Leaking brake line

1989 Toyota Pickup Truck, rear-wheel drive.



Front disc brakes, rear drum brakes.

I use this vehicle on my property for hauling tools and dirt etc.

Last week, one of the brake lines sprung a leak, and I lost most of the fluid in the master cylinder. I still have some braking, but the pedal goes most of the way to the floor and is spongy.

There seem to be TWO brake lines, running side-by-side going to the rear of the vehicle. It is one of these lines that sprung the leak.
Both of these lines go into some sort of small device at the rear of the vehicle. One line comes out of this device and goes to a second device. There are two lines coming out of the second device; one goes to each rear wheel. What is the purpose of this arrangement?

Can I simply crimp the bad line upstream of the leak, to prevent loss of fluid and retain full function of the front disc brakes?


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Best Answer


I believe you are describing proportional check-valves for the braking
system, not good to bypass them. Just get replace metal tubes, a cheap
tube-bender, drop the original lines, bend the new to shape, compression
fitting and nut, good to go.


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I have heard of others crimpint radiator tubes and brake lines, but my experience has never been successful at it. Brake fluid is very thin and slippery. I suppose a guy could try to solder it closes at the crimp, but why. Fixing it is quicker.


that is a valve used to very the braking force in proportion to the


weight in the bed of the truck. dont bypass anything just replace the
lines autozone and checkers sell brake line with fittings in various
lengths and sizes just take the leaker off buy one thats close bend
install and go..



Why are there 2 brake lines going to the rear of the vehicle? Is this
for redundancy, or do they serve different purposes?


Why not trace them back and see if each goes to a separate reservoir on the master?





>

I tried, but I don't have a visual the whole way. I'd have to take a
bunch of rusted-on stuff off to see where they go.

What I need is a hydraulic schematic of this vehicle's brake system.

I had an old Haynes manual laying around and looked in that, but all it
says is that the front and rear brakes are serviced by separate
hydraulic circuits.

I googled around quite a bit looking for a website with a hydraulic
schematic but couldn't find a thing.

If anyone out there has a manual for this model and year truck and
would be willing to answer a few questions about the brake hydraulics
it would be much appreciated.



"Ether Jones" wrote

>
> on the master?>>
>
> I tried, but I don't have a visual the whole way. I'd have to take a
> bunch of rusted-on stuff off to see where they go.
>
> What I need is a hydraulic schematic of this vehicle's brake system.

I can't find a map of the lines, but the first "device" at the back is apparently
called a "load sensing proportioning and bypass valve".

Bottom of page:

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/16/24/1a/0900823d8016241a.jsp

Here's a big picture of what you probably see under there:

http://www.autozone.com/images/cds/gif/medium/0900823d8016241e.gif

The second "device" is likely just a standard T-union to run the rear brakes
after the proportioner decides how much pressure they need.



>

Yup, that looks like it. And there's a linkage (steel rod) going from
it to a smaller pivot arm mounted to the differential. So when the
truck bed gets loaded down, the linkage moves.

Now, since it's called a *bypass* valve, I gotta assume there's some
bypassing going on, yes? and if so, there's gotta be some place for
the "bypassed" fluid to go. I assume that's what the second brake line
is for...

I bought the parts I needed but when I crawled under the truck (on
ramps) I quickly became discouraged. This is no easy job. A large
section of the lines is inaccessible (tucked between the frame and the
gas tank - yikes), with immobilizing clamps nestled in there. The nuts
retaining the lines going into the "load sensing proportioning and
bypass valve" are completely rusted over. They are not going to
succumb easily.

There is one section (foreward of the gas tank and upstream of the
leak) where the lines are accessible. I'm very tempted to just crimp
them shut to stop the leak. Not sure what sort of tool to use though.


That is the line for both rear brakes then. The valve varies the


pressure with the truck's load. If you crimp off that line, you will
have no rear brakes.

Jeep pickups have the same thing.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

Ether Jones wrote:
>
> is apparently
> called a "load sensing proportioning and bypass valve". >>
>
> Yup, that looks like it. And there's a linkage (steel rod) going from
> it to a smaller pivot arm mounted to the differential. So when the
> truck bed gets loaded down, the linkage moves.
>
> Now, since it's called a *bypass* valve, I gotta assume there's some
> bypassing going on, yes? and if so, there's gotta be some place for
> the "bypassed" fluid to go. I assume that's what the second brake line
> is for...
>
> I bought the parts I needed but when I crawled under the truck (on
> ramps) I quickly became discouraged. This is no easy job. A large
> section of the lines is inaccessible (tucked between the frame and the
> gas tank - yikes), with immobilizing clamps nestled in there. The nuts
> retaining the lines going into the "load sensing proportioning and
> bypass valve" are completely rusted over. They are not going to
> succumb easily.
>
> There is one section (foreward of the gas tank and upstream of the
> leak) where the lines are accessible. I'm very tempted to just crimp
> them shut to stop the leak. Not sure what sort of tool to use though.

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