Of High Humps and Low Humps

[hotrodmtodd]

Can someone give me the Cliffs Notes version of the difference in high and low hump floors (other than the OBVIOUS) I am converting an A/C cab to a standard dash for a friend on the board, and I want to make sure I am getting him the right set-up for his application. The cab was originally A/C, with clutch pedals. It has no VIN tag and no GB door, so I don't know for sure what exact configuration it was. The floor has been buggered up some in the hump area (the lip was removed), which I will be fixing, but I want to make sure HIS '70 Chevy 4X4 hump will mate up in the end. He lives an hour+ away, or I would just take his out and try it. Can anybody give me an idea what is correct. I have a new lip and hump that fits, from a 2WD, 4-speed donor truck, but I want to make sure the 4X4 is the same before I get TOO far. Thanks, Mike

[da-burb]

It's the same just with an additional T-case hole and the 4spd hole is a couple inches further back.

As far as the cliff notes, the only humps that are bolted in are the high humps. Low humps are part of the floor pan and not removable without some sort of cutting device. Cut it out and add the high hump and you are set.

[hotrodmtodd]

EXCELLENT! Thank you DB. So here is what I'm hearing: All 4-speed trucks are high humps. ALL 4x4s are high humps (auto OR manual). All column auto and 3-on-trees are LOW humps, which if you cut out the hole and drill the bolt holes, a high hump will bolt right to a low hump cab. Did I miss anything?

[67ChevyRedneck]

I think all that info is correct. To make the job a little easier (for future removal/instalation) some people will bolt it together and put a tack weld on the nuts to the underside of the cab floor. If the truck started out with a factory high hump cab it will already have square nuts welded to the underside of the floor.

[shifty]

Originally Posted by hotrodmtodd

EXCELLENT! Thank you DB. So here is what I'm hearing: All 4-speed trucks are high humps. ALL 4x4s are high humps (auto OR manual). All column auto and 3-on-trees are LOW humps, which if you cut out the hole and drill the bolt holes, a high hump will bolt right to a low hump cab. Did I miss anything?

And if you want pictures or details on how to do it, let me know. I just did mine. Some pictures:

http://satellitehead.com/gallery/thu...album=9&page=5

On the low hump floor, you'll see a little dimple all the way around the floor area - it lines up pretty well perfect with the high hump it's like an outline of where you should cut. Use a jigsaw with a really good finetooth blade and go slow to cut the old one out.

Even though the line is there, be sure to measure up b4 cutting anyway!

[hotrodmtodd]

Neck: I was thinking of splicing the whole section in with the factory nuts and all, but that might not be a bad idea what you suggested about tacking the nuts. I will have to get Chuck (Chucks70) up here to see what he would prefer. Thanks.

Shifty: I will have to check out your link when I get back from my sons basketball game. It sounds like you have taken some good notes for us all to share. Thanks to you as well.

[dwaite72lnghrn]

Add to the high hump-BB autos 2wd.

[Longhorn Man]

all 4 speeds
all 4X4
big block w/ auto
GMC 1/2 ton 305 V-6/TH400
All these would be high hump.

[Steve Vos]

I think you have the high hump application correct. It seems to me I saw a diagram and explaination in an LMC catalog. Can't find it now though. The low hump will fit over a BB w/TH400. Pretty close but it does work. I put one in my '69 GMC swb.

[hotrodmtodd]

Thanks Dave and Andy. I'm curious as to what would cause the need for a high hump with an auto. My factory BB truck was converted to a TH400 from a 3-on-tree and can't see any mods to the hump area. Was it for clearance purposes for the motor being further aft? If so, it doesn't appear to have been an issue with mine. I'm sure GM had their reasons. Thanks again, Mike