1986 GMC1T rearend and transmission swap to 1/2T Chevrolet - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Russ Brown · 02-28-2005, 05:09 PM

I am 19 years old and would like to change my 1987 ½ ton Chevrolet Silverado rear end to a 14 bolt 1 ton rear end for better towing capability. I also own a 22' Pace trailer with (2) 5,000 lb. axles. My trailer plus load is approximately 7,800 lbs. I have a small sound and lighting business and can't afford to buy a new truck and go to college, but my present truck rear end is a 3:07 and just doesn’t have the power to tow my trailer. The transmission is about ready to go. I do tow with it but I have to be very easy on it. I would like to change rear end to a 4:10 ratio floating axle for better starting capability. I am also going to change the transmission from a 700R4 to a Turbo 400 with a HD cooler. The truck is primarily used to tow short distances, never more than 100 miles.
I just purchased a 1986 1 ton GMC 6.2 Diesel for parts because it was only $200. The heads are off the motor but the person told me that the rear end was ok and the transmission was ok when it stopped running. The wheel base is 131.5 inches on both trucks and the rear half of the drive shaft and yoke measures the same on both trucks. I haven’t measured the front driveshaft. I am wondering if the yoke is the same on the 86 GMC and the 87 Chevrolet. I also plan to use the GMC Turbo 400 transmission and put it in my truck, after overhauling. Just looking for advice from someone that has done this swap, will it all work and how difficult. Brake bias is a question? Thanks Russ Brown (New Member)
I did a search found some items but not thorough enough. I think some of the experienced people on the board that has done this swap before, should start a study hall and put detailed articles in the study hall so that people like myself don’t have to ask the same question over, but could go to the study hall and read a complete articles on this swap.
If someone has done this please direct me to the article.

gchemist · 02-28-2005, 08:45 PM

Actually you can find most of the information on different sites. The 14 bolt axel swap is the similiar as a Blazer in this article http://www.coloradok5.com/axleswap.shtml
All 73-91 GMC and Chevy vehicles have the same parts. Only badging and trims levels were different. You are on the right path for towing a heavy trailer. Feel free to ask any questions. There are plenty of members here that have done most modifications you can imagine.
Welcome to the site.

magnethead · 02-28-2005, 09:28 PM

I'll add if you're putting a 1 ton corp 14 under it, you might have a problem with the hub sticking out (It'll look like a F-350 single wheel for comparison) since it's made for duallies. You'll want the 1 ton leaf springs too.

What motor does the 1/2 ton have? The 400 SHOULD bolt up to it, but might check to make sure. It's a good towing motor (you'll miss the OD though..4.10's only make it worse).

I assume it's 4x4? Assuming the rear driveshaft and wheelbase lengths are the same for both trucks, the front driveshaft should be the same (give or take a little on the driveshaft angle and rear springs).

Russ Brown · 02-28-2005, 11:29 PM

My truck is a 1/2 ton two wheel drive with a 350 motor in it. The GMC truck is a one ton truck with single rear wheeels. I was going to take the complete rear end plus springs from the GMC and mount them to my truck. I appreciate you taking the time in answering my post. Have a good day. Russ Brown

kblazer87 · 03-01-2005, 12:37 AM

Quote:

Originally Posted by Russ Brown

I am wondering if the yoke is the same on the 86 GMC and the 87 Chevrolet.

The u-joint cups will be different sizes from 1/2 ton to 1 ton drive shafts. If you are using the transmission from the one ton as well as the rear end and if the length of the shafts are the same then that is best. If the shafts are different in length you will need to make the 1 ton the right length or have one ton ends put on the 1/2 ton drive shaft. If using a 1/2 ton trans. you can have a different size yoke put on each end of the driveshaft or one of the special u-joints to adapt from a 1/2 ton to 1 ton yoke.

Russ Brown · 03-01-2005, 08:13 PM

I measured the spring pads on the 1986 GMC 1 ton and they measured approximately 40.5 inches pin to pin. I think the spring pads on my 1987 Chevrolet 1/2 ton is like 42.5
I may have to weld new spring pads on. I am planning on using the springs from under the GMC and the complete rear end. I hope everything from the rear to the Transmission will work. How much trouble is it to change spring pads?
Thank for the help.

*1FaastC10* · 03-01-2005, 08:37 PM

Quote:

Originally Posted by magnethead

I'll add if you're putting a 1 ton corp 14 under it, you might have a problem with the hub sticking out (It'll look like a F-350 single wheel for comparison) since it's made for duallies. You'll want the 1 ton leaf springs too.

incorrect. a SRW 1 ton 14FF is just as wide as a 10 or 12 bolt. the hubs onlt stick out a few inches, nothing that will be outside the wheel. a Cab and Chassis 14 bolt will have a longer hub, but should still cover with most wheels. what he is looking for is not even a 1 ton rear end, as the spring perches are 2" too narrow. he needs a 3/4 ton 14FF from a pre-82(?) truck. the spring perches are identical to his 1/2 ton, other than that the rears are identical.

