My S2 coupe bit of a rebuild and repair thread.

[B5NUT]

Well as I had nothing to lose with the actuator I just opened it up by prising it apart with a couple of flat blade screwdrivers and found the fault! looks like it was not assembled correctly

Diaphragm was not fitted correctly and is bent like a banana on one side.
seal.jpg

Straightened that out and put it back together and it's now working again Will keep it as another spare in case the Audi one fails at some point.

[Tractor Dave]

I pulled one apart to see what makes them tick. It's a simple rubber diaphragm between two halves with the actuator rod connected in the centre. Both the Audi and Merc unit are identical and made by the same company. Only the mounting holes are slightly different and obviously the rod end.

[B5NUT]

Thanks. I'm still wondering why the merc actuator failed. From what I can see the control unit provides a slight pressure down the pipe with the blue stripe, I guess that is to keep the actuator arm in. Now I'm guessing the Merc does not apply the pressure all the time to the unit, so has that caused the early failure? Anyone else running the Merc actuator and knows there's is still working?

[Tractor Dave]

Nice work.
Handy to know about the switch replacement.

[B5NUT]

Found the filter, it's part of the banjo bolt, and it was a good call Dave and it had a fair amount of dirt in it.
Screenshot 2023-07-03 191819.jpg

All washed out with brake cleaner.
filter.jpg

Fitted the refurbished bomb a few weeks ago, and thankfully the bomb light has not come back on. The fluid in the PAS reservoir does rise when the engine is switched off, but when started it only drops to the level it was filled to (next the maximum line) where as before it would rise to the top with the engine switched off but drop below the minimum line when the engine is first started only to rise above the line a few second later!

Have to say Pleiades Garage did an excellent job on the refurbishment looked band new when they sent it back.
bomb.jpg

Next up was to look at the diff lock indicator. I figured all of the bulbs had failed as both of the illumination bulbs did not work and the activation light did not work. I replaced the illumination flat top bulbs with grain of wheat bulb as much as I tried I could not find any of the flat top bulbs. Anyone know where you can buy these from?

1-bulb.jpg

Decided to bench test the light and to my surprise the diff indicator bulb did light up. So I had other faults with the diff locking setup.

After testing the vac line going to the control unit I tested the control unit and it switches the vacuum between the two pipes I looked at the new actuator I had fitted and sure enough it was dead. This was a new Mercedes unit that I picked up at the dealership! I know it was working when I picked it up, so in less than 2 years and 0 usage it's dead. Unfortunately the unit was modified so I cannot return it and did not what to spend another £50/£60 replacing it. So I dug out the original Audi unit off the car.

The down side to using this is I've had to mount the actuator upside down as the original mounting holes were damaged due to rust expanding the screw holes and cracking the plastic.

2-actuator.jpg

While I was there I also replaced the rubber boot as I did find a cut in the boot that was well hidden, so it was replaced with a spare I had.

So with that fixed the diff activation light was still not working, and I also read the ABS light should come on the dash which also did not activate when the switch was pressed. So the next test was the switch fitted to the back of the diff, and sure enough this was also dead. After cutting it open I found the internal seal had failed and it was full of oil and some dirt The contacts were also well tarnished and no longer made a good clean connection. So, surprise surprise the switch is now EoL and has been for many years, I asked around but could not find a replacement one. So looked around for another solution and the only one I could find is this switch. It's a reverse light switch used in older Audi gearboxes and it's still available.
3-switch.jpg

Next was to sort out the wiring, as the connectors are different and I didn't want to cut up the cars wiring harness I made an adapter using parts of the old switch. It's not the neatest solution at the moment, but will do until I can figure something better out.

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So with that all fitted I now have a fully working diff lock system (Not that I will ever use it), which started out with what I thought was just a failed bulb. Also thanks to Dave for help with fault finding and some knowledge on the rear differential as this is the first time I've delt with a system like this before.
6-working.jpg

Don't think I will ever need the system, but I hate faults on the car so had to get to working again. For the moment all of the electrical & mechanical systems are now working on the car. Still have a fair few tidy up jobs to do but it's a couple more jobs off the list.

[Tractor Dave]

Can't remember now. Down there somewhere

[Rikki Kitto]

Ill try find it for ya bud

[B5NUT]

Thanks Dave, the system has been flushed a couple of times since I got the car. Where is the filter is it near item number 7
filter.jpg
Also has anyone got a spare hose for sale (number 8) looks like mine could have a very small weep just near the pump.

[Tractor Dave]

Yes, just keep pumping the brake pedal 20 times and bomb will be discharged. There is a small filter on the bomb fitting that needs a clean while you are there. I also replaced the crush washers last time I did mine. Good time for new green mineral fluid to if it's not been done recently and clean out reservoir.

[B5NUT]

If you need a brake bomb for parts I have one that I took out of mine when I converted to doodaa brakes postage costs its yours if ya need it bro, think it worked but would need a refurb

Thanks for the offer Let me see what Pleiades say about the bomb I sent to them, as they should have received it today so I hope they get back to me in the next day or two. If it's scrap then I'll take it off your hands if that's OK.

[Rikki Kitto]

If you need a brake bomb for parts I have one that I took out of mine when I converted to doodaa brakes postage costs its yours if ya need it bro, think it worked but would need a refurb

[B5NUT]

So the fault with my speedo was due to the cluster, as suspected the pins needed cleaning. So stripped out the cluster and took it apart.
1-cluster.jpg

All the pins that I could find on the cluster were cleaned with a some 1000 grit paper and cleaned with isopropanol and then some dielectric grease was applied to the pins.
3-pins.jpg
2-pins.jpg

While I was there I also replaced the bulb in the external temperature display. Got a replacement bulb from a kind forum member (Cheers Dave) and got to work replacing it.
4-temp.jpg

The new bulb is slightly larger that the one fitted and there was an issue refitting so had to get the bulb as close to the board as possible. I've hunted around for some replacement bulbs and found some the right length so ill replace it when I next take the cluster out.
5-bulb.jpg

However for now it's all working, speedo is back to normal and I can see the temperature display again.

Next job on the list is to replace the brake bomb. The fluid level in the power steering reservoir fluctuates quite a lot when the car is first started in the morning, to the point it is bring the warning light on as the level temporally drops below the minimum so setting off the sensor in the reservoir. I had a spare bomb which I have just sent to Pleiades to hopefully be serviced, if that comes back OK then I'll send the one off the car to be serviced and keep it as a spare.

I take it that all I need to do to remove the pressure in the one fitted to the car is to pump the brake pedal with the engine off until the brake peddle goes hard then it can be removed?

[johne]

When my speedo stopped working it was the connections inside the cluster, some of which are just sliding pins through the PCB. The chip that actually drives the speedo is bullet proof but I do have some if it turns out you need one.

[B5NUT]

New sensor arrived today but did not fix the fault, have put the old sensor back in but swapped over the o-ring just so I don't get any new oil leaks. Think I'm going to take the cluster out next need to change the bulbs in the external temperature display anyway.

[B5NUT]

I think I will get a sensor, its only £19 for next day delivery, then will check the connectors under the dash and it that's all OK then I start work on the cluster. Need to change the bulbs on the temperature display anyway.