Hydraulic reservoir cap leak

E. Roy Wendell IV erwendell at mac.com
Mon Nov 28 17:59:42 EST 2005

> Hello folks,
> I've read the archives somewhat exhaustively on the subject, and the 
> only
> commonality is that Pentosin does indeed leak from the reservoir  cap 
> some
> times.
> It has been attributed to:
> 1. Bad Accumulators
> 2. Bad Pumps
> 3. Bad Brake Servos
> Rather than throw money wholesale at Gina ('86 5KTQA), could anyone 
> shed
> some light on this?

I second the diagnosis of faulty pump shaft seal. The other components 
of the hydraulic system can't, in theory, introduce air to the system 
as they are all on the pressure side and any sealing problem will cause 
fluid to exit rather than air entering. Leakage of the fluid from the 
top of the reservoir through the vent in the cap is due to foaming of 
the fluid as that's the only way the fluid level can get high enough. 
During normal operation, the amount of fluid entering the reservoir is 
exactly equal to that leaving as fluid is incompressible. The only 
variation is due to thermal expansion of the fluid. As long as the 
reservoir isn't filled above the high mark when warm there should be no 
problem. When you introduce air, the picture changes radically. The low 
pressure side of the system in in the center of the pump body around 
the shaft. When the pistons retract inward under spring pressure they 
take a gulp of fluid and then push it outward toward the check valves. 
Any air in the center of the pump body will get caught up, compressed, 
and then foam like mad once it passes through either the booster or 
rack and returns to atmospheric pressure. I've cured this symptom a 
couple of times by replacing all the pump seals including the shaft 
seal. You'll need a hydraulic press or three jaw puller to remove the 
pulley hub from the shaft and the usual drag link bit and an impact gun 
to get the piston bore caps off. Other than that it's all hand tools. 
You'll need a clean work area where you can lay out the parts in order 
so that you get the shaft shims back in the right spot. While it may 
not be strictly necessary, I also lay out the pistons in the same 
orientation that they came out of the pump so that they go back in 
their original bores during reassembly.

Roy Wendell
Morgantown WV, USA
turbo quattro type 44 times 3

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