Grinding Welds on Firewall Patch

[MuuMuu101]

So I had to patch a new plate to go in my firewall, but have been an awful lot of trouble with my grinder. As you can see I've ended up making new holes for myself and am going to have to cut those areas out, make a patch, and reweld them. I don't have a welder (don't even know how to weld) but am going to either buy or borrow one within the next month so I can finish this job. As you can see I'm inexperienced and my work looks pretty poopy. Basically I'm asking for any advice or help at this point on how to avoid screwing up. My main problems are the bottom corners of the box and clearly the bottom lip.

I've almost got most the welds down but it sure isn't pretty... :banghead: :violent1: :banghead: :newb:

 

[ef8340]

for areas like that I would use a right angle air grinder with a 36 grit pad, also take your time and let the sanding pad do the work you wont need to push hard on it

 

[Dartnut]

What he said. ^^^
Why are you welding a patch over the master cylinder holes anyway?
Just curious.

 

[72ScampTramp]

you could cut the bad part out. Looks as if it may have been rusted in that lower left corner before you started. Or it may take awhile but you could use a piece of copper on the back side and fill it in would take alot of welding.

 

[zkx14]

I usually use a 4 1/2" angle grinder with a grind wheel to knock down the welds then one with a flap disk with 60 to 80 grit to level it. I have 2 grinders so keep them set up that way. For inside a radius I use 90 degree die grinder with stones and/or sanding flap cylinders.
Most important as previous post said - whatever you use- LET THE TOOL DO THE WORK. Also, Try to minimize welds on inside angles unless you can leave them or cover them (seam seal or filler). Saves a lot of clean up.

 

[torredcuda]

Ya, a hard fiber grinding wheel works good for the welds and if your can turn down the speed to have more control. Once the welds are knocked down finish with a regular disc or flapper wheel.

 

[MuuMuu101]

What he said. ^^^
Why are you welding a patch over the master cylinder holes anyway?
Just curious.

It's a little bit of a long story. Old firewall was hacked and rusted due to the previous owner. Same for the brake pedal assembly. I have a 2 bolt master cylinder and a friend was helping me at the time, so we cut the mounting ears off the old mounting bracket and were going to make new ones to accept the new MC. Well, friend is out of the picture and we already welded this panel in its spot so I'm just trying to make due with what I've got.

 

[Dartnut]

It's a little bit of a long story. Old firewall was hacked and rusted due to the previous owner. Same for the brake pedal assembly. I have a 2 bolt master cylinder and a friend was helping me at the time, so we cut the mounting ears off the old mounting bracket and were going to make new ones to accept the new MC. Well, friend is out of the picture and we already welded this panel in its spot so I'm just trying to make due with what I've got.

Oh, i get it now.
I would cut a section out of a donor car and splice it in.
It needs to be strong in this area.
Maybe get it welded in by a professional, a lot cheaper and better if you don't have good welding skills or for that matter a welder.

 

[MuuMuu101]

Thanks for all the help everyone! I'm currently using an electric Dewalt angle grinder with a 4 1/2" cutting wheel I bought at Home Depot. Unfortunately, there's no adjustability in speed. There used to be rust in that lower corner but it didn't look that bad when my friend and I welded the patch in.




f

 

[zkx14]

Ouch! stop. change plans....
You need to get a doner section WITH the brake bracket. This is definitely not a 'learn to weld' job.

 

[MuuMuu101]

Ouch! stop. change plans....
You need to get a doner section WITH the brake bracket. This is definitely not a 'learn to weld' job.

I already bought a new brake pedal assembly out of a 75 Valiant. Pulled it out of the pick-a-part so I have all of the studs and everything. I may have to go with this option, but that still will require someone welding it in and grind welds again...

 

[jos51700]

Dude, the patch section from a donor car wasn't an option last time, but now's your chance. Take advantage of this "opportunity" to make it look factory.

 

[MuuMuu101]

Dude, the patch section from a donor car wasn't an option last time, but now's your chance. Take advantage of this "opportunity" to make it look factory.

If someone has a good sizeable chunk they are willing to cut off their car and offer, sure I guess.

