C4 Braking Problem

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Topic originally created by dwilliams on September 23, 2011 2:42 PM and viewed 2622 times in the old forum.

[Guest]

Originally posted by dwilliams on September 23, 2011 2:42 PM

My C4 does not stop well at all -- to the point of being quite dangerous. I have had the vacuum booster rebuilt as well as the master cylinder, brake calipers and pads. It seems like there is something really wrong with the braking system. It is as if my power brakes are not working at all. Any help would be greatly appreciated.

[Guest]

Originally posted by Ian Levy on September 23, 2011 6:22 PM
Hello from England.
Assuming all the overhauled components are working & that you have a firm brake pedal you should try changing the brake pads.
If the brake pedal is not firm you should bleed again in the exact sequence advised in the repair manual
That is lower front circuit then upper front each side then lower rear circuit then upper each side.Each wheel in turn both circuits.
I do not know what pad material you have in there but a similar thing happened to me many years back with an E-type Jaguar.
If not I am afraid you have to check out all the individual components starting at the servo
Best regards
Ian L

[Guest]

Originally posted by dkblueUK on September 23, 2011 8:54 PM
I agree with Ian, but would add a few comments.
Working brake pads usually make the wheels dirty - too hard a pad = cleans wheels and no stopping !
When you had the calipers rebuilt, did you replace the flexible brake hoses - these can close up internally with old age.
I assume that there is a non-return valve in the vacuum line, although the manual doesn't seem to mention it. I looked on my car, and there is an aluminium cylinder in the line at the rear of the engine, which could be one. If this is faulty, you will not have the correct vacuum assistance. Perhaps someone else can confirm whether this is the non-return valve, since I've never had need to strip my system.
Whatever - you need to find the problem - it's not a thing to live with !
Neil.

[Guest]

Originally posted by Mike Meehan on September 23, 2011 9:50 PM
I found a collapsed hose from my booster that was not pulling vaccuum once. It needs to be the proper reinforced hose. Pull the hoses off the booster while the car is running to confirm if you are getting suction. I also foung that it took quite alot of bleeding to fully purge the system. I used a vaccuum bleeder and tapped each caliper wwith a plastic hammer as I bled each one. Are you sure each flex hose is OK ? They do fail internally with age, just like me. Good luck, Mike

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Originally posted by dkblueUK on September 23, 2011 10:29 PM
Just checked in the parts book - Tav 28. Item 27 is the non-return valve.
Regards
Neil.

[Guest]

Originally posted by Ian Levy on September 23, 2011 11:09 PM
Hi Neil & Mike
Thanks Neil for your constructive additions & I agree with Mike about the strength of the walls of the vacuum hoses.
I have had the non-return valve on the bench.& iI looks the same both sides from the outside.
Any chance it might have gone back the wrong way for correct flow or is that a silly question??
Regards
Ian

[Guest]

Originally posted by dwilliams on September 24, 2011 11:38 PM
Thanks to all for you suggestions. I have a plan now and will concentrate in the hoses, non return valve and completely flush the system. I will keep you posted.. Regards, Dennis

[Guest]

Originally posted by dwilliams on December 22, 2013 6:01 AM
Sorry for the delay. But the braking problem was a bad booster. The first mechanic I took it to had the booster rebuilt however it apparently wasn't rebuilt right. Finally, F&M motorsports purchased a used booster and rebuilt it themselves. Problem solved! C4 stops like it should. Thanks again for all your suggestions.

[Guest]

Originally posted by rickkaufman on December 25, 2013 2:16 PM
Glad to hear it was fixed. Save that old booster. They are hard to come by, and expensive if found. To properly redo one, with new plating and all, reach out to The Power Brake Exchange in San Jose, CA; they are an amazing rebuilder of those units. I have had them do several for me over the years. 800-322-1775. Ask for Michael or Martin.

[Bill Mihalic]

Just a short note to say that I had good results with The Power Brake Exchange in San Jose. After I traced my braking problems to the booster I shipped it to San Jose based on Rick Kaufman's recommendations (thanks, Rick). They did a nice rebuild, including re-plating of the housing, all for $200, which is a great price. I reinstalled it last week and then went for a test ride. Perfect.

I did have a little trouble with the Exchange keeping track of my info. In one phone call they told me the repaired booster would ship out the following day, but it sat for 2 more weeks because they misplaced my contact info (and my credit card number), and were waiting for me to call. I recommend etching contact info on the unit itself so it won't get lost and the re-plating won't obliterate it.

It took me three years to track down this brake problem. For the first two years it was very occasional and I couldn't replicate it. This year it was more regular and I found that braking was always good during the first application of the brakes, but the power assist dropped off in subsequent applications. I found that I was normally getting good vacuum from the vac pump and engine vacuum, but on that second brake application the input vacuum dropped quite low. Something like a leak or a stuck valve in the booster was apparently "venting" the vacuum after that first stab at the brakes.

In bleeding the brakes after re-assembly I found that the rear calipers weren't draining much. Loosening upstream connectors seemed to indicate the blockage was in the hoses. So, this weekend's chore is replacing the four rear hoses. An easy job--or it would be if the hose connectors didn't seem to be frozen to the large backing nuts. Another one of those things that turns a two-hour job into a two-day job.

Bill

[Dbone]

Great info Bill,

looking to replate my booster, but i won't until i need to fix my brakes.

[RaymondSBaxterIII]

Just saw this series of posts and thought I would add a few comments based upon my recent experience. For over a year we have been looking for answers and the "right" fix for the gradual lose of braking ability due to the break peddle migrating to the floor after several uses. Went through the usual fixes, i.e. checking the brake lines, calipers, master cylinder, etc. Brake fluid was not visibly leaking anywhere. Replaced the master cylinder to no avail. Finally traced the problem to the value just prior to the wheel cylinder. Apparently the 365 GTC/4 has a dual/redundant breaking system that is "balanced" by these values prior to the wheel cylinders. Chuck Wray of Grand Touring Enterprises LLC discovered the problem and finally found a supplier, after several failed attempts, in Italy with replacements that worked! He was glad to uncover the problem since a Daytona in his shop had the identical problem.