Quote:

What motor does the 1/2 ton have? The 400 SHOULD bolt up to it, but might check to make sure. It's a good towing motor (you'll miss the OD though..4.10's only make it worse).

there is absolutely nothing wrong with the TBI 350 that is in the truck now for a towing engine. the problem lies in the transmission. the 700R4 is not up to pulling that kind of load on a regular basis. converting your 1/2 ton truck so that it will be able to pull that kind of load reliably is likely going to cost you just as much as the truck is worth. maybe you should look into buying a truck already equipped for such a task, or fix the 1 ton and keep your 87 as a driver.

Russ Brown · 03-02-2005, 07:07 PM

Thanks, I have measured the tire width outside to outside on the 1 ton and the 1/2 ton and they are within 1 inch. I am sure that I will have to reposition the spring pads. I am not in a positon to buy a new truck because my truck only has about 120,000 miles on it and it is in perfect conditon as far a body and interior, always garaged. As I have stated I want to start at the rear end and put everything from springs to rear drive shaft to front drive shaft to Turbo 400 from the 1 Ton GMC. I only use the truck to pull my trailer on a Friday or Saturday night and it is usually for a short distance. I am going to pull the rear end from the GMC ,sand blast and put in new seals, and brakes, completly check rear end etc. Will a 3/4 ton rear end from a 1987 Chevrolet have the same distance on the spring pads as my 1/2 ton? I have never repositioned spring pads but I am sure some of my friends can do it for me as I am not a welder. I know where there are several 3/4 ton trucks, but everyone wants to give me the whole truck just to move them, but I don't want the whole truck. I only purchased the 1 Ton as it had several parts on it that I could sell and the wrecking company towed it to my house for free. I was lucky it had 4 16 inch Michelin tires with less that 6,000 miles. I would also like to use the 8 lug spindles from the GMC ton. I wonder if that is possible, and how much you would have to do to make this work.

*1FaastC10* · 03-02-2005, 07:49 PM

why not swap your body and engine? should be fairly easy to do if the 1 ton is complete (brake lines, fuel lines and such.)

Russ Brown · 03-02-2005, 08:21 PM

The one ton is not complete. My truck is immaculate. I only need the rear end and the transmission and I will have a perfect truck.

*1FaastC10* · 03-02-2005, 09:00 PM

ok, so what DOES that "truck" include?

Russ Brown · 03-03-2005, 07:31 PM

The 1986 1 ton GMC had a 6.2 Diesel Engine that quit running and someone robbed the heads off of and it also had a work body that was taken off the vehicle before I got it. The 1986 had all of the running gear but misc parts were taken from it. I just wanted the complete rear and driveshafts and Turbo 400 transmission. I would also like to put the friont 8 lug spindles under my truck. It has been so wet I haven't had time to work on my project. My good truck 1987 Chevrolet 1/2 ton Silverado came with a 10 bolt 3:07 rear end, 700 R4 transmission and a 350 CI Engine. Perfect condition.

*1FaastC10* · 03-03-2005, 09:37 PM

the rear axle is going to require you to either move the perches on the rear axle, or install 1 ton hangers on the frame. swapping on the 8 lug spindles will require removal of the entire front suspension crossmember. in both cases you may run into problems because the 1 ton frame is taller than the 1/2 and 3/4 ton units.

02-28-2005, 05:09 PM	#1
Russ Brown Registered User Join Date: Feb 2005 Posts: 6	1986 GMC1T rearend and transmission swap to 1/2T Chevrolet I am 19 years old and would like to change my 1987 ½ ton Chevrolet Silverado rear end to a 14 bolt 1 ton rear end for better towing capability. I also own a 22' Pace trailer with (2) 5,000 lb. axles. My trailer plus load is approximately 7,800 lbs. I have a small sound and lighting business and can't afford to buy a new truck and go to college, but my present truck rear end is a 3:07 and just doesn’t have the power to tow my trailer. The transmission is about ready to go. I do tow with it but I have to be very easy on it. I would like to change rear end to a 4:10 ratio floating axle for better starting capability. I am also going to change the transmission from a 700R4 to a Turbo 400 with a HD cooler. The truck is primarily used to tow short distances, never more than 100 miles. I just purchased a 1986 1 ton GMC 6.2 Diesel for parts because it was only $200. The heads are off the motor but the person told me that the rear end was ok and the transmission was ok when it stopped running. The wheel base is 131.5 inches on both trucks and the rear half of the drive shaft and yoke measures the same on both trucks. I haven’t measured the front driveshaft. I am wondering if the yoke is the same on the 86 GMC and the 87 Chevrolet. I also plan to use the GMC Turbo 400 transmission and put it in my truck, after overhauling. Just looking for advice from someone that has done this swap, will it all work and how difficult. Brake bias is a question? Thanks Russ Brown (New Member) I did a search found some items but not thorough enough. I think some of the experienced people on the board that has done this swap before, should start a study hall and put detailed articles in the study hall so that people like myself don’t have to ask the same question over, but could go to the study hall and read a complete articles on this swap. If someone has done this please direct me to the article.

