Brakes Locked up?

On a test drive yesterday, my brakes locked up. I posted here because the Master Cylinder (MC) isn't stock for the M715 it's from a J10 or J20 Pickup.

The MC is new (not rebuilt). The wheel cylinders are new (not rebuilt). The lines are mostly original including the rubber flex lines. The brake fluid was new in May 2019.

The truck has been sitting since July 2019 (I had engine issues).

The brakes locked after driving 10 miles, and when I stopped and applied parking brake the brakes locked up. I had to bleed them a bit to release the pressure.

Some suggested that the free play between the MC plunger and the brake pedal lever needs adjustment (blocks the return fluid inlet when the fluid gets hot and expands). Others have suggested that the return line inlet in the MC might have crud from the old brake lines. One person said that the wheel cylinders could have condensation in them and the return spring couldn't push the cylinder back to its original position.

I didn't check if the brakes were locked on just one wheel or on all wheels (It felt like all wheels were locked though). I didn't have a jack or jack stands with me so I could check, and I was stopped on the road! Not a good place for maintenance*.

Anybody have other ideas or can shed a little light on this for me?

I have been asked to drive in the Veteran's Day Parade, but I can't (won't) do it until I fix these brakes. Stopping is Boucoup important!

Time for a complete brake system overhaul. I would replace the rubber lines with new lines (not NOS, which are 50 years old). Then use DOT5, it will last longer and perform better than DOT3.

The rubber lines deteriorate with age and can swell or have chunks come loose inside the lines plugging them.

Anyone have a good idea for the exact items to replace the stock rubber hoses to the front and rear brakes? Photos could be helpful. Better yet, how about a URL?

I conducted a search for jeep brake lines and I couldn't tell if any of those would work. They don't give measurements or thread counts, etc.

If I don't hear back, I guess the only thing I can do is go to auto parts stores with the rubber brake lines and ask if they have something comparable, or I can buy NOS.

Try ORD in colorado (offroad design). The make custom brake lines and probably know what fittings work with stock m715. If you have the lines already removed even better, since you can measure them.

https://www.offroaddesign.com/index.htm

or BJ's offroad.

http://www.bjsoffroad.com/

Great, Thanks!

I found this site too, and there is a kit for the M715, but to find it, you will need to use the search feature:

https://classictube.com/products/

I bought the rubber hoses and other brake hardware from Memphis Equipment.
http://www.memphisequipment.com/M715...rake-Hose.html

I bought from Memphis Equipment too. Worked great.

Weird that when you applied the parking brake that the wheel brakes locked up...the stock parking brake is on the rear of the tcase and doesnt share anything with the fluid/wheel mounted brake system...

Maybe i am missing something...

I think the hydraulic brakes just locked up because there is either a clog in the Master Cylinder return fluid inlet hole, or the master cylinder rod and the pedal interface needs adjustment. The fluid just got hot and expended I think.

I am going to drain the fluid Friday and replace one section of steel line (kinked a bit) and all three sections of rubber line. Then I will put in new DOT 4 and try to duplicate the lock up. Dot 5 has a different chemical composition and will leak in places that DOT3 and DOT4 will not. DOT4 (I am told) is for rubber brake lines.

If I can't duplicate the lockup, then I will go to the parade. If the brakes lock up again, I will need to replace the entire brake system and I will miss the parade this year.

I am prepared for either outcome.

Good luck, I hope you get to drive in the parade this year.
As for the Dot 5 fluid. If you should decide to replace the entire brake system (highly recommended) then you can use it.

https://i.imgur.com/qiE2Ejoh.jpg

Dan,
Does this kit look correct to you? $212 includes shipping cost.

https://imagizer.imageshack.com/img922/9848/NCv7nd.jpg

Quote:

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Dot 5 has a different chemical composition and will leak in places that DOT3 and DOT4 will not

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Yes and No.

Dot 5 is a silicone based fluid is doesn't absorb water the way DOT3 and DOT4 (glycol based) do. That is why the military uses it. It keeps the brake system from corroding.

I have been using in my vehicles for more than 10 years. I have fewer brake problems with DOT5 than I have with DOT3. I don't know where the leak info comes from but I have not seen any of higher incidence of leaks. Actually, less since I have fewer brake system problems with DOT5. My ranch M715 with DOT5 hasn't had to have brakes replaced in over 10 years and they still work fine.

I use DOT5 in all my vehicles without ABS brakes. It keeps the system working better.

Kwai,
You have me convinced to replace the entire brake system. Well, that and the fact that my system is completely corroded. I couldn't get the fittings out of the rubber lines and the steel brake lines lines twisted and snapped when I had to force the fittings loose. Lots of rust. The truck was in Michigan.

I couldn't find DOT 4, but I found a DOT 3/4 combo with a higher boiling point (470 degrees). When I replace the system, I'll try DOT 5 as you suggest. The NAPA parts guy at my local shop recommended DOT 3 because that's what these old cars used back then, but I had to tell him the M715 used silicone fluid because these trucks were originally made to be waterproof up to 60".

