We Still Don't Know What Made That Noise on the Saab

"Urambo Tauro" (urambotauro) 05/14/2018 at 12:00 • Filed to: saab 900, project, wrenching

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But here’s the progress we’ve made so far.

Before draining the engine or gearbox, we took a chance and ran the engine one more time. The noise had disappeared right before we hurriedly shut it off, and sure enough- everything sounded pretty normal when we fired it back up. But once the engine warmed up a bit, we started to hear a bit of a rattling sound that seemed to come from behind the “primary” cover.

You see, on these Saabs, the clutch connects not immediately to the input shaft of the transmission, but to a “primary” shaft with a set of sprockets on it. Three chains then transfer power down to sprockets on the input shaft of the transmission, and the rest of the transmission (and the differential) is laid out underneath the engine. (Basically, the top of the gearbox doubles as the engine’s oil pan.)

So we decided to focus on the gearbox and its primary drive first. We didn’t have a 12mm allen key to remove the drain plug, so we removed the side access covers to drain most of the oil out. My brother removed the hood, electric fans, & radiator, placed a jack under the front of the gearbox, and unbolted the front mount integrated into the primary cover from the chassis. The cover+mount could then be removed from the transmission.

Alas, nothing looked out-of-place. I was honestly expecting to find a loose link or two here, which would have perfectly explained the noise we heard. But alas, all three chains were intact. The tensioner seemed fine as well, although to be fair, we don’t have a reference for how much tensioner extension is too much. So we can’t quite give it a clean bill of health quite yet. Perhaps we should proceed with removing the tensioner, chains, and sprockets in order to get a look behind the sprockets? It’s kind of a pain, and I don’t want to waste time on a wild goose chase...

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But hey, since the side covers were open anyway, we could at least take a minute to try to find why it wouldn’t go into 5th gear. I’d like to accomplish something this weekend.

I’d often wondered if the surface tension of oil (10W30 in this case) would keep things from getting rusty when something sits for over a decade. As we peeked inside, we found no signs of rust or moisture whatsoever. The oil was dirty, but not cloudy or milkshaken. Just dark. And all the hardware inside looked relatively clean, too.

With the side access covers out of the way, we moved the shifter around to help get a sense of how the linkage was supposed to operate. There was a finger that swept from side to side as the shifter was moved through Neutral. At rest, it settled in a brass pocket on the end of what we soon realized was the 3/4 shift rail, ready to engage 3rd or 4th gear. When the shifter was moved towards Reverse, this finger swept over into a brass pocket on another shift rail. This pocket was stamped with a big “5”, and it moved forward when shifted into Reverse, but it would not budge the other way to engage 5th.

But there was a lever that pivoted when this rail was moved from Neutral to Reverse. And it pivoted in such a way that it seemed like the lever was going to hit a wall before ever allowing the rail to move the other way, towards 5th gear. We were starting to wonder if that number “5” was a red herring...

My brother consulted a Saab group on Facebook with some very helpful folks (including fellow Opponaut Akio, who had a similar problem on !!!error: Indecipherable SUB-paragraph formatting!!! ). It turns out that despite the shift pattern displayed on the shift knob, 5th and Reverse positions were NOT supposed to be on the same plane. We were never going to find 5th gear by simply moving the shifter forward from the Reverse position.

So that brass pocket stamped “5” was only for Reverse, and had nothing to do with 5th gear after all. There was another pocket between the brass pockets for 3/4 and R, but this one was grey, which is another reason why we had overlooked it until now. I had just assumed that it was a “gate” to help separate the shifter positions, making them more distinct and impossible to overlap. Besides, the shifter didn’t seem to want to move forward into 5th once the finger was lined up in that grey pocket anyway.

But behind the other side access cover was the 5th gear selector fork, and I carefully placed some prybars between that fork and the case to help engage 5th. I put some pressure on it, and just as I thought I was starting to lean into it a little too hard, it clicked into place. The grey “gate” had moved rearward, and 5th gear was now engaged.

We put it back into Neutral, and shifted in and out of 5th a few more times. There was still some resistance at first, but it seemed to fade away with each shift. Before long, we were able to row through all gears with equal effort.

In retrospect, it seems all the more silly to have ever thought that 5th and Reverse would be on the same plane. Sure, the shift knob was a little misleading, but there’s a lock-out collar below the knob which must be pulled up in order to access Reverse. For these past few months, I’d thought it awfully strange to have such a lockout preventing one from engaging 5th gear. Turns out, that was never the case at all, and 5th gear can be found by moving the shifter as far to the right as it will go without pulling up on that collar . Now we know.

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So we managed to achieve one victory over the weekend. Now, it’s back to that noise . Maybe we’ll have to take those chains and sprockets off of the primary drive after all, even though nothing looks wrong from here.

I did pick up a 12mm allen key so that we could remove the gearbox drain plug and drain the rest of the oil out. Lo and behold, the drain plug is magnetic, and... well, it caught something.

Mostly very fine particles, but a few distinct chunks, too:

Well that’s not good. Maybe not catastrophic... but an unpleasant sight, all the same. !!!error: Indecipherable SUB-paragraph formatting!!! gives us good a reason to double-check the reverse idler gear, which might explain the broken chunks, but I don’t think it has anything to do with the rattling sound we heard. (Dang, shoulda recorded it...)

We still haven’t drained the engine oil though, so maybe we should do that first. I just really thought that we were onto something when the rattling seemed to be coming from the primary chain area. Huh.

Curiouser and curiouser...

RamblinRover Luxury-Yacht > Urambo Tauro 05/14/2018 at 12:43

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Am I allowed to make fun of Saab for using two single chains for timing instead of one double row like sanity would suggest? Because I want to do that.

Spanfeller is a twat > RamblinRover Luxury-Yacht 05/14/2018 at 13:06

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Nah, first rule of comedy.

Never.
punch.
down.

Urambo Tauro > RamblinRover Luxury-Yacht 05/14/2018 at 13:07

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I’m just glad they’re not belts.

RamblinRover Luxury-Yacht > Urambo Tauro 05/14/2018 at 13:19

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*begins plotting timing belt setup with toothed belt *and* V-belt which also drives oil pump, because the toothed belt isn’t hefty enough*

Akio Ohtori - RIP Oppo > Urambo Tauro 05/18/2018 at 01:28

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Somehow I didn’t put 2 and 2 together on that facebook post haha. Well glad you got 5th back and yes, oops, reverse and 5th aren’t inline. I guess we/ I just assumed everyone knew that.

Urambo Tauro > Akio Ohtori - RIP Oppo 05/18/2018 at 09:39

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Haha, yeah I’m not on Facebook but my brother is. He was showing me some posts on the Saab group, and I couldn’t help but recognize some of the pics you shared as having been posted here, too.

I’ve never had a hard time finding 5th before, nor have I ever had a need to shift directly between 5th and reverse before on any car, so I haven’t developed a notion of whether or not it’s normal for them to be in line with one another. I just went with whatever was on the knob, as my car’s shift knob does actually indicate an offset.

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