Brake Caliper Bad? Brake Bleeding? - 1990 Infiniti Q45

[gniknave]

[I'm posting this with a bad migraine please forgive any spelling errors or lack of info]

I've been going on low front pads for a couple of months now, not because I chose to but because I've had to. Last Saturday I started getting grinding from my passenger side front brakes (bad grinding). It would grind even when I wasn't pressing the petal, but much worse when I did press it.

After that, I didn't drive the car, and haven't driven the car since. I finally got around to buying new pads and rotors today (I had drilled ones that were obviously warped because they'd been vibrating for a while). Was going to put them on and I noticed the first issue on the drivers side.

ISSUE #1: The pistons leak fluid when they're pressed in. Common sense tells me this shouldn't happen. This was the side that didn't grind at all. Both pads on this side were completely even. However I didn't notice if maybe the piston had been 'seeping' before hand or not, but now it's just all out leaking when pressed. I also noticed the piston was quite easy to press, but I wasn't sure if it was supposed to be this way or not.

When I put it all back together and put the wheel back on, the wheel was able to spin 100% freely. [damn this Excedrin Migraine works!] I do know it didn't spin freely before hand, there was slight 'seemingly normal' restriction.

I definitely need a new caliper on the drivers side, is that correct?

ISSUE #2 I went on and replaced the passenger side pads and rotor. Now, this side went very smooth. Took me literally 5 minutes to get the caliper off, slap on the new rotor, torque it, put on the pads... you get the point....

However I did notice the pads wore unevenly. The pad that was grinding was the inner piston side pad - and it was metal on metal. There was 1.8mm remaining on the outer pad. Now, when I was working on Honda's, this usually meant a new caliper is needed. On this side, the piston did NOT leak when pressed, but it was quite stiff (but did press well with the C-Clamp).

Question(s)

1. Should the caliper piston be easy to press by hand (with little effort), or should it be very stiff and need to be pressed by the C-Clamp only?

2. On a Q45, does uneven pad wear mean caliper replacement?

Brake bleeding

I have searched for threads on this, but maybe whoever created a thread on this topic used a title that isn't so easy to find....

I am wondering what the exact procedure is to do this. I have read the FSM, but it doesn't explain this for the complete brake dummy (well, not complete, but almost). I'm hoping someone can be kind and post the procedure for me or link me to a thread where this is explained in detail.

Thanks in advance!

-Evan #2

[3Q Jay]

Evan- every nissan/inf product i have owned would wear out the right inboard pad first. i do not have a technical explanation for this--maybe the 'squealer' pad is slightly thinner from the start, maybe the pad material for the squealer pad is just a hair softer, maybe the system hydraulics are biased to wear the right just a bit more than the left.

anyway--i DO believe that part is normal. on your LF caliper, you can just reseal it, don't need to buy a whole exchange caliper from joe (unless you want to).

[JedCoop]

I recently got a driver's side caliper from a junk yard. Looks in good condition, i.e. doesn't leak. I just needed the caliper bracket and bolts, not the caliper itself. If you come down to San Jose you can have it.

As far as the inboard pad wearing first, that is also the pad with the wear indicator... you would not want the pad without the indicator to wear out first .

Brake bleeding the old fashioned/manual way requires two people.One to step on the brake, and a second to open and close the valve on the caliper. Also, when doing brakes I usually bleed off the excess fluid instead of forcing it back up into the system.

Open the valve up and have someone step on the brake. Watch the fluid coming out for air pockets. If you changed just the caliper then it'll be air for a while and then fluid. If you changed the master cylnder, you'll see lots of nice fluid for a while, and then air pockets. Be sure to keep the resevoir filled while doing this. If you let it get empty, air wil get in and you'll have to start over.

Pnce the air pockets stop close the valve on that wheel. Repat the process for all wheels that might have air in the lines. Sometimes you will see air only on two wheels even though you changed out the master cylinder... I do not know haw amny pumps it takes to clear a line out completely on the Q.

Once all wheels have been bled once. Go back and ask the other person to step on the brake softly... then open the valve and let fluid out slowly, and close the valve before the pedal goes all the way down. When there is no air left in the brakes the person in the driver's seat will fell the pedal movement stop when you close the valve.

I generally completely bleed one wheel at a time as long as there isn't another wheel with air in the lines.

There has to be a better tutorial on this rather than my ramblings somewhere on the net.

Good luck.

[gniknave]

JedCoop, you got mail...

[texasoil]

A caliper rebuild kit (seals and shields) is cheap at autoparts store. Pistons should be hard to move by hand--seal has to be tight

If one does not clean AND PROPERLY lubricate the bolts/pins that the caliper 'floats-on' with moly-sulfide grease, the pads will probably not wear evenly--and you will not have a smooth braking as possible.

[DrewQ45]

A caliper rebuild kit (seals and shields) is cheap at autoparts store. Pistons should be hard to move by hand--seal has to be tight

If one does not clean AND PROPERLY lubricate the bolts/pins that the caliper 'floats-on' with moly-sulfide grease, the pads will probably not wear evenly--and you will not have a smooth braking as possible.

Texasoil hit the nail on the head.

I want to add that if a piston's angle is changed when pushing in, it's quite possible for it to leak badly since the ability to seal is compromised by the bad angle... an easy possiblity when pushing in by hand and it may lead you to think the seal is bad since fluid is gushing out and allowing easy compression.

Best way is to inspect for leaks is using a mirror when the car has just been driven (Push hard on brakes before shutting car off). The piston must be perfectly level when being lowered during a brake job. I usually use an old brake pad over it then compress with C clamp sitting dead center of pad. Very important to lube the slide pins for best even wear. There are some green ketchup type packets you can pick up at any autoparts store, however, If you're buying a seal kit, it should already come with grease packets.

BTW, installing seal kit was a PITA for me...especially seating the locking ring to hold in the expandable rubber boot.