GhiaMonster Reader
10/31/19 9:42 a.m.

A simple soft line replacement on an old Fiat has turned into an ongoing project. What a surprise.  Uncle’s 80's 124 needed a new soft line to the front caliper. Trying to get his car on the road for the summer I grabbed some wrenches and set to replacing it.  The hardline wasn’t long for the world and twisted at a rusty section, adding to the project.  With new hard and soft lines in place I went to vacuum bleed the system and didn’t have any luck.  As this was spread out over several months I suspected the master cylinder since it had been sitting open.  New master with the same result, won’t bleed at either the caliper or master cylinder itself.

Full remote reservoir with confirmation that fluid is flowing to the master.  Several bench bleed attempts tried on the master and it has been filled with fluid from both the reservoir and line sides. Confirmed the piston is actually moving inside.  The one thing on my mind that hasn’t been tried is a pressure bleed with an adaptor to the reservoir. A Miata slave cylinder gave a good fight along with a fully new system on an old Mustang but I’ve never been bested by a hydraulic system before.

What other methods do you have to deal with difficult systems?

Bob_S New Reader
10/31/19 9:51 a.m.

Could it be that the bleeder screw is plugged?  Its quite common for the passageway in the bleeder screw to get full of dirt and rust if they aren't covered.

Best of luck


914Driver MegaDork
10/31/19 9:51 a.m.

Oh my!   Following this diligently as I have a BMW R-90 with the exact same issue.  I bled it down, pushed fluid from the caliper up to the Master, nuttin'.

I'm assuming it doesn't have ABS, that just makes it tougher.


GhiaMonster Reader
10/31/19 9:56 a.m.

Will confirm bleeder screw next time. Also tried to bleed from the other caliper just in case I did something dumb with the new lines.  I did confirm airflow through all the new sections.  I'm stuck at the fact that I can't get any fluid to move through either master cylinder. 

NOT A TA SuperDork
10/31/19 10:16 a.m.

The pressure differential valve in the combination valve (often called proportioning valve) is probably over to one side. This would prevent bleeding. Is the brake warning light on?

Shadeux Reader
10/31/19 12:37 p.m.

In reply to GhiaMonster :

The pressure bleed is amazing. I would give that a try.

GhiaMonster Reader
10/31/19 3:57 p.m.

No proportioning valve in this guy, two lines on the front circuit, one on the back right out if the master cylinder.  Since they readily offer a pressure bleeding cap for this car I'll take that as a sign I'm not the first to get to this point.  

outasite HalfDork
10/31/19 5:09 p.m.

That is a simple system and should bleed easily. The front calipers should gravity bleed by opening the bleeders and allow them to drip and continue to top up master cylinder. Did you bleed the master cylinder lines after installing it? Did you replace the hard line all the way back to the master cylinder? I prefer using a helper pumping the brakes for bleeding instead of vacuum pumps. Too slow and chance of air returning to system.

TurnerX19 Dork
11/1/19 12:46 p.m.

Fiat 124s also have a pressure limiting valve to the rear brakes. This is connected to the rear axle with a delicate link that looks like a sway bar linkage. I have seen these fail in every conceivable manner, and I saw a car where it had been removed. 

GhiaMonster Reader
11/1/19 1:58 p.m.

One side has a new line right to the master cylinder which is a straight shot of tubing, no distribution block.  I would also think fluid should flow through the master with gravity but am not seeing that.  Pressure bleeder cap is in the mail, will try that next.  Did try every conceivable combo of pedal application and cracking lines open as well as combining with vacuum but didn't have any luck.

Good to know about the proportioning valve in the back, I had an old Audi with a similar setup.  Found it hose clamped in the full open position and had to figure out what it was.

PMRacing SuperDork
11/1/19 2:06 p.m.

When installing new lines I have had to do the one pump, open bleeder, close bleeder and release method.  Otherwise they would just not bleed. 

I have also had the issue where I needed to open the bleeder more than 3/4 a turn for anything to come out. Good luck!

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