M2B4 gearbox downshift issue 4th gen

Post by **vanzep** » Wed Oct 18, 2023 4:45 pm

only had time to lift the bonnet and check the clutch slave cylinder - found the boot is split and looks a bit wet around that part of the cylinder but cant see any drips or leaks. Probably best to change it.Thinking of buying Blueprint ADH23605 is only about £30.Next up is checking inside the drivers footwell for leaks from the master cylinder.

Post by **vanzep** » Mon Oct 23, 2023 4:44 pm

Checked the master cylinder today - it is leaking quite badly into the drivers footwell.
So i now need to change both slave and master cylinder. I have both parts here (Blueprint).
I have some comma dot4 synthetic clutch fluid but not sure if thats the best clutch fluid to use. Also need to see how much fluid is needed cant be much. Any recommendations welcome

Post by **Merlin** » Mon Oct 23, 2023 4:47 pm

I have enough Motul RBF 600 Super DOT 4 brake fluid that can be used as clutch fluid. We can do it on Wednesday if you like.

Post by **vanzep** » Mon Oct 23, 2023 4:52 pm

yes that would be great - much appreciated

i have read a few write ups on how to do the job - only potential problem that i can see is bleeding the slave cylinder can be tricky - some say fit it without pin in then compress the cylinder and fit the pin - others say use a lever to push pin in then bleed it.

Post by **Merlin** » Mon Oct 23, 2023 4:54 pm

Yeah, bleeding the system can be tricky but have done it to the BB4 a few times in the past.

I'll print the bits from the service manual.

Scott560 · Post by **Scott560** » Mon Oct 23, 2023 8:48 pm

My advice is to fill the master cylinder on the bench, and pump it / orientate it to get it primed. Doing it on the car is a bitch and will take ages to get any fluid pumping.

As for bleeding I like to pump and hold, then release pressure in the slave, close the bleed and then finally lift the pedal back up. This purges the most air from the slave and ensures you are really circulating fluid in the slave. Slightly moot if you are replacing both. Doing it this way though does mean you can do the job by yourself with just a pole to keep the clutch depressed.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Tue Oct 24, 2023 11:01 am

I replaced the slave cylinder on the BB4 last year and yep, the system can be a right pita to bleed.
I forget what I did in the end to sort it, but you and Merlin will definitely get it sorted!

Post by **vanzep** » Wed Oct 25, 2023 10:26 pm

Just to close this out- Fitted new clutch master cylinder and slave cylinder. flushed nasty old black cloudy oil out and replaced with motul racing fluid. Thanks to Merlin for helping with this - it was a bit of a pain and i managed to damage the thread on the master cylinder so that had to come back off and get the threads cleaned up. After that it all went back together fine and pedal feels great far better than ever before.

All the same - Hope I dont have to do that job again