VR Brake problems :(

[holdenboy]

OK, long story short i replaced the M/C on my VR V6 with ABS and when i went to bleed the brakes i couldnt get any fluid out of the rear lines, the front ones bled fine. So i thought i'd take it for a drive to cycle the ABS etc (thinking i had air in the ABS module). Brakes were better than before but still not great.

Halfway through the test drive the brakes started to stay on, in the end they were probably 20-30% on (no change in brake pedal height). So i got home and flushed the system again, after this the brakes seemed better (certainly not great though). During the first test drive the brake warning light stayed on, after i flushed the system it came on when i was hard on the brakes. After a while the brakes started to stick on again.......and thats where im at now.

The master cylinder was second hand but was working fine on the old car.....its was also from a V8 with ABS.

The only problem i can think of is the rod coming out of the brake booster is pretty-well rusted, and it may be sticking to the M/C after a few applications?

But it still dosent explain no fluid coming through to the rear calipers?


Got me stumped, any help is appreciated.

[Brett_jjj]

There might be air getting sucked into the master cylinder somewhere,and that could be why there is no fluid getting pumped back to the rear calipers.Its best to use a new master cylinder when replacing them.Or at least put a rebuild/seal kit through the second hand master cylinder before fitting it.Ive seen a few people have similar problems to yours after fitting second hand master cylinders.Its not worth the hassle as you have found out.Try putting the seal kit through your old one.Im not sure what they cost.They are usually cheap though.

[holdenboy]

Thanks for the reply, the original one is no longer able to be rebuilt. One of the brake lines were seized on to the M/C so i had to replace that line. So im still thinking it could be alot of air in the ABS module as i had to remove the brake line from it also.

I dont think theres air getting through to the lines as the fronts are always fine (no air) when i bleed them. But again, i could be wrong.

Ive also taken the lines off the M/C and pumped the brake pedal, the bottom output (on the front of the M/C) spurts out plenty of fluid. But the bigger, rear line rarely spurts out much at all? Im not sure if this is normal or not.

[RX25SE]

Make sure the rod out of the booster is allowing the master cylinder piston to retract the full distance, otherwise the compensating port may not open allowing the cylinder to fill with fluid.
If there is a PD (pressure differential) switch in the master, did you remove it to blled the brakes? This really should be done.

[Brett_jjj]

You might have to see someone with a scantool that can cycle the ABS while you bleed the brakes to get the air out properly.You can try locking the wheels up on some grass or gravel a few times.Then re bleed them, and then do the same again,lock it up a few times,and bleed it again.If it doesnt improve,another master cylinder might be the only way to fix it.

[holdenboy]

Do you mean the switch on the underside of the M/C? If so then no i didnt remove that when bleeding the brakes. Also, how do i check the booster rod is not allowing the cylinder to fill?

Brett - I did initially try locking the brakes up one gravel, but that seemed to cause the brakes to stick on more?

[Brett_jjj]

Ive bled heaps of these systems and never had to remove anything from the master cylinder, Ive never had any problems.

[holdenboy]

Hmm, well im starting to think theres something going on with either the master cylinder or the the booster......the brakes maybe sticking on because the rears arent working?

[Brett_jjj]

I did initially try locking the brakes up one gravel, but that seemed to cause the brakes to stick on more?

They might be locking on as the air gets pushed out through the hydraulic system to the calipers,Id try it a few more times and re bleed it to see what happens.It might come good.And at this stage you have nothing to loose.

[holdenboy]

Yeah true. The brake pedal at the moment is really spongy and dosent do much.

I might have to take my tools with me and bleed them on the gravel......the brakes locked up that bad last time the engine couldnt push the car!

[Brett_jjj]

Yeah true. The brake pedal at the moment is really spongy and dosent do much.

I might have to take my tools with me and bleed them on the gravel......the brakes locked up that bad last time the engine couldnt push the car!

If they are spongy then 99% chance theres air trapped in the system somewhere.Just try it anyway and see what it does.Definitely take your tools if theres a chance they will lock on altogether.At least then you will be able to do something about it if it does happen.Id try locking it up a few times then re bleed them and see how they are then.

[holdenboy]

Yep i will do. Thanks alot for your help.

I read somewhere else (done alot of searching) that the reason why the rear lines arent getting any fluid is because the ABS thinks the wheels are skidding and restricting the fluid?
Sometimes i do get very small amounts of fluid from both rear calipers but its certainly not enough to bleed them.

Sorry if i sound abit simple, i sort of understand the concept of ABS but not the nitty gritty workings of the ABS unit

[Brett_jjj]

You definitely should not get any fluid around the rear calipers at all.If there is fluid leaking ,even if its just weeping it needs a rebuild kit put through the calipers to make them serviceable again.Its probably whats causing your problem.Its dangerous to drive it like that.It sounds like the whole braking system needs an overhaul.Get a workshop manual and get the rebuild kits for the calipers ,sit down and rebuild them all.Its the cheapest way to go about it.You can sometimes buy overhauled or brand new calipers from ebay.I dont know what they would cost though..
The rebuild kits are usually cheap.You could also take it to a mechanic and get them to do it,but that means $$$.

