RS2 - rock hard brake pedal after refurbishing PAS pump

[JonRS2]

Thank you. Here is the latest in the saga:

The mechanic checked that he had refurbished the tandem vane pump correctly with new seals and x-plugs. In fact, the lower of the two x-plugs was so tight it could not be removed. The upper of the two x-plugs was removed with its old o-ring and replaced with a new x-plug and o-ring covered in green hydraulic fluid. The internal seals were replaced, except for the o-ring attached to the x-plug that could not be removed. There was some corrosion between the high and low pressure parts of the pump but that was removed / scrubbed away. The seal at the very front of the pump was not removed or replaced.

I was told that the rock hard brake pedal had been caused by the hydraulic fluid system not having finished self-bleeding. It did so somehow and the mechanic road tested the RS2 for 3 miles without incident. I collected the RS2 from the mechanic yesterday evening. All seemed fine, the green hydraulic fluid level in the reservoir was at the maximum line, the brake pedal was normal and the power steering worked.

8 miles into my journey home, the red (!) came on, accompanied by the beeping warning sound. It went off and on over a few miles and then the red (!) remained on. 25 miles into my journey, I felt the steering get harder and the pump started to make an unpleasant noise. The brake pedal was fine. It was difficult to park the car at home with no power steering.

I immediately called the mechanic, who thought that the system must have self-bled on the journey, lowering the hydraulic fluid level in the reservoir. He asked me to check the hydraulic fluid level in the reservoir. Empty. So, I called the mechanic and to his great credit, he drove to me late yesterday evening with more green hydraulic fluid to fill the reservoir.

As soon as the mechanic inspected the pump, it became clear that it was leaking worse than before. It was leaking from the new upper x-plug / o-ring. The reservoir was then refilled to above the maximum with new green hydraulic fluid (above the maximum to account for bleeding). The mechanic removed parts from the car to get to the x-plug, removed the new leaking x-plug and o-ring with the pump in situ and replaced them with a second new x-plug and new o-ring coated in new green hydraulic fluid.

After running the engine, there was no leak from the latest x-plug and o-ring. We took the RS2 for a 15-mile drive. The brake pedal was quite hard. OK at each each first application of brakes but harder on each second or subsequent application. After returning and checking the area around the pump, it was evident that there was no leak from the latest x-plug and o-ring. However, the hydraulic fluid was still above the maximum in the reservoir and the brake pedal was still quite hard. I was told the system needs to self-bleed more.

So, optimistic scenario: the system will self bleed and all is now fine. Pessimistic scenario: the issue has not been fixed and at some point there will be another hydraulic fluid leak, draining the hydraulic fluid reservoir.

I have the following questions:

1. Which company made the tandem vane pump?
2. Where can I get a new tandem vane pump of equivalent quality to a new one from Audi at a reasonable price, given that Audi's price is around £1,100, Audi don't have them and "on back order" at Audi could mean anything.
3. If I wanted a gearbox rebuilt, I would take it to a company who specialises in rebuilding gearboxes. Which companies specialise in rebuilding tandem vane pumps to a very high standard?
4. Do I stick with my existing tandem vane pump or do I need to buy a new one for peace of mind and to end the saga?
5. What happens if the hydraulic fluid level is above the maximum in the hydraulic fluid reservoir and there is no more air to expel by self-bleeding?

Many thanks.

[newsh]

Run the engine for a minute or two, switch it off. Press the brake pedal repeatedly and count how many times you press it before it goes hard. It should be up to 20 or so times, less than 10 and the bomb has gone bad.

Have you turned the steering wheel from lock to lock to bleed the steering circuit?

You can always remove a little fluid from the reservoir with a syringe or piece of tube.

[JonRS2]

Yes - Yesterday it was 30-40 times repeatedly on the brake pedal while simultaneously turning lock to lock 20 or so times. But the brake pedal stayed hard after that. How long should it take for the brake pedal to return to normal after testing the bomb? Thanks. I will try this again at some point in the next few days.

