0verb00st

I recently changed my break pads and now the pedal sinks all the way to the ground when trying to break. I checked all of the lines and they don't appear to have any leaks. I had this problem before but it wasn't that bad so I got used to it. It only sinks when I am lightly breaking. I tried hard breaking and it stopped just fine. I dont think its the master cylinder but it might be. Any ideas?

0verb00st

should I just assume its the master cylinder and replace it?

bl00dlust

yes

Icemark

Break = broken
Brake = stopping mechanism on a vehicle

and did you bleed the brakes when you changed the pads?

0verb00st

no, i didnt think I had to since I only changed the pads.

glh-fc

you might wanna bleed the system and see if that helps.check each caliper and see if there are any leaks.

Icemark

pretty much a mandatory thing to bleed the brakes after changing pads.

mike_merryguy

iTrader: (8)

bleed brakes after changing pads??!?!?!

WTF never heard of that, no part of changing pads opens the fluid system !!
typically I remove the cap from the master cyl and push the pistons in, then replace the cap and pump the pedal once new pads are in, even if you don't remove the cap it shouldn't matter, since its not full to the top no fluid will leak out of the resivoir.

I have seen a few topics regarding replacing the rubber brake lines with flexable steel lines, some have said that helps from having a weak pedal, other people have had to replace the master cyl or power booster, one guy that did the power booster thought that it was good until he removed it and had it pressure tested, I guess they are hard to pinpoint with small leaks

pistones

iTrader: (5)

its probably a good idea to replace the 20 year old fluid anyways. see what happens after you flush and bleed the system.

Icemark

How are you pushing in the pistons on the front brakes to fit the new pads without opening the bleeder valve?

If you just cram the pistons back in without bleeding out the fluid you easily can damage the boots, and seals... well alone pushing all that crappy brake fluid that is in the piston back into the lines to work its way through out the system.

Only the worst mechanic would not bleed out the brakes when changing the brake pads.

furthermore the brake fluid should be changed every 24 months or 24K miles anyway just for system longevity.

SS flexible lines are not recommended for street driven vehicles. And master cyl replacement is usually a result in not changing the brake fluid often enough or too much crap in the brake fluid. Brake boosters almost never fail, and when they do, it results in heavier brake pressure, but no change in stopping distance or system operation other than that.

mike_merryguy

iTrader: (8)

My friend check the FSM no where does it say you are required to bleed for pad replacement, I never said it wasn't smart to change the fluid every so many miles but its not a requirement to bleed or change fluid with pads, and its a sealed system so how is the fluid in the pistons any different from the fluid in the lines, I have rebuilt many pistons and never seen any "dirty" fluid come out of them unless the piston was broken to begin with.

0verb00st

I just inspected my master cylinder and found liquid (probably brake fluid) all around it. I will definitely replace it, my question is what are the symptoms of a bad brake booster? I looked in the archives and couldn't find anything on the booster.

mike_merryguy

iTrader: (8)

http://www.teamfc3s.org/main/factory...ual/1986_1988/

that is the link to the FSM - factory service manual for the 86 to 88, found at this page

https://www.rx7club.com/showthread.p...18#post5131218

which in turn is a sticky at the top of 2nd gen section called FAQ, in there you will find all kinds of brake system troubleshooting and how to go about testing the booster as well as replacing it

Icemark

A bad brake booster will just result in additional pressure needed to stop the car... in essence you won't have the power assist.

But you still should have a firm pedal and even stopping... just would take more pressure to stop

Icemark

You didn't answer the question... how do you push the pistons in, without opening up the bleed valve?

If you open the bleed valve, you need to bleed the system.

And okay you never saw "dirty fluid come out"??? What color was the fluid that came out when you rebuilt the many pistons that you have?

Was it clear?

Was it dark?

was it green?

sktrowley

Just curious but why would having ss lines be bad on a street car? I've always heard it referred to as an upgrade. I'm not saying your wrong I just have never heard that?

