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Brake Fluid Level Dropping But No Visible Leaks

sweefu
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sweefu Mentor

sweefu

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Posted

Hi all,

As per the title I have a braking problem. This week I'm taking the car to a 'Brake and Clutch Specialist' to be diagnosed (or to get the official all clear) but it would be good to see if anyone has experienced anything similar or if anyone can shed some light on my problem.

My brake components (Car is S14 200sx)

- R33 front calipers

- QFM A1RM pads front and rear

- DBA 4000 T3 rotors front

- RDA OEM replacement rotors rear

- Nulon brake fluid (Dry boiling point 280deg)

- OEM rear calipers/all OEM lines/BMC etc

- Pads/rotors/fluid all replaced in November 2014

Basically, the brake fluid has needed topping up twice in the last couple of months but I can't see any leaks. I understand fluid level will drop with brake pad wear, but I can't see the brake pads having worn enough for two top ups to be necessary. Please see below for the story

In March I attended a figure 8 drifting night, before driving I checked all my fluids and brake fluid was at 'max' line. During drifting the brake light on the dash flashed every now and again - I assumed this was the ABS system being upset with drifting (has happened before). Some days the event the brake fluid needed topping up, it was sitting maybe 1/8th below the 'max' line on the fluid reservoir. My assumptions could be the cause of my problems here, I assumed this was OK and that I had worn the rear brake pads at the drift event - rear pads were noticeably more worn. I topped up the fluid and carried on for a few more weeks of daily driving.

Some weeks later the fluid level was again about 1/8th below 'max' line, but the car had only been daily driven since the last drifting event. This weekend I put the car on stands and inspected all the components and I couldn't see any leaks. No fluid hanging around bleed nipples or brake lines, or around caliper pistons or the BMC/brake pedal. I scuffed the pads, topped the fluid and I will keep inspecting it until it sees the mechanic, but I am curious to know if anyone can suggest what might be wrong. The only thing I can think of is a failing BMC leaking fluid into the booster - what do you think?

The pedal feel is fine as far as I can tell, and after scuffing the pads (were slightly glazed) the car pulls up really well.

Any help would be appreciated, thank you everyone!

XKLABA Grand Master

XKLABA

Posted
Posted

3mm isn't a great deal of fluid and could very well be pad wear, though hard to beleive it would drop that far DDing it :/

Test the BMC by pumping the brake pedal with car switch off till the booster has stopped assisting the push pedal down hard and if it keeps dropping then your BMC is on its way out

sweefu Mentor

sweefu

Posted
  • Author
Posted

Look inside the car under the pedal behind the carpet.

Thanks, I did this yesterday with the other checks and nothing visible. There was some grease on the rubber part of the pedal where it passes through the fire wall but no signs of leaks or brake fluid.

3mm isn't a great deal of fluid and could very well be pad wear, though hard to beleive it would drop that far DDing it :/

Test the BMC by pumping the brake pedal with car switch off till the booster has stopped assisting the push pedal down hard and if it keeps dropping then your BMC is on its way out

If I push the pedal while the car is off it stays hard and the fluid level remains the same - would this indicate the master could be OK?

Also, get underneath and check for leaks between the master cylinder and vacuum booster, if there is a leak there you will see drips bubbled paint and possibly rust.

Thanks, have done this also. All looks clean/clear, no leaks in sight and paintwork etc all OK still.

XKLABA Grand Master

XKLABA

Posted
Posted

If I push the pedal while the car is off it stays hard and the fluid level remains the same - would this indicate the master could be OK?

Yeah, if it was leaking the pedal would slowly drop to the floor as the fluid passed around the piston which it has to do to leak out of the BMC into the cab

This test can be done with car on or off, i just find the booster can interfere sometimes

sweefu Mentor

sweefu

Posted
  • Author
Posted

Thanks for all the help here guys.

Since scuffing the pads and checking it all, the car pulls up really well. Fingers crossed it was just pad wear.

In any case I'm getting a 'Brake and Clutch Specialist' to check it out in the morning, they said they will pressure test it to see if there's a leak which should give me peace of mind before going back on a track!

sweefu Mentor

sweefu

Posted
  • Author
Posted

Update:

Mechanic diagnosed it as a leaking seal in the driver side rear caliper, just barely weeping. They quoted me an interesting $695 to rebuild the rear calipers.

