Rear Junction Block Leak Leak After Axle Swap

[97Sandbox]

This weekend I completed the installation of the rear end from my old '97 XLT onto my '00 Sport. It all went pretty well, but I now have a slight leak at the junction block on the left side.

I was very careful to clean the threads in the junction black and on the hard line when I assembled everything, but nonetheless, I have a leak.

Anyone who has run into this issue before: do you recommend replacing the hard line, the soft line/junction block, or just go ahead and replace it both? Is there anything I could possibly improve by disassembling, cleaning more, and carefully reassembling? The reason I don't want to dive into replacing everything is because I don't want to damage the main hard line that runs through the left frame rail because I don't currently have a leak there and that line would not be fun to replace.

Thanks!

 

[CDW6212R]

Hi Grant, that OEM main brake lines looks pretty good, not badly corroded. I would say R&R the junction block and clean it well, but you already say that's done. I guess I'd still take it apart and look it over more. If the line connector end seems very easy to move and turn, I'd put it back on and crank it very tight. Use a very tight fitting flare wrench, and put torque on it nearing 40-50lbft. The brake hose and block you could replace, but the issue is likely an issue with the shapes, a burr etc, or not being tight enough.

Try not to hurt the brake line, that runs all the way up to the ABS module, and the fuel tank would have to be dropped to get it out and in.

 

[97Sandbox]

Thanks Don. The hard line on the axle is from the '00 and is in very good shape.

I will certainly give the threads on the line connector another wire brushing and double check the block. I cranked it pretty good, but I don't think anywhere near 40-50 ftlbs, so I'll crank it a little more when I put it back together.

 

[CDW6212R]

The force they can take is less for a rusted line or end fitting etc, that's why I remarked on the condition a lot. I have installed a lot of calipers over many cars, and at least 3-4 times it took a lot more torque to stop the brake line from leaking at the caliper, with new copper washers. The copper washers are very hard to crush(imprint with the banjo surface ridges).

My mention of 40lbft isn't a known force, just a big guess to say, very tight. I go by hand feel, experience, and old rusted line fittings cannot take the high force it might to stop a leak between two parts not originally put together. So go at it carefully when you tighten it the next time. Be sure the wrench is tight fitting and doesn't round off the fitting corners.

 

[imp]

This weekend I completed the installation of the rear end from my old '97 XLT onto my '00 Sport. It all went pretty well, but I now have a slight leak at the junction block on the left side.
View attachment 341608

I was very careful to clean the threads in the junction black and on the hard line when I assembled everything, but nonetheless, I have a leak.

Anyone who has run into this issue before: do you recommend replacing the hard line, the soft line/junction block, or just go ahead and replace it both? Is there anything I could possibly improve by disassembling, cleaning more, and carefully reassembling? The reason I don't want to dive into replacing everything is because I don't want to damage the main hard line that runs through the left frame rail because I don't currently have a leak there and that line would not be fun to replace.

Thanks!

That is known as a "reverse flare fitting", or inverted flare fitting. Look closely at the image:

Inside this fitting you can see an angled bevel which mates with the threaded fitting on the brake line. Assembled, they look like this:

If the bevel in the brass fitting you pictured is damaged, or cracked, no amount of tightening it will stop the leak. Disassemble it and check. If the bevel looks OK, try reassembling and tightening. Since it is a metal to metal connection, application of a sealant is not likely to work.

 

[CDW6212R]

Those inverted flare connections are really good, but for high pressure brakes use they have to be in perfect shape. The same fittings are used for the transmission lines, and those it's simple to install an o-ring in the base of each female fitting.

 

[97Sandbox]

I took everything back apart tonight and thoroughly and carefully cleaned it all. Then I cranked down the nut right to the point where the tab on the junction block started to deflect. Unfortunately, this did not resolve the leak.

Next up, I plan to order a new junction block/brake hose assembly because replacing that seems easier than bending a new hard line. Question: when replacing the hose to the rear caliper, will I need a new banjo bolt and crush washer? I'm assuming at least the washer, but wanted to check before I order the parts.

Thanks y'all!

 

[CDW6212R]

Oh well, it was worth another try. A new brake hose should come with two new copper crush washers.

 

[97Sandbox]

New junction block did the trick -- no more leaks! Very relieved not to have to bend hard line haha

 

[CDW6212R]

Excellent, and good work on the urethane parts too.