Problem getting pressure from brake pump.

[2seater]

This started out to be a simple brake pressure switch replacement. I never had brake warning lights but could hear the pump run for a few seconds after a single brake application on many occasions. My conjecture was the pressure switch had the turn on and turn off points too close together. Luckily, Dave convinced me to take the entire pump, motor, switch and accumulator assembly from a fresh addition to the boneyard. The switch looks new. When I went to remove the pressure switch from the pump on my car, it wouldn't budge. I finally resorted to an impact wrench just to break it loose, which it did. I then used a ratchet to try to finish the removal. After less than one turn, it started to seize. I tried rocking it in and out but no soap. I finally had to resort to the impact to force the removal, and it almost rounded the outside as well. Of course the soft aluminum threads are almost gone and much is inside the iron threads of the pump. I thought the best route was to replace the pump with the takeoff that donated the switch, so far so good.

I cannot get the new pump to prime? I did swap my pump motor to the replacement pump because the paint was clean and black. The pump turns freely and seems to pull vacuum on the inlet elbow when I ran it on the bench. I checked the inlet hose for unrestricted flow by draining the reservoir completely and replaced the 1qt of fluid with new fluid and the hose clamped off. I checked the hose flowed again after the new fluid addition by loosening the clamp a little to be sure the hose was full. The pump starts and runs very quietly but there is no change in reservoir fluid level. The pump did start to "gurgle" a little after a couple of minutes (cavitation?) but no apparent load on the motor or drop in fluid level. The FSM doesn't mention any sort of bleed procedure but I did loosen the accumulator and the steel pressure line but it didn't help. Does this sound familiar to anyone?

[Guest Mc_Reatta]

Ronnie's site to the rescue:

How To Purge Air From The Brake Pump - Reatta Owners Journal

[2seater]

Thanks Mc. I have tried loose steel line and accumulator but maybe I need to be more patient? Now I have good headlights and no brakes, sheesh.

Edit: No success with just leaving the line and accumulator loose for five minutes. I finally resorted to applying 15 psi to the reservoir through the modified cap I have for bleeding the brakes. That took about 30 seconds and fluid was finally moving. Now everything looks good, although there is only a slight improvement in the time to pump start with brake application. Only time with tell if it is completely cured.

Edited September 1, 2013 by 2seater (see edit history)

[Barney Eaton]

From your post, it appears you have two available accumulators and they both could be bad. The accumulator fails usually with one of two symptoms.

(1) with age the factory nitrogen charge (about 750psi) leaks down. As this charge deminishes, more brake fluid is forced into the accumulator and the reduced compressed reserve gives you fewer pedal pushes before the motor kick on. This can be observed by the amount the fluid drops in the reservoir between a charged and uncharged accumulator. When the fluid drop gets close to 1/2 inch, order a new accumulator.

(2) the second failure is a total loss of preload pressure usually caused by a failed diaphragm in the accumulator. The pump will only run a short time (there is nothing to compress) and the fluid level in the reservoir does not move. You will usually have a very hard pedal.

Edited September 1, 2013 by Barney Eaton (see edit history)

[2seater]

I was thinking the same as you describe a few months ago. Fluid drop was in the 3/4" area, so I did install a new accumulator, labeled made in Germany. The fluid drop was reduced to approx. 1/2" with only limited change in the number of pedal applications before pump engagement. My follow on reasoning was the pressure switch on and off pressures were defective, either it turned off to soon or started too early, so the spread was smaller than it should be. The switch that I removed was a light green color as was the one I just installed, so I believe they were both replacements. I know there is a special tool to install below the accumulator to allow checking the pressures but no other easy way to do so. I am going to drive it a while to see how it settles out. To be clear, I have never had warning lights nor poor operation of the brakes, it just doesn't seem to fall in the range mentioned in the brake tests, which I believe may contain some errors.

[wws944]

.... The switch that I removed was a light green color as was the one I just installed, so I believe they were both replacements...

My car has the factory original, and it is greenish colored.

At the 2012 Reatta Rally, someone mentioned to me that there was a design change in the switch, due to the leaking problems. Apparently the color of the metal was changed to the greenish version at the time, so that one could visually see if it was an older version or newer version. However I don't know if this is true or not. Perhaps Barney knows?

[Barney Eaton]

I don't recall anything about a known pressure switch change in design/calibration. One ongoing concern is the possibility that NEW accumulators may have been somewhere in a warehouse for several years. At one time there was a post attempting to decode the Teves date code. I don't believe anyone ever accomplished that. That pressure testing tool/gage that is shown in the service manual has metric ends and is not that simple to make unless you have a good machine shop at your fingertips. I was thinking an alternative would be to use standard flexible brake hoses to make a tester. It would not install under the accumulator but you would remove the steel line that goes from the pump housing to the booster. That line has common brake fittings. You would need a gage that goes past 2500 psi, (tractor supply has 3000 psi gages) You would have a short steel line that would screw into the pump housing, it would attach to a "T" that would hold the gage. Out the remaining fitting on the "T" you would use a brake flex hose (should be good for the pressure) or have a hydraulic hose made. You need something with flex to be able to align the two holes. That line goes directly to the same port as the accumulator so you would get good readings. GM or Teves used the design shown in the manual because it is simpler to install.