02-28-2005, 08:45 PM	#2
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Actually you can find most of the information on different sites. The 14 bolt axel swap is the similiar as a Blazer in this article http://www.coloradok5.com/axleswap.shtml All 73-91 GMC and Chevy vehicles have the same parts. Only badging and trims levels were different. You are on the right path for towing a heavy trailer. Feel free to ask any questions. There are plenty of members here that have done most modifications you can imagine. Welcome to the site. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

02-28-2005, 09:28 PM	#3
magnethead 7000 #'s of american IRON Join Date: Dec 2004 Location: north tx Posts: 883	I'll add if you're putting a 1 ton corp 14 under it, you might have a problem with the hub sticking out (It'll look like a F-350 single wheel for comparison) since it's made for duallies. You'll want the 1 ton leaf springs too. What motor does the 1/2 ton have? The 400 SHOULD bolt up to it, but might check to make sure. It's a good towing motor (you'll miss the OD though..4.10's only make it worse). I assume it's 4x4? Assuming the rear driveshaft and wheelbase lengths are the same for both trucks, the front driveshaft should be the same (give or take a little on the driveshaft angle and rear springs).

02-28-2005, 11:29 PM	#4
Russ Brown Registered User Join Date: Feb 2005 Posts: 6	My truck is a 1/2 ton two wheel drive with a 350 motor in it. The GMC truck is a one ton truck with single rear wheeels. I was going to take the complete rear end plus springs from the GMC and mount them to my truck. I appreciate you taking the time in answering my post. Have a good day. Russ Brown

03-01-2005, 08:13 PM	#6
Russ Brown Registered User Join Date: Feb 2005 Posts: 6	I measured the spring pads on the 1986 GMC 1 ton and they measured approximately 40.5 inches pin to pin. I think the spring pads on my 1987 Chevrolet 1/2 ton is like 42.5 I may have to weld new spring pads on. I am planning on using the springs from under the GMC and the complete rear end. I hope everything from the rear to the Transmission will work. How much trouble is it to change spring pads? Thank for the help.

03-02-2005, 07:07 PM	#8
Russ Brown Registered User Join Date: Feb 2005 Posts: 6	Thanks, I have measured the tire width outside to outside on the 1 ton and the 1/2 ton and they are within 1 inch. I am sure that I will have to reposition the spring pads. I am not in a positon to buy a new truck because my truck only has about 120,000 miles on it and it is in perfect conditon as far a body and interior, always garaged. As I have stated I want to start at the rear end and put everything from springs to rear drive shaft to front drive shaft to Turbo 400 from the 1 Ton GMC. I only use the truck to pull my trailer on a Friday or Saturday night and it is usually for a short distance. I am going to pull the rear end from the GMC ,sand blast and put in new seals, and brakes, completly check rear end etc. Will a 3/4 ton rear end from a 1987 Chevrolet have the same distance on the spring pads as my 1/2 ton? I have never repositioned spring pads but I am sure some of my friends can do it for me as I am not a welder. I know where there are several 3/4 ton trucks, but everyone wants to give me the whole truck just to move them, but I don't want the whole truck. I only purchased the 1 Ton as it had several parts on it that I could sell and the wrecking company towed it to my house for free. I was lucky it had 4 16 inch Michelin tires with less that 6,000 miles. I would also like to use the 8 lug spindles from the GMC ton. I wonder if that is possible, and how much you would have to do to make this work.

03-02-2005, 07:49 PM	#9
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	why not swap your body and engine? should be fairly easy to do if the 1 ton is complete (brake lines, fuel lines and such.)

03-02-2005, 08:21 PM	#10
Russ Brown Registered User Join Date: Feb 2005 Posts: 6	The one ton is not complete. My truck is immaculate. I only need the rear end and the transmission and I will have a perfect truck.

03-02-2005, 09:00 PM	#11
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	ok, so what DOES that "truck" include?

03-03-2005, 07:31 PM	#12
Russ Brown Registered User Join Date: Feb 2005 Posts: 6	The 1986 1 ton GMC had a 6.2 Diesel Engine that quit running and someone robbed the heads off of and it also had a work body that was taken off the vehicle before I got it. The 1986 had all of the running gear but misc parts were taken from it. I just wanted the complete rear and driveshafts and Turbo 400 transmission. I would also like to put the friont 8 lug spindles under my truck. It has been so wet I haven't had time to work on my project. My good truck 1987 Chevrolet 1/2 ton Silverado came with a 10 bolt 3:07 rear end, 700 R4 transmission and a 350 CI Engine. Perfect condition.

03-03-2005, 09:37 PM	#13
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,399	the rear axle is going to require you to either move the perches on the rear axle, or install 1 ton hangers on the frame. swapping on the 8 lug spindles will require removal of the entire front suspension crossmember. in both cases you may run into problems because the 1 ton frame is taller than the 1/2 and 3/4 ton units.



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