tonydls400

Hi folks,

My car LS400 1999 with 142K miles has code P171 (system running lean) due to vacuum leak. With an OBDII reader watching the trimming (long and short trims), at IDLE it is way over %30 in total for both banks. If I press the accelerate pedal, the trim went down to < %10. My mechanic did a check and he told me my brake booster is bad (after $700 replacing the intake gasket). To prove it he clamped the vacuum hose that connects to the booster from the intake, at idle, I can see the trimming gone down to < %10. Now comes the hard part, he want +1000$ for replacing the booster with re manufactured part and almost $2000 for OEM one. Ouch! I think I can handle the R/R for this thing once the weather is nice enough

So here are some question for experts out there:

1. Is re manufactured brake booster , particularly from CARDONE A1, any good? Or should I look for an used OEM one?

2. How easy to get access to the 4 nuts inside cabin to take out the booster? I download the service manual and it seem not that hard but want to tips/opinion from expert out there.

3. is it possible that the master cylinder might be the culprit and cause the leak?

Thanks a lot
Tony

kevvo

From what you have described, it seems to be a faulty booster. The MC, whilst connected to the booster, is a discrete component. Can you hear any hissing that's new?

kevvo

Something else you can try:

With the engine off, pump the brake pedal a few times and then maintain firm pressure on it. Start the engine. With a good booster the brake pedal should further depress about an inch or so within a second or so of the engine running.

Kingsoup

I got mine from the scrapyard for 30$, the new ones cost a fortune, I think the earlier and later model LS400 brake boosters are the same.

I just replaced mine, so its fresh in the memory, heed my warnings.
Its a bit difficult to get at the nuts, but not impossible of course. Two bolts on the front to the brake master cylinder, then 4 nuts underneath including the pin to the brake pedal.

Now the scrapyard one came out no problem, but the one in my car....
I took off 4 nuts and one stud would not move. I spent hours hammering on it, big hammers, wrenching, prying, nothing.
Then I spent 4 hrs meticulously cutting through the brake booster, layer after layer to get to the stud.
Turns out someone had hidden another nut on the stud inbetween layers of the firewall, for what reason, I will never know, it was totally hidden and not accesable, watch out for that.

Good luck! my pedal went to the floor but then would stop the car, as I have read its common symptom on these cars when the booster fails.