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Discussion Starter #1 (Edited)
Hi. I wonder if anyone here might be to help. Recently noticed that my old 1986 900 rear brakes weren't quite what they ought to be, that is that they worked but only rather poorly ('no effort', as my local MOT man would put it). I put on new pads, pads, but no difference. Bled the system, but still no difference. The front brakes are working fine, there has been no brake fluid loss at all in the last ten days, but no matter what, unless I actually get someone to "stand" on the brake pedal, the rear brakes, although they do work some, remain weak enough for me to turn the rear wheels by hand when applied normally. This aside, the only thing I can find wrong with the braking system is that, when first pressed in the morning, the brake pedal produces a small "psss" spongy sound, but then goes back to feeling and staying firm.
The only thing I can think of checking next is the master cylinder, but before I do, I wonder if anyone here might have some idea of what's up with the old horse. Any suggestion would be really appreciated.
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Discussion Starter #4
Thanks for the suggestions.
Don't know about the servo, but if it would affect both front and rear, then the problem must be somewhere else has the front brakes are working fine.But will look into it tomorrow.
About the rear calipers, both sides seem to be working fine.

???
 

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You're testing it with it on a jackstand, engine running and someone standing on the brakes? Because if you're just testing it with the ebrake or something else that might point elsewhere.

Perhaps there is some corroded line somewhere along the way to the back. No real loss yet, just a dribble.
 

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Discussion Starter #6
Yes, tested on jackstands (all 4 wheels off the ground), engine running/off and someone on the brakes. I inspected the fluid lines but can't find any sign of leakage, or much rust for that matter.

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Discussion Starter #7
Ok. So spent some more time re-checking the entire brake system after taking apart and putting back together the master cylinder. From fluid to brake pads via master cylinder to lines and calipers, can't find anything wrong with any part of the brake system, still both rear brakes refuse to work to strength.
A real shame since, as I haven't got the space right now, and the old horse is not really safe to drive as is, it probably mean that time has come to abandon or break it for spares. Terribly sad thing to see another great 8V Saab 900 hit the dust on account of what is probably little more than "lack of a nail". A terribly sad thing...
 

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Now this might scare some people, but you get most of your braking from the front anyway. If you're getting some out of the back and if its a manual, not auto it personally wouldnt be causing me too much concern. I hate to see the 8v go too, love them much more than the 16v. You're not in Toronto, Canada trying to get rid of that car cheap are you? :cheesy:
 

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Is there a load balancing valve in the rear brake circuit? It's supposed to adjust the rear braking effort depending on vehicle load. Should be hooked up to the rear suspension in some fashion. If that is going bad or not hooked up, it might be limiting the rear brakes...
 

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failed brake booster make a "pssssssssssss" sound from what i have read. causes spongyness.
 

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Discussion Starter #11
Am with you about the front brake doing most of the work, Jetman. However, these here rear brakes are really "underpower", as in only really work when you "stand on the brake pedal, and besides, it's MOT time again... Yep, hard to have to let go of the old 8v. My other car is a 1990 16v i and it's nowhere near as great a drive (a good cruiser once you get to 60MPH and above for sure, but little more than a glorified tank when pulling out or at low speed). And no, sorry, this Saab is across the ocean from Toronto, Canada, in Gwynedd, North Wales.

Thanks cdaly, but no, no load balancing valve on this one.

Er, woywitka, I'm sorry but am not too sure what you mean by a "brake booster"? Servo?

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Brake booster is above the actual brake pedal. But in my experience when it goes, the pedal becomes extremely stiff.

Ah yes MOT, well in my parts you have a one time inspection when you first register the car and after that, well, you have my cars;).
 

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Discussion Starter #13
"... in my parts you have a one time inspection when you first register the car and after that, well, you have my cars ..."

Now someone's telling me. To think I nearly moved to Quebec a few years back. Had I been told about this, well... :)
 

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There is quite a trade in hot certifications around here as well. I'm torn between public safety and the notion of government fundraising:evil:
 

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Discussion Starter #15
"...There is quite a trade in hot certifications around here as well. I'm torn between public safety and the notion of government fundraising..."

Then again, in spite of what some say, caring about public safety and struggling with the notion of government fundraising aren't mutually exclusive. Still, take the case of an old Saab almost perfect in all aspects bar its rear brakes, how many folks would be willing to believe that it can be driven safely when getting it properly certified and stamped by an authorized licensed mechanic every year would provide such a boost to the national economy?
You got to figure these things out.
 

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I guess that's my problem. I dont really care what other people think. I know what my limits and the limits of my car are. I suspect that your country's constant MOTing keeps the new car market brisk. At least it also keeps a lot of working folk (mechanics) fed too.
Pitty, still, those brakes cant be sorted. Have you considered taking it to a specialist? Could be they could sort it out rather cheaply, given you've already established that the major components (the big $) are in decent working order?
 

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Discussion Starter #17
"... I suspect that your country's constant MOTing keeps the new car market brisk. At least it also keeps a lot of working folk (mechanics) fed too...."

Absolutely.

About taking the car to a specialist, whatever way you look at it it's a big $ affair in these parts. But maybe I'm not quite ready to give up on her yet. I'll sleep on it and probably have another go at the weekend...;)
 

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I just cant imagine what's been missed. It sounds like you've been very thorough.
 

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Discussion Starter #19
"I just cant imagine what's been missed..."

Neither can I. But, as they still underperform in spite of everything, something's got to be wrong somewhere. So maybe I'll hit on it on next looking. Maybe I'll get there by trying to figure out how the front brakes can work great while the ones at the back are uniformely weak. The answer's got to be in there somewhere. Even though I can't fault it, I keep coming back to the master cylinder. Could be the pressure to the rear brakes lines isn't building enough in there.
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travisq said:
I keep coming back to the master cylinder. Could be the pressure to the rear brakes lines isn't building enough in there.
This seems unlikely. The brake system is dual circuit {unless you have ABS in which case it's triple circuit}, front left and rear right in one circuit, front right and rear left in the other. If there was a master cylinder fault, you would see one front and the opposite rear being weak rather than both rear.

OTOH, if you have ABS, is the ABS light coming on when you switch on? Is the ABS pump running? The ABS system uses pressure stored by the pump for the rear brakes. If that was not working, you would see reduced rear brake performance...
 
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