Adrian

Those who can remember back some months will remember the heated debate about the brake hydraulic pump on the C4. Well recently a C4 owners had a catstrophic failure of the pump and shared the experience publicly. Since this time others have admitted similar experiences. Failure of the hydraulic pump causes total loss of brakes requiring the use of the emergency brake to stop. Oump failure was accompanied by all the required warning lights being activated as well as the warn horn. Below is the post I made just a few minutes ago to the email rennlist system. I feel that this is a serious enough issue to ask 964 owners with the affected pump system installed to be more vigilant in future. I will certainly add this to my PPI guide. This is purely a component age issue. This is not about the 964 itself it is simply, "Nothing lasts forever"!! This in no way affects my feelings about the C4 in any negative way.
Ciao,
Adrian
911C4

Since I originally posted the email on the Brake hyd pump failure on this C4 I have received a number of emails from others saying that they had similar experiences. So I think it is important that C4 owners and others with the hydraulic pump, Turbos, Turbolooks, Cup Cars, 964RS might wish to take some preventitive measures in future.
Once the brake pressure warn light comes on you are in some trouble. How long your brakes work will be governed by the actual failure. Electrical loss of the pump alone will I am sure give you a little more time but from the drivers seat you are not going to know this. All the faults reported to me this morning involve pump fail accompanied by seal failure (after investigation of course). It is hard to work out which occurs first but all (5) report burned pumps, melted or damaged control circuits and loss of brake fluid. It is quite possible that an overheating or failed/jameed up pump, actually starts to melt the seals or expands the metal around the seals. We will probably never know. Pumping out the brake fluid will accelerate the loss of brake pressure. I have no intention of arguing or splitting hairs on this one. When that "Brake Pressure Warn Light" comes on for a genuine reason it is clear that braking is almost immediately lost. The aim now is to try and avoid the situation in the first place. One ounce of prevention is better than a pound of cure.
I recommend at an interval not exceeding one month that each C4 (and others) owner check their brake fluid levels. If the level has dropped, remove the carpet from the lower section of the luggage compartment, remove the plastic cover over the ABS hydraulic unit and then inspect the area for brake fluid seepage.
If the brake fluid level has not dropped I would still recommend an inspection of the pump assembly once every 3000miles or so.
Obviously this is a safety issue and whilst this problem is very rare in the numbers game, I feel it is appropriate to advise a change in maintenance procedures to keep a lid on this problem. Everything that burns and turns, fails in time. The pumps in the C4 are getting on in years (mine is 13 years old) and I am quite sure that these pumps may be approaching their life limits.
Ciao,
Adrian
911C4

PS: A similar thing happened to our soon to be retired latest brand new Embraer 145 this week. A seal failed in a spoiler hydraulic actuator and dumped the entire hydraulic system contents into the atmosphere and what remained in the wing onto the ground. These aircraft have 2 hydraulic systems but we were quite shocked that there was no isolation valve in these systems as there are on other aircraft types. Seal goes, so does the hydraulic fluid.

MB965

Adrian,

It is always good to have a "case in point" to refer to when discussing a potential problem. Too bad for the people who have experienced the failures. This should be MAJOR WARNING to all wise owners who have the hydraulically boosted brake systems.

Are you listening Bill and Bob?

I could not agree with you more about being very diligent with the braking system and in particular about the fluid level.
One of the most valuable checks I do when using my car is to backup and then look at the area where I was parked to see if there is anything under the car. Sometimes a leak may be occurring in a concealed location and only by finding a "spot" on the ground do you have a clue that a problem is occurring.
This check has identified a oil filter leak (hole)and coolant leak which I would never had seen from a normal visual inspection.

Mike Behrman

Bill Wagner

Dear Mr. Behrman:

If you recall the thread correctly, my argument was that I could get the brakes to work IN THE EVENT OF AN ELECTRICAL FAILURE. Adrian is referring to what I would call catastrophic failure, with fluid loss.

If you got the impression that I was advocating taking stupid chances on driving around with a failed or failing brake system, then either you didn't understand what I was saying or I didn't present my points properly.

My test was as follows:

1. Take the car to the top of a hill, turn the power off.

2. Pump the brake pedal until it becomes hard.

3. Let the car coast down the hill, and then when up to speed (not too great a speed, might I add) apply the brakes and see if the car can stop. This was done in an area that fed into an empty parking lot about 1/2 mile by 1/2 mile, so there was PLENTY of room and time for me to stop the car in this test.

The test above simulates electrical power being cut to the car and hence the hydraulic brake pump. There is no way I can realistically test (or be willing to test) driving a car around with the brake pump disabled. One would be UTTERLY STUPID to be driving around with a car that was telling them brakes were in process of failing.

Could you please do me a favor and go back to that thread (I'm assuming it's in the archives) and point out where I tell people that driving around with failing brakes is "OK"???

