Hydraulic brake set up, fluid question

[Gavin]

I’ve just finished plumbing in an old 735 H31 hydraulic brake booster system into my e30 (for the reason as to why on earth I would do this see my “ITB’s are GO” thread in the M20 engine section). I have a few quick questions about hydraulic fluid.

The reservoir for the H31 system warns only to use “Pentosin” hydraulic fluid, but I believe this is for reason of the self levelling strut system in the old 7 series my H31 system came out of. So, my questions are as follows:

1. Does anyone know if I can run the same ATF I would normally run through the PS system in the H31 booster?

2. If I have to use Pentosin can anyone tell me if this product is compatible with ATF (am I going to have any weird reactions between the Pen and trace ATF remaining in the system after I drain it)?

3. If Pentosin and ATF no mix’ie mix’ie, how do I best flush the system?

[jlevie]

It has been a while, but... My recollection is that Pentosin and ATF are mutually exclusive. The seals in a system meant for one will be destroyed by the other fluid. If that is the case, you can't pressurize this booster via the PS pump as Pentosin will destroy its and the rack's seals and ATF will destroy the booster's seals. I suppose you could replace the A/C compressor with a Pentosin compatible pump from a 735...