Changing from low hump to high hump? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

nutsforchevys · 11-11-2008, 08:49 PM

I have a 3/4 ton 70 GMC 4x4 4 speed that I will be using the frame and running gear from. I will be putting my 72 1/2 ton automatic cab on it. What do I do to make it fit?
Thanks in advance.

FLEET72 · 11-11-2008, 09:02 PM

If you still have the 70 cab, just the sheet metal that you need out of it..

Longhorn Man · 11-11-2008, 09:23 PM

yep, the high hump bolts in/out of the old cab.
Toss it in onto the floor of the new cab, trace it, cut a hole one inche smaller than the traced shape, drill holes, bolt it in place with some seam sealer or good silicone (the right stuff by permitex) and call it a day.

71stub · 11-11-2008, 10:25 PM

I need to do the exact opposite! I dont have an automatic cab layin around to cut the floor out of tho...

**Dieselwrencher** · 11-11-2008, 10:54 PM

Can anyone tell me if the 2wd 4 speed humps are the same heighth as the 4x4 4 speed humps? Thanks Ryan.

8mpg · 11-11-2008, 11:16 PM

Quote:

Originally Posted by 71stub

I need to do the exact opposite! I dont have an automatic cab layin around to cut the floor out of tho...

Edited content

I have an automatic cab...just trying to see how I can cut mine out and still bolt in the high hump. Is the high hump wider?

Longhorn Man · 11-11-2008, 11:40 PM

All high humps are the same size. So if you locate a big block autmomatic hump with no holes, then it'll be the same height as any other high hump with hols in it for shifters.

dan42 · 11-12-2008, 12:53 AM

Just a note - the high humps with shifter holes have 3 different locations for the holes. Don't ask me how I know.

8mpg · 11-12-2008, 11:09 AM

Quote:

Originally Posted by Longhorn Man

All high humps are the same size. So if you locate a big block autmomatic hump with no holes, then it'll be the same height as any other high hump with hols in it for shifters.

interesting... The truck I bought is a bigblock auto and I believe it is a small hump. It does not bolt in, it is a solid floor piece.

71stub · 11-12-2008, 12:08 PM

I have also heard that 2wd big block/auto trucks had high hump trans covers.

Spray-Bomb · 11-12-2008, 12:20 PM

Here is what I did on my truck Killer

71stub · 11-12-2008, 01:43 PM

That looks like a very clean install. Nice work!

**Dieselwrencher** · 11-12-2008, 04:39 PM

Very nice! My Longhorn was a BBC truck with a 4 speed and it has a high hump.

Longhorn Man · 11-12-2008, 05:06 PM

Quote:

Originally Posted by 8mpg

interesting... The truck I bought is a bigblock auto and I believe it is a small hump. It does not bolt in, it is a solid floor piece.

There's been a handfull of trucks that have popped up here and there that were factory big block/autos with a low hump... but they were supposed to get high hump. The only big block that was supposed to get the low hump is a big block with a 3 sppedmanual... not a common combination.

nutsforchevys · 11-12-2008, 07:41 PM

Thanks for the info. I am sure I will have more questions as this is my first body swap.

Richard8971 · 11-13-2008, 12:08 AM

I just plaz'ed my low hump out and welded in the new one where it bolts up and seam sealed it really good.

I had custom carpet put in so I didn't have to worry about my old stuff fitting.

Don

Brock · 11-13-2008, 03:02 PM

I switched from a I6 - 3 OTT combo to 307 - 700R4 combo. For some reason the tranny hit the low hump and wouldn't fit (wrong mounts, moved mounts, too tall tranny...whatever) so a sawzall and a $18.00 Highhump off ebay and problem solved. its not "bolted" in yet but it fits great...My (and probably one you will have if your going from low to high) question is how to attach and what kind of sealer if any. I'm thinking about using a bead of silicone and short self-tapping screws since there are no previous holes in the cab floor. Any suggestions?

11-11-2008, 08:49 PM	#1
nutsforchevys Registered User Join Date: Dec 2004 Location: Stephenville, Texas Posts: 420	Changing from low hump to high hump? I have a 3/4 ton 70 GMC 4x4 4 speed that I will be using the frame and running gear from. I will be putting my 72 1/2 ton automatic cab on it. What do I do to make it fit? Thanks in advance. __________________ 72 Super Cheyenne lwb 4X4 Ocra / White 88 Chevy 1 ton Dumptruck 88 Chevy 1ton Flat bed 4X4 white

11-11-2008, 09:02 PM	#2
FLEET72 Registered User Join Date: Jan 2007 Location: Sonoma, CA Posts: 521	Re: Changing from low hump to high hump? If you still have the 70 cab, just the sheet metal that you need out of it.. __________________ Oscar '72 Shortbed Fleetside '95 Jimmy 4X4 '69 GMC Custom Camper

11-11-2008, 09:23 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Changing from low hump to high hump? yep, the high hump bolts in/out of the old cab. Toss it in onto the floor of the new cab, trace it, cut a hole one inche smaller than the traced shape, drill holes, bolt it in place with some seam sealer or good silicone (the right stuff by permitex) and call it a day.