I am using the DOT3/4 for now just to get in the parade, but after installing that brake line kit, I will use the DOT 5 I guess.

Kwai, do you think that brake line kit looks accurate? I'd like t order it before I take out the brake lines of my truck, so I have it and I don't have a lot of downtime again. I am not retired yet, so I don't have much time except in Summer, and I want to rebuild (remanufacture) a second engine this year.

Quote:

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Originally Posted by plumas.placer.miner

Dan,
Does this kit look correct to you? $212 includes shipping cost.

https://imagizer.imageshack.com/img922/9848/NCv7nd.jpg

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No, I don't think so.
That looks to be for an early full size jeep truck, but not the M715.
Let me look through my junk, as I kept my old lines for reference. Maybe I can take a few photos.
I don't think that I ever wadded them up and tossed them out.

Wow, that would be great Dan! They advertise that kit as being for the M715.
That's not the first time I bought parts that weren't right but were advertised as being for the M715. Thanks for the head's up!

I was able to get the new rubber lines installed, but I had to buy new brake line segments and use compression fittings.

The rear wheel cylinders were a bear. For some reason the bleed screws were rusted in solidly so they stripped, and the driver's side rear wheel cylinder bolts were rusted in and stripped. I had to take the brakes out of both rear wheels to do the job. My last two days were in brake H**l ! haha... I was working on brakes at night.

Then I flushed the system with alcohol. I blew the lines out with compressed air and opened up all the lines for the alcohol to evaporate overnight. I wanted to get any crud in the old lines out and I wanted the DOT 3 out.

This morn I will put in the DOT 3/4 fluid, push all the air out of the lines, and take her for a test drive.

Fingers crossed. Photos forthcoming.

Photos to come as soon as I get new batteries for my camera:confused:

That said, the lines shown in that illustration have to be for a civilian J truck. Not a M715

One dead giveaway is that the line going to the rear has the hose fitting on the passenger side, and it doesn't have the proper rise up over the transfer case cross member. Original rearward line is also two pieces joined by a coupler.

The others do not look correct either.

Honestly, you should pull the old lines out and make your own.
Not that difficult with a few tools that you buy at the auto parts store.

And make sure that you use flare fittings, not compression. Also, no copper lines, it must be steel.

The first picture is a compression fitting. Suitable for plumbing but not for brake lines.

The second one is for steel (or stainless steel) brake line. It must be a double flare, not single flare (which is used in copper gas lines and copper water tubing etc.) It is OK for the union to be brass. All of this stuff can be gotten from O'Reilly Auto Parts, NAPA etc. If you cut and flare your own tubing, there is a special double flare tool that does that. Not hard to do. I did all of the brake lines and fuel lines on my truck here at home.

Third item is the double flare tool. I would bet that you can get one rather inexpensively at Harbor Freight or Northern Tools.

I will be in the parade boys. Ooooh Raaah!

Photos tomorrow.

Yep, I double flared the tubing ends. Bending tubing, even with a bender is challenging.

Thanks for the info about the brakes. I am sooo grateful!

Free meals at Famous Dave's BBQ for lunch. All the military vehicles will be there. Parking lot is going to look so cool tomorrow!

All right!
Please get a few photos for us to see.

We had a member send the stock brake lines to classic tube years back and they duplicated them...several have bought them and they are correct...they do come in a box that changes them around a bit and it can be challenging to figure which is which and get them back to the shape needed to mount them correctly...we must have old threads on it but don’t know if the pics links are good yet...will try to find and post a link...

http://m715zone.com/vb/showthread.php?t=3209

Thanks Brute!

A great day had by all! All the Vets loved the new canvas smell! haha

https://imagizer.imageshack.com/img923/2326/uKq2Kc.jpg


https://imagizer.imageshack.com/img922/8952/JUCw0V.jpg


https://imagizer.imageshack.com/img923/4633/c3rDU2.jpg

Very, very nice!:)
So glad that you were able to go.

I forgot to tell you what I did to stop the brakes from locking up...

I replaced the master cylinder with a new (rebuilt) one. It was a little smaller than the first one I had. I also made a 1/16" plate for between the master cylinder and the firewall. This gave me some free play in the pedal.

The brake pedal goes down too much (to within 2" of the floor). New Master cylinder has a shorter push rod, coupled with the 1/16" spacer plate, so now I have to fix that. Maybe the wheels need brake adjustment? I'll try that first.

The brakes work though (don't lock up), so that's good.

Yes, adjust the brakes.

I ordered my new brake line kit from classic tube. $179 plus $30 for shipping. No tax. :) I will post photos when I receive them.

I will also need to buy the correct fittings. I used the ones for gas lines (brass compression fittings). I am grateful for the info Brute...(and everyone).

Brakes are muy importante! Don't skimp on the safety features! Must keep my family and friends safe. And...there are 1000 ft cliffs next to the road on the 26 mile, single-wide dirt road leading up to my claims. Some dirt bikers, ATV and UTV enthusiasts drive super fast around those blind curves. I know why they do it...I just wish they wouldn't.

You are most welcome...thats why we are here!!