Axle swap
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Junior User
Joined: Mar 2006
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Axle swap
Hey all.
I currently have an 1988 F250 diesel, 5 speed, and stock 3.55 gears. There is, for sale in my area, a rear end from an F350 complete with springs and drums. He tells me it came from a 1987 4X4, and tells me the ford dealer told him that it is a limited slip unit according to the tag info. How can I find out for sure? I will also assume that it will fit regardless of what motor and tranny it was with, or does that matter as well?
Finally, if I take it, I would want to put disc brakes on it. I've read about some coversion kits from other threads on here, but what does a compelte disc brake package cost for something like that? I want discs because the old Ford drums I currently have like to hang up when cold and it makes for some interesting driving in slippery conditions, like when it snowed last week and coming through a down hill S curve with cars all over the place. I assume that a rear disc brake will also get me better braking when loaded with materials, which is what I'm after.
I currently have an 1988 F250 diesel, 5 speed, and stock 3.55 gears. There is, for sale in my area, a rear end from an F350 complete with springs and drums. He tells me it came from a 1987 4X4, and tells me the ford dealer told him that it is a limited slip unit according to the tag info. How can I find out for sure? I will also assume that it will fit regardless of what motor and tranny it was with, or does that matter as well?
Finally, if I take it, I would want to put disc brakes on it. I've read about some coversion kits from other threads on here, but what does a compelte disc brake package cost for something like that? I want discs because the old Ford drums I currently have like to hang up when cold and it makes for some interesting driving in slippery conditions, like when it snowed last week and coming through a down hill S curve with cars all over the place. I assume that a rear disc brake will also get me better braking when loaded with materials, which is what I'm after.
Post Fiend
Joined: Oct 2007
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From: Faibanks Ak.
You need to measure it very well if it came off a cab and chassis it WILL NOT work the frames were a different width. If it came off a pickup that came from the factory with a regular dually box with the fenders it will work. This was a very rare to be factory dually and 4x4 not sure they were even built.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
Measure your axle, back plate to back plate.
Now measure the dually axle, in the same location.
A dually axle is 4" wider than a SRW axle.
If it left the factory with a pickup box installed, the frame is 37.5" wide.
If it left the factory as a cab and chassis, the rear frame is 34" wide.
Pickups had 3" wide rear springs, cab and chassis had 2.5" wide rear springs.
The axle under a cab and chassis is the same width as a SRW pickup, but the narrow springs and frame let duals clear the springs.
A cab and chassis axle will not bolt up to a pickup without moving the spring perches, and then you would have a SRW pickup axle that could not run duals.
Transmission or transfer case makes no difference.
I have seen several disc conversions, and most of them are expensive.
You have to watch which conversion you use, so you still have a parking brake, not all conversions are equal.
Does your truck have RABS?
Not sure if the 87's had RABS or not.
Now measure the dually axle, in the same location.
A dually axle is 4" wider than a SRW axle.
If it left the factory with a pickup box installed, the frame is 37.5" wide.
If it left the factory as a cab and chassis, the rear frame is 34" wide.
Pickups had 3" wide rear springs, cab and chassis had 2.5" wide rear springs.
The axle under a cab and chassis is the same width as a SRW pickup, but the narrow springs and frame let duals clear the springs.
A cab and chassis axle will not bolt up to a pickup without moving the spring perches, and then you would have a SRW pickup axle that could not run duals.
Transmission or transfer case makes no difference.
I have seen several disc conversions, and most of them are expensive.
You have to watch which conversion you use, so you still have a parking brake, not all conversions are equal.
Does your truck have RABS?
Not sure if the 87's had RABS or not.
Posting Guru
Joined: Dec 2005
Posts: 1,528
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From: Peterborough, Ontario
Measure your axle, back plate to back plate.
Now measure the dually axle, in the same location.
A dually axle is 4" wider than a SRW axle.
If it left the factory with a pickup box installed, the frame is 37.5" wide.
If it left the factory as a cab and chassis, the rear frame is 34" wide.
Pickups had 3" wide rear springs, cab and chassis had 2.5" wide rear springs.
Now measure the dually axle, in the same location.
A dually axle is 4" wider than a SRW axle.
If it left the factory with a pickup box installed, the frame is 37.5" wide.
If it left the factory as a cab and chassis, the rear frame is 34" wide.
Pickups had 3" wide rear springs, cab and chassis had 2.5" wide rear springs.
Post Fiend
Joined: Oct 2007
Posts: 10,501
Likes: 5
From: Faibanks Ak.
I have a 79 srw F350 with dually adapters so when a dually rear came along for a good price I snatched it up. I now jerked the rearend out and slid the new one in and there was noway I could use it and it came out of the same model, they will work in the old highboys though. I happened to have a 69 flatbed that needed a rearend so it wasn't wasted.
