Gear swap
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Junior User
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Gear swap
Hi guys, saw the thread by Dave 7.3 about the gear swap from 4.10 to 3.55. We've got a '88 F250 4X4 with the 7.3 (no turbo) and C-6. I'm pretty sure it has 4.10 gears, as you can really only drive about 55 mph, and then the motor is wailing pretty loudly. Will taller tires bring the rpm's down, and how tall could I actually go without lifting the truck (wide tires not needed)?
Being a 4X4, we'd be swapping both front & rear gears; sounds like a 1000.00 job to have someone do it? We don't use the truck much (seasonally) and not much heavy hauling/towing at all, sometimes small boat (16' aluminum), but the rig tops out at about 75 mph and rev limiter cuts in. Gear swaps are probably not for the backyard novice, huh? Any idea on mileage improvement from 4.10 to 3.55?
Thanks everybody,
glasstruck
Being a 4X4, we'd be swapping both front & rear gears; sounds like a 1000.00 job to have someone do it? We don't use the truck much (seasonally) and not much heavy hauling/towing at all, sometimes small boat (16' aluminum), but the rig tops out at about 75 mph and rev limiter cuts in. Gear swaps are probably not for the backyard novice, huh? Any idea on mileage improvement from 4.10 to 3.55?
Thanks everybody,
glasstruck
Senior User
Joined: Dec 2003
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From: Grosse Ile Mi.
With out a lift kit you can go up to P285s on the front you may have to shim the front bumper out so it wont rub on the tires.. on the rear you can run p315s with out a problem even on a two wheel drive
Fleet Mechanic
Joined: Sep 2005
Posts: 1,509
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From: Ladner, British Columbia
Those 3:55 gears sure would be nice, they make a big difference. I really notice the difference on fuel consumption between my 91 and 93 even with both truck having OD trannies.
You are right on the cost, you are looking at about $1000 to swap gears and if you don't drive it a lot the payback on fuel consumption is not going to be good.
Seb....
You are right on the cost, you are looking at about $1000 to swap gears and if you don't drive it a lot the payback on fuel consumption is not going to be good.
Seb....
Elder User
Joined: Sep 2005
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From: Delta B.C.
I have an 87 F250 4X4 with 3.55 gears... I am running 315/75/R16 tires, and still find my self looking for 5th gear all the time.... the larger tires helped, but itwas not the final answer...
Are you sure you have 4.11s in the truck?? I was fairly sure most C6s and 4 speeds were 3.55s
I know with 265/75/R16s on mine with the 3.55s, 55MPH - 60MPH was getting up in the RPM range....
Are you sure you have 4.11s in the truck?? I was fairly sure most C6s and 4 speeds were 3.55s
I know with 265/75/R16s on mine with the 3.55s, 55MPH - 60MPH was getting up in the RPM range....
Senior User
Joined: Oct 2006
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From: Bath, Michigan
I'm going to change my truck over to 3.55 gears soon. I figured the best way would be just to buy the whole darn rearend from a similar truck, have it rebuilt and swap them out! So I went on eBay and darned if I didn't find TWO of them in about 5 minutes within about 50 miles of home! $100 ain't bad for a complete rearend (including brakes & springs). Says it only has 40K on it too.
My Truck:
1992 2WD F-250 7.3L 5-spd - 21K on new Jasper longblock, Bought from local University for $1500 - (MSU - 09/20/06). Completely stock as far as I can see - LOTS of new parts on her- 163,829 miles as of yesterday. Now on to tackling Biodiesel!!
My Truck:
1992 2WD F-250 7.3L 5-spd - 21K on new Jasper longblock, Bought from local University for $1500 - (MSU - 09/20/06). Completely stock as far as I can see - LOTS of new parts on her- 163,829 miles as of yesterday. Now on to tackling Biodiesel!!
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Junior User
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Hi guys, I'm not positive the truck has 4.11's. I just assumed so because it wails at 55 mph. The truck was an Alaskan North Slope rig, meaning speed is not important, so I figured it to have the 4.11's. Are you guys saying that going to 3.55's will not bring the rpm's down noticably? The limited speed on the highway keeps us from taking the truck on long road trips.
Thanks!
Thanks!
Senior User
Joined: Oct 2006
Posts: 152
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From: Bath, Michigan
Sure it will drop RPMs!
Changing from 4.10's to 3.55's will drop your RPMs by about 500 @ 55mph.
My Truck:
1992 2WD F-250 7.3L 5-spd - 21K on new Jasper longblock, Bought from local University for $1500 - (MSU - 09/20/06). Completely stock as far as I can see - LOTS of new parts on her- 163,829 miles as of yesterday. Now on to tackling Biodiesel!!
Changing from 4.10's to 3.55's will drop your RPMs by about 500 @ 55mph.
My Truck:
1992 2WD F-250 7.3L 5-spd - 21K on new Jasper longblock, Bought from local University for $1500 - (MSU - 09/20/06). Completely stock as far as I can see - LOTS of new parts on her- 163,829 miles as of yesterday. Now on to tackling Biodiesel!!
