Locating brake fluid leakage

[my name is alex]

Edit - [turns out to be my brake proportioning valve]



My brake fluid reservoir is emptying itself out every couple of months. I don't see any obvious leakage. Any suggestions as to where to look?

The larger reservoir is down to the bottom, pretty much empty, but the smaller reservoir is still about half full - in case that means anything. I'm fairly brake system ignorant (all system ignorant compared to most of you guys).

Speaking of ignorance, what is the box just forward of the master cylinder that seems to be attached to the master cylinder via steel lines? This thing has quite a bit of residue on the bottom half, though nothing looks all that fresh.

 

[my name is alex]

Speaking of ignorance, what is the box just forward of the master cylinder that seems to be attached to the master cylinder via steel lines? This thing has quite a bit of residue on the bottom half, though nothing looks all that fresh.

ABS controller?

 

[Rogue]

If I recall correctly, the larger portion is for the lines to the front brakes. The box forward of the reservoir is the ABS. I had leakage going on with mine, but it was the smaller part which led me to trouble shoot the back lines...turned out to be the rear wheel cylinders, but that's not the case here. I have had friends who lines leak at a joint just inside the engine bay in the front wheel well.

 

[my name is alex]

I have had friends who lines leak at a joint just inside the engine bay in the front wheel well.

Thanks. I'll try and find this joint tomorrow and take a look.

 

[Rogue]

Thanks. I'll try and find this joint tomorrow and take a look.

That's no problem...the part about the joint is just hearsay, I've never had first hand experience with it. Each side has one (at least on my '97) on the frame. If you trace the line from your caliper to under that flap in the front wheel well it's right there where metal line meets the flex line. Supposedly those rust out...but that's further hearsay from people I know. Though I would think there'd be a noticeable puddle under the truck. If it were me, I'd check all the lines to the front calipers if my fuzzy memory is correct about the bigger chamber being for the front brakes. Maybe have someone else pump the pedal while tracing the line. Just my .02 FRNs.

 

[Rogue]

Thanks. I'll try and find this joint tomorrow and take a look.

By the way, I just noticed you have a K2500 with 454....so I have no idea if the brake system is the same or similar. I should have seen that first! I'm familiar with my K1500's with 5.7L....

 

[skylark]

Most common is a wheel cylinder. If it is a line leak just treat her like a chunky chick, cover her in baby powder, pump her hard and look for the wet spot. Or in non layman's terms, spray baby powder over all of the lines and fittings then pump the brake pedal. Look for the wet spot to find the leak.

 

[my name is alex]

Thanks for the tips guys. Hopefully I'll be able to track this down now.

I did inspect where the lines connect to the wheels yesterday, but didn't see any wetness there. The only suspicious looking thing so far is the gunky ABS Controller. But I'll check the lines further.

My truck has very little rust, as it's a California truck with under 70k, so I doubt anything is rusted out. But who knows...

 

[my name is alex]

I have had friends who lines leak at a joint just inside the engine bay in the front wheel well.

I do have this same joint, but mine are clean.


I think I found the leak though. I stood up on the front bumper to get a better view of the bottom half of the ABS controller and realized there's been years of buildup from a mild leak heading straight down from the ABS controller. It's not enough to puddle - the truck doesn't drip anything noticeable.

It looks like it may be from a nipple looking metal nub that goes to nowhere. Overflow valve or something? I'm going to have my wife press the brake tomorrow and see if I can see an ooze. Does it matter if the truck is running or not for this 'test'?

 

[east302]

Got a picture of where the leak is? I just replaced mine on my 1998 K1500. Does yours look like this?

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In the diagram, #2 is the computer control or module (EBCM), #12 is the combination valve and #4 is the brake pressure modulator valve (bpmv). They're expensive new, I think the combination valve was around $150 and the bpmv pushing $500. I bought the whole assembly at a junkyard for $75. It's not hard to replace (bleeding the brakes afterward took a little longer).