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'91 Transmission Maintenance

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I checked the tranny fluid level today, and although it was right where it should be on the dip stick the fluid color was not bright red but dark red leaning towards brown.  I had it flushed when I first bought it but that was 7.5 years ago and have traveled 10,300 miles (current mileage is 108,340).  There have been absolutely no issues with it to date....shifts when its suppose to, etc.  Would like you folks opinion...get it flushed...leave it alone?? 

Edited by ship
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You stirred my curiosity about how my transmission fluid looks so I went to the garage and pulled out the dipstick. My records indicate my fluid and filter was changed shortly after I got my car in 2007. That was about 29,000 miles ago. The fluid in my car is still bright red and smells normal.

 

If I were you I would be a little concerned about why your fluid is leaning toward being brown instead of red as it should be. Dark fluid, especially if it has a burned smell, could be an indication that something might not be right with the transmission causing the fluid to get too hot. Generally speaking, heat is what causes fluid to turn dark. That heat is usually caused by the transmission slipping too much when it changes gears. My experience is fluid with only 10,300 miles should still be like new. 

 

I think it would be wise to drop the transmission pan and change the fluid and filter. When you, or whoever does the work, removes the pan allow the fluid to pour out slowly so it leaves any small particles in the pan. Then examine any pieces of material you find in the pan closely to determine if they are metal, plastic or clutch material. There should be a magnet in the pan that you can examine to see how much metal it has picked up. Finding a little bit of clutch material in the pan and finding a little metal particles on the magnet is normal at 108,000 if the pan has never been off before and only a flush was done. If you find some larger pieces in the pan you can bet something is going on with the transmission but it may not mean the transmission is going out anytime soon. It is something you want to know about and it might give you some idea of what is causing the fluid to turn brown so quickly.

 

I don't know if your electrically shifted '91 transmission has a vacuum modulator valve on it or not. If it does, a bad modulator valve can cause the transmission shifts to be too soft causing excessive slipping of the clutches between gears. That slipping generates excessive heat in the fluid and can turn it dark even if the transmission is otherwise good internally. When you drive it again take note of how the transmission shifts when accelerating quickly through the gears.  If it seems to just slide from one gear to another instead of having a good firm shift the modulator valve (if the '91 has one) could be the problem.

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Ronnie, as always, thanks for the info and going the extra mile referencing your own tranny.  I will look into re: modulator valve.  Since I can't get under cars any longer, I will contact a very reputable tranny service shop in my home town...they rebuilt the tranny on my once owned '85 Riviera about ten years ago. 

 

Update: the '91 tranny does have a modulator valve....looked it up in the parts and illustrations book.

Edited by ship
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I took my '89 Black in for a tranny filter and change and when they dropped the pan they actually had a piece of the fiber clutch. I watched through the window in the waiting room when the guy dropped the pan and pull the piece out and then show it to another tech. I had them finish and continued to drive the car. I got about another 30,000 miles out of the tranny, but then when the tranny died, it died fast [slipped badly with severe shudders]. 

 But keep in mind I drive a lot of highway miles so that probably gave me extra time. I later swapped it out with a ultra low mileage tranny from a salvage yard [the car 2seaters son has] about 5 years ago and it works great with no problems.

 The Red also got a tranny swap when I did my engine swap. Not so much that it was bad, it just wouldn't shift out of 1st at wide open throttle. I got a fresh rebuild tranny out of a salvage yard and knew I would never be able to swap it out for cheaper ever again. It proved to be a wise decision as the replaced tranny performs flawlessly in every way.

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Had the same type of tranny in my '92 Riviera go on me in CO.  But then again it had 160K on it.  You guys might remember my saga that I reported on back in 2014....shipping it home, securing plane tickets home, etc., etc.

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