Brake Under Boosted - 98 LX470 (1 Viewer)

[ClassyJalopy]

Issue: My brakes (were done at Lexus dealership before I got the car) don't seem to bite hard when I press the pedal. The pedal is not low and the brake action is pretty linear but to get any significant response I have to dig in more.
Interestingly, if I take my foot off and then press back immediately the brakes respond great.

So - first at first push brakes don't bite well unless I push deeper. Second push (immediately after the first) and the brakes respond great. This happens every single time, no matter how often I used the brakes, whether they are cold or warm and regardless of speed.

Front pads are at least 60% and rears are basically 100%

I am thinking that can't be normal, so how should I go about diagnosing it?

 

[Leandro]

seems that you don't have enough pressure on the first push, that then builds up for the second.
I occasionally get this, I remember some old posts about it, try the search function. shouldn't be hard to find if I could....

 

[ClassyJalopy]

Thank you for your comment. I did search but didn't find anything relevant.
Oh well, I guess its time to take it to the local Toyota dealer for diagnosis.

 

[SurfSwitch]

This could be a sign of master cylinder seals starting to fail IIRC.

 

[MuseChaser]

I don't know much, but have you tried bleeding them again? If a second pump restores strong braking, could it not just be some trapped air in the system?

 

[SurfSwitch]

I don't know much, but have you tried bleeding them again? If a second pump restores strong braking, could it not just be some trapped air in the system?

And note, you need to have the ignition turned on to properly bleed the rears.

 

[ClassyJalopy]

I love this forum!
I will bleed this weekend to see if anything improves.

 

[MuseChaser]

I love this forum!
I will bleed this weekend to see if anything improves.

Read this..

Brake system flush

 

[ClassyJalopy]

After reading that and multiple other warnings about how easy it seems to toast the ABS unit, I called the local Toyota dealer and got a quote for $130+tax for brake fluid flush.
I am happy to fork that much to have the peace of mind.

 

[AllLC]

Please let us know if this helps. I experience the same thing. brakes aren't terrible but if i pump one time breaks are excellent! I have bled with ignition on (figured this out the hard way . I'm so use to doing this i find myself tapping the breaks twice in my other vehicles too!

Thanks for posting

 

[ClassyJalopy]

Will do. My appt is in 2 weeks so you mayn't see much update here until then.

 

[ClassyJalopy]

The truck had to go into a body shop for over a couple of weeks for rust repair. I then have an indy shop look at my brakes and bleed them this is what they found out:

I NEED TO REPLACE THE WHOLE BRAKE BOOSTER ASSEMBLY WITH MC!! Part number:47050-60010: Brake Booster Assy, W/Master Cylinder - $2350!!
Total cost would be around $2700

They diagnosed it as having a bad accumulator. I suggested just rebuilding the master cylinder and replacing the 47070-60010: Pump Assy, Brake Booster W/Accumulator for $810 but they are recommending against.

I am not sure I want to drop close to 3 grand on a truck that's only worth maybe 7 grand

 

[Johnnie]

Ouch! I have what seems to be a similar issue on my '98. On first push, it stops fine, but the pedal is low. Second push, pedal is firm and up at the top. It's been that way since I bought the truck several months ago.

 

[AllLC]

Unfortunately this is consistent with what i am reading as far as functional fix and some pretty mean $$$. I wonder why they dont like the idea of a rebuild?

 

[ClassyJalopy]

Their argument against rebuilding is that at 242,000 miles the master cylinder probably has its bore enlarged and/or has some gorging that the rebuild is not going to help. I am not sure if I agree with that.

Right now, I want to try adjusting the brake spindle and see if that gets the pedal feel back.

 

[Johnnie]

What's a brake spindle and how is it adjusted?

 

[ClassyJalopy]

Take a gander:
Master Cylinder Rebuild - DIY

 

[CLEcruiser]

A company on eBay sells the whole assembly rebuilt for alot cheaper. Search it, quite a few people on here have gone that route

 

[ClassyJalopy]

Thanks for pointer. I spoke with the shop again to get a little more detail. They think that the booster (accumulator) itself is faulty. How in the world can they even figure that out?
I know the pump works just fine (did the 40+ pump -> turn key ON -> run for 40 sec test)

A company on eBay sells the whole assembly rebuilt for alot cheaper. Search it, quite a few people on here have gone that route

 

[Phat1842Many]

I had the same issue recently and replaced the whole unit. Expensive but problem solved. Peace of mind doesn't hurt either.

The mc/accumulator unit is one of very few problem areas on this truck, both for keeping them well maintained and in some instances for safety. See the brake failure poll sticky for more.