C6 problems
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C6 problems
I have a 1987 Bronco with a 302 and C6 trans. The problem is when I drop it into gear, it drops my rpms alot and almost kills the motor. It feels like the trans is fighting the motor, as if it were a 5 speed and you didnt release the clutch. I've searched and searched and haven't found any answers. I did the band adjustment on the drivers side, and the vacuum modulator is hooked up properly and is not leaking. Any ideas?
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I just put the motor in after a fresh rebuild, everything is new. It's close to tuned in, no misfires and it runs strong in park, revs up nice and quick and idles good. I noticed something else funny about the trans last night, put it on jack stands and at idle the trans is spinning the tires 25 mph in drive but only 15 mph in first, so I would think it's starting in second gear. However, I do feel 3 distinct shifts in drive, at about 35 and 55. I know I need to adjust the modulator because that's awful high, but I don't think that would be causing my current problem? I think I'm missing something stupid here....
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It takes quite a bit of engine torque once you select drive with the brakes on. Make sure the engine timing is good and there are no vacuum leaks.
Are those shift speeds when up on stands or on the road? Only worry about shift points when road testing and make sure you have full manifold vacuum to the trans.
Are those shift speeds when up on stands or on the road? Only worry about shift points when road testing and make sure you have full manifold vacuum to the trans.
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I should explain that this motor is mildly built and has a holley 4150 600 cfm carb on it. I do not have any vacuum leaks that I know of, I pull a steady 16-18 at the manifold. I've got the timing set to 6 BTDC, and and idle is 675ish with trans in drive, but about 2000 in park which seems awful high. It still seems to me that it just takes an awful lot of brake pedal to stop this thing in drive, I'm just not sure where to go from here now.
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I understand that, but the book specifically says to adjust idle in drive. If i adjust to say 900 in park, then when I put it in gear it'll be at 300 and die. So what am I missing here? So aren't I stuck with adjusting it in drive, and then living with where it sits in park? I've got to be missing something.
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Post Fiend
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From: Lost
Sounds like you either have a vacuum leak, or the torque converter in the trans is going bad. It shouldn't drop RPM like that.
I thought you couldn't get the idle to go any lower than 2000 in park/neutral, and therefore misunderstood the issue.
I thought you couldn't get the idle to go any lower than 2000 in park/neutral, and therefore misunderstood the issue.
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Post Fiend
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You say mildly built, did that include a cam? If so are you confident that the cam timing is correct? Are you sure that 6 degrees BTDC is correct for the ign timing? Have you tried spraying carb cleaner around the intake manifold and carb base to check for vacuum leaks?
What is the history of the torque converter? Was it OK before this engine was installed. Was it properly seated in the trans before the engine was bolted up?
With a no load idle speed of 2000rpm it is going to take a lot of brakes to hold it back.
What is the history of the torque converter? Was it OK before this engine was installed. Was it properly seated in the trans before the engine was bolted up?
With a no load idle speed of 2000rpm it is going to take a lot of brakes to hold it back.
Last edited by Lazy K; Apr 6, 2010 at 12:46 PM. Reason: wrong question
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Rebuild did include cam, and I am absolutely confident it is correct, I degreed it to be sure and have done it before. As for 6 degrees, I have no idea if thats correct, I have been playing around with it but it hasn't made a difference with this problem, just sort of going off the old cars with 302 and C6's being 6 degrees, so I'm using that as a baseline. You did make me think of something though, Lazy. When I installed the motor, It was a pain to get the TC lined up because the studs were hiting the flexplate. I have done motors before, but they have all been bolt on TC, so I figured the studs on this one were too long. Maybe It is not seated all the way after all? What should I expect the rpm SHOULD drop when going from park to drive? Thanks for all the help so far... (O, and the trans is a rebuilt by who knows who, the sticker on the side says it was done May of 2008, it worked fine before I pulled the motor.)
Post Fiend
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At normal operating temp and idle speed of say 850rpm in Park I would think that would drop to 600rpm or so in Drive.
As for ign timing 6 degrees BTDC is right for a carbed motor with a distributer that has mechanical advance and vacuum advance. The later engines with EFI would be timed at 10 degrees BTDC with the computer disconnected.
You say that when fitting the engine the converter studs seemed too long. Did the engine and trans fit tight together without needing to be drawn together with the bellhousing bolts?
As for ign timing 6 degrees BTDC is right for a carbed motor with a distributer that has mechanical advance and vacuum advance. The later engines with EFI would be timed at 10 degrees BTDC with the computer disconnected.
You say that when fitting the engine the converter studs seemed too long. Did the engine and trans fit tight together without needing to be drawn together with the bellhousing bolts?
Hotshot
Joined: Oct 2002
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From: The Big, Oregon
6º at 2000rpm is about 2º AFTER TDC at idle, so your timing is retarded way too far. Get the idle down, set the timing to 8-10º, and give it a try then. If it pings, back the timing off a hair, if not you may want to advance a little further.
Cargo Master
Joined: Jun 2003
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From: Somewhere Saskatchewan
But
Did you have the convertor out?
If the input shaft was removed it could have been installed bassackwards.
There is a longer spline on one end.
If it was installed wrong the convertor will not seat properly and will push the turbine against the cover.
If the input shaft was removed it could have been installed bassackwards.
There is a longer spline on one end.
If it was installed wrong the convertor will not seat properly and will push the turbine against the cover.
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The motor was timed at the correct rpm, right after i did the break in period for the cam, and then I started messing with this trans problem. I did not have the input shaft out of the trans, so I dont think thats the problem, it worked ok before. I did have to draw the engine and trans together with the bolts, but whoever had the trans out installed the mount backwards and it was holding the trans to far back, so its hard to say. I have the mount flipped the right way now. Lets say the TC is not in all the way, could that cause this problem, and is anything going to be damaged in there? And the TC was never out, but it did sit for a while with no motor, so it could have slid. *Sigh*. Sounds like that trans is coming out this weekend.
