No_snivelling

Those of you who read my posts might remember that a few years ago, I rescued a 964 that had sat in a warehouse for 15 years.

I knew when I bought it that it would need a lot of work, but I never imagined that my work would take me years. Sure, I am slow. I take my time and overthink everything and having never owned or worked on a Porsche, the learning curve for me was steep. I am doing all the work myself and every time I think I am on the home stretch, some other issue pops up. I guess that means that when it is FINALLY all sorted, the drives will be that much sweeter, right???

Last year, I thought I was on the home stretch and was driving the 964 to get the motor vehicle safety inspection done. This was the final hurdle before my wife and I could take Sleeping Beauty on its maiden voyage. That's when it started making an awful thumping sound from the rear end. I cancelled the safety inspection and put her back up on the lift. It took a lot of research and testing but the problem was finally isolated to a seized lateral differential lock cylinder. I ended up buying a new one as the push rod had welded itself to the bellows.

But now it was winter. As the snow piled up outside I pondered if I should pull the longitudinal lock cylinder on spec. I had not noticed anything out of the ordinary on my prior very short (illegal) test runs, but what do I know?
I eyeballed the job of pulling that cylinder and initially said no way. Access was minimal and I had read how hard it is to remove the cylinder. What if I go to all that work and the cylinder is fine? But on the other hand if I wait for driving season and the cylinder is bad, then I will lose precious driving time, so I dove in and pulled the cylinder. It's a good thing I did because it too, was totally seized.

This one was rebuildable and I already had some of Goughary's seals on hand. With driving season just around the corner I was getting pretty revved up. I got the cylinder rebuilt and back in the car. Now all it needed was another bleed and I would be on the road. The home stretch was in sight again. I had done a total brake fluid flush/bleed just last fall but that was before I knew I needed slave cylinder work. So I started off by bleeding the bomb and the solenoid valve block with my nitrogen powered Motive power bleeder. It worked really well. So far, so good.

But when I went to bleed the diff locks, the home stretch suddenly became much longer once again. My UDT999 software refused to start the diff lock bleeds. This was odd since the UDT worked fine just last fall. The software acted as if it was bleeding, but no pulsing of brake fluid happened like it was supposed to. After multiple tries, I scanned the PDAS ECU for error codes and found one I had seen before; "error 42 Front-rear acceleration sensor short-circuit/break".
This must be what was preventing the valve block from sending fluid to the diff locks.

Since I had previously had this sensor apart and cleaned, and after a bunch of internet research, mostly here on Rennlist, I decided to go ahead and upgrade to solid state accelerometers from JDS Porsche in England. I did so on the strength of long term ownership testing and comments by fellow Rennlisters. I thank you all for your posts including John Speake, Rob Goughary, GeorgeK, Andy964ch, Joe J, Uwe_911 and tdiquattro.

I called Mike Parris at JDS Porsche in England on Wednesday, and the accelerometers arrived today (Friday). I got the 10% discount for ordering two and Mike got them shipped out the same day and amazingly they arrived in only 3 days. A big shout out to Mike at JDS.

Now I just need to get them installed and finish the bleed and then... I am not going to jinx it by saying anything more about a home stretch.

Goughary

I have piles of the oem accelerometers...could have sent you one!

If you drive hard on bumpy roads - you will love the solid state units. This is where they excel.

Good luck getting it going! Let us know...

No_snivelling

Thanks Rob, it would have been nice to get a couple of your accelerometers, but in the long run I am convinced I did the right thing. The OEM ones tend to be troublesome based on posts and my very limited experience. I wanted a "set and forget" install and the ones from JDS fit the bill.

I will let you all know how it goes. Pardon the puns but this has been a long, winding road with lots of unexpected twists and turns most of which occurred in the garage while I struggled with things like the Christmas tree effect. I gotta tell you, when that last light was extinguished, I cannot describe the sense of joy and accomplishment I felt.

Goughary

I was one of first to put those in a C4...they had made them originally for the 928 S4 since that car uses the same system for the rear diff.

So basically I've had them installed since 2010 or 2011 or there abouts. I've never had any issue at all, and I've tested them - butt tested- back to back with other 964 c4 on same roads with and without them. They are well worth the purchase, although as an "upgrade" i never put them at the top of the list before lots of other performance parts...but they are always on the list of "must haves"...

As a side note, i am planning to hot glue the spring arm on a couple of the oem ones, so the signal never changes, and i want to see how the system reacts. Should be fun. Im also planning to install an adjustable length arm in the diff locks to make them never go to full lock...also want to see how that goes. I'll probably dig through the clutch packs quickly, but my imagination sees less under steer.