Volvo A35 brake issue

[chickenminer]

Thanks for the info guys! Yes, looking for a rebuild kit or the component parts.
My Volvo dealer parts guy has been searching but can't find anything OEM or aftermarket.

 

[sfrs4]

Thanks for the info guys! Yes, looking for a rebuild kit or the component parts.
My Volvo dealer parts guy has been searching but can't find anything OEM or aftermarket.

Same this side of the pond, so it looks like there is nothing available except the new unit :-(

 

[chickenminer]

Just an update on this brake issue of mine. I got some parts last winter and this Spring I rebuilt the non-return valve. I could not find any parts to rebuild the unloading/relief valve or find a used valve. So I took the old one off and tore it apart. Nothing looked obviously bad in the valve, springs seemed fine and all components move freely. I did replace o-rings when I put it back together.
Got it all back together and I still have the same issue of no brake pressure! Gauge still shows PSI will not go above 800 and as soon as I shut the machine down the pressure drops to zero rapidly.
So I must have oil bypassing somewhere in the system.
Sure wish I could find a used unloading/relief valve so I could be sure to rule that out.

 

[sfrs4]

Ok so I've gone back through this and realised that the parts drawing FWF supplied is for the wrong serial number range, the part number you want is 11061801. There doesn't seem to be a supersession between the two parts so I can only assume they are different, and there is no parts breakdown of the actual valve for that part number, but it also appears in an A35C so it opens up the chances of getting one used a little more.
also something else to look at, there are a couple of none return valves in the valve block before it, could they be allowing pressure to seep back past them?

 

[chickenminer]

Thanks! I did replace the two non-return valves in the non-return valve block. Those were the only new parts I could get.
The breakdown of the relief valve that FWF sent is correct. I used that for reference when I took mine apart.
I fail to see, unless something in the relief valve is bad, why it will not build pressure beyond 800 PSI.
I installed new filter in the pressure side but I could find no filter on the suction side and no mention of a screen in the oil tank.

 

[funwithfuel]

Can you plumb a choke valve or steel ball valve in the hose that feeds the unloading valve with a gauge Teed in? I think you have to go back to the beginning. Establish that the pump is capable. I know it's new, but new doesn't always mean good.

 

[funwithfuel]

I've been studying this back and forth. The non-returns are a non-issue while she's running.
Did you change the oil when you replaced the pump? You said you did the filter but no mention of the oil.

 

[chickenminer]

I pulled the pump off and had the Volvo guys check it. They said it was fine so I have to take their word and rule out the pump as the issue.
No, I did not change oil but I am going to dump it and make sure it's cleaned out.
I did finally find a used unloading/relief valve that is suppose to be in good shape. We'll see if that solves the problem when it gets here.

 

[funwithfuel]

Good luck, I know you've been fighting this for a while. A needle valve in-line to the unloading valve gauged will tell you without a doubt that the pump is up to task. Just don't deadhead it

 

[chickenminer]

Well I finally got my truck fixed! It was indeed a bad unloading/relief valve.

Swapped for the used one I managed to find and my truck brake pressure is back up to normal.
Thanks guys for all the help/suggestions!
Now I'm back to hauling paydirt