Re: 1979 900 GLE auto transmission needs warm up - Saabnet.com Bulletin Board
This is the classic symptom of a stuck governor in the Borg-Warner Type 35 and 37 transmissions. The governor body is made of aluminum and the piston sliding inside it is made of steel. The hole in the governor body is machined precisely for the piston, so if any dust from a slipping band or clutch gets in there, the piston will get stuck and won't allow governor pressure to increase with speed. When the transmission gets warm, the governor warms up and the body expands more than the steel piston, so the piston can move more freely in spite of the dust. The solution is to clean the governor.
On the Type 35, which is what your car came with, there should be a governor access hole in the side of the transmission, covered with a cover plate held on by two screws. If this access hole/plate isn't there, you will have to drop the rear pan. The governor is held onto the main shaft by two slotted screws. Once you get it off, you can disassemble it and clean it out. There will be sediment inside all the little passageways.
However, transmission dust doesn't just come from nowhere, and your transmission likely has been grinding itself up for a while. There is likely a slipping band or clutch. Usual culprits are the second gear band, as Bernie suggests, and the front clutch. And it's a feedback loop: the bands and clutches slip, making dust, which sticks up the valves, causing lower hydraulic pressure, which makes for weaker application of the bands and clutches, causing more slipping and more dust. The only permanent solution is to renew the bands and clutches, which requires a full rebuild.
The best solution, therefore, is to limp along until you can switch to a manual. You can clean the governor. You can change the fluid (use only type F, NO DEXRON). You can clean the cooler, which can act as a band and clutch dust filter until it gets saturated with dust and the same amount of dust comes out as is coming in. You can adjust the second gear band, if it hasn't been adjusted already. But at the end of the day, the Borg Warner 35/37 as seen in the Saab 900 is an inefficient unreliable time bomb. With proper service, they can last as long as a manual. Yours probably already has. But neglected or worn out, they are hard to bring back. Harder than switching to a manual. And your transmission is showing the first signs of neglect or wear.
posted by 140.247.10...
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