[baza]

holdenboy , before you put the replacement master cylinder on your car did you " bench bleed " it . you may still have some air trapped in the master cylinder, and its standard practice to bleed them before connecting the brake lines to master cylinder. you can do a search on the forum , or google to find a " how to ". and with your rear brakes could be worth checking the bleeder screws to make sure they are not clogged up with crap , that can restrict the fluid.......cheers.

[holdenboy]

Thanks guys, there is no fluid coming through to the rear lines at all.....ive disconnected the brake lines from the calipers and i still dont get much fluid out of the lines......sometimes i get a dribble after 1-2 minutes of pushing the pedal, other times nothing at all.

The master cylinder still had fluid in it and yes i did bleed it before installing it, ive replaced many a master cylinder / brake line before but never with an ABS-equipped car.

Im going to head out in the next hour and see if i can cycle the ABS and re-bleed the system....fingers crossed

[python_hunter1]

defintley sounds like you still have air trapped in the system. they can be a pain in the ass to bleed at times, but persevere and you should get it done. if not take it in to a mechanic and get them pressure bled. works every time.

[holdenboy]

Well just got back. Took it out onto gravel and locked the brakes up 5-6 times (had to push pedal to floor) and the ABS definitely still works ok.
So then i bled the system, still no huge amounts of fluid coming out of the rear lines. Repeated and re-bled. Repeated and re-bled.
Did make a small amount of difference though, probably around 50% of what it should be (started off at probably 30%).
One thing i did notice about the rear lines is when i crack the nipples a small amount of fluid slowly comes out, with air bubbles.

Because it has gotten better i'll head back out later on and do it again.......atleast the brakes didnt lock on this time!

[Brett_jjj]

Just keep repeating what you are doing.Lock it up,re bleed it and so on.Once enough air is bled out of the rear system,the MC should push the fluid through easily and at a higher rate until its back to normal.How are you doing the bleeding process.Theres two ways,you can get someone to slowly pump the pedal a few times and then hold the brake pedal in while you release the nipple on the caliper,then close it again once the air and fluid comes out and pump the pedal up again and repeat the bleeding until no more air comes out..Or you can get a piece of plastic tubing that will fit tightly over the bleeder nipple and then you get a jar and put about 2 inches of clean brake fluid in the jar.Then put the other end of the tubing into the fluid in the jar.Make sure it is right at the bottom of the jar under the fluid and then release the bleeder nipple and pump the pedal slowly to pump fluid through.Make sure someone keeps an eye on the MC fluid level because if it gets low it will just suck in more air.The fluid in the jar stops air being drawn back into the plastic tubing and back into the system as the pedal is released.Just make sure the pedal is pumped and released slowly.It might be worth trying bleeding it both ways if you havent already.

[holdenboy]

Do i need to keep bleeding the fronts? I can get to the rear calipers easy enough but the fronts are a touch harder (with the wheels on and without a jack). Plus the fronts never have any air in the lines.

Thanks alot for your help Brett......anytime you need advice on a stereo system / electrical let me know

[Brett_jjj]

Just do ther rear ones for now and get them working first.Then once they are working ok you might want to give it a final 4 caliper bleed just to be sure every bit of air is removed..How have you been doing the bleeding process?

[holdenboy]

Well, using a "one man" tube and one way valve i start with the rear p/s caliper. I connect the tube and pump on the brake pedal, probably do this for a minute or two just to see if i can get some fluid. Then after i dont i tighten the nipple and move on to the rear d/s caliper. Same with the fronts (p/s then d/s).
I dont even get enough fluid in the tube to fill it on the rears.(15-20cm long). The fronts fill the tube on the first pump.

[Brett_jjj]

Try the method I described above with the jar and plastic tubing.You will obviously neeed another person to do it this way,preferably another 2 people ,one to pump the pedal and one to keep an eye on the MC fluid level.The MC fluid level will go down really quickly when bleeding this way so keep a good eye on it.Its also worth trying the other way,just pumping them up and releasing the nipple and tightening it up again,pumping it back up etc and repeating this process.Actually Id try this first.Some of them one man bleeding kits can be a bit bodgey.

[moose man]

Post No. 4 has the answer.

If you didn't adjust the booster pushrod before you fitted the master cylinder, the brakes are already applied slightly, and the rubber piston is covering the compensation port part way up the master cylinder.

1. This explains why your brakes gradually apply as they get warm and the fluid in the caliper expands, and;
2. also why very little fluid comes out when you bleed them.

No fluid can transfer from the reservoir to inside the master cylinder piston, and vice-versa.

Take your master cylinder back off and put a piece of bubble gum/clay/playdough (anything squashy you can find on the tip of the pushrod. Lightly bolt the master cylinder back on and then remove it again and check it's not touching. Should be close but not touching.

See page 52 of this Lexus manual for more info:

http://www.autoshop101.com/forms/brake05.pdf

[holdenboy]

Hi moose man, if this is the case and the rod from the booster is too long / short and is preventing the fluid from getting into the lines etc. Why do the front brakes work?

[Brett_jjj]

I have looked at a workshop manual and there is no mention of any adjustment for the master cylinder push rod,or even how to adjust this when fitting the master cylinder or brake booster.It just says to prime the MC with some fluid and bolt the MC to the booster,then connect the lines and bleed the system.