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 Another brake fluid leak
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green96v4
V4 Mad

Canada
737 Posts

Posted - 30 Jan 2019 :  11:11:05 Show Profile Reply with Quote
So I have the large reservoir cap BMC (69-71) that was refurbished in the UK before we emigrated. It started leaking between the BMC and the servo and dripping down onto the engine bay floor, doing wonders for the paint!

took it off and ordered a new seal kit from John Saab and refitted it along with a new piston from a LHD BMC off Tradera, put it all back on and still leaked!

Found a specialist repair company in Ontario who re-chromed the piston and confirmed it no longer leaked, send it back - I left it in my bench vice for a number of weeks at an angle that should have leaked with gravity and sporadically pushed on the piston to move fluid around - no leak :)

Refitted it to the car thinking it was cured, still leaked, AHHHHHH!

Sent it back to the Specialist, they bench tested it again and confirmed it doesn't leak - I told them I wasn't happy with that, so they suggested taking off the servo and sending it to them, did that and they phoned yesterday to say when they mate the servo to the BMC, they feel the "architecture" of the actuator in the servo is "off" and putting angled pressure on the piston causing it to leak...and they're stumped (and they're the Specialists....!!)

and insights? Is there adjustment to the actuator that would change the pressure/angle??
I have chased so much time and money into this and I'm thinking I should cut my loses and abandon it, but if it's a simple fix that someone can share, the beer's on me!

I spoke to Malbrad a while ago and they told me the 69-71 BMC was utter garbage (he's always been a straight talker!) so should I give up on this.....




thanks all!

melle
V4 Guru

United Kingdom
3830 Posts

Posted - 30 Jan 2019 :  12:01:51 Show Profile Reply with Quote
Never heard this before. I have the same type on my 96; I've put a new seal kit in it in 2007, but otherwise never had issue. I was planning on overhauling one this year to swap out the current one, as even with new brake hoses and refurbished calipers, I find brake performance still a bit disappointing. I was thinking of changing to the later type ATE BMC, which has a different servo as well, just because I have a few of them.

www.saabv4.com
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green96v4
V4 Mad

Canada
737 Posts

Posted - 30 Jan 2019 :  13:22:05 Show Profile Reply with Quote
Thanks Melle

I've also sourced a later Servo and BMC (bolt pattern is different on the Servo) it's shipping from the UK as we speak, so I might just cut my loses on this one....
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Derek
V4 Guru

United Kingdom
2187 Posts

Posted - 30 Jan 2019 :  14:31:38 Show Profile Reply with Quote
There can be a similar problem with slave cylinders. The whole item and the piston is shorter and fatter but the piston can still cock slightly in the cylinder when pushed in. This can cause the angle of the lip seal to be compromised and cause a leak. This is usually when it is pushed in but when it returns to rest the angle of the pushrod can still keep it at an angle. This can also mean that the outer end can rub on the bore and score it enough to damage the seal. You won't get this effect when on the bench. The angling of the pushrod will certainly be greater than that of the BMC pushrod unless the fitting of the BMC to the servo is out of line which it might be. If there is any slop in the BMC holes or the servo face is distorted that might lead to the pushrod being a bit out of line. When fitting the BMC it will usually mean the BMC will hang on the studs, but by lifting the BMC it might correct that. All that is a bit of a ramble but it's a bit more than theoretical.

I don't know of anyone who does the following mod commercially but with the slave cylinder piston, you can machine a groove into the outside end a fit an O ring to virtually eliminate the cocking of the piston. I'm not saying that this mod would solve your problem but it might. Some more reading here.
https://www.sw-em.com/hydraulic_clutch_tech_article.htm#Clutch_Slave_Improper_angle
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green96v4
V4 Mad

Canada
737 Posts

Posted - 30 Jan 2019 :  15:18:08 Show Profile Reply with Quote
thanks Derek

I'm wondering if there's any "installation" adjustment, ie can the pedal block or even mounting of the servo have an impact (or can the actuator be adjusted in or out to change the angle? - it looks like the hex/thread suggests there is some potential fine tuning that can be performed.....

If the later model I've got coming from the UK performs and just needs a cosmetic overhaul I think I'm going to swap it out and be done with it. Stephen at Malbrad wrote the large reservoir BMC off as "garbage" so I maybe chasing something that never worked that well in the first place (often wondered why SAAB changed it after only 2 years, but how many times have we all heard "oh if only you had the 72/73/74/whatever-you-don't-have-MY"!!!)

thanks for the responses
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