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I am about to embark on a total flush of all brake fluids in my 1992 C4. I have never done this before and to prepare I have done a lot of reading and understand this will involve 13 bleeds.
I do have one question though and I have searched on Rennlist, Pelican etc and not found a definitive answer to the question of:
Does the order of bleeding matter? IE brakes first? Accumulator first? Perhaps the order does not matter but I would welcome any input.
FYI, I have the UDT tool that should allow me to bleed the diff locks.
Thanks ffc, I have that thread bookmarked and was planning on following it. But there is no explanation as to why he did them in that order or even if the order is important. He only says that he started with the brakes because he changed all the flex lines to his brakes. If there is a correct order, I would like to understand why. But like I said, perhaps the order does not matter as long as all bleeds are done at the same time.
Thanks ffc. I have the WSM and had a quick read of it before turning to Rennlist, but will go back and read it over carefully. Meanwhile I have run into a snag. I am trying to remove the brake fluid cup filter/screen and it does not want to budge. I don't want to break it.
Research indicates some people use needle nose pliers but is that just to exert a pure upwards force on the top lip of the filter, or am I supposed to grip somewhere down inside where I see some slots? I am using a turkey baster to remove the old fluid first and the filter gets in the way of removing the last inch or so of fluid.
Ok, maybe it is not a filter. This site calls it a "bush" others have called it a filter. But whatever it is, it prevents removal of a lot of brake fluid. It sits right below the filling cap. Part number 964 355 187 01.
Last edited by No_snivelling; 07-17-2021 at 09:29 AM.
Reason: added part number
Second that - I have used a power bleeder to flush the fluid from my 964 - never needed to remove the little white sleeve/cup from the master cylinder reservoir.
Same; not removed the filter (didn't even notice one being there in my case). Proper pressure bleeder definitely the way.
Traditionally it was/is a case of starting bleeding furthest point from the reservoir (in helping to ensure max air bleeding of the system pipework). On my C4 I started brakes first (furthest away), then diff lock slave cylinders - they took ages as there is not much in the way of 'swept volume' (fluid pressure for lock-on in a tiny cylinder) then clutch slave. All this I did manually and not with the PDT - it just takes a quite while and more fiddle work underneath. Can leave then as is, or move into the frunk and start on the C4 brake solenoids, PDAS, accumulator etc. Many or most may they are a must and while I think they can be done manually a PDT999 is probably the way to go. However, I left as is in my case as I've never had a 'charging' delay longer than prescribed or any different feel other than bang solid. What I do do is every month I slam the ABS into life on a piece of quiet straight road - a working check and also moves the fluid (and hopefully air/condensation that might be trapped) through the valves.
Much of the above you'll have read in various threads already. If it helps I have many C4 thread bookmarks I can pass on - there might be one or two there you haven't seen, maybe(?)
Hey LM964, thanks for your answer and I would greatly appreciate your offer of any relevant bookmarks for C4 brake fluid flush. You are correct that I may have missed a few and besides, a compendium of all bookmarks might be useful to others in the future.
So the consensus is to leave the cup filter in place. Got it.
All relevant ones from my browser bookmark list as below. Many/most you probably have. A few others there more specifically looking at components within the system - these all improved my understanding of the C4's complicated set up and helped diagnose any likely problems I might come across. I had the added issue (which was the root cause of needing to perform a full bleed in the first place) of a failed and leaking longitudinal diff-lock slave cylinder, which in the end I had no option but to replace with a new one from Germany. I had plenty of help and advice from Goughary and others on the forum. Hope this all helps. Post up your own experiences and any useful notes, findings or home-grown tips. Good luck.https://rennlist.com/forums/964-foru...procedure.html
I went through the entire reading list of bookmarks. Very useful. I learned a lot. One thing I learned from one of the pictures is that my car is missing the brake fluid cup filter. I have pasted that photo here so that others can check to make sure their filters are not missing. It is not entirely obvious that the filter is missing because the cup filter sits inside another, larger cup. The larger cup however, appears to be integral to the reservoir itself and cannot be removed.
In the photo below, the filter is the bright white object that sits directly below where the reservoir cap screws on and has 4 little grooves on top. It was probably removed by the former owner to flush fluids and then not replaced.
Photo credit to Garrett376.
07-14-2021, 02:03 PM
Total brake fluid flush on C4