Getting some more quotes tomorrow, I've even got a seal kit to do it here.

What would be a reasonable labour charge? 3 hours?

Cheers

sweefu Mentor

sweefu

Posted
  • Author
Posted

If I were you, I would do it myself, and spend the cash on hookers and coke.

Man, I would love to :(

I don't have the space to do it though. Could do it at a friends house - might have to if all these quotes are around $600!

89CAL Grand Master

89CAL

Posted
Posted

Jack the car, remove wheel, remove the caliper, re-fit wheel, lower car

That way you only need a small space to rebuild the brake :)

The shop may have been quoting worst case, if the pistons need replacing etc

I have the part number for the seal kit somewhere. Think they are only $40-$50 a kit. Should be fairly easy to rebuild. Hopefully the most they will need is a light hone.

Otherwise you could buy a second hand caliper

Missileman Veteran

Missileman

Posted
Posted

One more tip, if you buy a second hand caliper, only take it off a wrecked car with a hard pedal, once the caliper is off the car, moisture will be drawn in via the fluid as it's hygroscopic, i.e sucks in water from the air, which can corrode the bore of the caliper or the steel piston.

sweefu Mentor

sweefu

Posted
  • Author
Posted

Jack the car, remove wheel, remove the caliper, re-fit wheel, lower car

That way you only need a small space to rebuild the brake :)

The shop may have been quoting worst case, if the pistons need replacing etc

I have the part number for the seal kit somewhere. Think they are only $40-$50 a kit. Should be fairly easy to rebuild. Hopefully the most they will need is a light hone.

Otherwise you could buy a second hand caliper

Thanks man! I ordered a seal kit from Taark today ($99 genuine Nissan). I'm going to call a few shops and see if anyone will do it for reasonable money.

Was tempted to buy a second hand caliper but thought it might be in similar shape anyway - already paid for Wakefield on May 9/10 so hoping to get it buttoned up buy then.

Are you in Vic or NSW.. I'm sure there is someone who could give you a hand if you thought you would struggle

You guys are all such champs! I'm in NSW now mate. I've never rebuilt a rear caliper before but I don't have a driveway to do it in unfortunately - otherwise I'd give it a crack.

One more tip, if you buy a second hand caliper, only take it off a wrecked car with a hard pedal, once the caliper is off the car, moisture will be drawn in via the fluid as it's hygroscopic, i.e sucks in water from the air, which can corrode the bore of the caliper or the steel piston.

Thanks for this mate, good tip. Going to avoid going with second hand calipers to try and fix it first go. Hopefully I can find a shop to do it for reasonable money, $695 is crazy

GTR_JOEY Grand Master

GTR_JOEY

Posted
Posted

I'm in WA for a couple of weeks atm but like i said I'm sure there's someone who can spare an hour to give you a hand

It's quite simple if you take your time but you will need a hand to bleed it up

GTRPSI Mentor

GTRPSI

Posted
Posted

Also check to see that the pistons not rusting, pointless putting new seals on a damaged piston, its very common to see rusted up pistons and the main cause of leaking seals.

warps Mentor

warps

Posted
Posted

Do the Nissan rear calipers have the funky screw in handbrake adjuster post inside the piston? I've just rebuilt a pair of Honda DC2R rear calipers and the handbrake assembly is a bitch to get apart without the correct Honda tools (was going to spin up a mandrel on the lathe, but then need the long nose circlip plliers as well - in the end I cbf for a one-off job). In the end I just rebuilt the main part and washed the handbrake mechanism with a toothbrush and brake fluid. It's only going on a track car so the handbrake isn't that critical.

If they don't have this screw adjuster, then the rebuild will be easy peasy. It takes a bit of time (I sandblast the caliper and thoroughly clean it with brake cleen / 2k thinner) hence possibly part of the reason for the cost. Of course you can rip a caliper apart and throw new seals in there in about 20 minutes, but you won't end up with a better job than what you started with. Interestingly, I paid $30 per seal kit from Honda in USA, whereas the local dealer wanted $100 a pop. fkn ripoff merchants.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Do the Nissan rear calipers have the funky screw in handbrake adjuster post inside the piston?

They might on some of the pox cars. But Skylines have a separate drum brake inside the rotor hat for handbrake. Makes it a pretty piss poor handbrake, but does eradicate the f**k-knuckle designs that put them mechanism in the caliper.

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