Smallest tunnel hole for A833 conversion from A904 inquiry

[like_A_pike]

seems folks trace the shifter insert sheet metal and cut a giant piece out of the original floor. Anyone try cutting less and being happy with the result? What did you do?

The subject is an automatic/318 factory 1968 Barracuda. Now 340 with cheap older headers and planning to install an A833 4 speed

Thanks

 

[MOPAROFFICIAL]

Put it in, then cut where you need to.

I too only cut what was needed and not the entire floor hump...but to help...the area around the torsion bar anchor/support same area as the trans cross memeber. You're clearing for the shifter mostly... been a long time since I did mine in 2002

 

[Clarkos]

I just did mine, and because I was having to modify the hump insert to suit my car, I made lots of small cuts till I was happy with the shape. But in the end, I cut so there was a small amount of overlap all the way round. If you leave too much original floor then won't that just allow too many places for water and other crud to collect......

 

[Oldmanmopar]

Set the hump on the floor and trace it. Cut the floor an inch smaller. You will need the room for the trans linkage to move without hitting the floor.

 

[like_A_pike]

If you leave too much original floor then won't that just allow too many places for water and other crud to collect

Hmm interesting point. Likely so.

You will need the room for the trans linkage to move without hitting the floor.

That’s what I suspected was the main reason. Do the top two go over it (where the floor currently is) and reverse below it?

 

[halfafish]

Hmm interesting point. Likely so.



That’s what I suspected was the main reason. Do the top two go over it (where the floor currently is) and reverse below it?

Yes. 1/2 and 3/4 go over, R goes under.

 

[MOPAROFFICIAL]

Funny that it went from..
"smallest tunnel hole for 833 trans"
To cutting a huge one. Lmao

frame connectors and how a unibody works ..lol

 

[matthon]

Original 4 speed car, has 67 aftermarket Hurst bench shifter, clearance needed on the torsion bar crossmember Clarence.

Cut that hole nice and large.

 

[RustyRatRod]

There's no harm in doing it the way the factory did. They did it that way to make facilitating servicing the shift levers less of a pain.

 

[72bluNblu]

So this is the size of the factory cut out. I left the floor pan attached to the crossmember which I don’t think the factory did, but otherwise these holes were traced from a factory floor cut out.

The rear hole pretty much has to be the size the factory cut it, there isn’t much room for the shifter otherwise. The forward hole for the linkage could be smaller, you wouldn’t have to take it all the way up to the top of the tunnel if you didn’t want to. Keep in mind of course that the 4 speed hump is typically welded in, so you can’t access the transmission like this picture shows once the 4 speed hump is installed.

 

[gdonovan]

Floor cut out for hump.

 

[gdonovan]

I just did mine, and because I was having to modify the hump insert to suit my car, I made lots of small cuts till I was happy with the shape. But in the end, I cut so there was a small amount of overlap all the way round. If you leave too much original floor then won't that just allow too many places for water and other crud to collect......

I suspect this is the reason the factory hole size is what it is. There is really nothing to be gained by leaving the flap at the top and all it would do is collected debris.

 

[Dan Brewer]

I would cut the hole the same way factory did. You are going to want all the room in the tunnel to adjust the shifter & linkage once you have everything installed.

 

[like_A_pike]

The previous owner used self tapping screws on the hump sheet metal and some sort of weather strip for maintenance. Also why it was available for re-use. I’ve seen a few posters advocate for the “removable” or access tunnel mod. I can see sealing it needs to be addressed but anyone have a take on major disadvantages of this approach?

 

[gdonovan]

The previous owner used self tapping screws on the hump sheet metal and some sort of weather strip for maintenance. Also why it was available for re-use. I’ve seen a few posters advocate for the “removable” or access tunnel mod. I can see sealing it needs to be addressed but anyone have a take on major disadvantages of this approach?

Weakens the tunnel and floor pan, and yes they flex around a lot on an a-body.

 

[matthon]

I "maintain" my 4 speed and adjust the shifter/rods before install.