[JonRS2]

Actually, when I pumped the brake pedal yesterday while turning the steering wheel lock to lock, I think the engine must have been idling. I tried the bomb test this morning as you described - engine idling for a few minutes before switching off engine and then pumping the brake pedal. The problem is that the brake pedal was hard to start with and is now rock hard with almost no travel at all. There is no point in guessing the number of pumps required as the pedal travel was so minimal. However, the red (!) is not on at all and has not been on since the hydraulic fluid in the reservoir was topped up. If the bomb needed replacing, wouldn't the red (!) come on?

Is there only one switch for the red (!) for both brake pressure (bomb not working) and hydraulic fluid level too low in the reservoir? Or are there two switches for the red (!) - one for the brake pressure (bomb not working) and one for the hydraulic fluid level too low in the reservoir?

If two switches for the red (!), is it possible that the switch for brake pressure (bomb not working) has failed or somehow become disconnected such that the red (!) does not come on anymore if the bomb is not working? Where is that switch located? Is it part of the bomb or a separate part?

Where is the best place to purchase a new bomb for an RS2 (ADU) and a new switch for brake pressure (bomb not working)?

If not the bomb, what else could be causing the rock hard brake pedal?

Rock hard brake pedal, no hydraulic brake fluid leaking, PAS pump apparently working (currently), no red (!).

Many thanks.

[Error404]

Bomb - OEM part is no longer available as far as I know. P/n 4A0612061D
Febi 26538 is a replacement although I believe it has been discontinued.
http://www.amazon.co.uk/febi-bilstei.../dp/B006DHTZZK

The pressure switch is located on the underside of the brake servo.

OE PAS pump was manufactured by ZF.

[JonRS2]

Thank you. There is another symptom which may help with the diagnosis. If the engine is switched on and left to idle for 5 minutes and while it is idling I push my foot down firmly but gradually on the brake pedal, it now feels like there is a pulsing / strange juddering / vibrating sensation in the ball of my foot unlike anything I have felt when braking before. There is no unusual noise - just the sound of the engine idling. The car is parked absolutely flat, handbrake on. The hydraulic fluid level is still high in the reservoir. The power steering clearly works well as I turn the steering wheel lock to lock easily. There does not appear to be a leak from the tandem vane pump. The area around the new x-plug and o-ring is totally dry. What could be the cause of the pulsing / juddering / vibrating sensation when depressing the brake pedal in a stationary car, engine idling? The tandem vane pump? The brake bomb / accumulator? The brake master cylinder? The brake servo? A failed switch? Air trapped somewhere? My RS2 has not had problems with the brake pedal / braking system until the repair of the tandem vane pump. The brake pedal has always had a good, smooth travel.

Thank you for information re: ZF as manufacturer of the tandem vane pump. I called them and was told that the pump was made by ZF Lenksysteme and was their part number 8691.955.166. ZF Lenksysteme was sold to Bosch recently and ZF no longer manufactures the pumps and no longer has any stock of the pumps. I think it was an EU competition requirement that ZF Lenksysteme was sold to Bosch because ZF was acquiring TRW. I will follow up with Bosch to see if they will be manufacturing the pumps or if they have acquired any stock of ZF Lenksysteme 8691.955.166.

Thank you also for the Febi-Bilstein bomb part number.

Merry Christmas to all.

[newsh]

I think the pulsing in the pedal is the brake servo gone bad, pretty sure mine was like this when mine went a year or so ago.

[twoqu]

Its difficult to comment but as more than one thing was done it might be an idea to look again at the brake job!
To be honest without a high pressure gauge you are just guessing about the pump hydraulic system. A measurement at the servo would determine whether there is an issue or not. Obviously it worked before but somebody has disturbed it so we cannot discount it entirely. A hard pedal would suggest a lack of servo assistance. This part of the pump is relatively simple so a check to see if all the componets are there might be prudent using the guide. As the other X plug was not disassembled, as long as the shaft was not removed it should still have all its components.
The calipers on the RS2 and indeed the other Porsche models that share the design suffer from lifting of the pad guides that the pads slide on due to corrosion underneath. Perhaps the pads are getting hung up on the guides and not moving freely and therefore you are getting a hard pedal. Again it may have not been an issue with the old pads if they were beyond were the guide was lifting, whereas it might be an issue with new pads.
The pad guide problem can be seen visually if you are capable of removing the wheel. It might also explain why the brakes appear to work once but get worse.

