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Justin, so there's no confusion, let's recap Posted by Notnoel [Email]  (#23) [Profile/Gallery]
(more from Notnoel) on Wed, 30 May 2018 07:17:13
In Reply to: Re: Official 1989 Quick Reference Parts Catalogue, Justin VanAbrahams  [Profile/Gallery]
, Tue, 29 May 2018 14:22:32
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You raise interesting points, and no, you are not reading this wrong. I am a scientist by trade, so here are the essentials of my reasoning and an experiment I propose to bring resolution:
1) You are correct, Saab never sold the combination I am discussing, nor could I see that anyone had actually done this and posted about it. Not having a lot of choices in the matter, I went a head and tried it and it seems to be fine.
2) Saab did apparently use the new booster/MC combo with the older calipers in 1987.
3) #2 above, combined with the fact that the cars themselves are nearly identical in weight (which varies model to model)as well as all other dimensions, lead me to conclude that the force necessary to stop the car within safety limits would be similar (size of disk and pad, as well as force applied).
4) Under the assumption #3 above, I noted that people had successfully reported using larger 9000 calipers on the 900, which further encouraged me to believe the tolerances involved were not critical per reasoning #2 above.
5) I agree with your reasoning vis a vis a too small MC could be dangerous. A Saab mechanic I discussed this with told me he never liked the feel of the 87 brakes, leading me to believe the newer MC was likely smaller than required to drive the pistons of the older style calipers (and supporting my feeling that the older MC had a larger fluid capacity/stroke).
6) From its outward appearances, the 1979-86 MC appears to be much larger (its piston length is clearly longer, both in total length and in the spacing of the connections), and outwardly appears to be larger in diameter. However, the only truly important thing is its bore and fluid displacement per stroke, and I'll admit that is currently an unknown.
7) My initial concern was that it was too large and might blow out the seals in the calipers, but that concern was somewhat mollified by item #2. #3, and #4 above. However, your post of yesterday concerning the effects of a too large an MC makes this less of a concern to me now.
8) I've got this installed and have been driving on it since Saturday and I am happy to report that everything feels just fine. It is more than functional (I can't really feel any perceptible difference from the earlier set-up). Perhaps it is a little more sensitive, but that may be psychological since I was driving with no power assist for two weeks).
9) There really aren't a lot of other options out there for us:
9a) Driving without power assist is genuinely frightening (I did it for 2 weeks);
9b) The 87-89 boosters are gone or nearly gone;
9c) Upgrading to ABS isn't really an option either since the ABS accumulator is even more scarce and ABS lines are plumbed differently (with electronics it'd be a royal PITA to install);
9d) Switching to a booster from an entirely different vehicle brings in a whole host of other variables (see item #3, plus issues mounting it into the car)and given the lack of specs would be a monumental experiment.
10) I suppose another obvious option would be to switch over the calipers to match the booster/MC, and while that would certainly be a way to go, it would be a lot of time and expense.
11) The scientist in me thinks there's an easier route. All we really need to know to put this to rest is how much fluid each each MC delivers to each piston under a full stroke. If they are comparable (as item #2 suggests), or the older MC delivers slightly more fluid per stroke (items #6 & 7), then I think we can agree this is an appropriate way around the lack of 87-89 boosters.
12) It should be very easy to get these metrics. All I need is an operational early MC car and a later MC car (and I think know where I can get both). I'll simply bleed one stoke of the MC from each set of calipers into a graduated cylinder and measure the results.
13) No math need be involved, other than comparing the differences in the volumes. I strongly suspect that the early MC is the same bore or slightly larger, and qualitatively, I am already satisfied with the results. I'll post my findings on the board when I've got the data.
->Posting last edited on Wed, 30 May 2018 07:26:57.
, Sat, 26 May 2018 15:38:29
, Sat, 26 May 2018 19:38:31, Sun, 27 May 2018 19:14:35, Mon, 28 May 2018 13:33:36, Tue, 29 May 2018 06:23:36, Tue, 29 May 2018 09:45:37, Tue, 29 May 2018 12:16:57, Tue, 29 May 2018 12:22:01, Tue, 29 May 2018 12:27:12, Tue, 29 May 2018 13:13:45, Tue, 29 May 2018 14:22:32, Wed, 30 May 2018 07:17:13 <-- Viewing This Message, Tue, 29 May 2018 12:49:00, Tue, 29 May 2018 13:01:20
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