Icemark

I have not seen SS lines that have not failed within 2 years... on a daily driver/ street car.

The uncovered ones, sand and dirt work their way through the braids and eat the hose up under the braid.

The covered ones, tend to leak at the crimps and eventually you start pumping brake fluid into the cover between the braid and the cover, reducing break efficiency to the point of 20 year old stock flexible lines.

Sure they work great when new... but put 10k or 20k miles on them and see how well they are still working.

SS lines were designed for race cars that had their whole brake system overhauled every season.

sktrowley

ok thanks you just saved me ~$100ish!

magus2222

iTrader: (22)

idk about that one icemark. very true in the fact that SS lines were designed for that very reason that you stated, but i havent experienced any problems on my datsun, or even people that have had ssb lines for the life of the car.
really, it all comes down to maintainence.
and back to the original post. YOU ALWAYS BLEED THE BRAKES when changing ANYTHING dealing with the brake lines. common sense dictates that if you are changing or maintaining the most important safety feature in a car, you go out of your way to make sure there are no weak points in that system. good brake fluid could save your life, and it does sound like either a bubble in the system or a bad master.
hell, check the brake booster while youre at it.

peace

mike_merryguy

iTrader: (8)

well since my fc is a 4 piston i would use something that was rather long, with a rubber handle, not to thick though as to fit between the rotor and piston, and gently push/pry the piston back into the caliper, not to hard of a process there...

a normal vehicle with regular single piston, well they sell a tool, typically it is called a C clamp but there is a "special" tool that many will buy, as a matter of fact I just gave one to my friend because he indited that a regular C clamp would not work, and I didn't need it

If you are changing your rotors, well get a damn tire iron and leave the old pads on as to not damage the piston with the sharp edge, just push/pry that tire iron between your old rotor and your old pad until the pad is flush with the caliper...
again use gentle pressure..

the pistons are designed to go both ways, if they were not then when you hit the brake pedal then well your wheels would simply just lock up and never release, therefore by design they are made to be put back into the caliper without having to open the bleeder screw

so don't open it... open the master... and on an FC if you do one wheel at a time y ou don't even need to open that, there is a tiny pin hole that allows air to flow out, and a MAX fill line. so if you are not over the max fill and you push the piston in then no fluid will spill out of that hole, its such a small amount you may not even notice it moved...

say you have an old GM with the large metal master they open it, suck a little fluid out say 1/4" from top no more than 2/3 of fluid or so, push in pistons, fill to 1/8" from top of master, replace pads, replace cap pump pedal, remove cap, fill to 1/8" from top of master, replace cap, roll out... very simple....

as long as you don't drop below the MIN line, then you should never get air in the line from hitting the pedal

well as long as the system has been maintained as specified for that particular vehicle it will be clear, I have seen really dark fluid but that was only working on very high mileage vehicle with little to no maintenance performed (after asking customer) I used to help my friend out with odd jobs back in the day and lots of his jobs were brakes, seems to be a good business to get into because people don't think about them until they fail or seem to fail, hell most of the people that came through would refuse brake service unless something was already broken because its just so damn expensive most places, and as I stated the majority say like 90% of the jobs that I have personally done (not specifying anything for the industry just personal jobs) the fluid would usually be dirty if a piston had failed, in which case you can never tell when it failed, the stupid customer will drive till they feel they just can't stop safely anymore i have also seen dirty fluid if a customer claimed replacing a part such as a master or piston with a junk yard part without properly flushing or cleaning said part

you figure the majority of drivers just want to get from point a to point b, they know they have a user manual but probably don't know about he FSM inside that or included separately, they go to midas every time the sticker on the windshield catches their attention, or somewhere close to that get the oil changed and just keep driving till they notice a problem, a vehicle with good maintenance can probably last a life time...

J-Rat

iTrader: (2)

Uhh..

I never had to actually bleed a braking system either after a pad change either, I just use the brake tool to retract the pistons, but no matter.

To the OP. Sounds like in your case a bleed IS in order as the problem was there before you did the pad change.