converting viggen to ng900/og9-3 brake master/booster - The Saab Link Forums

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Old 09-22-2013, 05:53 PM   #1
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converting viggen to ng900/og9-3 brake master/booster

First question some of you might be asking is "why?". The primary motivation for me was cost and availability. Viggen boosters are almost twice the price ($750 or so), frequently must be special ordered from Europe, and in my experience with two viggens, BOTH have eventually had the original boosters fail resulting in bad vacuum leaks that made the cars stall under braking.

But, you might then ask, isn't the viggen system bigger/better/upgraded? Not really. Both it and the stock systems are more than capable of locking up viggen brakes, which I confirmed firsthand with the ng900 race car from the other thread. It has stock 1997 booster/master paired with viggen disks and caliper brackets, and the brakes are not only fine, they're great. I've heard that the decision was about pedal feel more than performance; they wanted it to not require much effort to apply heavy braking. To me, the viggen system feels more mushy than effortless. To each their own.

The first viggen, the booster started leaking years ago, before I had the race car with the hybrid brakes, and I played it safe with the OEM part. The second time was on the silver car I had just, just finished rebuilding and hadn't even finished break-in on yet when I found this latest irritation. I should probably fix it before I drive the car hard again. Hey... bad vacuum leak, lean running, maybe this is why it blew up in the first place and I'd just never noticed before.

If you try to buy all new catalog parts, which I did for the most part because I didn't know what I was in for, you will need to be meticulous. Now that I've done this swap the hard way, my advice would be to start with a donor ng900 or og9-3 and take EVERYTHING you need from the same car, because there are a lot of slightly different parts.

The left hand drive viggen booster is actually from a right hand drive 9-5 turned upside down, and vice-versa for the RHD market. I hadn't considered beforehand that the vacuum lines were special to make this work, and indeed they are. These cars have a lot of different brake booster vacuum lines. Behold:

- Naturally aspirated manual LHD ng900/og9-3
- Naturally aspirated manual RHD ng900/og9-3
- Automatic (NA and turbo shared) LHD ng900/og9-3
- Automatic (NA and turbo shared) RHD ng900/og9-3
- Turbo manual t5 (one line with check valve) LHD
- Turbo manual t5 (one line with check valve) RHD
- Turbo manual t7 (venturi) LHD
- Turbo manual t7 (venturi) RHD
- Viggen LHD
- Viggen RHD

There are also several different brake boosters and masters. I don't know about LH/RH differences with these, but at minimum each of these three has a special booster-master combo.

- ng900, og9-3 1999 and 2000
- og9-3 2001 and 2002 (and 2003 cv)
- Viggen

Then there are the reservoirs. If you order a new master from the catalog, it will not come with a reservoir attached unless it explicitly says so, and you'll need one of those because the viggen reservoir is different. Be warned that the fluid level indicator is incompatible between the reservoirs, so your viggen plug that used to go to the sensor integrated with the reservoir will not plug into your replacement reservoir cap's socket. I just left it unplugged, but if this bothers you, you could snip the connectors off of both and re-solder. As far as I can tell the "sensors" on both are just a float that closes the circuit when empty. Piece of cake. Since unplugged and full are both an open circuit, no red warning triangle will haunt your dash if you leave it off.

Then there are the hard lines that connect the master to the TCS controller. These lines are all the same diameter, but there are two significant differences. First, on the viggen, the master has the same M14x1.0 flare nuts for both the front and back cylinders on the master, while on the other cars the front nut is M14x1.0 and the back nut is M12x1.0. Second, the viggen lines are bent into a different configuration for fitment. You COULD replace the big flare nut on the back line with a small one and re-flare the line, and then bend them both to hook up to the right places, but it's infinitely easier to steal the lines off a donor car, which are already bent to fit and have the right hardware.

In the end I ended up with a used booster, new master and new reservoir from an ng900, and used master to TCS hard lines from a 2000 9-3. And my viggen feels great.
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Old 09-23-2013, 09:33 AM   #2
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So when I need to do this just go to the junkyard and pull a booster,master,resevoir and the hard lines to the ABS distribution thingy?

I have a 99 and therefor no TCS.
Originally Posted by Delorean
- pretend you are watering delicate plants...
Originally Posted by SAABseanSCANIA
can be prone to failure due to increased localized stresses in the hole penetrations
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Old 09-23-2013, 01:33 PM   #3
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Yeah, that's the short answer.

It's worth noting that viggen brake rotors and caliper brackets on a 9-3 brake system gives it more front brake bias; moving the point where the brake pad grips the rotor further away from the hub increases its mechanical advantage slightly. I don't know if the stock viggen setup made any attempt to compensate for this with a different fluid pressure bias than the 9-3 master, or whatever, so putting the base master/booster on a viggen might be doing something similar.

Braking loads the front wheels and unloads the rears. In theory too much front bias combined with an abs system that is not expecting to deal with it (or no ABS) will result in the rear wheels losing a lot more grip than intended and the car will be unstable under braking. For a race car that's probably what you want anyways, maximum stopping power and let the driver figure out how to keep it under control.

In practice I believe that the ABS system favors stability over absolute stopping power (as virtually all factory ABSes do), to the point where any of these combinations is well within the safety margins. Neither the viggen nor the race car feel unstable under braking to me.
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