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Re: Bizarre behavior, bad miss in certain gears, reverse AWOL 1 Saabers Like This Post! Posted by JerseySaab [Email] (#666) [Profile/Gallery] (more from JerseySaab) on Sat, 23 Jul 2022 17:34:31 In Reply to: Re: Bizarre behavior, bad miss in certain gears, reverse AWOL, un4gvn1 [Profile/Gallery] , Sat, 23 Jul 2022 14:04:43 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The transmission is a ZF 4HP18 and has no electronics, it is old-school 100% mechanical and hydraulic control. One of the problems we have is that this transmission is at this point nearly unknown in the United States. It was only ever used in a handful of low-volume models in the 1980s and 1990s and almost no one knows how to work on them.
The valve body is extremely complex with a crazy number of valves and springs. (Looks almost like something that came out of a space ship!) Saab used to recommend Lubegard Red additive to prevent control valves from sticking. Broken or weak springs can also affect shifting.
There is a vacuum hose on the trans but I don't know what its function is. Shift quality is controlled mainly by the cable attached to the throttle and that's a critical adjustment.
The transmission in my '97 CSE failed suddenly back in 2016 with over 300,000 miles on it. The symptoms were loss of drive shifting out of 1st gear and no reverse. I swapped out the valve body with a spare but it didn't help. Talking with Eriksson Industries, well-known for Saab transmissions, the problem appeared to be due to a broken band. I wound up buying a junkyard transmission and installing it myself - I lucked out and it still is working well.
Although they have since stopped supporting pre-GM Saabs it might be worth contacting Eriksson to see if any of their tech people have suggestions on what the problem with yours may be.
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