My friend has a 1996 Lexus LX450 with a brake problem and since it doesn’t appear to be car specific I’m going to take the liberty of running it by you my long time forum friends.
The Problem is this, every now and then at very slow speed when you press the brake pedal it will not move and appears to be frozen. Meanwhile the car keeps rolling along … YIKES ! If you release the pressure on the pedal and try braking again everything works normally. This only happens infrequently but as you can imagine is quite unnerving.
My friend is a damsel in distress who doesn’t know a thing about cars (well actually these things are more like trucks and built like a tank … kinda of drives that way too). After looking at the wear on the front Brake pads I decided to replace those and the rotors. While I was in there I replaced both front calipers for good measure. I will never again complain about doing this job on my XJ40 because this thing with 4 wheel drive was about 10 times as difficult…crazy complicated.
All to no avail as the problem still persists.
No ABS lights so I’m kind of ruling that out.
Which leaves me with the brake booster and master cylinder. If it was master cylinder related I don’t see why that would “freeze” the brake pedal. So I’m inclined to replace the booster after I examine the one way vacuum check valve in the hose going to the booster.
Doesn’t sound like a typical failure mode for a servo (They usually fail by either not releasing the brakes, or by not providing boost… but I mostly work with the Lockheed/Girling style servos, so it may be that some of the more newfangled ones fail this way (but since you mention a vacuum hose going to the servo it probably isn’t all that different from our Jags).
Take the car to a sandy/gravelly stretch of (unused) road and get the ABS kicking in a few times. Then remove (and plug) the vacuum line to the servo and try the same again.
And I apologize for this non XJ40 topic but since youse be the smartest guys around where else would I turn.
Well my friend called this morning and said yesterday she took the car to a place that specializes in Toyotas and they told her their diagnostic codes told her it was either the booster or master brake cylinder. Of course since she’s a flight attendant (and as I mentioned knows absolutely nothing abut cars) I believe they’re just feeding her a line about “CODES” for the booster or master brake cylinders.
But not to worry because they can fix her right up for $2000 or $1800 if she brings them a pillow, blanket, and some peanuts.
I can’t think of anyway that the master brake cylinder could cause the pedal to momentarily lock. If the seals were going bad I believe fluid would be leaking between them an result in soft not locked pedal.
I honestly can’t think of how the vacuum booster could malfunction every once in a while either. Supposedly the booster should store enough vacuum for 2 or 3 pedal activations even if the vacuum source is blocked or removed. But all this is just thinking outloud.
I think just to take another stab at it I’ll replace her vacuum booster first (remanufactured unit $175) and I won’t have to open up the brake lines. Also I think the job should go a heck of a lot easier with my warm blanket and soda of my choice.
Hi Grooveman,
I think the clue here might be in that it only ever happens at very low speeds ( thankfully ) I can’t see how speed could affect a master cylinder, and I can’t see any company designing an ABS system that completely disables the brakes at any speed if it ever goes faulty, so I think you could rule that out too.
Also, I’m guessing you must have had to pump the pedal several times when bleeding the system following fitting the new calipers and I think somebody like yourself who has done this lots of times would have detected a master cylinder fault if it had one.
I’m thinking a lower engine rpm at low speed would produce less vacuum, if the servo/ booster was faulty maybe the reduced vacuum brings the fault on. I just can’t come up with an explanation for how it could work normally most of the time, and also every time on the second press when it does go faulty ? Maybe a vacuum hose could have a leak that closes up when the vacuum is raised, or even collapses in on itself causing a blockage.
You could show a little sensitivity, Some of us only have plastic sheets and a cup of tea.
I appreciate your insight. Your troubleshooting logic follows mine exactly. Why in the name of all Japanese Emperors would any failure mode of the ABS system result in a locked pedal ?? I agree with you, I really don’t think that’s where the problem is.
So I’m going to replace her brake vacuum booster and give a close look at the vacuum hose and check valve. But … I don’t really see the cause and effect there either. However I think it’s the next logical step. Ah yes, the game is afoot.