[Error404]

Pulsing through the pedal is often a sign of a bad servo.

[JonRS2]

Further update: I purchased a new Febi-Bilstein brake pressure accumulator / bomb from Amazon following the link provided by Error404 (for which, many thanks). That was fitted by the mechanic yesterday and the bleeding of the hydraulic fluid system was apparently much quicker and easier than before with instant power steering and power to brakes and a proper brake pedal feel with no pulsing through the pedal. Great. The mechanic then took the RS2 for a spirited road test to check all was in order. Towards the end of that test, during which the RS2 had performed well, with no apparent issues, the red (!) came on. Once again, 65 miles or so after fitting the latest x-plug and o-ring at the top right of the tandem vane pump, it had worked itself loose and had leaked hydraulic fluid.

The mechanic has heard that sometimes there have been problems with the high pressure pipe from the tandem vane pump to the brake pressure accumulator / bomb. Apparently people have replaced those pipes in the past. Audi part number 895612065B and NLA since 2010. EUR 230.27 from Audi Tradition.

Does it seem likely that this pipe is the source of the problem? If so, is there an alternative part number from the manufacturer of the pipe? Is there somewhere I could buy a new one for less than at Audi Tradition?

If unlikely to be the pipe, what else could it be? The RS2 seems fine with all hydraulic fluid system components apparently working until the x-plug works itself loose. Why would it do that? It does not look like it was designed to be torqued. The tandem vane pump refurbishment article I read suggests that the x-plug does not need to be torqued. What would cause a sudden build up of pressure sufficient to loosen the x-plug?

Yet another new x-plug and o-ring required? Exchange tandem vane pump required? New tandem vane pump required? New high pressure hose required? Something else? I think we can now rule out the brake servo and brake pressure accumulator?

Any ideas gratefully received. Thanks.

[JonRS2]

I meant to add that I spoke to the technical team at Bosch who confirmed that Bosch have acquired ZF Lenksysteme, who made the RS2's tandem vane pump for Audi. Part numbers for the RS2 tandem vane pump are apparently: Audi 8G0145165X; ZF Lenksysteme: 8691955166; Bosch: KS00001375 (new); Bosch: KS01001335 (exchange). I have no idea who sells these at a reasonable price or at all. I just wanted to pass on the information. If you know who sells these tandem vane pumps with these new Bosch part numbers, please let me know. Thank you.

[Error404]

So to clarify the brakes work correctly now, the X-plug is jut working loose and you are losing fluid?
What is your man torquing the plug to? It does certainly need to be torqued, I would guess at around 50-60nm.
There is a specific tool for it, which looks like this:


You can modify a a drag link socket to work. I have used a cold chisel in the past to tighten the plug. It does need to be TAF Tight AS F...

[JonRS2]

Thank you. Yes, your clarification is a fair summary of what I have been told. I do not know how much the new X-plug and o-ring were tightened but I think strong hand tight using a generic tool rather than torqued to 50-60 Nm using a special tool. Does that specific tool / bit have a name and size and make / part number? I am thinking it is worth getting one to carry in the car (with extra hydraulic fluid) in case the X-plug comes loose at some point in the middle of nowhere. Are you thinking it is probably just the X-plug not being tight enough rather than the tandem vane pump or high pressure hose needing replacement? That would be good news.

[SteveH]

If all was working fine and then the X plug worked loose and you lost fluid/pressure, I would guess it just wasn't tightened sufficiently.

[Error404]

Can't see that the hose has anything to do with it.
The OEM tool is no longer available apparently, so you will need to improvise - welcome to S2/RS2 ownership