I've been experiencing a soft intiial brake pedal on my 98 GS4 since I bought it a year ago last May. Lately I've noticed a bid of pulsing on braking as well, especially at low speed. If I tapped the brakes and re-applied, I'd get good solid pedal without any fading.
I talked to a couple of techs and they agreed that the pulsing was most likely due to warped rotors. It was also assumed the warping was causing me to have to 'pump' to get good pedal.
So this weekend I bought the parts and got to work replacing the rotors and pads on the front of the car.
The right side R & R was smooth with no issues.
The left side had me baffled for a bit. The take-off went fine, no stuck bolts or other issues. Putting it back together was another thing altogether.
Rotor went on, pads in place, caliper compressed. Everything bolted up. Tried spinning the rotor and it was pretty much locked up. Put the wheel on and installed a couple lugs and tried spinning the wheel. ( I was hoping it would free up) Still stiff as a board. So I took everything back apart. Nothing out the ordinary at first sight. Rotor turned freely with the caliper off. Compressed the caliper some more and put back together. Same issue.
Then I noticed that the top slide pin moved freely while the bottom one was frozen. I couldn't even get it to move with a wrench. Put a ratchet on it and hit the ratchet handle with a dead blow hammer and finally got it to break free. I took the assembly apart and tons of rust dust came out of the hole. I cleaned up the pin and sprayed some white grease in the hole and put it all back together.
Put the pads on, then caliper and finally the wheel. Everything turned freely now.
Car brakes better than ever since I bought it.
In retrospect, I probably had a bit of warping, but the rotors may have been turnable. The real problem was with the slide pin being frozen, not allowing the caliper to move properly, giving me a soft pedal.

JimA

 

great info man... ill be doing this next weekend.

 

yea good fix...

You were fortunate to unseize the pin from the bracket. I sheared one off and had to replace the bracket. Not cheap...

Always, when doing brake work, make sure that those slide pins are well lubricated.

 

I had to replace one of those sliding bolts when I did my brakes recently. passenger side lower sliding pin/bolt was stuck in torque plate. after I hammered it out, I noticed the slide pin was pitted and damaged so I got a new one. you also have to be careful what grease you use on those. it has to be high temp. there is a special grease recommended in the lexus manual, but good luck finding it. it's called lithium soap based grease.

 

Yup. Those sliding pins gave me a headache too, causing one side of the pads to wear out unevenly. My solution? LS400 brakes

 

I wouldn't use lithium grease. I use high temp synthetic brake caliper grease. It's the actual stuff that's made for use on calipers. You can buy a little one time use packet for $1 at any auto parts store.

 

Aren't they the same?

 

You saved your self quite a few of these $$$$

 

Looks like the fix I performed has lived its life. I'm getting the soft pedal again. Picking up new pins and boots to fix it once and forever tomorrow.

 

since youre getting new pins dont forget the lower pins i believe has a extra rubber sleeve on the tip of the sliding pins, they cost around 1$ a pop. that was the reason my pins seized up from when i had the issue as well. the rubber sleeve broke into pieces inside and i guess kinda melted in place causing the pins to get stuck. a torch and hammer took care of that.

 

I recently greased my slider pins with high temp copper grease. Seems to work just fine. I also put on some on all the bolts holding the brackets and calipers.

 

Finally got around to doing the repair yesterday. Unfortunately the frozen pin was REALLY frozen and sheared off in the bracket. Of course a replacement bracket had to be special ordered so I ended up buying a whole new 'loaded' caliper assembly in order to just get the bracket.
Anyway, the repair did its job. Brakes are great now. Really wish I wouldn't of waited so long.

 

Ditto. Had one freeze up and it was a serious pain and an expensive fix. I never used to grease those pins...didn't think it needed it. I've done tons of brake jobs on numerous cars and never had a problem. I learned my lesson. Hi Temp grease every time those bad boys come out.

 

I would have to say as a former Lexus technician that your best bet to really fixing or helping the soft pedal problem is a new master cylinder. On my GS4 after about 130K the pedal started to get really soft like that. I replaced the master cylinder and brake pedal became much more responsive. Now, unfortunately I think that it costs about $2500. I picked one up for cheep off of a used GS with about 50K on it. Fortunately I think you can just replace the accumulator since it is hydro boost system. And yeah the Lexus/Toyota caliper slides tend to stick more than any other make and model I have worked on in my experience. Blows my mind considering the quality and longevity of almost everything they engineer. I could see a warped rotor causing the pedal pulsation but from what I have seen most of the time that is caused by a rear warped rotor. Fronts usually cause a steering wheel shimmy. I have had front rotors cause a pedal pulsation before though so its sometimes hard to say. And YES you should ALWAYS grease your caliper slides and also the calipers and points that they meet with the pads (with high temp caliper grease). And its never a bad idea to use "never cease" on the threads. Not sure what brand of tools you guys are using or the way they are being used but that is a huge factor in saving or trashing many fasteners. I have never broken or stripped these slides pins coming out. I also have heard that the late model supra calipers (4 piston), and rotors, bolt right up and have a two inch larger diameter than the GS. I really want to try this.

 

Had that happen on my 1992 Camry ages ago.

Good thing to check when changing pads.