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Discussion Starter · #1 ·
Could anybody give me an idea as to the likely cause of the speedo failing on my 1997,saab 9000 cse. Soon after the failure, the care now stalls on braking, the revs fall to zero on braking causing the engine to cut out.

Is there any single fault that could explain all these problems occuring at the same time?
 

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Hi, Zed, and welcome to Saabscene.
Failure of the speedo drive will account for all of these problems simultaneously. As well as driving the speedometer, the speed signal is also used by the engine management system and loss of this signal will cause the symptoms you describe.

The fault is commonly one of three things:

1) An electrical problem - the speed transducer mounted on the gearbox produces an electrical signal (there is no mechanical cable as in other cars) and a broken cable or, more likely, corroded connector near the transducer can cause loss of speed signal. However, this often starts as an intermittent fault, while yours sounds like a permanent one.

2) A mechanical problem - the small nylon drive gear mounted on the transducer may strip or fall off and leave the transducer with no drive. The part is cheap and replacing it is not a huge job. It is documented somewhere on this site.

3) Another mechanical problem - much more expensive, unfortunately. The large nylon drive gear in the gearbox which drives the smaller one may have failed. This requires dismantling of the gearbox to replace. A really good garage will take at least 3 hours just to remove and replace the gearbox (most will take quite a bit longer), plus however long it takes to dismantle it and replace the gear. A Saab dealer is more likely to prescribe a reconditioned gearbox as they end to avoid dismantling gearboxes themselves.

My '96 Aero suffered from the first problem shortly after I bought it. A new connector cured the problem.

My '95 CSE has apparently had a reconditioned gearbox fitted by a Saab dealer just 1K miles before I bought it, to rectify the third problem.
 

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Discussion Starter · #3 ·
Thankyou very much for your reply, i spoke to saab dealer this morning and he explained (in less detail), something along the lines of what you have said. I will be hoping that it is a straightforward job and wont require dismantling of the gearbox. Thanks.
 
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