11-11-2008, 10:25 PM	#4
71stub Registered User Join Date: Mar 2008 Location: Forman, ND Posts: 365	Re: Changing from low hump to high hump? I need to do the exact opposite! I dont have an automatic cab layin around to cut the floor out of tho...

11-11-2008, 10:54 PM	#5
Dieselwrencher 6>8 Plugless........ Join Date: Sep 2007 Location: Prairie City, Ia Posts: 17,141	Re: Changing from low hump to high hump? Can anyone tell me if the 2wd 4 speed humps are the same heighth as the 4x4 4 speed humps? Thanks Ryan.

11-11-2008, 11:40 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Changing from low hump to high hump? All high humps are the same size. So if you locate a big block autmomatic hump with no holes, then it'll be the same height as any other high hump with hols in it for shifters.

11-12-2008, 12:53 AM	#8
dan42 Registered User Join Date: Feb 2007 Location: Cali Central Coast Posts: 5,191	Re: Changing from low hump to high hump? Just a note - the high humps with shifter holes have 3 different locations for the holes. Don't ask me how I know. __________________ '67 SWB Fleetside ZZ4/350/Tremec 5-speed/4link/Scott's IFS - and fun as heck! SOLD Click here to support the board Philippians 4: 6-7

11-12-2008, 12:08 PM	#10
71stub Registered User Join Date: Mar 2008 Location: Forman, ND Posts: 365	Re: Changing from low hump to high hump? I have also heard that 2wd big block/auto trucks had high hump trans covers. __________________ 1971 Cheyenne Short Fleet - 468BB/TH400, Tilt, Tach, PS, PB 1967 Custom Short Fleet - 327/4spd

11-12-2008, 12:20 PM	#11
Spray-Bomb Texas Big Wig Join Date: Jan 2007 Location: Mineola, Texas Posts: 5,620	Re: Changing from low hump to high hump? Here is what I did on my truck Killer __________________ Just not low enough... ----------------------------- Sinister Killer Last edited by Spray-Bomb; 11-12-2008 at 12:24 PM.

11-12-2008, 01:43 PM	#12
71stub Registered User Join Date: Mar 2008 Location: Forman, ND Posts: 365	Re: Changing from low hump to high hump? That looks like a very clean install. Nice work! __________________ 1971 Cheyenne Short Fleet - 468BB/TH400, Tilt, Tach, PS, PB 1967 Custom Short Fleet - 327/4spd

11-12-2008, 04:39 PM	#13
Dieselwrencher 6>8 Plugless........ Join Date: Sep 2007 Location: Prairie City, Ia Posts: 17,141	Re: Changing from low hump to high hump? Very nice! My Longhorn was a BBC truck with a 4 speed and it has a high hump.

11-12-2008, 07:41 PM	#15
nutsforchevys Registered User Join Date: Dec 2004 Location: Stephenville, Texas Posts: 420	Re: Changing from low hump to high hump? Thanks for the info. I am sure I will have more questions as this is my first body swap. __________________ 72 Super Cheyenne lwb 4X4 Ocra / White 88 Chevy 1 ton Dumptruck 88 Chevy 1ton Flat bed 4X4 white

11-13-2008, 12:08 AM	#16
Richard8971 Still livin the "dream" in '54 Join Date: Nov 2006 Location: Tucson, AZ Posts: 2,656	Re: Changing from low hump to high hump? I just plaz'ed my low hump out and welded in the new one where it bolts up and seam sealed it really good. I had custom carpet put in so I didn't have to worry about my old stuff fitting. Don __________________ Current build. 1954 Chevrolet 3800 "Ella" SOLD! My '67 stepper "Tangerine Dream" "Anything worth doing is worth doing right" James Dean “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.” Sherlock Holmes "There is no spoon." Neo

11-13-2008, 03:02 PM	#17
Brock upgrading to an older model Join Date: Aug 2007 Location: Sacramento, KY Posts: 346	Re: Changing from low hump to high hump? I switched from a I6 - 3 OTT combo to 307 - 700R4 combo. For some reason the tranny hit the low hump and wouldn't fit (wrong mounts, moved mounts, too tall tranny...whatever) so a sawzall and a $18.00 Highhump off ebay and problem solved. its not "bolted" in yet but it fits great...My (and probably one you will have if your going from low to high) question is how to attach and what kind of sealer if any. I'm thinking about using a bead of silicone and short self-tapping screws since there are no previous holes in the cab floor. Any suggestions? __________________ 68 stepside, short-box, multi-colored (for now)



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