How to change transmission fluid and how often?

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by Terrorizer, Nov 2, 2010.

  1. Terrorizer

    Terrorizer SHO or GTFO

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    I have a few questions about changing the transmission fluid on my 1990 MTX SHO.

    1. I removed the bolt in the side of the transmission housing with an extension and put my finger down an inch or so and didn't touch the transmission fluid. Should the transmission fluid be filled up to that hole?

    2. How often should the transmission fluid be changed? I checked both my owners manual and service manual and neither mentioned a service interval or draining procedure, just how to refill. I would think something like a transmission would need new fluid periodically just like an engine needs oil changes. Also, does a manual transmission have a transmission fluid filter?

    3. Is there a drain plug on the transmission for draining the transmission?

    4. Does the differential share fluid with the transmission or is it separate?

    thanks for any info!
     
  2. LOUDSHO92

    LOUDSHO92 Club Mod Staff Member Sponsoring Member

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    1. Yes should be to the top

    2. I dont know if there is an interval. Maybe every 100k or when you do a clutch. There is no filter. The gears just sit in the fluid.

    3. No you need to add one.

    4. All the same.
     
  3. ViPER1313

    ViPER1313 SHO Member

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    In regards to #3 - you don't **have** to add a drain plug, although it is recommended. Search on the forum if you want to go through the hassle.

    You can also drain the transmission with a piece of rubber hose and a vacuum pump through the fill hole on the side. You can get about 95% of the fluid out like this.

    I don't recommend removing the bolt that looks like a drain plug - it holds in a spring (or ball bearing, I forget) for a shifting fork??... if I recall correctly. I do know that if the shifter moves while the bolt is out the item will shoot out of the transmission and you will be in a world of hurt.
     
  4. Terrorizer

    Terrorizer SHO or GTFO

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    I used the one that goes in the side that has the square opening, I used a ratchet with no socket on it. Did I use the right plug?
     
  5. gmorrell

    gmorrell Never been a noob...

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    On the forward face of the case? Yep, that's the fill plug. If the transaxle is completely filled, you should be able to put your fingertip into this hole and feel fluid just barely below it.

    If you want to install a drain plug, here's some directions. They were written by an old SHO sage who by now should be dead and buried.
    http://www.shotimes.com/php-bin/mod...le=article&mode=thread&order=0&thold=0&sid=93

    There is a flange head bolt on the transaxle case with a 13mm hex, this is the shift fork interlock retaining pin. Removing it will allow you to drain about 1/2 the fluid from the transaxle, BUT, if you move the shift linkage while this bolt is out, you're screwed, and the transaxle may need to be dis-assembled to realign the shift fork mechanism.
     
  6. jayro

    jayro SHO Member

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    I would definatly recommend installing a drain plug. Easy to do and makes changing your fluid 100 times easier. Plus if you decide to try different fluids to see which works best in your trans its a huge time saver. Just my 2 cents
     
  7. itwonder

    itwonder SHO Member

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    Don't fear installing the drain plug as instructed on the Shotimes link post above by Gary. It is easy to do, and it makes changing the fluid a cinch. When you refill, Mobil 1 Synthetic ATF is recommended. Some prefer others, but Mobil 1 is a consistent forum favorite for the MTX.
     
  8. Terrorizer

    Terrorizer SHO or GTFO

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    I have come to the conclusion that I am going to eventually drill a drain plug and drain all of the fluid and fill it with Mobil 1 synthetic. In the mean time I want to top it off since I can tell it is considerably low right now. I don't know what kind of fluid is in it now, I'm assuming it hasn't been changed since most people don't ever change their transmission fluid. Would topping it off with mobil 1 be a problem if its mixing with non synthetic? If mobil 1 is a problem what should I use? The service manual says to use ford motorcraft but is there an alternative I can buy at my local parts store?
     
  9. LOUDSHO92

    LOUDSHO92 Club Mod Staff Member Sponsoring Member

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    I would just go with regular ATF Mercon fluid. If you are just adding I would go with the regular till you can do a drain and fill.
     