[Ronnie]

Why couldn't you just screw a gauge (with proper fitting and hose) in place of the accumulator? PSI is PSI while the pump is running no matter if the accumulator is storing a reserve or not. It would tell you if the pump was capable of building pressure and if the pressure switch was shutting the pump off at the proper pressure.

[Barney Eaton]

You could screw a gage into the accumulator port........ however, without the benefit of the accumulator you might need to read it real fast because it would be on-off-on-off. Maybe that is exaggerated but once it shut off, it would leak down (depending on wear) even without hitting the brake pedal.

With an accumulator attached, you could also evaluate the condition of it using the gage.

PS.... I would attach a sketch but my new computer made my scanner not work.... hope to get this Windows 8 figured out before I die.

[2seater]

I think the gauge connected to the port for the steel line might be doable. The accumulator opening has that long spike that sticks up above the threaded opening, which is an unknown o-ringed configuration, making a simple fitting screwed on unlikely unless tall enough to enclose the spike. I think I will investigate further on that idea. By the way, my fluid drop is right at .45" and the brakes work very well. Since the thing was apparently air bound, I would think it will take a while to work all the bubbles out of the accumulator? The pump is so quiet, I cannot tell if it turns on while driving or not.

[2seater]

I went out to the garage to look at the pump I removed and the steel line is indeed the common 3/16" standard tube nut thread, however it will only work with the long style nut on the tubing. It will probably seal okay even though the pump does not have the internal reverse flare like a normal female brake fitting. The original steel line seals on the flat bottom of the hole. I also looked under the capped hole on top just to the rear of the accumulator, but that passage contains what appears to be a check valve. I will investigate further.

[Barney Eaton]

Attached is a sketch made some time back. If you were able to use a flexible line on the booster end, it would make it easier to install.

[2seater]

I wish I had seen the sketch earlier but what I made will work with a tweak. I have not looked at where the other end of the steel line goes, but I would think easy access would be out of the question. Perhaps your intention is to connect to the open end of the steel line?

I did pick up a high pressure gauge, 8" long x 3/16" steel brake line and a couple of fittings to connect it. You must use the long nut on the brake line to connect to the pump. In order for it to bottom the line and seal properly, you must remove approx. 1/8" of the first threads on the tube nut. If you look at the stock steel line, you will see what I mean. It will not tighten all the way unless removed. The flaw in the ointment is there must be a way to relieve the pressure on the line to cycle the pump. Since there was no connection to the master cylinder, the pressure comes up to 2600 psi and the pump stops, but there is nowhere for the pressure to go, so it is trapped there ( I finally had to crack the tube fitting at the gauge end and let it drool into a drain pan. The setup will work just fine, but a needle valve needs to be installed in a tee below the gauge and a short drain line over to the reservoir so it can dump back into the opening. It can then be cycled by simply opening and closing the valve. All testing can be done under the hood, no pedal pumping needed and it can be attached with everything else in place except for removing the steel line. For reference, I saw 2600 psi for pump off and 2000 psi for pump on.

[Barney Eaton]

push the brake pedal and you start reducing the pressure...... you want to check the pressure that the pump turns back on and by pushing the pedal you will do that, the hardest part is pushing the pedal and watching the gage

[2seater]

Yes, I made the mistake that I could pump the pedal, but I wasn't thinking about the fact that I deadheaded the pump with no connection to the master cylinder. Pumping the pedal, which was rock hard, had no effect. The 8" long premade brake line places the gauge just above the strut brace so it can be read through the windshield below the rear of the open hood. The tube does need a couple of gentle bends to clear everything. I believe a relief line back to the reservoir is all that needs be added. The accumulator provides the cushion to slowly let the pressure down to pump cut-in pressure, which is really a separate integrated system from the master cylinder, pump, motor, accumulator and pressure switch potentially could be tested on the bench.

[Barney Eaton]

Making a bench tester is on the bucket list but low priority as my cars are all 1991's

[padgett]

Sounds like you changed everything but the pump. Why not try the other one ? My experience with a bad accumulator is that it will pump up and the pump will turn off but you have little or no reserve.

[2seater]

I did change the pump, but not that I suspected there was anything wrong with the original. The switch was so tightly installed, it tore the threads off of the initial 2/3 of the switch on removal. The aluminum is imbedded in the pump threads badly enough to prevent installing a new switch. I may be able to save it eventually but not while on the car. When I looked up the pressures I obtained in the FSM, they are spot on. I guess there are three possibilities; first it is normal, second, the new accumulator is defective, or third, the system takes more fluid than normal?

[2seater]

This is the test rig I made up. It dumps back to the reservoir through a hole in an old cap. The cap is normally used with a quick disconnect fitting when bleeding/flushing the brake system. Not strictly necessary but I didn't know if there would be any splash back from the discharge tube. The needle valve allows a very controlled bleed off.

[2seater]

This is an updated, and hopefully more clear, photo of the pressure test rig I made. One item changed from the original post is the fitting on the bottom is a metric bubble flare on the 3/16" steel tube. That works perfectly and takes less than five minutes to run a pressure test. The only item to be removed it the steel line connection on the pump.

[harry yarnell]

Beautiful. I've made up a similar jig for the brake system on Allanti's. Pressure gauge is available (cheaply) at Harbor Freight.