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Re: Questions about the 1979 99 4-speed gearbox... Posted by Larry West [Email]  (#1140)  [Profile/Gallery]
(more from Larry West) on Wed, 26 May 2010 11:02:02
In Reply to: Questions about the 1979 99 4-speed gearbox..., BAAB  [Profile/Gallery]
, Tue, 25 May 2010 15:15:02
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1978, along with the 99 turbo.
1977 & earlier had a three-gear arrangement to bring the power from the driveshaft to the input shaft. This was only ever a 1:1 arrangement. With the turbo, they wanted to "underdrive" the gearbox by a little (0.8:1 or so). This would have been hard to accomplish with the gears, and so they switched over to the chain arrangement. This allowed them to substitute different sprockets to get various ratios over the years, spanning 0.96:1 to about 0.78:1 (they never did 1:1 with the chain drive).
My last 99 (1980 GLi) had this box, with a lot of miles, and it ran - and shifted - very smoothly. What I'd say is:
If it ain't broke, DON'T fix it. This goes double for the oil in the box.
If you have to change the oil in the box DON'T use Red Line MTL, or any synthetic anything. If you can't source the 70-80 grade GL4 mineral-base gear oil (not GL5, and definitely not with any hypoid additives), just use plain old dino 10W30 or 40 as the manuals recommend.
If you're pushing it with a non-turbo motor, the motor will likely fail many times over, before this gearbox does. It can easily handle the stock 99/900 turbo 'B' motor. This was a time when the engineers at the gearbox office were ahead of the engineers at the engine office (which fell apart in 1980 with the early 5-speeds under the same turbo motors...).
(I hope I got the ratio directions right (0.8:1 vs 1:0.8...). Haven't looked them up in a long time...)
_______________________________________ Current: 2002 9-5 Aero Kombi Cosmic Blue 2000 9-5 SE sedan, Imola Red 1990 900S Rose Quartz, Auto Past: 1999 9-5 LPT Combi 1999 9-5 LPT sedan 2002 9-5 Arc 1990 900 5-speed 1986 900 turbo Convertible 1991 9000 turbo 1980 99 GLi 1986 900 turbo 1986 900 S 1991 900 turbo 1984 900 turbo 1976 99 GL
, Tue, 25 May 2010 15:15:02, Wed, 26 May 2010 11:02:02 <-- Viewing This Message
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