  10. Terrorizer

    Terrorizer SHO or GTFO

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    Is "Mercon" a type of transmission fluid used by all brands or is it only made by motorcraft? Also, is ATF safe to use in a manual transmission?

    Thanks for any info, I've worked on cars my whole life but I'm not very familiar with transmissions, I don't think I've ever had to change the fluid before.
     
  11. Devin

    Devin SHO owner

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    I'm not sure where the name came from but Mercon (and Dexron Mercon) are used by all types of cars.


    Edit: I was wrong... Mercon is a Ford name it seems, and Dexron is mainly GM.
     
    Last edited: Nov 3, 2010
  12. notbange

    notbange ---/\===\/---

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    But they don't call it Dexron III anymore. It'll now be on the shelves as "classic atf" or "dex/merc" because GM won't license the dexron III name now that they're on to Dexron VI. Something like that. But you won't find a bottle labled dexron unless it's old.
     
  13. LOUDSHO92

    LOUDSHO92 Club Mod Staff Member Sponsoring Member

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    Mercon is Ford Specification. Most ATF meet the specs for it.

    ATF is the fluid called out for the SHO MTX.
     
  14. RonPorter

    RonPorter Old Dude

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    I use an old vacuum brake bleeder hooked to my compressor. Not useful for brakes (INO) but great for sucking tranny fluid out of the fill hole.

    On fluids. When the trannies were new, the old ('89-'90) "brass" synchro trannies used gear oil, the newer "paper" synchro trannies wanted ATF-type fluid.

    Back a bunch of years ago, I got a used tranny ('91 with 93K miles, or a '93 with 91K miles....I forget which). Appears that the fluid was never changed. I went through three fluids before I found one that let it shift well. Synth ATF didn't work, GM Synchromesh didn't work, and I finally tried cheapo AZ Coastal gear oil, and it then shifted just fine.
     
  15. jedhead

    jedhead SHO Member

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    I installed a drain plug on my transmission and use Redline D4.

    Bob
     
  16. JRA2000TL

    JRA2000TL The Complainer

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    Here you go: http://www.shoforum.com/showthread.php?t=27845

    You can use this method until you get a drain plug intalled.

    I don't like drilling into the car if I don't have to (and if you don't like the "one shot to get it right" risk), you can rig up something like this. I haven't done a plug because I'm afraid of screwing it up.

    I did something similar to the procedure in the link. I got a 1/4 or 1/2" piece of radiator hose (one of them fits perfectly in the hole--I forget which size), and I ran it up through the top of the engine, attached a funnel, tied it to the top of the hood and filled through there.

    To evacuate the old tranny fluid, I used a Tempo Oil Boy oil pump (bought it for changing the oil on my jetski).
     
    Last edited: Nov 4, 2010
  17. RonPorter

    RonPorter Old Dude

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    I have been unwilling to drill a hole right into the aluminum. If it could be done right with a steel or brass threaded insert, it might be OK, but if you strip out that hole, you start creating more problems. Sucking it out with a vacuum pump is easy and doesn't take too long.
     
  18. itwonder

    itwonder SHO Member

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    If you are going to use the suck it out method, then drive the car first so the debris particles will be suspended in the fluid. Otherwise, you just leave all the bad stuff on the bottom.

    Fears expressed about drilling and tapping the drain hole are severely overblown. Unless you are an utter idiot, it is a simple job. Drill and tap for a 1/8" pipe thread plug. If you somehow totally botch the job, you can get somebody smarter to help you drill it out for a 1/4" plug. The drain plug is far superior because all the junk sits on the bottom.
     
  19. gmorrell

    gmorrell Never been a noob...

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    Don't fear the drain plug Ron, mine's huge, ;) but is now somewhat redundant because of the scavenge fitting for the cooler pump.

    [​IMG]
     
  20. SHOtime2511

    SHOtime2511 CGP

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    I'd reccomend changing the fluid at 20-30K intervals.
    100k is a long long time to have the same fluid.

    Sooner if you autoX/road race.
     

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