Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 2 of 2 Posts

·
Registered
Joined
·
329 Posts
Discussion Starter · #1 ·
Hi guys, I have a random question to ask. Is anyone hear really knowledgable about how the auto gearbox in the 9000s actually works? I understand the concept, and the workings of things like torque converters etc., and clutch bands etc., and how the "mind" of the gearbox chooses to change gear etc.

I recently had my car serviced (150,000 mile) and as part of the service I had the gearbox fluid completely replaced. Before the service, the gearbox ran fine but had a slightly odd gripe in that the change down from 4th to 3rd, while slowing gradually to a roundabout for example, was always pretty jerky. Almost like you'd stabbed the brakes momentarily at the same time as the gearchange. Having changed the fluid it's now much smoother on the downchange. My question is this - why would changing the fluid have this effect? Physically I'm not sure I understand why this would happen. I would be curious to learn as it might better my understanding of what is actually going on in the gearbox!

My other question is this, in third gear what on earth do they mean by partial lock-up? Surely if a mechanically locking device is involved in linking the wheels to the engine, it will take up 100% of the available torque? How can the torque converter carry some torque, and the direct lock-up carry the rest? It seems like an odd concept!

Cheers - Jules
 

·
Registered
Joined
·
172 Posts
As far as I know the torque converter is locked in third and fourth. You will always get a rougher gear change between 3rd and 4th as a result. I'm on my third full blown auto and they all did the same.
However the reason I got rid of the first two was because the gearbox expired. The first symptoms is the roughness increasing between 3rd and 4th and then a few weeks later when going between neutral to drive it became very jerky.
I believe you should change the oil every 30,000 miles although I now do mine every 10,000.
Apparently due to the complex internals of the gearbox and convertor it never drains completely and you normally leave 1/3rd of the old oil in the box.
New oil will run at a lower temp and the viscosity will be thinner hence why when the gearbox is on its way out it proves a temp solution. Gets past the bands inside easier.
If yours is a full blown your are lucky to get 150,000 out of on orginal box.
Hopefully there is nothing wrong with your box and I'm just looking at the bad side!!
 
1 - 2 of 2 Posts
Top