hydraulic low pressure switch question:

[Josh-stateside]

I'm in the process of building a coupe quattro with a 4.2L ABZ engine. I ditched hydraulic assisted brakes and it's now vacuum assist braking. I've got the low pressure switch from the old hydraulic system, and i've got a new hydraulic assisted power steering pump with the 10mm fitting for the brake system. Instead of using the v6 unit which is old and needs a rebuild I was going to consider adding the low pressure switch directly to the power steering pump. Auto check would work like this right? Would I have to ditch the pistons inside the pump or would it work normal with the brake pistons?

Does this make sense? Are there any catches that I'm not thinking about correctly?

Thanks
Josh

[S2central.net]

How you planning to put the pressure switch into the PAS pump ?

The switch is attached to the hydraulic brake servo on the S2/RS2 so yes it will be liked by Autocheck - I just dunno how you'd graft it onto PAS.

[Josh-stateside]

I was just going to use the brake supply 10mm threaded portion of the power steering pump?

It should screw right in and i should have clearance for it. I haven't checked it out yet, but i'm pretty positive they're both 10mm x 1.0mm.

I don't have enough of background in mechanics of things like this to figure out if the brake pump and the power steering pump are pressurized the same pressure? They should be right? I'm just wondering if a there was a pressure loss and it activated the lower pressure switch would it because of the main power steering pump or would it because of the piston pumps of the brake side of the power steering pump. Am I over thinking things? If I deleted the pistons inside of the pump would it allow the low pressure switch to only activate only if the main pump was faulty?

I don't have autocheck right now, it did but i'm going to worry about putting that in later after I get the v8 running and after I get some issuses here and there figured out. But when I do put it back in and I take the car to the track etc, it would be nice to have a warning if there is a pressure drop to the power steering system.

[Josh-stateside]

I can see why this might be confusing now..

To make more sense the S2/coupe quattro hydraulic pump fits directly on the ABZ engine power steering bracket. Basically the ABZ 4.2L engine uses the same power steering pump as the typical 2.6L and 2.8L audi v6 engines. Which people now use when running
20vT setups with vacuum boost brakes.

[mcandmar]

I would look into what the switch does, it may only be a simple switch that completes a circuit above a certain pressure. If that’s the case i would join the wires together to keep the auto check happy.

Not sure about the pump, that would be no different to blocking off the output with a large bolt? From what i can see the piston section pumps fluid into the bomb, and then into the master cyl with no return feed. A one way street if you like, so it may work. Personally i would remove the internals if possible, no point in pumping fluid and wasting energy if you don’t need to.

[Josh-stateside]

I would look into what the switch does, it may only be a simple switch that completes a circuit above a certain pressure. If that’s the case i would join the wires together to keep the auto check happy.

Not sure about the pump, that would be no different to blocking off the output with a large bolt? From what i can see the piston section pumps fluid into the bomb, and then into the master cyl with no return feed. A one way street if you like, so it may work. Personally i would remove the internals if possible, no point in pumping fluid and wasting energy if you don’t need to.

There is no autocheck what so ever right now in my coupe. I pulled out the harness and would have to make a custom unit in the engine bay for it to work. I would like it to work at some point possibly. I don't need to do anything to solve problems with auto-check. I'd just think it would be nice to have fault recognition on all my pumps switches etc. I've got gauges for oil pressure, oil temp, and water temp, why not have if not a gauge at least a switch that activates a warning for the power steering setup too even if it's not used for it's orginal purposes.


It returns, it tees into the power steering return hose. Basically i'm wondering about removing the internals.. I guess the next question to ask is if there would be a pressure loss to the system if the pistons were missing?

[WabTheKing]

dont see why u cant fit it to the master cylinder take off pipe from power assist circuit or is it brake pressure your wanting to monitor not hydrualic system pressure

[mcandmar]

To be honest, if you have low pressure on the steering side you wont need a light to tell you

I have never dismantled one of these pumps so i cant say for sure, i would expect the vane section of the pump to take care of the steering independent of the piston assembly. There is a great thread on the forum covering a rebuild here http://www.s2forum.com/forum/showthr...light=pas+pump. , it may be as simple as undoing the two plugs and pulling out the piston/spring assembly's.

