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Author
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Topic: shifting question
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tc67pony
Journeyman Posts: 12
From: st. louis, mo , usa
Registered: Aug 2001
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posted 08-12-2001 03:29 AM
  
I have a 67 stang with a stock 289, c4, and 2.79 gears. Well when I put the car in drive and get on it. it would shift into 2nd at 40mph, and shift into 3rd at 70mph, and now for some reason it won't go past 60mph into 3rd for some reason. Before if I held the car in 2nd gear it would go to 90mph and now it wont go past 75mph in 2nd when i hold it their. When I hold it in 2nd it screams to about 4500 r's, but when its in drive it shifts at about 3600 r's. Well thats the best explanation i can give. sorry for so long. thanks for any ideas..
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Toronado3800
Journeyman Posts: 63
From: St. Louis, MO
Registered: Jul 2001
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posted 08-12-2001 04:05 AM
On a C-4 how are the shift points controlled? Is there a vacume sensor where that long line between the carb and the tranny could be split? Did you shift quality go to heck as well?
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bluestreek
Gearhead Posts: 827
From: Athens,GA
Registered: Jul 2001
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posted 08-12-2001 02:06 PM
When I had a 68 with a C4, the shifts were controlled by the amount of vacuum that was sensed from the intake manifold to the modulator.. The only way that it should shift faster is to have more vacuum present, like a shorter cam profile, smaller carburetor, higher ingnition timing, etc..,
The place where the vacuum line is reading off the intake may make a little difference in the signal too..Hope this helps,
Dan
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RonnieT
Gearhead Posts: 381
From: Port Allen, La. 70767
Registered: Jun 99
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posted 08-12-2001 08:23 PM
Shift points are controled by a vacuum modulator on the C-4, but this is not his problem, it is shifting!
tc67pony we need a little more info.
What are the rpm's at when the car tops out at 60 mph? If the engine rpms are high, engine screaming, and you are only going 60 in 3rd your transmission is slipping and will need to be rebuilt. If the engine rpm's are not high, the engine just quits pulling, you could have carb, ignition, timing chain, or some other problem going on. Give us a little more info and we should be able to figure this out.
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Ronnie
69 mach1 351W-4V
70 Torino GT 351C-4v with a "shaker"
Mustangs and More Member #23
[This message has been edited by RonnieT (edited 08-12-2001).]
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tc67pony
Journeyman Posts: 12
From: st. louis, mo , usa
Registered: Aug 2001
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posted 08-13-2001 02:54 AM
"normally" shifts into 2nd at 40mph at 3800 rs. and shifts into 3rd at 70mph at 3800 rs. and when i hold it in 1st it'll shift into 2nd at 50mph at 4500 rs, and shifts into 3rd at 90 mph at 4500 rs, but now it shifts in drive into 2nd at 35 mph at 3800 rs, and into 3rd at 60mph at 3800 rs, and when i hold it in 1st it still goes up 2nd at 50 mph at 4500 rs, and when i hold it in 2nd it shifts into 3rd at 75 at 4500 rs. i hope this helps.
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RonnieT
Gearhead Posts: 381
From: Port Allen, La. 70767
Registered: Jun 99
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posted 08-13-2001 09:46 PM
tc67pony, Looking at the shift rpm's and speeds you listed it looks like 2nd gear is slipping in your transmission. The 1-2 shifts stayed pretty consistant, but your mph is down on the 2-3 shift point at the same rpm. You can try changing the transmision filter and adjusting the bands to see if this will help the problem. Are the shifts still "firm" or does it shift soft? You can probably plan on a transmisson rebuild in the future, with some good TCI parts.
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Ronnie
69 mach1 351W-4V
70 Torino GT 351C-4v with a "shaker"
Mustangs and More Member #23
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tc67pony
Journeyman Posts: 12
From: st. louis, mo , usa
Registered: Aug 2001
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posted 08-15-2001 01:16 AM
the trany was rebuilt 30k miles ago, and their is a new filter and fluid just put in 500 miles ago. could the problem be im just not making enough power anymore, just an idea.
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RonnieT
Gearhead Posts: 381
From: Port Allen, La. 70767
Registered: Jun 99
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posted 08-15-2001 10:19 PM
If the engine is turning the same rpm as before, but the speed is lower something is slipping. It may even be the torque converter slipping. Did this problem start after the filter and fluid change? If it did what type of transmisson fluid did you put in it?------------------
Ronnie
69 mach1 351W-4V
70 Torino GT 351C-4v with a "shaker"
Mustangs and More Member #23
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tc67pony
Journeyman Posts: 12
From: st. louis, mo , usa
Registered: Aug 2001
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posted 08-16-2001 03:46 PM
yes I would say it started a month or so after the fluid and filter change. I don't know what fluid it was though.
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RonnieT
Gearhead Posts: 381
From: Port Allen, La. 70767
Registered: Jun 99
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posted 08-16-2001 10:03 PM
I think that the Type "F" fluid is a higher viscosity than the Mercon II fluid.
I will have to look tomorrow in my Texaco Product Manual and verify that. If they put the Mercon II fluid in your C-4 that is designed for Type "F" the pressures are probably a little low and it could cause the torque converter to be slip more.------------------
Ronnie
69 mach1 351W-4V
70 Torino GT 351C-4v with a "shaker"
Mustangs and More Member #23
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