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#4375491 - 04/09/17 02:59 PM Gelled brake fluid?
nthach Offline


Registered: 01/02/04
Posts: 3994
Loc: California
A Chevy Tahoe I maintain for a friend had some weird brake issues - everytime the ABS cycles, the brakes will lock up and sometimes won't release. Yesterday I flushed the fluid - but the master cylinder diaphragm gasket was swollen and did recall a rag was wrapped on the reservoir before he put a proper cap on it. The fluid inside was black and gelled up to the consistency of a cold consomme.

I suspected contaminated fluid and I swapped out the master cylinder, flushed 1.5 quarts of fluid through all the wheels until it was mostly clear, did the "hillbilly" GM ABS bleed procedure by doing a few panic stops in an empty parking lot to cycle the modulator, I was expecting some air to be released and a soft/spongy pedal as a result - but my friend said there was no pedal change however he did say before we flushed the fluid when the ABS did cycle the wheels will lock up and he would be stopped in his tracks. We drove home and I pressure bled the system again, I did see a good bit of air escape. I used a total of 2.5 quarts of fluid. The truck does stop much better, the ABS system cycles as expected but there's some residual drag.

His suspicion was that his dad added power steering fluid to the system - I did find a bottle of Prestone-branded PS and brake fluid in the truck. The fluid level in the old MC was low. I did siphon out with a mityvac the old fluid and immediately swapped the MC to avoid pushing in old fluid. I know petroleum-based fluids in a glycol system are a no-no, but does plain neglect of a brake system, meaning no brake fluid flushes can also cause brake fluid to congeal and gel?

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#4375502 - 04/09/17 03:14 PM Re: Gelled brake fluid? [Re: nthach]
901Memphis Offline


Registered: 08/14/10
Posts: 12897
Loc: Northern Kentucky
I think the mixing of the wrong fluid did it.
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#4375515 - 04/09/17 03:33 PM Re: Gelled brake fluid? [Re: nthach]
mk378 Offline


Registered: 09/27/15
Posts: 1449
Loc: USA
The rubber swelling up means that an oil-based fluid has been introduced.

Often this will come down to replacing every part of the brake system that has a rubber component.

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#4375517 - 04/09/17 03:35 PM Re: Gelled brake fluid? [Re: mk378]
kschachn Offline


Registered: 12/26/05
Posts: 9535
Loc: Upper Midwest
Originally Posted By: mk378
The rubber swelling up means that an oil-based fluid has been introduced.

Often this will come down to replacing every part of the brake system that has a rubber component.


Yes, this. Every component that contains any elastomer in contact with the fluid should be replaced.
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#4375522 - 04/09/17 03:48 PM Re: Gelled brake fluid? [Re: kschachn]
nthach Offline


Registered: 01/02/04
Posts: 3994
Loc: California
Originally Posted By: kschachn
Originally Posted By: mk378
The rubber swelling up means that an oil-based fluid has been introduced.

Often this will come down to replacing every part of the brake system that has a rubber component.


Yes, this. Every component that contains any elastomer in contact with the fluid should be replaced.

I told him to keep an eye on things and to let me know if the brakes lock up again - he did have an ABS hard code that went away with a power cycle, my OBDII dongle doesn't do ABS.

Luckily, parts for these trucks are reasonably priced(calipers, wheel cylinders, hoses), and there's plenty of ABS modulators at the local junkyard.

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#4375540 - 04/09/17 04:12 PM Re: Gelled brake fluid? [Re: nthach]
eljefino Offline


Registered: 06/15/03
Posts: 32775
Loc: ME
I had gelled brake fluid in a motorcycle that was parked a few years outside, under cover, but without walls, in a tent like structure. I figured it was extreme humidity that did it.

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#4375550 - 04/09/17 04:37 PM Re: Gelled brake fluid? [Re: nthach]
Kestas Offline



Registered: 06/04/02
Posts: 12399
Loc: The Motor City
I have personal experience wi both gelled fluid and with petroleum contamination.

The gelled fluid I had was old fluid mixed with heavy moisture. Corrosion was prevalent in the area.

The petroleum contamination was a mishap with using mineral spirits I kept in an old brake fluid jar. The brakes locked up from the swelled components, and as mentioned above, required replacement of all elastomer components. Thankfully, for a 1974 Torino, it didn't take too long to fix this, nor was it expensive.

