C900 transmission - Forward and Reverse at the same time

[Geoff]

My dad called me today and said that he went to drive his '93 900S but when he started the car he heard what sounded like a loud rattling bearing. It went away when he depressed the clutch pedal so at first he thought the throw out bearing had gone bad. But then when he tried to back the car up it went back a few feet and then started going forward. The same type of thing happened when he tried going forward in 1st gear.

He said he's seen this happen on another car that a co-worker had. Has anyone else seen this? It sounds like 1st and reverse are selecting simultaneously and since they use the same gear... I'm wondering if there's something that can be fixed through the side cover on the transmission or if it's something that will take more effort to fix (i.e. rebuild).

[Crazyswede]

Problem with reverse idler perhaps?

[DeLorean]

I'm betting the pinion bearing popped apart, really odd stuff can happen when that goes on

[Geoff]

Yeah I was hoping it was a known failure that had something to do with the gear selector and some strange engagement issue, possibly to do with the little lever for the idler. But Jeff's point about the pinion bearing sounds pretty likely because that could cause all types of axial slop which could result in those two gears engaging. If I get a chance at some point I'll look at my disassembled box and see if I can come up with any hypotheses.

I think he'll probably get a box he pulled out of his '88 SPG put into the car.

[DeLorean]

I saw one once that had a failure on the needle bearigs between the counter shaft and the main gearcluster (the one piece 4 gear bit) - rides on a roller bearing and a needle bearing at the other end. That really made a mess. broke all shift forks, and would lock up at low speed. There was not a single piece that could be re-used from that transmission - though I think the car may have been driven extensively after it started going wrong.

[Rallyho]

Hey Geoff-

This past summer the S&R box selected a couple of gears at the same time, not sure which ones. Turns out that the big nut on the gear cluster shaft backed out letting the gears mesh wrong. Not sure why/how the nut backed off...but it did.

[Geoff]

Hey Mike, I had forgotten about that. Groo showed me the nut and it had been re-used so many times that the staking area on it didn't have much left to stake in and bite. I bet something like that happened on this car...

[Bennie]

This past summer the S&R box selected a couple of gears at the same time, not sure which ones.

Off Topic!!

I keep reading about S&R boxes on the forum and i do not have a clue what these are? Maybe a quote from someone that explains it?

[Crazyswede]

This past summer the S&R box selected a couple of gears at the same time, not sure which ones.

Off Topic!!

I keep reading about S&R boxes on the forum and i do not have a clue what these are? Maybe a quote from someone that explains it?

S&R is Sport and Rally. Back in the day when Saab was a lot more involved in rallying and motorsports they had a catalog of parts for sale to the customer called the Sport and Rally catalog. You could buy everything needed to build essentially a factory rally car which the dealer could even fit to your car if you were so inclined. The S&R gearboxes are built with stronger gear cases, stronger gear sets with very specific racing gear ratios, limited slip differentials etc. Today these gearboxes are somewhat rare...they can be built from scratch but are expensive. However they are worth their weight in increased competitiveness.

[Rallyho]

Yeah Geoff...it was definitely well-used. It's also possible that my forgetting to turn on the trans cooler pump the year before for 8 stage miles could have contributed to the thing getting hot and melting out the loktite...who knows.

It on the slate for a rebuild before the upcoming season.

[Bennie]

Thanks, now we need info on what there used to build these boxes so we can build it!

[Crazyswede]

Thanks, now we need info on what there used to build these boxes so we can build it!

You will want a chill cast 4 speed case, the appropriate gearset, a limited slip differential. If you want to go further you can install a steel differential cover, solid steel or welded up inner drivers. You will need the appropriate primary drive chain ratio and you may want the appropriate ring and pinion. Expect to pay about $5000 for the gear set, $1500 for the ring and pinion, $1000 to $2000 for the differential. Expect to pay anywhere from $4000 to $10,000 for an original box depending on its level of build. All the boxes are dog boxes in that they have no sychros. The early ones have a lot of dogs and are a bitch to shift. The later ones have fewer dogs and are easier to shift. The original boxes had helical gearset which run quieter and are stronger but harder to make. I think there are some straight cut gearboxes out there now though...make a lot more noise but a lot easier to make the gears.

There are several threads on this site and a lot of info on these on the internet.


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