jdavies77

I just picked up a '99 RX300 with a bunch of miles on it.

I think i got it for a fair price of $2,000 on Craigslist out of state and hauled it up here site unseen knowing it needed a transfer case. Looks much nicer than I expected considering I went on a whim.

My mechanic and i just finished the transfer case and fired it up for the first time yesterday. The idle is extremely rough but under acceleration and normal operation it's and runs and drives great. I'm going to put a code reader on the motor later this evening and see if any codes are kicking back.

I do not envy anyone who has to do the transfer case job, we went into it one piece at a time and what a pain. Same job as swapping the engine or tranny. Had it not already had a replaced tranny, i may have thrown one of those in as well.

On to my brake issue, the brake pedal is extremely soft for the first 40% of pressure to the point of no stopping whatsoever. At 50-80% of pressure the truck will slow down but to stop you have to practically get both feet on it and keep it pressed tight. Any slight release of pressure and it'll drive off.

I'm thinking power brake booster? But I'm no mechanic, and after the transfer case job, I'm not to found of my mechanic either.

How could one tell if it's a brake booster or something else? How hard is it to change?

Thanks!!

code58

Almost ALL power brake boosters are vacuum operated. Find the hose, disconnect and attach a vacuum guage. See what the vacuum is running. Vacuum on a good running engine should be in the range of 18-19 lbs. give or take, at idle. It sounds like you could have an IACV problem. Not do, but could. Normally with a dirty IACV valve, you have a real challenge keeping it running at idle at all. This needs to be addressed 1st because if it is causing a vacuum problem, that alone could be the brake problem. Do a search (I think it's a sticky so you don't even have to search) for IACV (idle air control valve) Tells you everything you need to know. Most of the time doesn't have to be replaced, just cleaned, but take it off and do it right. Probably should be done on a '99 anyway, just to rule it out. Good Luck!

P.S. If your vacuum is good, AND steady, it's a very good chance it's a booster. But 1st., the vacuum issue. Check all vacuum lines for any sign of cracking or holes. I'll bet you don't find any, Toyota puts good hoses on their vehicles.

gmann

Never ran into a brake booster issue on my Lexus, but from my days in working in an auto parts store, I sold many brake boosters (mostly for Chevys). The basic rule of thumb on brake boosters was that if it went bad, the pedal usually went very hard (like having manual non-power assisted brakes). Which is essentially what happens when the booster goes, since you you don't get the vacum assisted boost, you need to press down really hard to get the car to stop. Seems like you're having the opposite issue. Maybe you have air in the lines and need to bleed them?

salimshah

gmann has already stated how to check for lack of boost.

Major air in the hydraulics will cause what you experience. Minor air on the other hand cause a mush pedal feel (not so solid stop).

Leak in the master cylinder will also fell like no brakes as you press.

Since you picked the RX up recently, I would suggest replacing the fluid to start with and bleed them. Do not be in a hurry to bleed ... drain enough fluid to ensure there is no air trapped. Start by the farthest from the master cylinder to the closest.

If that does not fix the problem then try replacing the master cylinder.

Salim