 

[crackedback]

I've got a whole firewall in Indio.

Can cut out just about any section you want.

 

[Princess Valiant]

you have to be really careful about grinding welds ......make sure your grinding the weld and not the other metal .......its easy to weaken the metal around the weld by over grinding

 

[MuuMuu101]

Oh, i get it now.
I would cut a section out of a donor car and splice it in.
It needs to be strong in this area.
Maybe get it welded in by a professional, a lot cheaper and better if you don't have good welding skills or for that matter a welder.

Main problem with this is that I don't know how to weld and the car is on stands in the front. Until I get the calipers rebuilt (hopefully next week) and the hubs on the car, the car isn't rolling anywhere.

 

[MuuMuu101]

you have to be really careful about grinding welds ......make sure your grinding the weld and not the other metal .......its easy to weaken the metal around the weld by over grinding

I was more careful the second time around but after working all day long and spending hours grinding down the firewall till late I had a couple more slip ups. The problem for me is the welds are right next to bends and I've got wires all around I'm trying not to cut into.

 

[Woods74]

I made this mistake also, then I found out what a flap wheel was. Never again.

Might want to cut it out and re do that, that thin metal would keep me up at night.

60 grit, then 120 finish would work great.

 

[MuuMuu101]

So I went to a graduation party tonight and my uncle, who sees my posts on facebook, started asking me about the car. I told him I was having some troubles and showed him some really bad cell phone pictures so he insisted to see it in person to try and give me pointers and help me out. For those of you who don't know my uncle (which should be all of you), my uncle has been doing body work for over 50 years now. He started when he first immigrated here at 16 and now he's 68 doing the same thing trying to break even and live a semi-comfortable life. He took a look and I showed him some dimensions for MC placement I got off of my other thread. He thought I should just reweld the gaps and mark my holes for the master cylinder since I already have the dimensions in hand. He checked the quality of the welds where I grinded it and it was all fairly good except for that bottom portion which will be rewelded again. I'm going to try marking my holes and drilling them out either tomorrow or early this week. Then reweld and regrind the trouble spots when I have time to buy/borrow a welder. If I screw up again, I'm probably just going to ask a member for a patch from their firewall. Thank you for all your help!

 

[Princess Valiant]

if you need a patch i have one too ....i think someone already offered you one ....but just more options ...i have a cut up duster over here.

 

[dbphemi]

You need to get someone that knows how to weld to patch up your grind holes and i think it will be ok. the trick is gonna be figuring out were to cut the new holes. not too hard of a job if you know what your doing. I myself wouldn't mess around with cutting that out and welding in something from another car.

 

[MuuMuu101]

Had to drag my feet to work on the car today. Was really slow about it and not in the mood to work on it but a moparts member gave me some motivation. Anyways, I drilled the 4 MC holes out. I used 67Dart273's measurements and mocked up the holes as best I could. I made sure I triple checked my measurements before drilling (3/8" drill bit) and they were extremely close. Anyways, I tried to fit the brake pedal assembly in and it still doesn't fit. I think my friend and I recessed the firewall in too much as I can only get into the bottom holes partially and it's hitting the front of the dash frame when I'm trying lever it in. If I try taking the whole assembly and bringing it inside the dash and down into its spot, the top studs hit the firewall before the mounting screws fall into place (closest to the driver). Too tired to deal with it now, but help would be appreciated. Thank you for everything so far!

 

[67Dart273]

Those holes don't need to be anywhere near that "tight". I think the ones in the car I photo'd for you are at least 1/2"

 

[MuuMuu101]

Those holes don't need to be anywhere near that "tight". I think the ones in the car I photo'd for you are at least 1/2"

That's good to know. 3/8" drill bit was as large as I had. So I'll borrow a larger one this week.

 

[67Dart273]

I'll tell ya. One of the handiest things I ever bought is a step drill. Mine is only up to 1/2, and you can get much much larger sizes, but they are the best thing in the world for drilling holes in sheet metal. They don't tear up metal like a twist drill. Quality ones are not cheap, but my little 1/2 I've had since the HVAC days of the early 90's. And with that, I'm off to bed.