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Volvo A35 brake issue

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chickenminer

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Jun 19, 2016
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I have a '93 A35 with a brake issue that is driving me nuts! Have had brake issues every since I got this truck, low brake pressure light would go on/off. Finally a couple weeks ago I lost brakes altogether. No pressure at all. Pulled the brake pump and it looked wore out inside. So I got a new OEM brake pump that cost me 2K. Put the new pump on and all was good. Pressure light went out and had good brakes. Used the truck for two days and started having the brake light come on again !
Put a pressure gauge on the test port on the unloading valve and I can only get a max of 1000 psi. Ran through the whole brake bleeding procedure again and still no higher than 1000 psi.
So then I tried to adjust the pressure according to the book and no matter how much I turn the set screw on the adjustment the pressure never raises or lowers!
Could it be a bad unloading valve? How could I test this? I can't believe it's the pump as it is brand new. I also changed the filter when I installed the new pump.
What am I missing ?
 
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chickenminer

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No, I don't have any way to test each accumulator. Would a bad accumulator(s) keep it from getting up to pressure?
I would think it could still build pressure, just not maintain it when using the brakes.
 
sfrs4

sfrs4

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chickenminer said:
No, I don't have any way to test each accumulator. Would a bad accumulator(s) keep it from getting up to pressure?
I would think it could still build pressure, just not maintain it when using the brakes.
Click to expand...
The accumulators are what hold the pressure, see attached the last couple of lines describes the exact point you are at. you have tested pressure and can't get any higher, you have bled the system of air, and tried to increase the pressure through the adjustment, hopefully there is only 1 or 2 bad as they aren't cheap at £170 a piece to replace and there is possibly 14 on the machine
 

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funwithfuel

funwithfuel

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I am curious if the foot valve is perhaps allowing oil to bypass to tank. Either that or possibly a damaged spool/seat in the pressure reducing valve.
 
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chickenminer

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Thanks guys! It just seems that if it is a bad accumulator(s) I should still see it get to the precharge pressure of the accumulators and it gets no where near that pressure. Odd that when adjusting the pressure on the unloading valve I see no movement in pressure at all.
I'm leaning toward one of the valves in the pressure relief valve or unloading valve is bad or stuck.
 
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chickenminer

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Looks like I'll be pulling those and tearing them apart.
On the foot valve possibly leaking ..... do you think I could hear it in the valve if it was leaking ?
 
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chickenminer

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Dang ... I am having a devil of a time getting any parts to rebuild the unloading valve! My Volvo parts guy says everything is obsolete but the O-rings.
Anyone know a place that has parted out older Volvo trucks, especially an A35 !?
 
funwithfuel

funwithfuel

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chickenminer said:
Dang ... I am having a devil of a time getting any parts to rebuild the unloading valve! My Volvo parts guy says everything is obsolete but the O-rings.
Anyone know a place that has parted out older Volvo trucks, especially an A35 !?
Click to expand...
You could also contact your dealer and ask them to reach out to Lipperts. They buy up NOS dealer inventory. They might have what you're after
 
sfrs4

sfrs4

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There were 3 repair kits for the unloader valve, but all seem to be no longer available through any source I have, the only option left that I can see looks to be a complete unit, but they aren't cheap.
as FWF says there might be some NOS somewhere so try these, 11702321, 11702322 & 11702323
 
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