Progress Thread Floor pan repair/build thread

jrichker

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The floor pan where the seat bolts down is cracked. This is a headache because you must remove the carpet and interior to get to the damaged area to fix it.

This is what my solution to the problem looks like:

I don't have a welder and it would have been difficult to get the car to a place that could do a satisfactory job of welding up a suitable repair..

Two pieces of 16 gauge steel that overlap at the top to make an approximately 1/8" thick hat section.

The angle sections are riveted together with monel 1/8" diameter solid rivets.

The repair is secured in place with 18 each 1/8" Cherrylock Aircraft Structural rivets.These are NOT the same as cheap Pop rivets!!! Each rivet has ashear strength of greater than 600 pounds and there are 18 rivets. The total shear strength for the riveted joint is over 5400 pounds per side. Considering my body weight, that would hold over 25 G impact for each side of the repair.

Notice that the first picture shows the damaged material cut out and the cracks are stop drilled. This keeps the cracks from spreading further and is a necessary step. This necessary even if you weld whatever repair you do in place.

037-jpg.541038


039-jpg.541039


041-jpg.541040


042-jpg.541041






044-jpg.541042


Notice the contour cut into the Rh side of the lower leg. That was done using a contour gage from Home Depot to pick up the shape of the floor pan.
47969fd4-7f99-42a3-bdbc-e6cbf0ccabe5_400-jpg.541052




Also notice the one stud for the seat that is welded in place. This is the only weld in part.



045-jpg.541043


046-jpg.541044


The studs need to hold the wiring harness in place are flat head screws that were countersunk. The heads are flush and the locknuts used to hold them in place. A little Super Glue on the threads insures that they will never come loose.

048-jpg.541045


052-jpg.541046




Here’s what the finished repair looks like

054-jpg.541047




It may be that welding the "L" shaped pieces in place one at a time would work. Cut and fit one "L", drill the bolt hole and the weld a bolt in the hole that is for the missing stud. Then weld it in place. Then repeat the cut and fit of the next "L" and weld it in place.
 
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alutwon

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one more thing, when I did the deadener on the doors I didn't do it on the inside. I put it on the interior outer part where the door panel is. you just have to make sure you cut holes for the bolts and such and maybe leave an access for the lock actuator. also added a better base response to the door speakers.
 

sav22rem22

Active Member
Feb 6, 2020
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The floor pan where the seat bolts down is cracked. This is a headache because you must remove the carpet and interior to get to the damaged area to fix it.

This is what my solution to the problem looks like:

I don't have a welder and it would have been difficult to get the car to a place that could do a satisfactory job of welding up a suitable repair..

Two pieces of 16 gauge steel that overlap at the top to make an approximately 1/8" thick hat section.

The angle sections are riveted together with monel 1/8" diameter solid rivets.

The repair is secured in place with 18 each 1/8" Cherrylock Aircraft Structural rivets.These are NOT the same as cheap Pop rivets!!! Each rivet has ashear strength of greater than 600 pounds and there are 18 rivets. The total shear strength for the riveted joint is over 5400 pounds per side. Considering my body weight, that would hold over 25 G impact for each side of the repair.

Notice that the first picture shows the damaged material cut out and the cracks are stop drilled. This keeps the cracks from spreading further and is a necessary step. This necessary even if you weld whatever repair you do in place.

037-jpg.541038


039-jpg.541039


041-jpg.541040


042-jpg.541041






044-jpg.541042


Notice the contour cut into the Rh side of the lower leg. That was done using a contour gage from Home Depot to pick up the shape of the floor pan.
47969fd4-7f99-42a3-bdbc-e6cbf0ccabe5_400-jpg.541052




Also notice the one stud for the seat that is welded in place. This is the only weld in part.



045-jpg.541043


046-jpg.541044


The studs need to hold the wiring harness in place are flat head screws that were countersunk. The heads are flush and the locknuts used to hold them in place. A little Super Glue on the threads insures that they will never come loose.

048-jpg.541045


052-jpg.541046




Here’s what the finished repair looks like

054-jpg.541047




It may be that welding the "L" shaped pieces in place one at a time would work. Cut and fit one "L", drill the bolt hole and the weld a bolt in the hole that is for the missing stud. Then weld it in place. Then repeat the cut and fit of the next "L" and weld it in place.
Great write up. I was honestly lost on what to do with that. Someone had a long stud with a flat circular head on the bottom ran up through the floor to secure the seat and I kinda ignored it until now. Now I’ve got the motivation to fix it. Thanks jrichker
 

sav22rem22

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Feb 6, 2020
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one more thing, when I did the deadener on the doors I didn't do it on the inside. I put it on the interior outer part where the door panel is. you just have to make sure you cut holes for the bolts and such and maybe leave an access for the lock actuator. also added a better base response to the door speakers.
Yeah that’s another reason I want to sound deaden. I do enjoy my car audio and can almost barely hear it over road noise and exhaust noise. I’ve seen some people saying they put sound deadening on the inside of the interior quarter panels. Did you do this? I may look into it
 

Boostedpimp

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May 8, 2003
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Damn looks like someone didn't want to cut open the trans whole large enough to fit the manual shifter in like they are suppose to. Autos had a smaller whole in the shifter tunnel than manuals so to do it properly your suppose to trim that whole up larger and install a transmission hump cut out of a junk manual car or buy it new from lmr. https://lmr.com/item/LRS-7277A-K/1979-93-Mustang-Manual-Transmission-Hump-Kit

Do you need the trans hump? no but you do need to cut that whole out around that shifter some.

