RS2 Brakes or lack of.....

[saidur]

For sometime now it has taken a fair distance for the brake pedal to feel as if it is being assisted, probably half a mile of driving. I did the bomb test and found that I was only getting about 5 or 6 presses before the pedal hardened up. Today I swapped out my bomb for a second hand one bought from Audibits.

At the same time I have changed the fluid that was in the system to Pentosin 11S as other threads have said that this is the correct fluid to use. Mine was a cherry red colour probably Castrol TQ Dexron 3 as I found a half used container of that in the boot when I bought the car.

Unfortunately I now feel that there is no assistance on the brake pedal, the bomb is not being charged so 0 presses before the pedal hardens up and the pedal has to be jumped on for anything to happen. If I leave my foot on the brake pedal I feel a pumping sensation and eventually the pedal rests on the floor.

Please can anyone point me in the right direction for this problem.

The car in question is a LHD '94 RS2

[PeterS]

Saidur:

I just went through this with the Mrs' S6 wagon...
Replaced the existing pressure accumulator (would see brake light while engine was running after a few jabs of pedal, long "charge period" upon initial startup) with a recharged one...Initially I had boost, but after a week of driving, lost all assist unless my foot was on the gas pedal

Yes, I had to step on the gas pedal to have brake assist to stop

I feared a bad hydraulic pump, or worse brake servo.
Both cases, $$$ or your case GBP...

Thinking about what I replaced, what happened, etc, I took the conservative approach of again replacing the bomb first (since the high pressure hydraulic line goes from the pump to the pressure bomb ( accumulator) to the brake servo.

Remember that the bomb contains a pressure relief valve and a nitrogen bladder, which provides pressure assist when there is need beyond what the running pump supplies, or when the pump & engine aren't running.

it took me 15 minutes to replace the bomb and I had full assist back in 1 minute of engine start up.

Bottom line, the pressure relief valve on your "new" bomb is bad.
The person who recharged my bomb warned me that he couldn't test my check valve, so I knew that I was proceeding at risk...you are always at risk of getting a bomb with a bad check valve when using a "used" one, unless you know that it worked before it was removed from the donor vehicle.

[BrianSmith_S2]

For sometime now it has taken a fair distance for the brake pedal to feel as if it is being assisted, probably half a mile of driving. I did the bomb test and found that I was only getting about 5 or 6 presses before the pedal hardened up. Today I swapped out my bomb for a second hand one bought from Audibits.

At the same time I have changed the fluid that was in the system to Pentosin 11S as other threads have said that this is the correct fluid to use. Mine was a cherry red colour probably Castrol TQ Dexron 3 as I found a half used container of that in the boot when I bought the car.

Unfortunately I now feel that there is no assistance on the brake pedal, the bomb is not being charged so 0 presses before the pedal hardens up and the pedal has to be jumped on for anything to happen. If I leave my foot on the brake pedal I feel a pumping sensation and eventually the pedal rests on the floor.

Please can anyone point me in the right direction for this problem.

The car in question is a LHD '94 RS2

Think the problem is the fluid you have in the system . The dexron is advertised as suitable for auto boxes, and power steering systems, but the S2/RS2 require the G002 fluid ( new part number is G004 000 M2 @£7 a litre from G&S or Audi dealer) and its green in colour, not red . Anything else and it kills the system cos the seals etc dont like anything else but the G002.

I made the same mistake in my dads old Audi 100 and it made the breaks feel terribly spongy, with very little assistence till a few miles into a journey , and even then they were not 100% right.

Not sure how you can rectify this problem now other than a complete flush with the correct fluid and hope none of the seals are too badly damaged.

Brian

[PeterS]

btw, here's a cross section of the bomb...

Other folks have been able to "save" their hydraulics after the wrong fluid had been run.

Keep this simple.

Re install the old bomb. If you again have assist, you have verified that the "new" bomb is the issue...

[saidur]

Today I have swapped the bombs over again and rebled with fresh pentosin (G00 2000 replacement) and we are back with assisted braking but still with a longish charge period.

So I guess a brand new bomb is in order. Anyone know the best/cheapest place to buy one of these in the UK and how much ?