Mark.

[Josh-stateside]

dont see why u cant fit it to the master cylinder take off pipe from power assist circuit or is it brake pressure your wanting to monitor not hydrualic system pressure

Nope, this one is just for power steering pressure. At some point I'm going to figure out the brake pressure setup but i'll do that at a later point. The sensor activates if pressure drops between 127-87bar (1841-1261psi). The power steering pump is considered bad if at idle it's below 110bar. From what I'm reading on the bentley manual it seems that the brake side of the power steering pump creates more pressure than the power steering side of the pump.

Seemingly for this idea to work I think I would have to remove the pistons, and also find a 10mm x 1.0 pressure sensor that activates if it goes below 110bar.

[Josh-stateside]

To be honest, if you have low pressure on the steering side you wont need a light to tell you

I have never dismantled one of these pumps so i cant say for sure, i would expect the vane section of the pump to take care of the steering independent of the piston assembly. There is a great thread on the forum covering a rebuild here http://www.s2forum.com/forum/showthr...light=pas+pump. , it may be as simple as undoing the two plugs and pulling out the piston/spring assembly's.

Mark.

Yah I kinda have felt the same way about the fact that if it went I really wouldn't need a light to tell me that power steering sh*t itself. But at the same I can imagine myself coming into a hard corner quickly at one of the few race tracks, going down the straight and then having it sh*t itself while i'm doing 120+ down the straight away.. and get into the hard corner and struggle with it?

[Josh-stateside]

maybe i'll stick a temperature sender there instead. nice to have possibly a few options, might be real over kill I guess right now. I'll probably put this thought aside for a while and figure it out later.

[Josh-stateside]

the difference between the two pumps in weight is substantial. Enough where I won't be using the 20v hydraulic pump. X this idea out.

[johne]

I realise you've changed your mind on this idea but just to complete this thread,

The 20V pump does have two stages and the second brake pressure stage is higher than the steering pressure so the brake pressure sensor wouldn't close if used on the steering circuit.

Your original idea was spot on. If you used the 20V pump you'd have to blank off the brake circuit output so you might as well use the brake pressure switch to blank it off and you could use it to monitor pump health since if the pump can't generate brake pressure levels, it won't be generating healthy steering pressure.

If you do want a pressure switch for monitoring the steering pressure, I know that 944 16v had one on the hydraulic pump but not the regular 944.

[Josh-stateside]

the whole reasons why I thought about it too is because I built or had built all the lines myself. For now I'm going to keep the power steering oil cooler off it when eventually I do drive it. I'm going to keep everything at a bare minimum. I converted the metric fittings to AN/JIC 37 degree steel fittings and the high pressure hose is teflon with braided surround with crimped on fittings.. I've got alot of things to keep an eye on once the car hits the road. I also swapped the fuel, brake, and oil lines completely over to AN/JIC. There isn't a bubble flare fitting on my car now. I've got banjos on the master cylinder to plumb around the throttle cable and the vacuum booster and the heater hoses etc. My whole brake system is completely different from stock. It even runs back into the car from the rear over to handbrake area for my tilton proportional valve setup. I'm pretty much going to be nervous for a bit once the car is on the road. I wish i could of done in it stages a little but once the car is running I have alot of things to check out. The steel and the stainless steel stuff that i'm using is so nice. Do it once and hopefully forget about it for a long long time. Especially here in new england. There is alot of moisture and rust around here. I'm making the brake lines out of cunifer and the fittings for the hard lines are stainless steel.

Alot of the stuff I'm doing i've never done before, and i'm self taught, and i use the internet to help me out but i have the right tools. I'm just still going to be a little bothered once the car hits the road for a while. Any precautionary things I do I feel helps. I might stick the 20v power steering pump in for while because it's a rebuilt unit and plumb in the pressure sensor. I'm not sure. If I do want to do it at a later point it should be easy to source a tee fitting with 3/8" Jic fittings with one 1/8" npt and then try to find a 110bar or so pressure sensor to fit in the 1/8"npt threads. The funny thing is to do it I have to add a few jic fittings, and it's just extra threads and 37 flares to possibly go wrong with it.