As far as the seat stud being ripped out. that actually is pretty common with a car that has seen some light to light pulls hard and typically you need to replace that cross section https://lmr.com/item/LRS-10692/1979...DsKAE_VGrqaSOzAqzpfHPFjoy1UjLLogaAmpcEALw_wcB

but if you can clean it up you would probably be able to get by fine with this https://lmr.com/item/LRS-10692BRC-K/mustang-seat-brace-repair-kit-79-04
 

alutwon

New Member
Dec 10, 2020
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Yeah that’s another reason I want to sound deaden. I do enjoy my car audio and can almost barely hear it over road noise and exhaust noise. I’ve seen some people saying they put sound deadening on the inside of the interior quarter panels. Did you do this? I may look into it
if you mean on the plastic, no I didn't. I did put a few squares behind the window on the metal but there isn't much space and it probably didn't do much. I struggled for a few years trying to get decent audio but these cars just aren't set up for that. after the deadener I put an amp and a sub in the hatch and it I'm far happier with it now:)
 

sav22rem22

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Feb 6, 2020
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Damn looks like someone didn't want to cut open the trans whole large enough to fit the manual shifter in like they are suppose to. Autos had a smaller whole in the shifter tunnel than manuals so to do it properly your suppose to trim that whole up larger and install a transmission hump cut out of a junk manual car or buy it new from lmr. https://lmr.com/item/LRS-7277A-K/1979-93-Mustang-Manual-Transmission-Hump-Kit

Do you need the trans hump? no but you do need to cut that whole out around that shifter some.

As far as the seat stud being ripped out. that actually is pretty common with a car that has seen some light to light pulls hard and typically you need to replace that cross section https://lmr.com/item/LRS-10692/1979...DsKAE_VGrqaSOzAqzpfHPFjoy1UjLLogaAmpcEALw_wcB

but if you can clean it up you would probably be able to get by fine with this https://lmr.com/item/LRS-10692BRC-K/mustang-seat-brace-repair-kit-79-04
Yeah I think I failed to mention it but I actually have the tunnel hump in the house waiting to borrow a grinder with a cut off wheel so I can cut out the tunnel. The cross brace is basically ready for the seat brace repair kit but I’m just waiting for it to come back into stock I’m not sure why it’s still out of stock when they just released it like 3 weeks ago but it is a very useful looking kit.
 

sav22rem22

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Feb 6, 2020
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if you mean on the plastic, no I didn't. I did put a few squares behind the window on the metal but there isn't much space and it probably didn't do much. I struggled for a few years trying to get decent audio but these cars just aren't set up for that. after the deadener I put an amp and a sub in the hatch and it I'm far happier with it now:)
So one more question, I’m going to have to remove the factory sound deadening in the foot wells to uncover rust holes like I said but I am going to be putting back either noico or kilmat 80 mil. Would those be quieter than the factory sound deadening or would I be adding noise by removing it?
 

Boostedpimp

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May 8, 2003
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So one more question, I’m going to have to remove the factory sound deadening in the foot wells to uncover rust holes like I said but I am going to be putting back either noico or kilmat 80 mil. Would those be quieter than the factory sound deadening or would I be adding noise by removing it?
I've used noico and yes it will make a difference over the factory stuff.. you'll like it
 

Boostedpimp

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Yeah I think I failed to mention it but I actually have the tunnel hump in the house waiting to borrow a grinder with a cut off wheel so I can cut out the tunnel. The cross brace is basically ready for the seat brace repair kit but I’m just waiting for it to come back into stock I’m not sure why it’s still out of stock when they just released it like 3 weeks ago but it is a very useful looking kit.
Nice, yeah i've been waiting for the seat brace repair kit to get back into stock too
 

sav22rem22

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I've used noico and yes it will make a difference over the factory stuff.. you'll like it
Alright great. I’m assuming I’ll have to remove the factory sound deadening anyway to put any new deadener on especially since my factory deadener is peeling and most will have to be torn out anyway
 
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sav22rem22

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Well I removed the factory sound deadening at least up to the firewall on both sides and found the rust I was looking for and…yikes..
057769C4-F7C8-49BB-9CFC-9B59CBCC3997.jpeg

34876D3F-4855-469D-B930-3D7E010FDCEF.jpeg

Drivers side is worse off than the passenger side. I knew there was rust but I didn’t understand the scale of it. I’m sure worse has been fixed before. Also, the insulation on the passenger side firewall is absolutely disgusting. I guess when the heater core rotted all those years ago it soaked the insulation too. I probably need to get that mess out of my car and replace that too
 

sav22rem22

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yea definitely cut out that cancer
Yeah I’m probably going to go ahead and buy new pans now. Also the firewall insulation is absolutely disgusting and I think I’m going to also replace it. I guess where the old heater core went out all those years ago it stayed trapped in the insulation and made it smell rancid.
 

sav22rem22

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No bad smells at all. It's all covered by a new carpet, and other interior parts, but, no odors at all.
Hmm I’ll have to look into it then. I’ve lost a huge amount of motivation with the new rust found and the realization that my cowl under the windshield is probably rusted out as well
 
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sav22rem22

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Check the area where the doors bolt to the cowel, they may need attention too.
Yeah I looked at the area where the bottom hinge bolts to the body and of course it’s crusty. At least on the drivers side. At this point I’m too scared to even text the guy that’s going to be doing all the work in fear of the bill lol
 

a91what

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I used the 80mil Killmat and then 2 layers of the noico heat barrier. the car is very quite and it stopped the heat off the floorboard.
 

General karthief

wonder how much it would cost to ship you a pair
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I can say the Dynomat I put in the valdez did the job, it was very hot under my feet and down the trans tunnel before, the heat under this car is enough it melts the rubber seal at the shifter hole.
now it's barley warm.
 
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