Currently in the process of converting a solid rear axle from drum to discs, and had a question about flex lines. The way I've done it in the past is to have a single flex line to the axle from the car body, hard lines going out to each wheel, and then a flex line at each wheel/ caliper. This gives a total of 3 flex lines.
What I was thinking was to split the hard line before the axle, run one hard line to each side of the car, and then a flex line to each caliper- same as on front discs, basically. Then I'd only need two flex lines for the setup.
Is there any reason this couldn't be done? Anyone already done this, and have pictures to share?
Either way works. Gm fwd cars did this. Eliminating one rubber line is not a bad thing
In reply to Patrick :
"Eliminating one rubber line is not a bad thing"
My feeling exactly. I forgot, a FWD car with a solid beam rear would be essentially the same.
Why does the line from the axle housing to the caliper need to be a flex line? I have always just seen one flex line from the chassis to a T-fitting on the axle, then hard lines from that fitting to the calipers. If the calipers need to slide a bit for parking brake actuation, then a few coils between the axle and the caliper can take up the flex from the minimal movement.
In reply to Ian F (Forum Supporter) :
In this case, they're sliding calipers, so they will move in/out slightly. Agreed, a coil of hard line might work, but I get nervous about fatigue limits on brake components!
Will one flex line at each wheel give you enough slack when the axle is at full droop? I wouldn't want the brake line to be the limiting strap in the suspension. Good time to use a fixed caliper and then you don't need a flex line from the axle tube to the caliper!
STM317
UberDork
1/20/22 3:57 p.m.
I'd keep flex lines to each caliper just because they make it possible to unbolt the calipers for pad/disc/axle/differential work without having to bleed the brakes everytime.
flex lines at sliding calipers to allow the caliper to take up pad wear.
flex lines at all calipers to allow pad and rotor changes without opening the banjo fittings.
flex line all the things.
In reply to iansane :
If I use a long enough flex line, yes. This isn't an off road vehicle, very much tarmac only. Calipers are already bought and brackets welded on. Gm metric calipers, best bang for the buck out there!
A long enough flex line to not get stretched at full droop has a lot of stuff to rub on and get pinched by out there near the wheel, tire, spring, shock and bump stop. I'd leave the single flex in the middle, and then short flex lines at each wheel.
The long flex lines also sounds like it would probably lead to a softer pedal. Even really good flex lines will have a tiny bit of give that hard lines don't.
buzzboy
SuperDork
1/20/22 7:25 p.m.
What you're describing is how the brand lines are on a front solid axle. My Jeep has a lot more axle travel than your project and works fine with that setup.
On the 9 inch in my Mazda I have flex hoses that have hardlines incorporated, from the calipers' original application, and they are just sort of ziptied to the housing. When I pull the axles I just unbolt the calipers and let everything droop. When I pull the whole rearend it is cut two zip ties and remove the one bolt holding the axle end of the main flex line. Calipers stay connected to the hydraulics and handbrake cables.
A single line to the housing makes brake line routing tons easier.
Also, VW flex line hardlines are a weird metric size slightly larger than standard 3/16ths, or even standard metric 4.5mm, had to drill out the tube nuts and flaring them was a pain because they did not quite fit the mandrel.
AngryCorvair (Forum Supporter) said:
flex lines at sliding calipers to allow the caliper to take up pad wear.
flex lines at all calipers to allow pad and rotor changes without opening the banjo fittings.
flex line all the things.
Interesting. The ATE calipers on the Alfa solid axle are hard lined to the T just to the passenger side of the diff.
They are dual piston, non sliding, calipers, though. And to change the pads, just need to push back the pistons.
buzzboy said:
What you're describing is how the brand lines are on a front solid axle. My Jeep has a lot more axle travel than your project and works fine with that setup.
The difference is, though, that front wheelwells have a lot more width to play with. Rear wheelwells are usually right up against the inside of the tire, so the only realistic routing option would be along the suspension link. And there is a lot of floor and driveshaft in the way, so a tee would require one side to go up and over unless you had the tee inside the cabin over the driveshaft hump.
I do like Jeep's innovative "run the offside above the front bumper" brake line routing 
In reply to alfadriver :
Do you remove the caliper to push back the pistons?
In reply to AngryCorvair (Forum Supporter) :
Why would one?
I just replaced the pads in my fixed caliper Volvo with a hammer and a small punch. Was able to use my fingers to compress the pistons.
Am very impressed with Brembo's differential piston sizing. All four pads were worn to 1mm thick even across, no taper to speak of from leading to trailing. Now if only the rotors were about 2-3mm smaller in diameter so that the pads ride slightly past the edge of the rotor, so no rust ridge develops.
In reply to AngryCorvair (Forum Supporter) :
No. Just use leverage via the old pads, and the pistons get pushed back in. I know of a tool that will push the two pistons apart- but I'm too cheap to get one.
In reply to alfadriver :
I have one. It does not actually fit in any fixed caliper I have tried it on. I wouldn't bother.
Our dirt mods run a flex line to each rear caliper and have well over a foot of articulation without a problem.
On Volvo Amazons the front calipers are 3 piston fixed Girling. I found the easy way to compress the pistons, once the pads were out, was to stick the handle of a crescent wrench into the caliper, and twist the crescent wrench with another wrench (channel lock, vice grip, whatever). Must be about the only thing a crescent wrench is good for, other than tightening trailer ball nuts!
Luckily, on the vehicle in question for the rear disc conversion, there's copious room in the wheel wells and floor/ unibody structure. I put the axle in place last night and visualized the routing. I think it'll work well. Will post pics here when I get it all mounted up. Thanks for the input!
In reply to volvoclearinghouse :
Three piston?
Far out! I assume they did that for wheel clearance on one side and upright clearance on the other.
