C6 transmission issue
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C6 transmission issue
Well guys I have a 1980 f150 2wd with a 351m and a c6 trans. Since I inherited this truck it's always been really high RPMs on the highway. I just assumed that my grandpa had put really deep gears in it. But this morning it was our first freeze and as I drove from home I notice it shift differently and when I got on the highway I was hitting 60mph at about 2100rpm vs the usual 3200. Once it was parked outside my work for 9 hours and it warmed up outside I drove home and it shifted like it usually does and I was back at 3200rpm. Is there something in the trans I need to get looked at that could cause this? The shift from 2-3 has always felt off to me. But when it was freezing this morning it felt right. The truck originally came with 3.00 gears and I'm not sure if they were ever changed.
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Changing the fluid performs miracles sometimes. Pull the dipstick and look at the fluid. Brand new fluid will be a very bright pink on the dipstick. Good used oil will be a red to dark red color. Old fluid will be a very dark burgundy to a brownish color.
If the fluid is really dark, I think it would be worth it to spend the money and change it. I would not go to one of those flush shops, I would buy the gasket and filter and change it by pulling the pan. Pull the pan and see what's in the bottom of it. Some black stuff and some brass sparkles in the oil is normal. Big chunks and big flakes of paper looking stuff is not good.
You can pull the little cover off the flywheel and peek up in there at the flexplate. You can turn the engine around by hand and you may see a hole in the flexplate with a plug in the converter. If you do, you can rotate this to the bottom, and take the plug out and drain the torque converter. Drain it and pulling the pan will get all the old oil out, and it will take around 13 quarts to fill it back up. If you only pull the pan, then it will take about 4 quarts to fill it back up.
If the fluid is really dark, I think it would be worth it to spend the money and change it. I would not go to one of those flush shops, I would buy the gasket and filter and change it by pulling the pan. Pull the pan and see what's in the bottom of it. Some black stuff and some brass sparkles in the oil is normal. Big chunks and big flakes of paper looking stuff is not good.
You can pull the little cover off the flywheel and peek up in there at the flexplate. You can turn the engine around by hand and you may see a hole in the flexplate with a plug in the converter. If you do, you can rotate this to the bottom, and take the plug out and drain the torque converter. Drain it and pulling the pan will get all the old oil out, and it will take around 13 quarts to fill it back up. If you only pull the pan, then it will take about 4 quarts to fill it back up.
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From: Maryland
It definitely sounds like a trans slipping problem when warm, using the calculator on this site, with stock tires, 3.00 gears, and the C6 1:1 top gear, the engine would be turning at slightly over 2100 rpm, which is what you stated when the trans is cold. Try changing the fluid and filter at first, it may work temporarily or for a while, if it doesn't and the trans keeps slipping, it will need to be rebuilt.
Edit:Looks like Franklin posted the same time
Edit:Looks like Franklin posted the same time
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I appreciate the quick responses. It just seemed really strange that It would work regularly one day when it's freezing but never before. I changed they trans fluid when I got the truck but I didn't drain the torque converter.
Laughing Gas
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Wait a minute.
60 mph at 3,200 rpm most of the time, and 60 mph at 2,100 rpm today?
Sounds to me like you've been driving it in 2nd most of the time???
Check your fluid to make sure it's at the correct level and really check to be sure you're actually in 3rd gear. Maybe the shift linkage is misaligned or maybe the down shift linkage is jammed.
Come to think of it, check out your vacuum operated shift module. Make sure it's hooked up to manifold vacuum and that it's not leaking. Pull the vacuum line of the module and if there's tranny fluid in the vacuum line the module is shot.
60 mph at 3,200 rpm most of the time, and 60 mph at 2,100 rpm today?
Sounds to me like you've been driving it in 2nd most of the time???
Check your fluid to make sure it's at the correct level and really check to be sure you're actually in 3rd gear. Maybe the shift linkage is misaligned or maybe the down shift linkage is jammed.
Come to think of it, check out your vacuum operated shift module. Make sure it's hooked up to manifold vacuum and that it's not leaking. Pull the vacuum line of the module and if there's tranny fluid in the vacuum line the module is shot.
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I've made sure it was in 3rd. I just assumed that my grandpa put 4.56 gears cause he towed a 5th wheel with this truck. Fluid level is good and the fluid looks fine and doesn't smell burnt. I think I'm gonna drain the torque converter when I get a chance. I'll look into the vacuum modulator too
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Laughing Gas
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Just because the shifter says you're in 3rd doesn't mean the transmission is in 3rd. You could very well select 3rd but 60 mph at 3,200 rpm really suggests the transmission is in 2nd.
What happens when you let off the gas? Does it slow right down (compression braking)? If so that would suggest the transmission isn't slipping but rather is in 2nd. Also if it was slipping that badly on a hill your speed would drop but your RPMs would remain constant.
Anyway, really curious to know what you find out.
What happens when you let off the gas? Does it slow right down (compression braking)? If so that would suggest the transmission isn't slipping but rather is in 2nd. Also if it was slipping that badly on a hill your speed would drop but your RPMs would remain constant.
Anyway, really curious to know what you find out.
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Alright guys I have a small update. I know I'm in 3rd shifted up from first so I can feel it shift to 3rd. Today the truck was driving high again, 3200rpm at 60 just like always, I the stopped and shut the truck off to get my daughter. When I restarted the truck I noticed immediately the my idle was lower than usual and it was shifting like it should. And even had lower rpm through every gear.
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From: Virginia
Alright guys I have a small update. I know I'm in 3rd shifted up from first so I can feel it shift to 3rd. Today the truck was driving high again, 3200rpm at 60 just like always, I the stopped and shut the truck off to get my daughter. When I restarted the truck I noticed immediately the my idle was lower than usual and it was shifting like it should. And even had lower rpm through every gear.
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Well come to find out my kickdown cable was missing the spring to pull it back forward. Found one that looked about right and tried it out. Been cruising at 2100 rpm at 60 just like I should. I really appreciate the help guys.
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