hard shifting
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Junior User
Joined: Feb 2006
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hard shifting
Hello, i have a 1984 f-250 diesel, my question is it seems to run up to much RPM's and then shift very hard. i think/wish it would shift smoother. I was wondering if there is something i should look at or change or adjust to smooth it out. I just changed trans fluid. Any help would be great
Fleet Mechanic
Joined: May 2005
Posts: 1,575
Likes: 11
From: Puyallup, WA
Hello - this was a normal situation with the early diesels, at least as far as the higher rpm than expected before shifting.
There is a logical mechanical design reason for the higher rpms - and that is that the C6 as used behind these diesels, while a very strong transmission, is simply not capable of handling a large amount of low speed torque. Both Ford and Dodge had to either rpm limit, or horsepower limit there earlier offerings to make the transmissions (727 torqueflight in the Dodge) last.
Drives you craxy though (at least it did me) - no shift from first to around 25 mph, correct?
As far as the hard shift, well without feeling it firsthand, hard to say if it is too hard or not, a shift improvement kit may have been installed at one time, but I could not say. Do not expect a soft GASOLINE engine shift though. Your diesel produces signifigantly more torque at a lower engine speed, so in is imortant to get the trans shifted faster to keep the clutches / bands from burning during the shift overlap.
David
There is a logical mechanical design reason for the higher rpms - and that is that the C6 as used behind these diesels, while a very strong transmission, is simply not capable of handling a large amount of low speed torque. Both Ford and Dodge had to either rpm limit, or horsepower limit there earlier offerings to make the transmissions (727 torqueflight in the Dodge) last.
Drives you craxy though (at least it did me) - no shift from first to around 25 mph, correct?
As far as the hard shift, well without feeling it firsthand, hard to say if it is too hard or not, a shift improvement kit may have been installed at one time, but I could not say. Do not expect a soft GASOLINE engine shift though. Your diesel produces signifigantly more torque at a lower engine speed, so in is imortant to get the trans shifted faster to keep the clutches / bands from burning during the shift overlap.
David
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Junior User
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I think this shift is pretty extreme, I actually have to let out of it a bit to get it to shift and yes it acts just like a shift kit BAM! hits very hard. but i boiught it off my neighbor who has never had any trany work done. It revs up very high when accelerating fairly quick like pulling out onto a highway and is actually slowing me down due to it not shifting soon enough and i have to back off of it a bit to let it shift sooner so that i can pick up forward speed and not just RPM's
Senior User
Joined: Sep 2005
Posts: 306
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adjust the flp on the pump the ip this is the thing that has two vac lines coming out of it this is what tells the mod valve on rhe tranny to shift turn it up to the hood side will make it softer just mark it as it is now and start doing the deed till you get it where you like it mine shifts so smooth that sometimes i wonder if it shifted at all but it will work
Fleet Mechanic
Joined: May 2005
Posts: 1,575
Likes: 11
From: Puyallup, WA
Custom1 - sounds like you should take a look at the vacumme modulator , or the adjustment of the switch as suggested by dwaymar. it may be that your vaccumme source is kinked or plugged also, so make sure that you indeed have vaccume at the switch.
Do not let this trans shift early nor have the shifts feel like butter. You should feel a nice positive shift, not harsh, but positive with little gear overlap (the slower the shift, the more you are in "two" gears at once and are slippling your clutches / bands. This will eventually lead to glazing and slippage, and then you will be rebuilding your trans!)
You should not "bang" into the next higher gear though. That risks breaking a shaft, etc. Once again - a rebuild is in order.
When these trucks were newer and there were a lot of them out there, it was always a fine line to keep these transmissions in good operating condition, but it is very doable, and for a long life.
About the only thing these trans were really lacking were two more gears.
David
Do not let this trans shift early nor have the shifts feel like butter. You should feel a nice positive shift, not harsh, but positive with little gear overlap (the slower the shift, the more you are in "two" gears at once and are slippling your clutches / bands. This will eventually lead to glazing and slippage, and then you will be rebuilding your trans!)
You should not "bang" into the next higher gear though. That risks breaking a shaft, etc. Once again - a rebuild is in order.
When these trucks were newer and there were a lot of them out there, it was always a fine line to keep these transmissions in good operating condition, but it is very doable, and for a long life.
About the only thing these trans were really lacking were two more gears.
David
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Junior User
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Dwamar, this adjustment you are telling me about, the man i bought it from showed me an adjustment to make on a switch that was on the top front of the engine, like on top of the intake, he told me to loosen the back screw and roll the switch forward toward the front of the truck a little and it would soften it up, but i diddnt believe him.
does this sound correct? he had it rolled all the way up or back. sitting here now i cant remember just what it looked like but it souinds like what yu are saying. it is a very simple to get to and adjustment to make. what do you think does this sound right? i was just afraid to make adjustments on something i wasnt sure of and diddnt want to take his word for it. but now mabey he was correct
does this sound correct? he had it rolled all the way up or back. sitting here now i cant remember just what it looked like but it souinds like what yu are saying. it is a very simple to get to and adjustment to make. what do you think does this sound right? i was just afraid to make adjustments on something i wasnt sure of and diddnt want to take his word for it. but now mabey he was correct
i ain't rite
Joined: Mar 2005
Posts: 65,449
Likes: 5,518
From: Marlboro Mental Hospital.
check your vacuum pump. i bet it is only drawing about 16-17 inches of vacuum. the trans vacuum modulator needs at least 19 inches to function properly.
i just went through this last year with my 88. it was fine when it was a 5 speed. then i put the C/6 in it, and it did the same thing, no shift till i let off the throttle, then it slammed in gear. a new vacuum pump, and a proper adjusting of the injector pump vacuum control switch, and i am shifting like normal now.
i just went through this last year with my 88. it was fine when it was a 5 speed. then i put the C/6 in it, and it did the same thing, no shift till i let off the throttle, then it slammed in gear. a new vacuum pump, and a proper adjusting of the injector pump vacuum control switch, and i am shifting like normal now.
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Senior User
Joined: Sep 2005
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yes this is the flp it has two screws on the ip do yourself a big favor make it as it is now then start adjusting to the hood side if you go to far you will know cause you will have a caddy shift you want a firm shift but not something that will rattle your neck the softer you accel the smoother the shift don't be afraid to tinker cause you will never learn and the only stupid question i ever heard was the one that was never ask so feel free to ask away someone on this site will have a answer as my old dayy alway said if you can't dazzel them wit brilance then baffle them with BS hope all works out if not then ask again
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Joined: Jun 2006
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From: On A Lake
I just had my tranny rebuilt , new computer, new FIPL, some wireing was corroded (didn't really need the computer, I reckon)
It sometimes shifts like what your describing and other times its smooth - dunno
It sometimes shifts like what your describing and other times its smooth - dunno