Changing from a Low Hump to a High Hump

[NoNeck]

We searched for tips and how to's on removing a low hump trans tunnel and installing a high hump. Not much out there. So, I decided to document how we went about the task of making room for a TH400 in a '68 C10.

NOTE: We did not have access to a lift, plasma cutters or metal shears. If you have access to those tools or if the transmission is out of your truck you could vary how you remove the low hump.

First step... we picked up a new repro high hump from Chuck Hutchinson at Truck Haven in Unionville, TN. Chuck is a great guy and has anything you might need for a C10.

[NoNeck]

After removing the brand new low hump carpet that we had just installed, we placed the new high hump in positon over the low hump and temporarily installed Dorman bolts in the two existing holes in the floor pan. Using a permanent marker, we marked the location of the eight remaining holes. We then removed the high hump, center punched the hole locations and drilled them to size.

[NoNeck]

The existing floor pan has an continuous indention that can be followed when cutting. If the truck doesn’t have a transmission installed you can remove the old hump with a metal cutting wheel, plasma cutter, metal shears or pneumatic cutting saw.

Be sure to wear safety goggles and gloves for the next steps.
Since our truck had the transmission installed we used an Ingersol Rand pneumatic air saw with a medium tooth metal cutting blade. Be very careful while cutting to make sure that electrical wiring, modulator valve line, transmission dipstick tube and transmission cooling lines are clear of the blade.
Be careful lifting the cut out metal section because of sharp edges.

[NoNeck]

We trimmed the metal opening near the hole locations and installed Dorman fender clips.

This evening we are going to transfer the hole locations for the Lokar shifter to the new high hump and re-install the shifter hardware.

Stay tuned... more to come!

POP

[OregonNed]

Can’t wait to see!

[lolife99]

What was the reason for going to a high hump?.

[NoNeck]

What was the reason for going to a high hump?.

Keith, the underside of the Low Hump was hitting the top of the TH400 enough to fold over the metal.

POP

[NoNeck]

After applying a bead of Urethane Adhesive around the perimeter we finished installing the High Hump in the truck. Now the transmission has plenty of room. Not sure how others were able to use a Low Hump with TH400 and not experience clearance issues. In our case the High Hump is the only way to go.

We are going to apply more ThermoTec Heat/Sound Deadener to the panel and then new High Hump Carpet.

POP

[weq92f]

Nice work guys, thanks for the post!

-klb

[OregonNed]

Looks great! I bought a new high hump to convert to a Lokar. Can you tell
Me roughly the placement measurements you made for your shifter mounting location?

[lolife99]

Originally Posted by NoNeck

Keith, the underside of the Low Hump was hitting the top of the TH400 enough to fold over the metal.

POP

Thanks for the reply.

[Dustmaker65]

WOW...that looks nice!

What is the cost of a repop high hump?

[OregonNed]

Mine was from Cooper Restorations - $95 before
Shipping.

[NoNeck]

Can you tell me roughly the placement measurements you made for your shifter mounting location?

I will let my son Chad (CC69Rat) chime in on that. He measured everything out and installed the Lokar shifter.

What is the cost of a repop high hump?

We got ours from Chuck at Truck Haven and it was $95 dollars without shipping. It really is a quality piece.

[OregonNed]

Mine is labeled Key Parts underneath

[stsalvage]

I was wondering if they made that part cool

[adricar1]

yes i got mine fom summitracing. just cut the floor to fit it

[orangeblossomspcl]

Are these fender clips 1/4"? If not, what size did you use?

[Corts60]

Nice work!

[gmc684x4]

My understanding trucks with t400 came factory with high hump

I did this on my 68 gmc when i went from 2x4 to 4x4 there is a spot welded ring that is below the floor pan for use of bolts not sheetmetal screws to secure high hump pan

[gregbr]

Thanks for posting, nice work. That color looks familiar too....or close to my 70 GMC

[3757chevy]

Originally Posted by gmc684x4

My understanding trucks with t400 came factory with high hump

I did this on my 68 gmc when i went from 2x4 to 4x4 there is a spot welded ring that is below the floor pan for use of bolts not sheetmetal screws to secure high hump pan

...Yes TH400 trucks had high hump . I got a used cover from a donor truck 'cause my '67 C10 already had the floor cut and a truck 4 spd with a butchered high hump . I cut a fresh hole for a car 4 spd shifter and I'm still using it today(24 yrs later.) Now it has an TH400 shifter mounted in the same hole.

[firedemon]

i see a lot of posts where people say they have this problem . i wonder if i dont because i used aftermarket engine and trans mounts . it is really tight with the t400 but its almost a half inch . i have horsed it enough to snap the carrier bearing off the mount but never herd the trans rub or hit . i wonder if theres a way we could measure the height of the motor and trans using the factory mounts vs the aftermarket tubular ones

[SkidmoreGarage]

Originally Posted by 3757chevy

...Yes TH400 trucks had high hump . I got a used cover from a donor truck 'cause my '67 C10 already had the floor cut and a truck 4 spd with a butchered high hump . I cut a fresh hole for a car 4 spd shifter and I'm still using it today(24 yrs later.) Now it has an TH400 shifter mounted in the same hole.

Not to be disagreeable, but th400 does not indicate a high hump. This has bitten a few people with ordering cab carpet.

[3757chevy]

QUOTE:
Re: 72 one piece high hump cab floor
The big blocks with turbo 400 were high hump. The small blocks with th400 were low hump.:Quote......................................................................................... .................................................................................................... .................................................................................................... ........................... I stand corrected.