Tape up the rods, remove them with the shifter, install trans, reinstall shifter/linkage, adjust if necessary.

Then drive it for a few gazillion miles.

 

[like_A_pike]

I just removed the console and got a load of all the stuff that has to be chiseled from the top of the tunnel. I’m going to need some more cut off wheels!

Thanks all again for your guidance…

 

[atedepumpo]

I just removed the console and got a load of all the stuff that has to be chiseled from the top of the tunnel. I’m going to need some more cut off wheels!

Thanks all again for your guidance…

I literally welded my 4-speed hump in a few hours ago. I tried to make the cut like the factory. Here’s a few pictures of the process that I followed based on tips from FABO members in response to my recent post for help. Notice that I had to grind off the mounts for the automatic floor shifter and the front bracket for the console. (Based on a tip from FABO moparmat2000 I drilled two holes in the front console bracket and tunnel so I wouldn’t lose the location of the console bracket.) Initially I traced where the hump seemed to fit naturally. Then I cut out two holes so I could mockup the transmission and shifter. Before I cut the final hole, I confirmed that shifter and boot were reasonably centered. When I was happy with the location of the hump, I used sheet metal screws to mount the hump before I welded it in place, and then I welded the screw holes. I epoxy-primed and painted everything including the inside of the cross member. I also attached two photos that I found online that I used as guidance for where the shifter should be. If you’re interested I can take pictures of the finished product when I’m at the shop tomorrow. I might wait until I cover my amateur stitch welds with seam sealer.

 

[jeff ezell]

Here's some pics of the way I did mine. Laid the hump out of an original 73 340 Duster, traced the outline after taking measurements and reference point from the original car, then cut about an inch or so inside the lines. Drilled the corners with a 1/2" drill, then connected the dots so that is would have a nice radius on the corners. Left the strap of sheet metal along top of the cross member and welded the edges shut, ground them down and it looks seamless. Then after some cleanup underneath, hammer and dollied the floorpan sheet metal then applied some of the Por15 seam sealer. I am not a great fabricator, but I do things the best that I know how.

 

[like_A_pike]

Hmm, a lot to live up to.

I am trying to come to grips with having to replace the carpet. Aka figuring in another $400. What’s the story with “mass backing”? Are folks using a more modern approach for sound and temperature control?

 

[gdonovan]

Hmm, a lot to live up to.

I am trying to come to grips with having to replace the carpet. Aka figuring in another $400. What’s the story with “mass backing”? Are folks using a more modern approach for sound and temperature control?

My ACC had the "mass backing" which is just mulched rag padding and then also used generic butyl & aluminum floor covering.

 

[like_A_pike]

My ACC had the "mass backing" which is just mulched rag padding and then also used generic butyl & aluminum floor covering.

View attachment 1716531353

Both? Is it wicked quiet? Is it heavy? Interfere with reinstalling the seats at all?

 

[gdonovan]

Both? Is it wicked quiet? Is it heavy? Interfere with reinstalling the seats at all?

No problem with seats, can't tell you yet as project still in process.

 

[jeff ezell]

I was, and maybe still am, thinking about using Dynamat, but contacted them about their large kit and asked how much does 1 sheet weigh and they said about 16 oz. If you do your roof, doors, floors, rear wheelwells, etc., that would add up to some weight in a hurry. Then put the carpet on top of that with the padding and insulation in the roof...It'd be quieter, but it would add up quickly on the weight.
I guess it all boils down to a cruiser or a bruiser.

 

[gdonovan]

I was, and maybe still am, thinking about using Dynamat, but contacted them about their large kit and asked how much does 1 sheet weigh and they said about 16 oz. If you do your roof, doors, floors, rear wheelwells, etc., that would add up to some weight in a hurry. Then put the carpet on top of that with the padding and insulation in the roof...It'd be quieter, but it would add up quickly on the weight.
I guess it all boils down to a cruiser or a bruiser.

It only added a few pounds to my car and if I was concerned about weight I'd start by getting back on the treadmill.