Hydraulic to Vaccum servo conversion

[Pirvu Eugen]

I spoke with LhdKid about this issue and he suggested to make an excentric pedal adapter
to maintain the same piston travel as before...because installing the pin higher on the pedal will shorten the piston travel..and i dont want this.

[diesel des]

I gave up on the twin servos after having so many leak in my urs4. Using an a6 single vacuum unit now.

Sent from my LG-H955 using Tapatalk

[Pirvu Eugen]

Off... yes... the dual diaphragm one is more complicated and prone to failure as the single one..
Thank you Des for feedback!

[LHD_Kid]

Are the twin ones so prone to failure when they are in their original habitat? I mean, does an S8 or RS6 suffer a lot from servo failure, or is it just when they are messed with?

[Pirvu Eugen]

Dont think so... i searched and nothing came up. Not as the new mercedes ones.
I think that poppet valve rubber thing is not working ok with high rod angles.

[LHD_Kid]

Dont think so... i searched and nothing came up. Not as the new mercedes ones.
I think that poppet valve rubber thing is not working ok with high rod angles.

So, the answer really is to replace the standard fork which connects to the pedal with an eccentric one which can move the pivot point over the required amount to keep the pushrod going straight into the servo unit.

Looks like its between 5 and 10mm, will measure more accurately next week and get something made.

I wonder if just doing this will work, without having to swap the booster out.........

[LHD_Kid]

I've just measured the coupe... the deflection of the rod from straight is around 1mm

I don't think this issue affects the conversion on an S2 for example.....

[Pirvu Eugen]

I measured now at my 200 and the rod deflection is 10mm.
This explains why this failure happens only in C3..C4 chassis with these servos.

[audiman]

This thread is a mess!!! The OP I assume, as its not stated, is converting a LHD car?? Also, multiple people taking about fitting different servos on LHD and RHD non-S2 models!!!!

Can someone give a parts list required to convert a RHD S2 car to vacuum servo??

I am assuming that servo 8a2612105a is the required part and then there is the mounting bracket, is that or not required?

[A80Avant]

This thread is a mess!!! The OP I assume, as its not stated, is converting a LHD car?? Also, multiple people taking about fitting different servos on LHD and RHD non-S2 models!!!!

Can someone give a parts list required to convert a RHD S2 car to vacuum servo??

I am assuming that servo 8a2612105a is the required part and then there is the mounting bracket, is that or not required?

When I posted this I did use the document from the US, so an LHD car which you can see from the attached pdf. I didn't follow what others wrote about the RHD process, sorry

[Bowie69]

B3 no, B4 yes, I think.

When I got mine for my B3 CQ20V I asked that the servo came with the bracket and any pipework to save hassle, however I didn't need the bracket, as my Coupe had one already fitted

[Waje]

Hi Guys,

sometime last year i fitted the a8 d2 brake booster and master brake cylinder in my 7A quattro coupe and i thought it might be interesting for one or the other...

7x8 inch brake booster combined with the 25,4mm master brake cylinder.
the other option would be the 26,9mm i guess. but that would be overkill.


adapter plate needs to be fabricated. otherwise the brake booster will be leaky.




a6 v6 hydraulic steering pump. quite the same pump used for a long time at audi.
a4 b5/b6 or B4 v6 is also the same. bolt on directly to the 7A bracket.


brake booster without grommet. you see these tubes coming out of the brake booster for the bolts.
the "tubes" are not the same level as the brake booster surface. thats the reason for the adapter plate i made.


adapter plate alignment.


difference between the hydraulic spacer (short one) and the vacuum spacer (long one).


adapter rod and the grommet mounted.


adapter plate, vacuum spacer, adapter rod and that kind of fork mounted.


this adapter needs to be fabricated to increase the rod length:


ready for installation:

You can not see the photos, could you upload them again? I'm interested in making the change.

REGARDS

[Tom_]

Guys, i read whole topic, but i am not clever from it I have CQ 20V 7A B3 . I want to change hydraulic to vacuum booster. Someone said A8 D2 , another A8 D3. What is the best solution and not expensive and hard to find? I know that master cylinder could be used oem 7A which is 25.4mm but that vacuum booster bothers me

[Bowie69]

This one, done it myself on same car : 8A2 612 105A

[rxl]

i used brake booster and brake cilinder from audi a8 d2