specs no doubt.

 

[jonheld]

Like they're loosing the vacuum that holds the discs off their rotors.

I'm not going to be a great help with your issue, but that's not the way brakes work. When you step on the pedal, you're basically standing on a column of fluid that applies pressure to the pistons in the calipers, in turn applying pressure to the pads against the rotors.
When your foot comes off the pedal, the pads don't retract due to vacuum. You're just removing the fluid pressure. Actual piston/pad movement from no pressure to full pressure is minuscule. The pads are always resting on the rotors and there is virtually no fluid movement, just a change in fluid pressure.

 

[Saito]

I also replaced the rotors, calipers and pads immediately after buying my LC. Had an issue similar to yours with the front brakes engaging themselves(and getting super hot in the process). Putting in a new master cylinder took care of that issue. Turns out the rear brakes weren't engaging at all and under 20k miles the fronts were brake pad backing to rotor. On the shakes, I'd say it's possible your wheels bearings are shot. Be hard to say w/o looking at it though. I repacked my bearings the first time I did the brakes and then replaced them(along with the spindle nuts) when I put Power Stop pads and rotors on post M/C replacement. Big improvement there.

 

[BILT4ME]

This sounds to me like multiple issues. Check them in this order:

Wheel bearing adjustment (Adjust to 25 LB-Ft of torque while rotating the wheel.) Then install the locknut at 45 lb-ft.
Tie Rod End (TRE) wear
Lower knuckle studs properly torqued on the bottom of both knuckles
Upper knuckle bolts torqued properly
Caliper bolts torqued properly
Rotors installed properly. This means that they were torqued in place in a criss-cross pattern at even stages.
Wheels installed properly. This means that they were torqued in place in a criss-cross pattern at even stages.
Were the brakes "bedded in" properly?

When bleeding the brakes, go RR, LR, LSPV, RF, LF. Then do it again. May need to run it and activate the ABS in between in order to work air bubbles through the ABS pump.

Check adjustment on the LSPV per the FSM

If you don;t have an FSM, GET ONE!

 

[9780LC]

I had this problem too. Vibration when braking - The problem turned out to be that the holes in the steering arms where the tie rods ends go through were out of round. I had about 210k miles on the LC at the time. You should check yours. It was getting dangerous to drive my LC especially in traffic and like you said sometimes the vibration was violent.

I'd check the LSPV too.

 

[BILT4ME]

Some may refer to it as "death wobble"

 

[onomo]

This sounds to me like multiple issues. Check them in this order:

Wheel bearing adjustment (Adjust to 25 LB-Ft of torque while rotating the wheel.) Then install the locknut at 45 lb-ft...

...Check adjustment on the LSPV per the FSM

If you don;t have an FSM, GET ONE!

Bearings, rotors, brake lines, looked okay but replace at the go get and bled cleanly. As per FSM though after this post I know I'm gonna put it back on the stands and go over it again. This was/is to be a keeper. I fix it right the first time then I can move on. No adjusts to the LSPV though it could be faulty? maybe? And I could check that, but of late when I drive it and I do love so driving it like a big ole sedan attitudunidal to terrain, now I just lightly tap the brakes every couple of miles and it alleviates almost entirely.
But back to the original recurrences. Head out in the morning to work and touch really nothing but gas pedal for 10-12 miles or so steady highway at about 55-65 mph and it begins gradually along the way. Feel it in the road, steering wheel, hood'll even begin to shake, and when I brake its completely in the brake pedal. If I'm at a light by then I can pump the pedal a couple of times (feels normal no leaks) it will go away when the lights green. May not feel it again for the rest of the way usually another 5 miles or so. Until I get this fixed to work and back is the only journey it gets. And by then I may not feel it at all for the rest of the. Brakes like a dream effortlessly with no hint of a vibration.
Its something simple maybe I missing but my next lever pull is gonna be a master cylinder. Then a vacuum booster. Then the pockets will be empty again for a while.
Thank you very much for the reply.

