How to replace the front to rear brake line on a 91 Ford Explorer

I have a 91 4-door Explorer with 4 wheel drive and rear anti-lock brakes (RABS). While bleeding air from the brakes to try to solve a spongy pedal, the brake line that goes from the proportioning valve to the RABS pump “popped” and brake fluid began to drain onto the concrete.

Why does this brake line fail prematurely? Ford wrapped a spring around it for some reason, probably to dampen vibration, but the spring is an incompatible metal which corrodes the brake line in accelerated fashion. The result is total loss of rear brakes, a soft pedal, and a brake fluid leak.

Here is what to do about that problem. We will replace the broken brake line with Poly-Armour lines which are corrosion resistant, easy to bend, and which simply screw together with no flaring tool necessary.

Tools required

  • Standard wrench and socket set
  • Flathead screwdriver
  • 7/16 and 3/8 line wrenches
  • Small tubing bender (~$4 at auto parts store)
  • Mini tube cutter (~$6 at auto parts store)
  • PB Blaster spray
  • Anti seize compound

Parts required

  • (2) AGS PA-351 Poly-Armour brake lines (or other types adding up to approximately 100 inches of length)
  • (2) 3/16″ flare unions
  • 1 AGS PAA-R340 1/4″ to 3/16″ Adapter

Removing the broken brake line

Put a 2×4 next to the front wheels to prevent the truck from rolling while jacked up. Jack up the truck as high as you are comfortable with and place it on jackstands. Remove the driver’s side rear wheel. Through the wheel well reach around and find the bracket where the RABS rubber hose mates to the flare nut from the brake line. Spray the nut with PB Blaster. Then get under the driver’s floor and follow the spring-wrapped brake line along the frame rail until it meets the outlet of the proportional valve. Spray that nut with PB Blaster. Optionally, you can let this soak for a while, come back later (maybe a day later) and repeat as wanted. Soaking it beforehand will make the nuts easier to deal with.

When you are ready to tackle the nuts, grab a 7/16 and 3/8 line wrench. To get the flare nut out of the proportioning valve in the front, I started by popping the front brake line (spring wrapped) and a wiring harness out of the clips that they are clipped into, then bent these out of the way to get a clear shot at the nut. Use the 7/16 wrench and, being very careful to have the wrench straight on the nut so you don’t round it off (try pressing on it with your other thumb while trying to turn it), try to break the nut loose. It will help to hold onto the part the nut is screwed into with your other hand. For me, this approach broke it loose. There is very little room to work here so get a smaller size line wrench.

On the rear, use the 3/8 line wrench. I had enough room here to get a pipe over the wrench and try to break the nut loose. You have to hold onto the bracket so it doesn’t bend. It didn’t help though, I could feel the wrench rounding off the rusty nut. (Iron oxide is not very strong!) Since the old brake line is to be discarded, I used a mini tubing cutter purchased at O’Reilly to cut off the tube very close to the nut. After the tube was cut, I placed a deep 3/8 socket over the remaining tube and nut, and was able to break this loose.

With both nuts broken loose, you can now remove the brake line. I went ahead and dropped the gas tank to do this since there wasn’t much gas in it. Five bolts with 1/2 inch heads and a screw with an 8mm head will allow the metal shield to drop down, and then one more strap bolt with a 1/2 inch head and down comes the tank. Push it out of the way but don’t disconnect it. Now, to remove the brake line, use a flathead screwdriver and finger pressure to pop the brake line out of each of the 5 or 6 white clips that keep it spaced away from the frame. If you’re having trouble getting the line out of a particular clip, just pop that clip out of the frame and deal with removing it later. Once everything is loose, just pull the whole brake line out the rear wheel well. Remove any clips that you couldn’t remove earlier and pop them back into the frame.

Measure the length of the old brake line with a flexible measuring tape. Buy appropriate lengths of Poly-Armour brake line to match the length of the old line. A 2 door model will probably have a shorter length than my 4 door model. My 4 door took 2 lengths of 51″ line.

Installing the new brake lines

First, take the short 1/4 to 3/16 adapter and connect it to one of the long brake lines with a 3/16 union. Tighten the union as tight as you can. Then, move the 1/4 nut to the end of the adapter segment, and using the tubing bender, bend the adapter segment so that it is the approximate shape of the old brake line in that position.

Take the other length of brake line and the tube bender and approximately copy the bends from the RABS valve forward in the old brake line. Particularly important is the bend along the wheel well and the bend which takes the brake line below a gas tank strap and then back up.

Now, take your two line pieces, one with an adapter segment attached and one without, and blow out the two line pieces with compressed air and put masking tape over the ends. This will keep dirt from entering the line as you fish it through the frame rail. Dirt is very bad for brake components since it persists in the system forever. Also, spray out the exposed front and rear brake line ports with brake cleaner to flush dirt away.

Take the piece with the adapter attached and feed it into the frame rail such that 1) It is behind the 4×4 electrical connector, 2) it is behind the fuel filter, and 3) the bent end is correctly positioned so that it can enter the proportional valve outlet. Pop the line back into the two or three clips. Now, carefully bend the line so that it enters the outlet 100% straight on. When you have done this, then go start the 1/4 inch nut into the outlet by hand. If you cannot get the threads to catch, STOP and make sure the line is 100% straight on as it enters the outlet. Once the threads are started by hand about 3 complete turns, go ahead and finish tightening with the line wrench. Then, pop the front brake line that you pushed out of the way back into its clip, and make sure the wire bundles and fuel lines are back in their rubber “clips” if you popped them out.

Then take the new rear part of the line and, having taped over the ends, insert it through the rear wheel well. Guide it along the bottom of the frame and secure it into the clips. It must be long enough to reach the end of the front part of the line in order to be able to be mated with the other union. First hand thread the 3/8 nut into the RABS inlet and then tighten it down just as in the front. Then connect the two pieces along the frame with a union, tightening it down as tight as you can. At this point your installation is complete.


Before reinstalling the gas tank, and with the motor obviously OFF, bleed the air out of the rear brakes and then bleed the rest of the system as necessary in order to obtain a hard pedal. Also, check for brake fluid leaks at both union joints and both brake system fittings. Once you are satisfied that the brake system is free of both air and leaks reinstall the gas tank (put anti-seize on the usually very rusty bolts — consider replacing the bolts with new), start the truck and check the pedal for normal operation under vacuum boost.

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