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Hotshot
Joined: Feb 2004
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From: Marengo, Iowa
Hey Kleenax, maybe you already know this, but those rea axles you snagged, are they 92 and newer? The speedo reads from the rear axle starting in 92, if you don't get one from those years, you won't have a speedo... I don't know if the abs sensor could work or not, or if it is even in the right place...
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Brett Foote
Senior User
Joined: Oct 2006
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From: Bath, Michigan
Yea, this one that I mentioned is a 94, and my truck doesn't have ABS. At least, I'm pretty sure with the way it brakes that it doesn't! Who's friggin' idea was it to put the speedo gears in the REAR axle anyway? That's 20 miles away in a long-bed!
Hotshot
Joined: Feb 2004
Posts: 11,697
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From: Marengo, Iowa
It's all electronic, so it isn't an issue... if it has ABS, it piggybacks on the speedo. More accurate reading I would guess is why they went there. It did save me a lot of trouble when I planted the Cummins in the 92...
I have seen C6's with 3.55 and 4.10's. My dad's 84 with teh C6 has 3.55, one I was looking at that looked the same had 4.10's. My truck has 4.10 by code, haven't verified, and it is 4 speed. M<y dad's second 84 (2wd) has 4.10's definitely can tell that without verifiying, it howls more than my 86 at road speed... it's a 4 speed. Basically, it can come either way, trans did not decide rear gears.
I have seen C6's with 3.55 and 4.10's. My dad's 84 with teh C6 has 3.55, one I was looking at that looked the same had 4.10's. My truck has 4.10 by code, haven't verified, and it is 4 speed. M<y dad's second 84 (2wd) has 4.10's definitely can tell that without verifiying, it howls more than my 86 at road speed... it's a 4 speed. Basically, it can come either way, trans did not decide rear gears.
Senior User
Joined: Oct 2006
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From: Bath, Michigan
I keep forgetting that you 6.9/4spd guys have non-OD trannies. You may not notice has much difference in RPM as I do with the overdriven 5th gear; haven't done the math on that one.
By the way, what's the deal with putting your "signature file" on this forum? I can't even find a place for it! At dieselstop.com you just go to your profile area and put it in. Here, I have to cut-n-paste off an old post of mine.
My Truck:
1992 2WD F-250 7.3L ZF 5-spd - 21K on new Jasper longblock, Bought from local University for $1500 - (MSU - 09/20/06). Completely stock as far as I can see - LOTS of new parts on her- 163,829 miles as of yesterday. Now on to tackling Biodiesel!!
By the way, what's the deal with putting your "signature file" on this forum? I can't even find a place for it! At dieselstop.com you just go to your profile area and put it in. Here, I have to cut-n-paste off an old post of mine.
My Truck:
1992 2WD F-250 7.3L ZF 5-spd - 21K on new Jasper longblock, Bought from local University for $1500 - (MSU - 09/20/06). Completely stock as far as I can see - LOTS of new parts on her- 163,829 miles as of yesterday. Now on to tackling Biodiesel!!
Senior User
Joined: Dec 2004
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From: Mackinaw, IL
Kleenax: Go to the top of the page and look for UserCP. That is where you edit your signature and profile.
Also. My 88 250 4x4 c-6 has 4:10 gears. Made it difficult to find a new rearend that didn't need to be regeared. 3.55's would be so much better though.
Also. My 88 250 4x4 c-6 has 4:10 gears. Made it difficult to find a new rearend that didn't need to be regeared. 3.55's would be so much better though.
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
Kleenax,
You can only have a signature after 25 posts.
So you will not see the option till then if I remember correctly.
A four speed with 3.55 gears and 31" tires will go 57 MPH at 2200 RPM.
A four speed with 4.10 gears and 31" tires will go 49 MPH at 2200 RPM.
A five speed with 3.55 gears and 31" tires will go 75 MPH at 2200 RPM.
A five speed with 4.10 gears and 31" tires will go 65 MPH at 2200 RPM.
You can only have a signature after 25 posts.
So you will not see the option till then if I remember correctly.
A four speed with 3.55 gears and 31" tires will go 57 MPH at 2200 RPM.
A four speed with 4.10 gears and 31" tires will go 49 MPH at 2200 RPM.
A five speed with 3.55 gears and 31" tires will go 75 MPH at 2200 RPM.
A five speed with 4.10 gears and 31" tires will go 65 MPH at 2200 RPM.
Elder User
Joined: Sep 2005
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From: Delta B.C.
Hmm... that seems odd... I had 265/75/R16s ( 31s) on my truck when I first got it... Its a 4 speed with 3.55s.... At 60 MPH ( 100 KM/H ) I remembered turning like 2600 or 2700...
Right now, with 3.55 gears and 315/75/R16s ( 35s ) I'm at 3000 RPMs at 120ish KM/H... ??? MPH....
Right now, with 3.55 gears and 315/75/R16s ( 35s ) I'm at 3000 RPMs at 120ish KM/H... ??? MPH....