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2seater

Does anyone remember the German Reatta guy?

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3 hours ago, Ronnie said:

As a machinist I'm in awe of the machine work that went into those pumps.  It would have been possible to make a much simpler pump but I guess the reason they are made the way they are is to have a high pressure pump that can be powered by a small 12 volt motor in a very compact size.  Everything inside that pump seems to have really tight tolerances.  I'm wondering if priming the pump from a completely dry condition might require forcing fluid in through the inlet from the reservoir with something like a MitiVac set up to pressurize the fluid going in.  Or maybe you have to turn the pump slowly while forcing the fluid into the pump?

I agree it is a work of art and a close tolerance system plus very limited volume by the look of it, although it does bleed the rear brakes pretty effectively, so looks may be deceiving? Just from the look of the parts I see, the pump needs to rotate just to carry the air from inlet to discharge and then up through a check valve to the pressurized portion of the casting. The motor is part of the inlet chamber so it must be in place, which means the motor needs to be running to rotate, at least in short bursts? Applying suction to the discharge side, maybe the accumulator spigot or a fitting into the brake tubing outlet, would approximate low pressure to the inlet? That will be the next thing to try on the bench. I don't think vacuum alone will pull fluid through but will try it before turning on the pump. 

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Another series of photos and a muse about this design. I imagine, given the intricate design and fine machining, that the various design elements must have a purpose but it eludes me at the moment. There must be a purging system of some sort built in but it almost seems backwards with that in mind. Hmmm? 

 

From the investigation and the photos, the fluid enters from the top of the main chamber and only has an apparent path into the rotor chamber near the bottom per the cutout in the steel cover plate. The rotor is a close fit to the recess where the inlet hole to the suction side of the control shaft is located and again the apparent path for the fluid is through another scalloped out portion near the top of the deepest area where the control shaft inlet is located. There are no wear marks on any surface near the rotor so it must be guided by the ball bearings on the end of the pistons, and there is a corresponding groove in the outer race which is removed in these photos. So the fluid flows in from the top, which would seem logical then out through the bottom, also logical but then up again to the suction chamber opening and out again near the bottom where it is drawn horizontally for an inch or so in a tiny passage to the pumping pistons and the only way out I see is through the discharge side of the control shaft which is another one inch long horizontal tunnel to the drilled passage in the casting and then up at an angle of over two inches to the check valve which does seem to have a light spring load to the open position. It's a conundrum.IMG_1332.thumb.JPG.a16262c87ef804772d90e429607072dc.JPGIMG_1333.thumb.JPG.85c88490b8143df1f03b34d9e40f0cc1.JPGIMG_1334.thumb.JPG.28851f9259f867263547c2842d981c56.JPG774469054_TranslatedTevesII.jpg.094c223ea8309e431f3d2567eed2800a.jpg

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It's a really complicated design. When I look at the last photo, the diagram of the fluid flow, it would appear that taking the check valve out would make it easier for air to escape in order to prime the pump but I'm sure Henning would have tried that.  Maybe a search on a Volkswagen or some other car forum that used the Teves would turn up a procedure for getting the air out of the pump.

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Success finally. 

 

I connected my graduated cylinder used for the fluid reservoir and everything on the discharge side was either open or removed; the plug over the check valve, the steel output tube, the accumulator and even the pressure switch. After an initial 5cc's of fluid drained from the reservoir, the flow stopped. It looked like the initial fluid drop was attributable to filling the hose from the pump to the reservoir which is twelve inches about the pump inlet. I left it like that for three hours and no fluid movement observed. I then cycled the pump on for one minute and off two minutes and repeated the cycle three times with no fluid movement evident. I installed my gauge, a dead accumulator, the pressure switch and the plug over the check valve. I then applied about 20"Hg vacuum to the outlet of my gauge setup, the same as applying vacuum to the outlet port for the steel line. I activated the brake pump and in less than ten seconds, fluid began to drop in the reservoir, and it took another ten or fifteen seconds before fluid appeared in my catch can attached to the vacuum pump, where a lot of air was evident.  I removed the purge vacuum and ran my normal test setup, which verified the pump is fully capable of 3000psi plus, it draws fluid reliably every time. The pump was totally empty when the above testing was started save for a film of brake fluid applied to the moving parts and seals upon assembly. I made no attempt to purge the pump manually as I had in the past by tilting it up and down which didn't seem to help when I tried that originally. 

 

In the past, I have used my homemade pressure bleeder to purge the front brakes, and I had no leaks or other issues up to about fifteen psi applied to the reservoir through a replacement cap drilled and tapped for an air fitting. In the case above I applied vacuum to the outlet because it was most convenient, but I believe it would be possible to use positive pressure to the inlet as Ronnie suggested. 

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Great! We learn something new about these Reattas all the time even though we have been tinkering with them for years. Now if we can just remember what you had to do to get the pump to prime.  🙂  I have featured this thread (green star in front of title) to help us find it.

 

I think pulling fluid through the brake pump with a vacuum pump is the way to go to prime a dry pump. Where should a fitting with a nipple to connect a vacuum pump be installed to pull fluid through the pump if you don't have the test setup.  Maybe where the accumulator screws in? Any ideas?

 

I wonder of priming a pump this way that has stuck pistons from not being used would free it up and get it going again?

 

BTW, if you wanted to write a tutorial on how you think the best way is to prime a dry pump I would be happy to add it to the How-to guides here on ROJ but I don't know how much it would be used..

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I have thought about how best to do it on the car. Of course it's easy to see when fluid is moving on the bench so avoiding a big mess and maybe damaged paint is easy. I would think at the very least, a reliable helper on the key to start or interrupt power would be a must. Alternately, a handheld pushbutton like used for bumping a starter over could be made up to supply power to the motor directly so the operator would have total control. I did look at the applying vacuum to the spike that inserts into the accumulator but there is a drilled opening at the bottom of the threads for the accumulator which seems to lead back to the chamber above the check valve so I do not know if it supplies pressure or is a drain hole when removing the accumulator? In any case, the simplest from my view is to disconnect the steel pressure line and apply vacuum at that opening. A rubber cone shaped adapter can be pressed against the hole, much like a basic compression tester. I would recommend a short line to a liquid catch can then extend to the MityVac, pretty much what is supplied in a hand vacuum pump kit. That might require a helper too, even with a pushbutton under the hood or  simply buy a short 3/16" bubble flare brake line at the FLAPS and screw one end into the brake pump opening and slip the vacuum pump hose over the other end where the flare makes a nice secure connection.

 

I agree that generally there is not a great need for all these gymnastics and the pumps themselves are darned reliable. The three pumps I have, which have unknown history, show no discernable internal wear. I suspect the motor is the weak link and contains the most wearable parts. The good news is, they can be taken apart to clean them internally if they are very derelict, but there are some passages that may need cleaning through indirect means. If the brake fluid is given reasonable care, system flushed every few years and moisture kept out of the system, they should lead a long happy life. A good accumulator will keep the motor happy too.

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I appreciate you posting all this. The photos helped me with better understanding how the pump works. Now I know how to prime the pump if I ever need to. I have a spare Teves unit if that I got from Dave. He plugged all the lines to keep the fluid in. Hopefully if I need to use it it won't be dry and need priming. It's good to know what to do if it does. I doubt I would have figured it out on my own without seeing this write up on how the pump works.  Thanks for taking the time to explain how the pump works.

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