3/4 ton axle swap

86M10086.2L

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Location
Long Island, New York
Because my plow truck (a 1985 GMC K2500) has quite literally rotted away. It’s far and away the rustiest vehicle I’ve ever personally seen. The picture doesn’t truly tell the tale. With nearly 99% of that rust/rot happening before I got it. I’ve decided to get my M1009 back on the road and throw the plow on it for the few times a year it snows by me. But before I send the plow truck to the scrap yard. I’m gonna pull some parts, mostly the SM465/NP208, pedal assembly, steering column, and associated manual tranny bits as well as some of the glass and universal squarebody GM parts. I’ve always wanted to manual swap a CUCV. But I’d also like to pull the 3/4 ton axles out of the plow truck and throw them in the M1009. They are 3.73 a geared 10bolt and a 14bolt semi floater with the oversized brakes because the plow truck also has the camper special package. 90% of the swap is pretty straight forward. I’m not worried about that. My main question is will the M1009 master work with the bigger brakes on the new axles? Or should I look into swapping to a M1008 master cylinder? There was an issue with the brakes which was the main reason I stoped driving the M1009 in the first place and I think it’s likely the master. So to swap one or the other on now is nothing I likely wouldn’t have done anyway. Thanks for any input. 765AAC9E-D699-4F34-9D7B-F15F605D7E83.jpeg
 

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Skinny

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Whatever you have, end up with hydroboost brakes.

In 85 I think GM switched to a hydraulic clutch. If that's the case, congratulations! You have one of the most rarest parts. The hydraulic pedal bracket for a square nose.

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Recovry4x4

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I'm thinking the M1009 MC will be fine. I've done this swap twice. Once on 1 77 half ton. The rear I had for that was from a bonus cab meaning 13" drums. full floater and relocating spring perches. Worked fine with the half ton master cylinder. Second was a 91 half ton suburban. It got a 10 bolt and 14 bolt SF rear, same as yours. Again, the half ton MC was fine.

For future reference, if the plow truck does not have hydroboost, all is not lost with the pedal assy. You can transfer the return spring and pedal from the M1009 to the pedal assy coming out of the plow truck. Of course you would have to trim down the pedal. We can walk you through that when you get ready.
 

Recovry4x4

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Oh, if your flintstone truck has a removable pan above the trans, keep that and about 6" of the floor all the way around. Another seemingly hot commodity is the area of the dash where the radio goes. If it's not molested, cut that out too. Here is the best way to cut them.
 

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Skinny

Well-known member
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Location
Portsmouth, NH
Yeah that just needs some patch panels...

Looks like the front axle is pushed back. Like broken leaf spring center pin.

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86M10086.2L

Member
386
2
18
Location
Long Island, New York
Believe me, the pictures don’t tell the true story. The rockers are gone on both sides, inner and outer. not rusty, not rotted, gone. Floors, toast, holes through the firewall, cab corners gone, bed floor ventilated, every body and bed support you can almost push you finger through. The frame is flaking apart at an alarming rate. I’m genuinely shocked it hasn’t broken yet. The only rust free/salvageable panel on the truck is the tailgate and that’s because its new. If it were just the matter of some patch panels. We wouldn’t even be having this conversation.
 

LT67

Active member
299
75
28
Location
Bowdon, GA
Because my plow truck (a 1985 GMC K2500) has quite literally rotted away. It’s far and away the rustiest vehicle I’ve ever personally seen. The picture doesn’t truly tell the tale. With nearly 99% of that rust/rot happening before I got it. I’ve decided to get my M1009 back on the road and throw the plow on it for the few times a year it snows by me. But before I send the plow truck to the scrap yard. I’m gonna pull some parts, mostly the SM465/NP208, pedal assembly, steering column, and associated manual tranny bits as well as some of the glass and universal squarebody GM parts. I’ve always wanted to manual swap a CUCV. But I’d also like to pull the 3/4 ton axles out of the plow truck and throw them in the M1009. They are 3.73 a geared 10bolt and a 14bolt semi floater with the oversized brakes because the plow truck also has the camper special package. 90% of the swap is pretty straight forward. I’m not worried about that. My main question is will the M1009 master work with the bigger brakes on the new axles? Or should I look into swapping to a M1008 master cylinder? There was an issue with the brakes which was the main reason I stoped driving the M1009 in the first place and I think it’s likely the master. So to swap one or the other on now is nothing I likely wouldn’t have done anyway. Thanks for any input. View attachment 823018
That 1st to 2nd gear shift on a SM465 might bog down the 6.2 diesel....
 

Skinny

Well-known member
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48
Location
Portsmouth, NH
I definitely want to do a swap to get overdrive at this point. The obvious choice is NV4500 as you get a low first gear and overdrive. Plus it needs nothing to run which adds to the reliability factor.

But

The gear steps are terrible. Plus the overdrive isn't very tall. Where I live, 70mph is the minimum to no be run over on the interstate. All of the six speeds are very expensive and still lack tall or double overdrives.

The new Tremec that is in the Bronco has a crawler and double overdrives. I doubt it had the weight rating for a 1 ton truck but that gearing would be nice.

I really am liking the 6L80 more and more but you are talking about adding a very electronically complex component to an engine that needs one wire to run.

Decisions Decisions

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Recovry4x4

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I think the gear splits on the 465 are worse, We'll do a little comparo when mine gets out of the garage. I'm using the gasser version and a Dodge 208 which has a fixed rear yoke. should be okay.
 

chevymike

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Location
San Diego, CA
I definitely want to do a swap to get overdrive at this point. The obvious choice is NV4500 as you get a low first gear and overdrive. Plus it needs nothing to run which adds to the reliability factor.

But

The gear steps are terrible. Plus the overdrive isn't very tall. Where I live, 70mph is the minimum to no be run over on the interstate. All of the six speeds are very expensive and still lack tall or double overdrives.

The new Tremec that is in the Bronco has a crawler and double overdrives. I doubt it had the weight rating for a 1 ton truck but that gearing would be nice.

I really am liking the 6L80 more and more but you are talking about adding a very electronically complex component to an engine that needs one wire to run.

Decisions Decisions

Sent from my Moto G (5) Plus using Tapatalk
You could add a Gear Vendors to the end of a NV4500 to get double overdrive plus gear splitting between the other ones. Basically end up with a 10 speed
 

Skinny

Well-known member
1,858
91
48
Location
Portsmouth, NH
I guess you could. I am not a fan of the gear vendors. Way too long of a driveline, have to shrink the rear driveshaft, only works in 2wd, and costs about twice what it should be. I have less in an LS swap then what that thing costs.

Now the Ranger overdrive that goes in front of the transmission...now you are talking.

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LT67

Active member
299
75
28
Location
Bowdon, GA
Nv4500 with 4.56 gears will do 75 easy but you may find the truck lacks power up grades or when loaded.
Aaand that's why I want to eventually swap the gears to a 4:10 set up. With a BFG KM2 or Toyo MT 255 85 16 I can run 64-65mph at 2500 rpm. That way I can keep from getting ran over on the interstate and still have low gearing for when I need it. My 79 K20 has this set up and works just fine.
 
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