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#4375556 - 04/09/17 04:52 PM Re: Gelled brake fluid? [Re: nthach]
E150GT Offline


Registered: 03/11/12
Posts: 1160
Loc: San Antonio, TX
Originally Posted By: nthach
I know petroleum-based fluids in a glycol system are a no-no, but does plain neglect of a brake system, meaning no brake fluid flushes can also cause brake fluid to congeal and gel?

I doubt it. I recently flushed 21 year old brake fluid on my truck. It was nasty and chunky, but it seemed very much the same consistency of new brake fluid and my brakes never locked up like your friend experience. I am sure mine was loaded with water as my truck spent its whole life in humid S Texas and one of those years 1/4 mile from the beach. I knew I would need to do it but I put it off and I ended up rupturing a metal brake line while driving one day. I believe it corroded and rusted from the inside out.

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#4375712 - 04/09/17 08:00 PM Re: Gelled brake fluid? [Re: mk378]
Trav Offline


Registered: 11/20/06
Posts: 19346
Loc: MA, Mittelfranken.de
Originally Posted By: mk378
The rubber swelling up means that an oil-based fluid has been introduced.

Often this will come down to replacing every part of the brake system that has a rubber component.


+2, New seals and thoroughly clean or replace the MC, calipers/wheel cylinders. Replace all rubber brake hoses and ABS unit also, its all done. Wash all the metal lines out with brake cleaner until it comes out clear.
This can get a bit pricey but using rebuilt parts and a good used ABS unit can help keep cost down, just be sure to match the ABS unit numbers.
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#4375809 - 04/09/17 10:49 PM Re: Gelled brake fluid? [Re: nthach]
nthach Offline


Registered: 01/02/04
Posts: 3994
Loc: California
Already done the MC - if I hear the brakes are locking up again, I'll replace everything else. I just texted the owner and he said his brakes are working worlds better and no ABS light... yet.

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#4375941 - 04/10/17 07:43 AM Re: Gelled brake fluid? [Re: nthach]
Trav Offline


Registered: 11/20/06
Posts: 19346
Loc: MA, Mittelfranken.de
I am just concerned that whatever is left in the abs unit will recontaminate the new MC. The brake fluid doesn't act as a very good flushing agent for oil residue.
See what happens, I have run into this a few time over the years and its no fun.
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#4376918 - 04/11/17 12:50 PM Re: Gelled brake fluid? [Re: nthach]
nthach Offline


Registered: 01/02/04
Posts: 3994
Loc: California
I threw together a list of things from Amazon - except calipers - O'Reilly for that, it's gonna be a Cardone reman ultimately and for $5 less he gets a lifetime warranty.

One thing I did notice - there was no fluid coming out of the rear brakes when I did install the new MC and used a Motive Power Bleeder for pressure bleeding, I had my friend sit in the driver's seat and resorted to the pump and crack method until I got fluid coming out, I then used pressure to push out fluid until it was clear.

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#4635716 - 01/15/18 12:35 PM Re: Gelled brake fluid? [Re: nthach]
nthach Offline


Registered: 01/02/04
Posts: 3994
Loc: California
A 9 month recap on the whole situation:

Truck friend calls me up saying his brakes are making a grinding noise. I tell him he needs at the minimum, new rotors and pads. I suggested replacing the calipers and hoses since I suspected those got ruined by the petroleum contaminated fluid last year. I pull the front wheels and the passenger side caliper looked fine - pads were 50% worn but the driver side brake was a different story. The outboard pad was fine but the inboard pad was metal on metal against the rotor and the pad was ground down to the piston clip stakes.

2 new "value" series rotors(ACDelco Advantage on one side, Amazon didn't send the other one in time so I threw on an O'Reilly basic rotor, same as an Aimco), a set of Wagner ThemoQuiet Ceramics and a pair of calipers later I got the front brakes functional again.

I did apply some disc brake quiet spray against Wagner's wishes on TQ IMI pads - but I had hit or miss with noise on TQs and it wouldn't hurt on an car whose pads were originally riveted. I took a wire cup brush to the sliding surfaces on the steering knuckles and lubed them up with Permatex Ultra Brake Lube silicone formula and Dow 111 on the sliding pins and sleeve/bushings. A quart of house brand DOT 4 was ran through the new calipers and hoses, I noticed the Prestone DOT 3 I used for the initial flush when I replaced the MC turned dark fairly quickly. The fluid coming out of the calipers looked like typical used fluid - more on the amber side.

Besides from the dangerously-working front brakes, the truck's ABS system is functioning fine but I told him to keep an eye out. But so far, the truck stops 100% better.


Edited by nthach (01/15/18 12:37 PM)

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