Complete Brake Failure!!

[Rookie93]

Hey Guys, I am brand new to this forum and this is my first post.

I bought an 80 series LC a few months ago with a spun bearing. So, I yanked that motor and had a 5.9 cummins diesel put in it!

I get it back and it is amazing! I just love the way this rig drives and crawls in the mountains with the torque of a diesel. I couldn't be happier!........ Except..... coming down off the hill I lost the brakes completely.
Out of nowhere, complete failure, all the way to the floor! Oh $###!! I was able to pop her into neutral and pull the parking brake to slow down enough to come to a controlled stop when the trail got flat enough. I jumped out and searched the whole engine compartment and underneath looking for the spraying brake fluid everywhere..... but nothing. I sat and contemplated my options for a few minutes and decided that I would just crawl her home. After about ten minutes on the highway I could pump the brakes and she came back. By the time I got home I had full brakes and haven't had an issue since. WTHeck??

Now, I haven't owned this rig long and I don't have any experience with the braking system. But I know darn well it shouldn't do that! Lol. I thought that maybe it was the master cylinder, or maybe it was water in the fluid that had gotten hot and turned to steam. But I need to be sure. What are some thoughts here. I need to be able to put my wife and kids in this rig on the daily, ya know? Please advise.

~Rookie

 

[Firewout]

IMHO you could be right about water in the brake fluid. Especially when you mention it happening on a descend, so the brakes will get hot.
did you already change the brake fluid ? Or at least had it tested for water?
btw is the cummins the pre '97 one without the electronics? I've been driving a Ram in Mexico with that engine. Great machine, albeit not a cruiser...

 

[adrianr]

Id replace all the brake fluid and see how it holds up. Does sound like you have boiled the fluid which would suggest water contamination.

 

[frank rabbets]

Where did you get the vacuum for your servo from?

 

[StarCruiser]

Hi and Welcome Rookie [emoji4]. Sounds as the others have said likely to be fluid related. However, I have to question usage of the brakes downhill anyway. With a diesel like that under your bonnet you should have enough engine braking in the correct gear to be able to crawl downhill without hardly touching the brakes. I certainly wouldn't recommend taking it out of gear to brake downhill especially on the handbrake. Things could very quickly go pear shaped. This could be part of the reason your brakes have let go if you are only relying on them on a steep downhill. Also some of the earlier cruisers had smaller brake discs. More info on your truck would help greatly, plus photos of course when you get to15 posts when the forum allows posting photos. [emoji6]

 

[StarCruiser]

Where did you get the vacuum for your servo from?

Good point, hopefully there should be a vac pump on the engine.

 

[frank rabbets]

If the vacuum is not sufficient the pedal will go hard rather than soft but it is important to ensure you have adequate vacuum. If the brakes got very hot it's likely to be poor/contaminated brake fluid. Sometimes even the wrong fluid is put in. e.g. screen washer.

The only other possibility is a faulty master cylinder but I have never seen an intermittent working one.

 

[Lorin]

Are you sure they didn't just overheat? It isn't hard in an 80 and would result in total failure

 

[silvercruiser]

Or low(ish) brake fluid it happened to trevor in little blue when on a hill.

 

[adrianr]

Whatever the solution turns out to be I'd second that about staying off the brakes and using low ratio and engine braking.

 

[Dave2000]

The water in the brake scenario is very common, did the brake pedal fall to the floor? Or was it rock hard but no or poor retardation? Has the vehicle had any suspension changes i.e. lift?

Larger wheel will also add to the affect, as per Starcruiser, we need more info on the vehicle including mods.

regards

Dave

 

[Dave2000]

EDIT my last post, got it the pedal went to the floor, mods to the height of the vehicle, bigger wheels, early model smaller brakes, running downhill in neutral, all add to brake load and bound to show up any weakness, it seems your one of the few people who own an 80 with a handbrake capable of slowing the car, very lucky indeed.

regards

Dave

 

[clivehorridge]

Hi rookie, lucky you aren't reporting a write off by the sound of it!

All of the above coupled with a bit of glazing on the pads if they did overheat. I've had that and it's as if there's grease on the discs (sorry rotors!).

I'm guessing it's an auto judging by the flag, hence less engine brake than a manual.

Puzzles me why the pedal went to the floor. I've no experience with water in the fluid, but if it boiled, wouldn't that just encourage a complete lock-up from the uncontrolled pressure?

Neither water nor steam compress in an enclosed system, so why would the pedal have no resistance? (I'm trying to learn something here)

 

[StarCruiser]

I would have thought steam would be compressible Clive, being vapour and subject to hydraulic pressures.

 

[clivehorridge]

Ok, technically yes, but if the water is boiling then the massive increase in volume in a closed circuit would (likely) create far more pressure than the master produces even with a heavy size 10 behind it.

I'll stop now because I'm way over my knowledge, just mulling the logic....

Also, with foot off the pedal, I would have thought an injection of steam pressure at the calipers would have blown fluid out of the master cylinder cap vent...

 

[StarCruiser]

I'm with you on that.

Theory…Perhaps if the brakes were a bit stuck and boiled, the steam would expand in the system forcing fluid back into the reservoir. When the size 10 stomps on the pedal there's fluid and steam and the steam compresses under the newly increased system pressure.

 

[clivehorridge]

Mm mm, maybe rookie's a size 11...

 

[Shayne]

I would imagine if yo have a 50/50 mix of brake fluid and water the steam under pressure will go to the reservoir leaving you with half the brake fluid required to operate the brakes ?

 

[24carrot]

Hi hope you have sorted your brakes now. Can you post some more info on your engine change .and may be some pics.

Sent from my SM-T555 using Tapatalk

 

[Firewout]

I think the volume increase is not that impressive. When i look at a kettle at the moment the water starts to boil, i notice a lot of bubbles forming but it takes some time before the water starts to cook 'violently' and takes a lot more volume.
the same happens with the brake fluid : your foot is on the brake pedal, friction on the disc and pads causes heat. Because the fluid is under pressure, the boiling point is higher so the fluid stays liquid but gets very hot. When you release the brake pedal, pressure decreases, boiling point gets lower and now your kettle starts boiling : nice gas bubbles where you don't want them! Next time you hit the brake pedal, you floor it because gas is compressible.
just my 2 cents and yes pics please