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Last summer I replaced the pressure switch in the hydraulic pump in my C4. Initial discussion here.
Everything seems to be working perfectly now, but it was touch and go for a bit...
Getting the switch out was a total PITA. Could not be done in the car; I had to pull out the pump and clamp it in my bench vise. To be fair, the oversize socket I bought was a 12-point ('cause that's what I could find). If you try this at home, source a 6 point. For my car it took a vise and BA pipe wrench. Golly, wonder why?
The switch body is alu, and over the long term it didn't get along well with the cast pump body. The pump body didn't come thru unscathed either:
Of note is the corrosion at the mouth of the switch bore and the pitting at the bottom. On the upside, the very high quality elastomeric cushions visible in the picture above remain remarkably supple for 26 years old!
At this point I was already out nearly $300 for the switch (Sunset, always) and committed to trying to make it work. A new pump is... a lot of money. Enter weapons of choice:
The brush is stainless and 1" OD. Tap is pretty self-explanatory...
This isn't for the faint of heart; more than once I asked myself if I was being pennywise but pound foolish. Look at the debris at the bottom of the bore and think about the mess it could make of all the hyper expensive stuff downstream (ABS pump, bomb, PDAS valve block, wheel cylinders, diff lock actuators... wtf was I thinking?!) I used several cans of brake-kleen to get everything sauber before reassembly....
The switch bore cleaned up pretty nicely- brush, tap, brush again. Here's a shot after I applied molycoat to the mouth and upper threads:
And the product I used:
My hope is that the molycoat (and the anti-sieze applied to the switch) will let me spin the switch right out in the event it fails again.
Since the bottom of the bore where the switch o-ring sits was visibly pitted I applied Hylomar to the o-ring. Lots of pressure here, and while measurements seemed to indicate that the pitting was above the o-ring better safe than sorry.
If you're buying a switch, don't order the separate o-ring; one comes with...
I guess the jury is still out, but it's been nearly 1000 miles and I have no leaks and the pump cycles as it ought. I'm *almost* ready to put the cover back on the pump and the carpet in the trunk
Overnight about 30s or so; if you need hard data I can time it. The failure mode was that the pump never turned off; it does now, which is definitely an improvement. I don't think the actual pump-up time changed much.
If you think it's taking too long, get the FSM and go thru a proper bleed process. The system is pretty complicated mechanically and there are multiple bleed points which need to be addressed in sequence to ensure the bubbles are all out. I'll do it again in the spring to be sure and to avoid another nasty rusty mess.
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DIY Hydraulic Pump Switch Replacement