Adrian

Guys,
I am following up on this thread because well it fits here.
I have just had a report in from a UK 964 owner who had a total brake failure on his C4. He had no warnings, no nothing just a rock hard pedal and no brakes. He was coming out of a multi-story car park and the pedal would not move anymore whn he reached the traffic lights just after the exit. The problem was diagnosed and it was found that the pump would not run. Fluid levels were all okay. It just simply stopped running. Total electrical failure. However no warnings were issued from the system. No brake pressure warn no PDAS warn not even the exclamation mark. Turned out to be the pump pressure switch. Totally failed, did not activate the pump or the warn system. A massive internal failure. We will try and find out how and why the pressure switch failed but the switch controls the pump. It also supplies the low pressure signal to the PDAS/ABS control unit.
I mean this is just a bad luck failure. One cannot predict these things happening. Just proves though that even with just the pump not running but full of fluid, you still end up quickly with no brakes. The really strange thing is that the start up sequence of lights worked. I suspect brake fluid inside the electrical part of the switch. Oh by the way, the pump itself is not fused. The 12VDC comes straight off the battery.
Ciao,
Adrian
911C4

PS: Just heard from the owner. Pressure switch and pump relay replaced. All is fine again and he is back on the road.

Roygarth

Thanks Adrian, something else to worry about!

Just kidding, many thanks for the warning.

Best regards
Piers
1990 C4 Coupe
54K miles

Devils son

Adrian,

Since a brake failure at high speed can be lethal, is it a good idea to replace the pressure switch, pump relay, hydralic pump just in case?

If so: what needs to be replaced and what will be the costs?

Adrian

I do not recommend that you replace these components. The pump is very expensive. As far as a brake failure at high speed. Yes this is a problem but you have the gearbox and the emergency brake. This is a very rare occurrence. Your brake lines can fracture causing the same result. Loose the fluid any other way, same result.
This fault was highlighted only because we had a debate sometime ago about failures and what happens and since this time a couple of failures have happened which provide a conclusion to the debate.
Ciao,
Adrian
911C4

PS: You could have picked a better log on name.

MB965

Adrian,

Not good that this guy had the failure but good to confirm that an electrical failure which results in the pump not running will quickly lead to a brake system failure. A little distressing that a pressure switch failure caused the warning system to not warn.
A point to consider is that even with the warning system it is still very important to know your vehicle and its "norms".
On start-up I always note if I hear the pump running, if not I apply the brakes a few times until I do get a running noise. Seems like this is even more important in light of this most recent failure.

Do you think the pump is not fused due the critical nature of the pump function?
It would be similar to building fire protection system pumps which are installed without overcurrent protection with the design concept that if the building was on fire it would be better to run the pump to destruction rather than have it shutoff on overload and have the building burn down.

Mike

Adrian

Dear Mike,
This kind of failure has to be put inperspective. On my files I have 7, 964 total brake failures. 5 of them on C4s. 57000 plus 964s rolled out of the factory. If we say that 25,000 had brake pumps installed we are talking 0.00028% failure rate. This is not something I would worry about as being a fleet wide problem.
The key issue is knowledge. This forum is to pass on what we know to others but more importantly "MAINTENANCE". None of these problems just occur. When you investigate these issues deeply like I do I "ALWAYS" find out that there were warning signs of a potential problem which in some cases go back a year. Intermittant warn lights. Unexplained loss of brake fluid. Inadequate or non existent brake bleeding and the list goes on. From my research none of these failures were straight out of the blue. So apart from being very rare they were avoidable. The last problem is still under research and I have asked for a report on the pressure switch internal condition and the motor pump relay. I hope I get them.
As for the pump being hard wired to the battery via a control relay which is also basically hard wired. Yes this is a design requirement. The pump must stay running. Even if you are on fire, you cannot jump out at 60mph. The most important thing to be able to do in any emergency is stop. The pump will run until it burns out or the battery is flat. Hopefully you will have stopped before this happens.
You never drive around with the brake pressure warn light "ON". Never drive off with this light "ON". You know how many times do you see postsa of people driving around with the airbag light on. Will the airbags actually work. People take the risk. That is their choice of course but I just wish people would take a little more notice of the warn lights and not assume that the warn system has failed but it is actually telling the truth. Something is wrong with the system being monitored. Believe me, we have the same discussions with our pilots. GPWS activated, must be unserviceable. Investigation shows that the system was fine, the pilot was too low over the mountains. Scary stuff but it happens.
Ciao,
Adrian
911C4

Wachuko

Had a similar situation June 8, 2000.

I was using the car and had to make a sudden stop
at a speed bump. The ABS came to play. Since it was the first time I had sense the system in action I decided to give it another try. It worked flawlessly. Close to my house I made a normal stop and to my surprise the brake pedal would not respond. I had to push it extremly hard to make the car stop.

The problem was solved by: Pressure Sensor replaced(US$247.55 - Part # 964-606-904-00), Relay replaced (US$33.81 Part # 964-615-135-00), Rubber O-Ring replaced(US$4.99 Part # 999-707-094-40). Labor US$147.90 Minus PCA discount.

d.manzella

I have had to work on this susyem on my '90 C4. I did in fact have a leak from the O-ring seal between the pressure sensor and the pump. I replaced the seal and all has been well. At that time I was told by my mechanic that he had seen the sensors fail, leading to continuos operation of the pump (therefore overheating the pump and leading to its failure). So I think that in some cases it may in fact be something else that leads to the pump failure other than the age off the pump itself. In my case routinely checking the brake fluid reservoir averted and problems while driving. Regards,
Dave

Kienle

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