Computamedic

I've seen lots of mention in previous threads about the time it takes for the hydraulic pump to stop when you first turn on the ignition - and there seem to be wide variations from car to car.

What I don't recall ever seeing is any mention regarding the change that can be brought about by doing a bleed to the primary hydraulic circuit. I had previously believed that the "pump time" was pretty much a consequence of the condition of the pump and the "bomb", but as part of the investigations into my recent ABS issues the shop did a full bleed and I was astonished at the impact that had on the "pump time".

Having read the warnings in Adrian's book about the implications of the pump running for more than 2 minutes (it overheats) I had always been aware that mine seemed to consistently run about 90 seconds after an overnight stop. However, after the full bleed, it's down to less than 20 seconds!! Reading the other thread about the PDAS warning coming up during a DE session I wonder if extended times reaching the required pressure during enthusiastic driving might explain the phenomenon?? Is it likely a full bleed might improve the pressure build time to a point of eliminating the warning??

Regards

Dave

dfinnegan

Dave,

That has been my experience, as well. Full bleed, noticeably reduced pump run-time at start up.

Interestingly, I once had an Indy do a "fluid change" for me. He did not bleed the accumulator or valve control block. And, he did not do a "proper" bleed of the lock cylinders or clutch slave cylinder. I know this because I was there to see it and, though I didn't know it at the time, he did not do the bomb or valve block. Then, when I did my own full fluid change I saw lots of crud come out of the lock cylinder nipples. Obviously, they had not seen a full fluid change in a long time.

I was thinking the same thing about the Diff Warning Light thread, but figured that level checks would be the first step.

How's your car running? Sounds like the hydraulics are sorted. What about the ABS?

Cheers

DWS964

I have experienced the same improvement on both of my cars. Pump time was exceeding the time limit for the alarm, any time the car sat for more than 8 hrs. After bleeding the full system (accumulator and solenoid (per Adrians book) and diff locks (without a Hammer)), the pump time dropped to <20 seconds (haven't put a stop watch on it, but it is short), and I started hearing solid clicks from the diff locks test that the system does when you first turn the key on.
I cannot say if there was a change in ABS or PDAS system operation or performance after doing the full bleed, but I would certainly question whether it had been operating properly prior to the bleed. On car #1, the fluid coming from the diff locks was very nasty brown/black.
Highly recommend this for all C4's. There is a good chance that it has not been done, even if the records show brake fluid flushes. If you don't do it yourself, make sure your shop knows what to do.
Be safe, and have fun.

dfinnegan

+1 on the diff lock clicks at start up. First time I heard that I thought something was wrong!

Bluey964

Again, I agree with the other posters having just done my entire system. I suspect most indy's do not know to do the high pressure side and just do the brakes and possibly slave cylinder. My pump is now 20-30 seconds to finish, and before was about a minute.

DaveK

Interesting. I was thinking the other day that it's a good few years since I had a full bleed. Service time in a couple of weeks - might add that to the list.

Computamedic

Dave,

I put a little note at the end of the ABS thread, but I took the accelerometers out over the weekend and, despite the shop assuring me they had cleaned them, it was obvious that one of them was "catching" on the PCB at the bottom in that the sprung arm wouldn't return to the central position if gently moved to one side, whereas it would work OK to the other side.

I sprayed some contact cleaner in there and agitated under the sprung arm with a small brush and, after a couple of cleans the sprung arm would then return to the central point. For the moment I'm going to assume that the thing works as expected although testing the ABS is no mean feat on dry roads. Maybe I'll wait until Winter to check it!!!

It's difficult to justify spending money to replace them when you have no convincing method of testing to prove if the new ones are any better than the old.

Thanks for your help in locating some replacements but I e-mailed Dieter just to confirm that I wouldn't need them for the moment.

Regards

Dave