bomb recharge pressure.

[cadiddy]

Hi, I'm looking at getting my brake accumulator recharged by a friend with the means and know how but just want to check the nitrogen pressure that needs to be in it? I think it is about 90 bar which is roughly 2/3 the working pressure of the system I think.
Would just like someone to clarify this if possible.
Cheers
Cadan

[Error404]

No its more like 200 bar IIRC. I am sure there will be some info about it somewhere in the workshop manual, I'll will have a look later

[s2driveruk]

Would he be interested in doing others? I'm sure a few peoples bombs are in need of attention.

[cadiddy]

I was reading on s2 central that system pressure at idle is 140 bar, so if you could double check that Error that would be brilliant.
Hopefully if it all goes well I can ask the chap if he would be interested in doing some more.
Cheers

[twoqu]

On the Type 44 its quoted that the gas pressure of a new accumulator is 78-82bar @ 20C. It also states the operating pressure at idle is 140 bar. The systems are very similar.
Seem to recall that the earlier hydraulic system used on the UR and some BMW models with the seperate bomb sphere was rated at 90bar. Think it was even stamped on it!

[cadiddy]

So if I tell him 85 bar and see how that goes? There's nothing stamped on the canister, apart from the part number.

[Error404]

I checked it out and I stand corrected.
Workshop manual states pressure when new should be 73-77bar at 20c, minimum pressure 30bar at 20c

for reference, the system working pressure is quoted at 140bar

[twoqu]

The figure is also quoted in psi as 1131/1189 which I make a bit lower than the bar pressures!
Not sure what the consequences would be of over charging it. It appears the issues are with the membrane integrity so I guess its better to err on the side of caution. Unfortunately its a bit of an experiment.

[cadiddy]

Well in that case I think I'll say 70 bar and see how that goes, its going in today so I'll let you all know how it's gone when I get it back.
Cheers for your help chaps.
Cadan

[twoqu]

Think I might have gone nearer 75/80bar which is nearer the factory specs.
I guess anything over the minimum (30bar) will be ok. Its just going to be how long the sphere retains the charge assuming its not damaged.

[cadiddy]

Okay, after doing a bit of reading and a lot of thinking I think I'm gunna ditch the hydraulic system for the vac system, I think I have it right in my head as regards 't'ing off the isv line for the vacuum and installing the vacuum servo, but I do have a few questions on areas I'm not so sure on.
Firstly can I use a servo from a tdi 80?
Will the 20v master cylinder mate up to that?
What exactly do I need to do to the pump to disable the brake assist side of things and just have PAS?
It's a 7A engine I intend to do this conversion on.
My reason for wanting to do this is that even if I get the bomb recharged, how long is that gunna last? Not indefinitely that's for sure, also if the hydraulic servo packs up that's more grief more money and another pain in the *** I could prevent by doing this conversion.
Cadan

[Error404]

You need a vac servo, pretty sure all the RHD B4 ones are the same fitment, the one I have here for my coupe is 8A2 612 105 A. 7A master cylinder etc bolts right up. You just need to run a vacuum line and tee in somewhere on the intake (a couple of ideal spots on the rear of the 7A intake manifold).

Pump wise you can either remove the pistons from the brake assist stage of the PAS pump and plug the outlet, or run a single stage pump as fitted to the factory vac assist cars (better option IMHO). Then you just need to plug the fluid return line from the rack where it tee's off for the bomb.

HTH

[A80Avant]

Look on here. There is a guide for the swap

[cadiddy]

So is there a difference between the vacuum servos on diesel and petrols? Looking at the system on my tdi 80 there's a round thing with braided (vacuum?) hoses going to and from it what exactly is it? And the larger diameter rigid hose that comes from the vac servo down the right hand side of the engine, what's this? Also can I use a PAS pump off of the tdi I'm breaking?
I think those are the last of the questions
Cadan

[norheim]

http://nordicaudi.com/

There is a guide under faq.