Bleeding brakes 964RS

[964RS.]

Advice needed please.

Car: 1993 RS Lightweight LHD.

I needed to replace the brake fluid as the brake pedal was going to the floor at the track and the diagnosis was that the brake fluid had boiled and needed replacement. I do not know when it was last changed. The existing fluid is 'normal' brake fluid colour.

I bought a Gunsons Eezibleed kit and 2L of ATE Super blue fluid. Following their instructions I:

Clamped the brake fluid reservoir vent tube at the flexible section. Connected the Eezibleed to the tyre at 20psi. I drained all 4 corners under pressure (is this where I went wrong?) in the order: Right Rear, Left Rear, Right Front, Left Front.

Filled the Eezibleed canister with ATE brake fluid. Re-pressurised the tyre and bled the brakes in the order: Right Rear, Left Rear, Right Front, Left Front until old brake fluid and then blue brake fluid came through and no air bubbles - didn't take long.

Problem: the brake pedal goes straight to the floor and there is little or no braking effort. If I pump the pedal: the effort builds up (I can hear the pump whirring) - then the pedal goes solid after about 5 cycles but only for a second and then the pump (or a pressure relief valve perhaps) starts whirring, the brake warning light illuminates and the warning buzzer beeps about 5 times. I take my foot off the pedal and after a few seconds try again but the brake pedal goes straight to the floor. Brake fluid is also pouring out through the ventilation tube onto the road during all this activity. If I go round to the front the pump is running and running and then eventually stops.

Help!

By clamping the flexible pipe have I starved the pump of fluid? Do I need to bleed the pump too? Where have I gone wrong and what do I need to do?

[davisriley]

I would say that you still have a lot of air in the system. Am I reading it right, did you drain the system of fluid, and then refill it next round? If so, that's the problem. You will probably just need to keep pushing fluid through the system. Take a rubber mallet and tap on the calipers a bit as you bleed them. The flexible line that you clamped is only the overflow, you didn't starve anything by doing that. The reason you do that is that when you pressurise the system without clamping it, you push all of your nice new expensive fluid on to the ground behind the drivers front wheel(ask me how I know). As to why it is puking out of the overflow now, I don't know. I would try bleeding the system more. It may need to go to somome with a hammer or pst-2 to try and get the air out at the abs module. Good luck.

[craig001]

Don't need any special tools for a C2. Don't forget to get your clutch slave cylinder while you are in the back.

[Bill Verburg]

there are 3 separate sections of the electro-hydraulic brake system that need to be bled.
1)m/c circuits - requires depressurization of the booster circuit at the pressure accumulator **caution 180bar pressurized fluid can be found here**

2)ABD circuits - requires a "Hammer"

3)brake booster circuit see causation above

This is a complicated very high pressure system that requires specific knowledge to maintain.

JMO, take it to a pro that is familiar w/ that system.

Just a WAG, the "bomb" can fail internally w/ resulting symptoms as described.

[voodoo964]

I recently began bleeding mine but did not clamp the overflow. I lost all pressure as a result. I then clamped it and used a pressure bleeder at 30psi. I started at the at the back right wheel, then the back left, front right and front left. This brought the brakes back to full pressure again.
Maybe you need to follow this order?

I have not bled my clutch slave as yet (not enough time, last time). Can i do this independently? My clutch appears a little soft at the moment, will this "harden" it?

[Newsboy]

I'm not familiar with your bleeder, but use a pressure bleeder like"Motec" Clamp the overflow tube. Fill you bleeder with 2 liters of fluid. Pump it up to appox. 20 lbs. of pressure. Bleed both upper & lower bleeder screws in the order you described. You will need to run about1.6 liters through for a full flush. Tightening torque of the bleeder bolts is 6-9 Ft/lbs. You should also bleed the clutch slave cylinder at the same time. You may have to add pressure as you bleed.

[964RS.]

Thanks to Bill and everyone.

Re-bled the system with plenty of fluid this time - managed to get a few more air bubbles out. Pedal feels great - maybe 1 inch of travel and then full pressure. Pump whirrs as normal after about 4 presses. All warning lights out.

Didn't bleed the clutch. Only have a trolley jack and havn't bled the clutch before. I believe that you have to bear-hug the gearbox to get to it! Maybe this week I will use some axle stands and get underneath. Clutch pedal action feels OK but could be firmer. If I can get the same improvement gained on the brake pedal it would be worthwhile.

Didn't bleed the ABS system, of course, as I don't have the Hammer kit or the PST2 kit. I spoke with a specialist today that can do it for me at short notice (new and keen for business) if I realise that I need it doing.

Going on the track next Wednesday and now intend to bleed just a little fluid after each track day when I clean the wheels and remove the build up from the brake disks.