A cup of tea … brilliant, but why do you need a plastic sheet are you planning on painting the cabin ?
Since the car in question is a 1996 it has OBD2 as original equipment so begin there. Get the codes read at AutoZone and see if they give you a place to start. The booster can be tested by ( engine off ) pump the brakes and hold the pedal down. If the booster is good the pedal will fall 1/2 inch or so when you start the engine. Pete
I know that there are thousands of you waiting with bated ? (adjective ; in great suspense; very anxiously or excitedly) breath to hear the answer to this problem, so I’ll keep you in suspense no longer.
The hard pedal had progressed from occasional to routine. Couldn’t have her drive it to my place so I packed up a box full of every tool I could think of and headed out on the 45 minute ride to our gals house. Remember a screwdriver is a specialty instrument to her !
I stopped along the way and purchased a rebuilt booster and some new vacuum line. Let me say that removing the old booster was like a greek tragedy ! First I had to unbolt it from inside the car way up under the steering wheel. Not much room to operate but even less because her power seat was BROKEN and wouldn’t move back out of the way.
Once everything was unbolted and I pulled the master brake cylinder forward enough to clear, all I had to do was just pull out the booster … NOT ! If you will direct your attention to the photo you’ll notice the largest silver intake manifold I’ve ever seen sitting right in the way. I had to literally use a crowbar (that she went next door to borrow) to wedge the thing in and out … twice.
The first time I put it in upside down (there was literally a microscopic difference in the relationship between the booster shaft and the 4 mounting bolts) and no markings that indicated which was the correct way to install it. Did I mention the crowbar?
Throughout the whole process she kept asking me “Do you want me to get some Windex”! Someone had once told her that if you have trouble fitting something spray Windex on it.
After everything was back together the problem was repaired. But if it was the booster (that had passed all my troubleshooting tests) or the check valve located inside the vacuum hose (that came flying out propelled by it’s little spring) I’ll never know. No way was I putting that old hose back on.
So the morale of this story is always keep a crowbar and Windex handy.
There was 1 last act to this tragedy. When I buttoned everything up and it was time for a test ride … the battery was dead … $#&!
Of course the car was positioned at the end of a long single lane driveway with absolutely no access.
Groan, now I’ll have to pull the battery out of my car and carry it all the way over to jump it. But wait, that very morning I’d cleaned out my trunk and somehow left my jumper cables at home. She suggested that instead of jumper cables maybe some extra Windex might work (just kidding).
So out of the blue she says “I think I have something that might work”. Then goes in the house and comes out with this hand held gizmo I’ve never seen before, and it actually did work.
This thing is smaller than a video cassette and really slick. She said it’s all the rage with the Flight Attendants who park their cars at the airport for extended periods of time.
You can’t substitute it for the starter battery (look at the connectors - there is no way they will carry full cranking current for long enough to get the car started), but for the case where the starter battery has enough oompf to turn the engine but the voltage drop means that the ignition won’t fire, those mini boosters give enough boost to get the ignition firing.
They’re also great for hotwiring an ignition or a fuel pump if your ignition switch or wiring to the fuel pump dies when you’re out and about. And for bench testing stuff.
Now go and have a look at that attendant’s seat. Use your own judgement and get her permission before posting pictures though.
You’re certainly correct about that. It seemed to have JUST enough power to turn the engine over a few times, but I’ll be darn if it wasn’t enough to start the thing.
As far as her seat goes, can you believe that I actually repaired that thing for her years ago. The problem is two cheap little nylon gears that fit onto a shaft that drives the seat forward and back.
Of course the Lexus solution is to replace the next higher subassembly (the bottom of the seat) at
$1600 a pop.
Well enter a machinist named Nackman who started making these little gears and has actually become somewhat of a legend in the Lexus/Toyota world. For $20 I received two gears and a decal that says “Seats powered by Nackman”.
But nothing lasts forever so I guess it’s time to order another seat of “Nackmans”.