 

[onomo]

I also replaced the rotors, calipers and pads immediately after buying my LC. Had an issue similar to yours with the front brakes engaging themselves(and getting super hot in the process). Putting in a new master cylinder took care of that issue. Turns out the rear brakes weren't engaging at all and under 20k miles the fronts were brake pad backing to rotor. On the shakes, I'd say it's possible your wheels bearings are shot. Be hard to say w/o looking at it though. I repacked my bearings the first time I did the brakes and then replaced them(along with the spindle nuts) when I put Power Stop pads and rotors on post M/C replacement. Big improvement there.

Suspect the master cylinder is my problem as well. But at 100K with little, really no sign of abuse it just seems odd. Oh well it and the vacuum booster and the lspv (and the lines to it) are the only things I haven't replaced. Thanks.

 

[BILT4ME]

Don't just throw parts and money at it. Analyze the source of the issue. If you have an idea, then focus on proving or disproving that part for failure.

 

[onomo]

I'm not going to be a great help with your issue, but that's not the way brakes work. When you step on the pedal, you're basically standing on a column of fluid that applies pressure to the pistons in the calipers, in turn applying pressure to the pads against the rotors.
When your foot comes off the pedal, the pads don't retract due to vacuum. You're just removing the fluid pressure. Actual piston/pad movement from no pressure to full pressure is minuscule. The pads are always resting on the rotors and there is virtually no fluid movement, just a change in fluid pressure.

I get this fixed (and I will get this fixed) I'll post the solution find. Thanks.

 

[onomo]

Don't just throw parts and money at it. Analyze the source of the issue. If you have an idea, then focus on proving or disproving that part for failure.

Oh BILT4ME were I to have been privy to that 4thought some 500 bucks ago. You know I was so successful with my 1st Yota project (Uhm I found a great deal on a set of new FJ wheels... and that was that) I didn't look far for things. Missing? Occasionally like the fuel pump is going bad? No thought about the little idiot light (it was out-"odd") or hooking up the reader, or paying attention to it when I did. Just tuned it up and popped in a new fuel pump what the heck no big. When I finally gave in to the mechanic the exhaust sensors (and exhaust) were beyond pc recognition. Looking totally at the wrong end there as well.
Hey exhaust. Vacuum loss? I need to check the FSM. Thanks again. Bilt4me.

 

[onomo]

Update. I thought I'd check hub preload once more, and sure enough the left front brake has clearly been grabbing all along. Pads are finished and in a short time. I have to say its finally good to see an obvious. When I first replaced everything shortly after purchase and for the same symptoms I seem to remember left and right pads were equal in wear.
So now it looks as though I have a sticking caliber (new/rebuilt) or maybe sticking on the sliding pins (yeah they look to be the culprit but we'll see). Maybe a collapsed or twisted (new and carefully installed from the go get) rubber line or blocked metal line. I'll check that metal line before I finish up.
But question; I understand a master cylinder with a blocked vent port can cause brakes to grab as well. If so what is the likelihood it could cause just the left front to grab instead of both sides? Or all four wheels?

 

[onomo]

FOUNT IT! Looks like previous owner had master cylinder replaced. Just a 100k but the front left fender has been repainted. Likely a an unneeded remedy for a fender bender the garage was more than happy to oblige. That explains the mc's

bright shiny like new appearance, no gasket, and the pushrod being app. 2-3 mm too far out for proper fit as per fsm, and the just previous short term owner saying he'd had everything checked out and mention the brakes (only) being perfect. This was an original owner's repair and probable reason for selling.
After about 6-7 miles a back pressure begins to build that is vented when the master cylinder is in it proper position. The pushrod being too far out changed the alignment inside the master cylinder blocking that venting process. A matter of not enough to notice but just enough to bother you. alot.
Thanks guys. For allowing ME to vent.