Since I abandoned the Hydroboost aspect of this project, I installed a 4th power steering pump. This one was a used but functioning unit I had in the shed. It started off like the others. Steering assist worked at all engine speeds but then started to fail at idle. Ultimately, I had to rev the engine to get it to make any boost at all which made low speed steering very difficult.
I was blaming the hydroboost unit for killing these power steering pumps but now I had the same exact thing happen to the 4th pump and THIS one was installed with no hydroboost in the car.
Today while I was replacing the pump yet again,
I found a kink in a hard line of the inline cooler. The return line from the steering box attached to the kinked line on the cooler. Flow was restricted on the return side as a result. I can only guess but flow was probably restricted by half. It may be hard to see but the kinked line is the top one and the kink is near the bend.
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After straightening the kink and changing the pump, the steering assist seems fine. It started me wondering if the other pumps are still okay.
It also got me wondering if this Hydroboost unit is actually okay and is not defective.
Since I know very little about hydraulic function, I'm curious if a flow restriction in the return side could cause the HB to fail to work. The pump never made any sounds like it was struggling. No grinding sounds, no belt squealing, no chatter and the fluid wasn't foamy.
I'll do an internet search on fluid flow and see what I find out. In the meantime, I sent an email to Dr Diff about this. I hope that he responds soon.
When I pulled the hydroboost unit off, I installed a 15/16" manual master cylinder. The system isn't fully bled out yet but I have driven the car. The pedal does firm up and the car does stop but it isn't confidence inspiring. Oddly, it rips to a stop at slow speeds but doesn't feel as good over 20 mph.
I'm willing to admit that my efforts of a manual brake setup are another failure and that I need some type of power assist. I have the option of using the old '75 Dart vacuum booster again but with 7" of idle vacuum, I'll also need to dust off the vacuum booster and wire it in.
The other option is to take another stab at this hydroboost unit from Dr Diff.
Either way, I have the stuff here to make either work.