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Junior User
Joined: Mar 2006
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Okay, it looks like this axle will fit my truck and should bolt in easily. The only other thing is how my mileage will be effected by installing taller gears. I guess with the 4:10 ratio I'll be able to pull a little more weight at the expense of a little highway speed and mileage. I guess the bottom line is this:
Will the expense of buying this axle and having it installed be worth the gains in traction, rear wheel torque, and the larger spring pack?
The guy is asking $250.
Will the expense of buying this axle and having it installed be worth the gains in traction, rear wheel torque, and the larger spring pack?
The guy is asking $250.
Post Fiend
Joined: Oct 2007
Posts: 10,501
Likes: 5
From: Faibanks Ak.
Whoa you will not gain traction with duals you actually lose some.
You will be able to haul more weight and there is more take off power after you are running a few mph there is not a lot of gain in pulling power it will slow your topend down but with the 5spd it isn't bad. If you are loaded a lot or do a lot of stop and go driving you might see an increase in mpg.
It is easier on the tranny, ujoints, driveshaft etc. with the 410 gears over your 3.55's
Many people think you have more traction with the duals, but on any slick surface you will have a lot less traction.
You will be able to haul more weight and there is more take off power after you are running a few mph there is not a lot of gain in pulling power it will slow your topend down but with the 5spd it isn't bad. If you are loaded a lot or do a lot of stop and go driving you might see an increase in mpg.
It is easier on the tranny, ujoints, driveshaft etc. with the 410 gears over your 3.55's
Many people think you have more traction with the duals, but on any slick surface you will have a lot less traction.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
Clean dry ground or pavement you will have more traction.
Loose dirt, mud, rain and snow, less traction and more likely to hydroplane since you have more surface area with the same amount of weight.
Back in the 70's they ran Michigan trains across I 94 from the Gary steel mills to Detroit auto plants.
11 axles, dual wheels on 10 of them with two 25 foot flatbed trailers hauling coil steel rolls.
They were legal to something like 160,000 pounds gross weight and rolled along just fine when loaded.
But on the return trip, a rain storm had them down to 30 MPH so they didn't float off the road.
Snow was even worse, they were stuck.
Loose dirt, mud, rain and snow, less traction and more likely to hydroplane since you have more surface area with the same amount of weight.
Back in the 70's they ran Michigan trains across I 94 from the Gary steel mills to Detroit auto plants.
11 axles, dual wheels on 10 of them with two 25 foot flatbed trailers hauling coil steel rolls.
They were legal to something like 160,000 pounds gross weight and rolled along just fine when loaded.
But on the return trip, a rain storm had them down to 30 MPH so they didn't float off the road.
Snow was even worse, they were stuck.
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Posting Guru
Joined: Dec 2005
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From: Peterborough, Ontario
I know my 2wd dually doesn't do well until there is about 1500-2000 lbs added to teh back for weight in snow etc, and ice, well, forget it.
I may be wrong, but wouldn't the guts be a direct swap, and in some ways easier to do than a full axle swap? Also, did you determine whether the axle, and the spring perches were the same spacings as your current axle?
I may be wrong, but wouldn't the guts be a direct swap, and in some ways easier to do than a full axle swap? Also, did you determine whether the axle, and the spring perches were the same spacings as your current axle?
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
To go from SRW to dually, the housing is what needs to be swapped.
Internals are the same except the dually axles are 2" longer.
Ring gears and pinions as well as the bearings/seals are the same.
Internals are the same except the dually axles are 2" longer.
Ring gears and pinions as well as the bearings/seals are the same.
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Junior User
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Sorry, I didn't clarify. The donar truck that this axle came from was a single rear wheel. It was a 4x4 though, and the axle is a limited slip. So with the limited slip feature, I would expect a bit more traction on gravel and snow. I'm not taking this thing to do some hard core off roading, it's my landscape truck. Soon to be customized for firewood hauling, hopefully.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
The limited slip will give you more traction as long as the clutches are not worn out.
Your truck is a two wheel drive?
If two wheel drive, swaping the rear axle with lower gears would not be a problem.
If I were doing that swap, I would have the limited slip unit rebuilt before I installed it so I knew it worked.
However if your truck is a 4x4, then you would also have to change the gear ratio in the front axle to match the rear ratio.
Your truck is a two wheel drive?
If two wheel drive, swaping the rear axle with lower gears would not be a problem.
If I were doing that swap, I would have the limited slip unit rebuilt before I installed it so I knew it worked.
However if your truck is a 4x4, then you would also have to change the gear ratio in the front axle to match the rear ratio.
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