Hi all, I've got a 1979 Ford Fairmont and this is the closest thing I can find to a forum for my car. I heard there are a few Fairmont owners among you, and the Fairmont is a Fox. So I thought I'd introduce myself (well, introduce my car at least) and ask a question that has been troubling me.

"Gertrude" is the aforementioned 1979 Ford Fairmont station wagon (yes, with wood paneling!). She's got the 3.3L (200ci) inline 6 with a C3 three-speed automatic behind it. I got her on Leap Day this year with 56K on the clock and she's been my daily driver since April. She is a blast to drive and very reliable except for one little problem.

The engine doesn't brake when the automatic transmission engages its clutches to shift, causing the engine to rev excessively between gears. It particularly happens when shifting from second to third; from first to second it's less noticeable. Also when climbing a hill at slow speeds, sometimes she shifts back and forth between second and third like she just can't decide which gear she wants to be in. This can be very frustrating on an uphill ramp when I'm trying to enter the highway. I've been babying her, not wanting to cause the little OHV engine to spool too much (I don't have a tach, I'm just going by feel).

Could this be a vacuum or mechanical linkage problem? I found the vacuum line going to the transmission housing; the rubber is new, it's not blocked, and it's firmly attached. All vacuum lines in that cluster seem to be shipshape. Has anybody else encountered this problem? Once in a while Gertrude will shift smoothly with no revving, usually when the engine hasn't warmed up yet. Any ideas as to where I should look?

Sorry for writing a novel, I wanted to present a clear picture.
 
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Davedacarpainter

I think I've messed my pants
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This might be a simple as adjusting the bands on the transmission. Got an inch pound torque wrench.

On the other hand, it's an automatic and my voodoo transmission skills stop at the band adjustments.

Though, if it sat a good while, it could be it.
 
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Moosee1955

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Sep 30, 2016
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I'm no automatic expert, but it sounds like something's sticking in valve body of trans. If the previous owner didn't service it, possible your valve body may be all gummed up. Not allowing plungers and springs to catch and release. I would take a chance and pull pan/ filter. Replace fluid, but I would get another rebuilt valve body. Before you do ,warm engine, pull stick and smell fluid. Hopefully it's not burnt. If it is I wouldn't drop fluid/ pan. If your valve body's misbehaving, your bands, and clutches won't function right. Oh yeah like Dave said, check band adjustment if adjustable. Keep us posted.


Sent from my iPhone using Tapatalk
 
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90sickfox

Wasn't a pretty sight...and I've got big hands
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If you let off the gas between shifts does it help ?

Everyone here has given good advice. Check fluid....change fluid and filter. Check band adjustment, vacuum lines, and kick down cable.
 
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5.0specialist

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Jul 10, 2016
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Revving during the shifting process itself? In that case, it sounds like your transmission is slipping. When the clutches slip, it kinda goes into neutral before it finally shifts. Like wooooweeeewoooo.
 
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Knowbody

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Sep 4, 2016
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Sounds like it's flaring between shifts. Common issue with worn bands, but also common with a bad vacuum modulator or the vacuum hose to the modulator.

Make sure the vacuum hose to the modulator is good. Just because it looks good, doesn't mean it is. It can collapse and cause this flaring between shifts. It's easy to replace the vacuum hose, and cheap, so you might as well do it while you're under the car. Also it must be hooked to full manifold vacuum, not ported vacuum.

Next, make sure the vacuum modulator is good. It's got a diaphragm inside, so you shouldn't be able to blow through it, but usually if the diaphragm is bad there will be trans fluid inside the vacuum hose. Easy to spot, and doesn't taste as bad. New modulators are cheap, so if the hose is good or new, and you've checked the modulator and it's still acting funny, I'd just replace it with a new one to be sure.

If that doesn't fix the issue, you're probably looking at adjusting the bands or possibly a rebuild. Good luck!
 
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Thanks, all! I have a good many things to check, then. I should add that the transmission fluid is and has been clean, full, and red--not burnt. I have already dropped the pan and changed the fluid and filter. There weren't any alarmingly large chunky bits in the pan. I didn't do a full tranny flush, just a drain and fill. I also adjusted the intermediate band already, using a torque wrench--it actually had been adjusted too tight. I had to detach some linkages in order to get room to swing the wrenches and I wonder if I didn't get them back on correctly. 90sickfox, I always let off the gas when the engine revs, then she shifts, then I slowly apply gas again. If I keep on the gas, she revs very high and often tries to backpedal into second gear again.

I wonder if the bands should be a little tighter than specified in the Haynes manual due to wear and tear? Also I will check the vacuum situation, test the diaphragm. The vacuum line I looked at doesn't go directly to the manifold, either, it goes to a cluster on the firewall, so I will try hooking that up more directly. The Haynes manual has one paragraph on adjusting the shift linkages; I just have to figure out what and where the heck the kick-down rod and its return spring are.

Let's hope it's a linkage or vacuum issue and not the valve body (eep!)
 
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Knowbody

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That "cluster" on the firewall is a vacuum block, and it should be full manifold vaccum. If you follow two of the other larger vacuum hoses off the block, one should go to the power brake booster, and the other to the intake manifold. "Ported" vacuum is usually on the carburetor body or carburetor base plate. If one of the vacuum hoses off the block on the firewall is cracked, missing, or collapsing, it could cause this issue as well, since your vacuum modulator hose is fed off the common block.

With that low of miles, and it seems like a well kept car, I'd suspect it's a minor issue. Good luck!
 
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89gtsleeper

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May 20, 2016
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Had almost identical issue with my 88 5.0 with a stock aod. It would slip really bad going from 3 to 4. All I needed to do was tighten my tv cable. It was super loose. Don't know if this at all translates to your setup, but thought I'd share anyway.
 
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I know it's been a while, but I'm putting this down for the record in case it may help someone some day.

Part of the problem was user error. I scored a copy of the glove box owner's manual on eBay and read it. I know, I know, I drove the car for over a year without ever having read the manual--shame on me! I learned that when climbing a hill at low speed, manual shifting is strongly recommended. Using this technique has yeilded great results. Moral of this story: Read the dang manual!

Still, the engine flared somewhat during shifts. I replaced the vacuum modulator and checked all vacuum connections, transmission bands, etc. Then I took the car to a reputable transmission shop to check everything over. They said all external connections, modulator, bands, etc. are good and that the problem is likely due to worn pistons. I am unsure whether they meant worn engine pistons causing vacuum inconsistencies on the intake stroke or if there are some sort of pistons within the transmission. Auto transmissions are beyond my understanding. At any rate, I decided that the flaring is annoying, but not $900 worth of annoying, so I'll live with it until the day comes when it needs a complete rebuild.