73-87 Converting a cab from low to high hump - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tx Firefighter · 02-12-2011, 07:33 PM

To discuss this topic go here- LINK

I have an 85 model low hump cab and have a line on a 78 model SM465 4 speed transmission and the bolt in high hump floor from the same truck. Thing is, I don't have a way to put hands on it right now and see for sure.

My question is, will the high hump cover drop into place if I cut the hole and make arrangements for the hold down bolts ?

This may seem a stupid question, but I know from first hand experience that 60-66 trucks have a different firewall and require a good bit of modding to make it work when swapping low to high. I further know that 67-72 trucks, it's just cut the hole and bolt the hump in place. But, I've never done this on a 73-87 and my current cab is finished to near show quality. If it requires more than cutting a hole and some weld nuts I won't mess with it.

Thank you,
Kevin

Tx Firefighter · 02-17-2011, 02:29 PM

Well the answers were kind of varied so I decided to just dive off into the project.

This is an 85 model cab and a 78 model high hump. Both trucks were 2wd. Best I can tell by looking at the junkyards, most newer model cabs like mine (85 model) had a built in high hump or a built in low hump. I could not find a later model cab with a bolt in hump around here. So, I had to use the 78 model bolt in hump. The two floor pans are quite different.

I had to reshape the edges with a hammer against a straight edge to get the contour proper to fit the floor. Figure about 10 minutes of bumping the metal, test fit, and repeat. The floors are similar but definitely not the same. The edges on the sides of the hump had to be dressed downward to make it hug the floor properly.

Lay the tunnel into place and mark the perimeter, then remove and mark a second line about an inch inside of the perimeter mark. That's your cut line.

Hillbilly Plasma Cutter...

Resulting hole...

Now bolt the tunnel in place with 5/16 bolts and nuts with washers on the underside...

Roll underneath and weld the nuts and washer combos to the cab floor.

All in all, pretty easy. Figure an hour and a half to do the work.

02-12-2011, 07:33 PM	#1
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	73-87 Converting a cab from low to high hump To discuss this topic go here- LINK I have an 85 model low hump cab and have a line on a 78 model SM465 4 speed transmission and the bolt in high hump floor from the same truck. Thing is, I don't have a way to put hands on it right now and see for sure. My question is, will the high hump cover drop into place if I cut the hole and make arrangements for the hold down bolts ? This may seem a stupid question, but I know from first hand experience that 60-66 trucks have a different firewall and require a good bit of modding to make it work when swapping low to high. I further know that 67-72 trucks, it's just cut the hole and bolt the hump in place. But, I've never done this on a 73-87 and my current cab is finished to near show quality. If it requires more than cutting a hole and some weld nuts I won't mess with it. Thank you, Kevin __________________ I'm on the Instagram- @Gearhead_Kevin Last edited by N2TRUX; 02-18-2011 at 08:57 PM.

02-17-2011, 02:29 PM	#2
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	73-87 Converting a cab from low to high hump Well the answers were kind of varied so I decided to just dive off into the project. This is an 85 model cab and a 78 model high hump. Both trucks were 2wd. Best I can tell by looking at the junkyards, most newer model cabs like mine (85 model) had a built in high hump or a built in low hump. I could not find a later model cab with a bolt in hump around here. So, I had to use the 78 model bolt in hump. The two floor pans are quite different. I had to reshape the edges with a hammer against a straight edge to get the contour proper to fit the floor. Figure about 10 minutes of bumping the metal, test fit, and repeat. The floors are similar but definitely not the same. The edges on the sides of the hump had to be dressed downward to make it hug the floor properly. Lay the tunnel into place and mark the perimeter, then remove and mark a second line about an inch inside of the perimeter mark. That's your cut line. Hillbilly Plasma Cutter... Resulting hole... Now bolt the tunnel in place with 5/16 bolts and nuts with washers on the underside... Roll underneath and weld the nuts and washer combos to the cab floor. All in all, pretty easy. Figure an hour and a half to do the work. __________________ I'm on the Instagram- @Gearhead_Kevin Last edited by N2TRUX; 02-18-2011 at 08:53 PM.



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