c6 question
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Junior User
Joined: Dec 2007
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c6 question
I have replaced the speed sensor and the diaphram on my c6 tranny. whats the rpms that your getting at about 55mph. I seem to think that its not shifting into 3rd but my buddy is saying it is. I am getting it in the 2300 range to go 55mph. I just want to make sure I am not going crazy. I know that it is a 3 speed but damn. thats some serious rpm out of a diesel to cruise at isnt it?
1987 f250 6.9 diesel
c6 tranny 2wd
67,000 orig miles
1987 f250 6.9 diesel
c6 tranny 2wd
67,000 orig miles
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Junior User
Joined: Dec 2007
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stock im guessing. I just bought my truck 2 weeks ago. It is a solid truck, just have to get a couple kinks worked out of it. I am a stickler for my vehicles operating as they must. I just read in another section that these "screamed like banshees."I assume they would due to the fact they are 3 speed but WOW! 2300 rpm at 55 thats a little extreme.
Posting Guru
Joined: Jan 2003
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From: Munroe falls, Ohio
My guess is you have 4.10 gears and you are in third gear. What does the door jam sticker say under axle? What about the metal tag that may or may not be still bolted on the diff cover.
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Junior User
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everything is bone stock. it says 410 on the diff. i think its ok but i was freaking out when I saw the rpm gauge. I think that the gauges on it are sorry as hell. they say one thing but dont sound like it. Im going to get some new gauges all the way around the truck. the sending units in the tanks suck. they dont register and the temp gauge never moves. I assume that all the stock gauges are garbage from everything I have read around this forum. This is the most informative forum out there IMO. Thanks everyone for the help.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
As the old saying goes: Well thaaars your Problem!
I had the exact same setup when I got my truck, C6 and 4.10s. Keep in mind, these trucks were designed when the american national speed limit was only 55MPH, and if you follow posted speeds, it will comfortably cruise with 2300. But it can be real sinking feeling to hit the rev limiter at only 70 mph
. not to mention the noise.
I swapped the stock 4.10s for 3.08 aftermarkets (my first mod on the truck), and couldn't be happier, but being the nut case that I am, I built an E4OD for it as well, even if the speedo only goes up to 85
.
I had the exact same setup when I got my truck, C6 and 4.10s. Keep in mind, these trucks were designed when the american national speed limit was only 55MPH, and if you follow posted speeds, it will comfortably cruise with 2300. But it can be real sinking feeling to hit the rev limiter at only 70 mph
. not to mention the noise.I swapped the stock 4.10s for 3.08 aftermarkets (my first mod on the truck), and couldn't be happier, but being the nut case that I am, I built an E4OD for it as well, even if the speedo only goes up to 85
.
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Post Fiend
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From: Nutter Fort, WV
Actually the fuel guage, tach, and speedo on mine reads fine.
The ammeter, oil pressure and coolant temp are worthless.
Mechanical oil pressure, temp gauge and a volt meter is a very good investment.
The ammeter, oil pressure and coolant temp are worthless.
Mechanical oil pressure, temp gauge and a volt meter is a very good investment.
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Laughing Gas
Joined: Mar 2006
Posts: 1,083
Likes: 1
From: Fitzpatrick Alabama
With 4.10 gears, 2300 sounds about right. If it was stuck in 2nd, it would be wide open at 55 mph or so, around 3300 rpm. I've never had any problems with any of my gauges on my 88, but on my 84 the temp and oil pressure don't work, but I just let it ride, don't worry about it.
Senior User
Joined: Mar 2007
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Here is a quick link for RPM calculation tool that I use at differentials.com Gearvendors.com has charts with the ratios of the gears for the transmisssions.
http://www.differentials.com/calc.html
http://www.differentials.com/calc.html
5th Wheeling
Joined: Dec 2007
Posts: 41
Likes: 0
From: Santa Clarita, California
Dave Sponaugle....I think you meant an electrical voltmeter guage, not mechanical...right? The first two were correct as mechanical though.
Beerman2therescue,
I have the 86 crew with 6.9, c-6, and 4:56 gears! Let's talk about the revs at 65mph. I'll be swapping out for the minimum of 3:73's, possibly 3:54's. I'm not towing anything that heavy and I like to hear the radio and myself think on the freeway.
1Saint is pretty close with the revs, but he did not anticipate converter slippage on the older c-6. They don't have lockup converters. Your revs will be about 2% to 5%higher.
Just an F.Y.I.
86crew4me
86 F350 Crewcab, 4x4, 6.9L, C-6, 4:56 Gears - Restoring
86 F250 Reg Cab, 4x4, 6.9L, C-6, 3:54 Gears - Thrown rod - On Hold
86 F250 Super Cab, 4x4, 6.9L, Manual trans, Banks turbo, G.V. O.D. - Rollover
86 F250 Reg Cab, 2wd, 7.5L, Manual trans - For Sale
93 Ford F150 Lightning - Black - Stock
64 Ford F100 - 400M, C-6 - Awaiting restoration
Beerman2therescue,
I have the 86 crew with 6.9, c-6, and 4:56 gears! Let's talk about the revs at 65mph. I'll be swapping out for the minimum of 3:73's, possibly 3:54's. I'm not towing anything that heavy and I like to hear the radio and myself think on the freeway.
1Saint is pretty close with the revs, but he did not anticipate converter slippage on the older c-6. They don't have lockup converters. Your revs will be about 2% to 5%higher.
Just an F.Y.I.
86crew4me
86 F350 Crewcab, 4x4, 6.9L, C-6, 4:56 Gears - Restoring
86 F250 Reg Cab, 4x4, 6.9L, C-6, 3:54 Gears - Thrown rod - On Hold
86 F250 Super Cab, 4x4, 6.9L, Manual trans, Banks turbo, G.V. O.D. - Rollover
86 F250 Reg Cab, 2wd, 7.5L, Manual trans - For Sale
93 Ford F150 Lightning - Black - Stock
64 Ford F100 - 400M, C-6 - Awaiting restoration
5th Wheeling
Joined: Dec 2007
Posts: 41
Likes: 0
From: Santa Clarita, California
Considering my truck originally had 3:54 gears, and the speedo was never recalibrated for the 4:56 gears. The speedometer is useless.
I did a check of my mileage by traveling a known distance repeatedly over several days. I calculated it at about 11 mpg. Not good. I'm hoping with "Gear Vendors" overdrive unit, it should drop my revs back down really close to the 3:54 gears. Hopefully I can see 15 to 18 mpg out of the truck.
The Turbo should help also. I would really love to see 20mpg on the highway and 15 to 18 around town. Well see....
I did a check of my mileage by traveling a known distance repeatedly over several days. I calculated it at about 11 mpg. Not good. I'm hoping with "Gear Vendors" overdrive unit, it should drop my revs back down really close to the 3:54 gears. Hopefully I can see 15 to 18 mpg out of the truck.
The Turbo should help also. I would really love to see 20mpg on the highway and 15 to 18 around town. Well see....