Allante Question - Sorry

[Richard S]

This is in the nature of ripping off some knowledge from folks on this forum for whom I have much respect. The Bosch ABS brakes on my 87 Allante failed. I disassembled the pump and found that the brushes on the pump, which is a separate unit, were worn. I had the brushes replaced, and bled the pump. I got fluid out of the pump bleeder, but the pump wants to run constantly. The manual says the master cylinder can be bled manually, but pumping the brake with the key off does not push much fluid although pedal is reasonably hard. I am thinking the constantly running pump means the accumulator has failed. But could the bad accumulator explain the lack of fluid from the master cylinder bleeder?

[D-a-n-i-e-l]

I would not think that the accumulator would cause any lack of fluid in the manual operation of the mastercylinder. The bosh system is identical to the teevse as far as operation. Also, the systems marked Alto, in the Caddys, are the same. I am currently running the later in my 89'.

As for the lack of fluid while manually bleeding is normal. At least from my experience. This would be why the cars stop horribely when there is not any pressure in the system.

[Rawja]

Maybe I'm missing something here, but the pump running continuously could be any number of things, like a bad pressure switch, a stuck relay, etc. I would think a bad accumulator would reach the pressure required, but would need to be refilled more often to maintain pressure.

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rawja</div><div class="ubbcode-body">Maybe I'm missing something here, but the pump running continuously could be any number of things, like a bad pressure switch, a stuck relay, etc. I would think a bad accumulator would reach the pressure required, but would need to be refilled more often to maintain pressure. </div></div>

I agree with your assessment. The accumulator would not make the pump run continuously.

[Guest DTerry]

If the diaphragm in the accumulator is ruptured, no pressure can be stored and the pump would <span style="font-style: italic">have</span> to run continuously to maintain pressure.

[Ronnie]

I disagree. Once the accumulator is full the fluid has no place to go, pressure is built in the system, and the pressure switch (if working properly) will shut off the pump. I know this from experience. I had a ruptured diaphragm in my old accumulator. The pump would run when the key was turned on until pressure was built. The lights on the dash would go out and the pump would stop. As soon as the brake pedal was pressed the lights would come back on and the pump would start. Then the whole process would start over.

[Richard S]

Well, it's not the relay because I replaced that when the pump would not run at all. I will have to see where the pressure switch is in the Bosch system.

Daniel, can you elaborate a little on what you called the Caddy "alto" system. What years, what models? When you say "the same" do you mean it is clone of the Bosch IV such that parts are interchangable? Even if not identical, is the mounting system and pushrod the same so that it would be a bolt on?

Just to clarify in my own mind, Ronnie, are you saying that with a ruptured diaphram the fluid that would have pressed on a good diaphram to compress the nitrogen in the upper chamber, now simply fills the entire accumulator? When that happens the pump shuts off but since there is no pressure to force the fluid back into the system in the way it was designed, the fluid just drains back and the pump comes back on?

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> Ronnie, are you saying that with a ruptured diaphram the fluid that would have pressed on a good diaphram to compress the nitrogen in the upper chamber, now simply fills the entire accumulator? When that happens the pump shuts off but since there is no pressure to force the fluid back into the system in the way it was designed, the fluid just drains back and the pump comes back on?</div></div>

Yes, the accumulator only has one hole in the bottom. When fluid fills the entire accumulator the pump will shut off, assuming the rest of the system is working properly.

I can't say with certainty that the pump will not come back on until the brake pedal is pressed but I can say from my experience that the brake lights on the dash will not come back on until the brake pedal is pressed. Once the pedal is pressed, the red brake light will come on, (and sometimes the yellow light), and the pump will start to run until proper pressure is again reached. Then the light(s) will again go off.

There must be check valves in the TEVES unit that keeps the pressure from draining back immediately as you described. A properly working TEVES brake system will hold pressure for a period of time without the brake light on the dash coming on after the power has been shut of and then restored. I have not had a TEVES unit apart so I can't say for sure.

[Richard S]

The need to pump the pedal 25 times to do any work on the system suggests to me that you are right, Ronnie. Most areas of a properly working system below the reservoir are probably under high pressure, which probably takes several hours to bleed off unless manually relieved.

[Barney Eaton]

Can I jump in?

The pump turns on and stays on until the upper pressure limit is reached. (the book says around 2600 psi)

The pressure switch senses the pressure and drops voltage to the relay coil.

If the pump continues to run, either the pressure switch or the relay has failed.

If the diaphram in the accumulator is defective/ruptured,

some air is trapped inside the accumulator and is compressed (remember you cannot compress fluids) this small amount of air will give you a very small pressure resevoir, enough for the pump to stay off until (1)either the system leaks down to the kick-on pressure level or (2) you hit the brake pedal.

[D-a-n-i-e-l]

Richard,

Sorry I ass-umed that the Allante would use the same ABS as the other Caddys in the time frame. I double checked and it is a monster all its own, and I have not seen one yet.

Also for any one wanting to know what other cars came with the Reatta version, here is a list.

http://www.partsamerica.com/ProductGuide.aspx?mfrcode=A1C&mfrpartnumber=124408

I have seen them branded Bosh, Alto, and our Teeves. The only diffrence is in what I-nut is used to hook to the brake pedal.

[Rawja]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> (remember you cannot compress fluids) </div></div>

Yeah, but while the fluid cannot be compressed, it can be pressurized so the state of the accumulator should not affect whether the system can reach pressure or no, just how much reserve there'll be when the brakes are applied.