How to replace the rear cab mount brackets - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Damien8086 · 05-05-2018, 06:53 PM

Hello,

I have a 1970 C10 CST and I had ordered the cab mounting kit from LMC in hopes to replace the worn out hardware and cushions on my truck.

Unfortunately once I got in there I found that the hex bolts that I took off of the rear appear to actually be the same size as the larger hex bolts that come with the kit that are meant for the front of the cab. Also the upper cushion does not really resemble the replacement upper cushion that I got with the kit. Worst of all the driver side rear bracket is completely rusted out. At some point someone appears to have put a couple of metal plates on the top of the cab mount bracket attached to the frame to (I guess) work as shims and to make up for the rusted out bolt hole in the bracket. I have attached some pictures.

My question is how do I replace the brackets themselves? I see a lot of posts about doing the cab mount kit job, but very little about the brackets. Is this a job that requires welding experience (I have none nor the tools)?

Thanks for any help that you can provide.

Damien8086 · 05-05-2018, 06:55 PM

Pictures...

bob8619 · 05-05-2018, 07:03 PM

Grind off those rivets holding it to the frame and use bolts to install some new used ones.

Damien8086 · 05-05-2018, 07:21 PM

Does that upper cushion that I removed look correct? It appears to have metal in it around the hole whereas the new one is just rubber.

I don't have a grinder, is there a specific one I should get and certain type of cutting wheel?

My other concern is that if I replace the bracket on the frame then the hex bolt will no longer fit in the nut welded to the inside cab floor. Would it make sense to replace the rusted out rear bracket with a new front bracket so that the bolt still fits?

BCOWANWHEELS · 05-05-2018, 07:29 PM

any metal shop can duplicate those frame brackets exactly or even rebuild yours

Artofdeath · 05-05-2018, 07:35 PM

I ordered front and rear brackets from LMC. Taking those rivets out isn't to bad. Grind them flat, drill them and use a heavy hammer and a punch to push em out.

I feel your pain brother. Doing this job myself.

Damien8086 · 05-05-2018, 07:41 PM

Thank you for the replies.

Should I also grind off the nut on the inside of the cab (on the floor under the gas tank), otherwise the hex bolt that goes with the new rear cab mount bracket won't fit.

What kind of bolts did you use on the bracket?

Artofdeath · 05-05-2018, 07:45 PM

Not sure about your budget. Harbor Freight has cheap grinders that will work but I recommend dewalt. The adjustable guard is the way to go.
http://tinyurl.com/y9frhlcu

Cut off wheel http://tinyurl.com/yadtscpe

Grinding wheel
https://www.harborfreight.com/4-12-i...eel-61152.html

Artofdeath · 05-05-2018, 07:49 PM

I haven't gotten that far yet. Did you get a mount kit with new bolts?

I am bolting, then welding my brackets on. I will use the bolts that came with my mount kit, if the nut doesn't fit I will grind it off and replace it.

Damien8086 · 05-05-2018, 08:06 PM

Yeah i got the mount kit, but the rear mount bolt is smaller than the nut attached to the inside floor. It looks like the larger bolts that are in the front were also used in the rear on this truck.

MQUnlimited · 05-05-2018, 08:15 PM

What's the reason why you can't reuse the old bolt that was removed or get the correct pitch/diameter bolt? That would be simpler than grinding the nut off because then you'll either have to weld on a new nut or you'll just have to hold it as you're tightening the hardware. Only reason I see being beneficial to grind it off is if it was strip IMO.

Damien8086 · 05-05-2018, 08:24 PM

The bolt and washers that came with the kit and I am assuming the hole in the new bracket (haven't bought that yet) are a smaller diameter

**Smitty** · 05-05-2018, 08:54 PM

Rather than grinding the not off the cab floor to make the wrong size bolt work doesn't make sense. Just buy a bolt that is the correct diameter and length. Not sure but common sense tells me that they would be the same diameter bolt front and rear.

Damien8086 · 05-05-2018, 10:19 PM

The bolt, washer, and shim for the rear that came in the kit that I received is definitely a smaller diameter than the bolt, washer, and square shaped shim that came in the kit for the front of the cab.

The kit I received could have been packed wrong, but I doubt it since the bolts are also listed individually at different prices ($7.95 for the front and $4.95 for the rear). Maybe someone else who has ordered a kit can confirm if the rear hardware is a smaller diameter.

I agree though, if the hole in the rear bracket will accept the larger bolt then I'd just get a new bolt, washer, and shim rather than mess with the nut on the inside floor.

TXGreaseMonkey · 05-05-2018, 11:05 PM

Ive been using Harbor Freight tools as a hobby mechanic (not professional) for years. Grinders, drills, sawzall, miter saw, air compressor, torque wrenches, shop press, etc. Very rarely do i have issues, and if i do i take it back and they swap it. They're at least a good option to get started in welding/grinding/etc for tools you might only periodically use. If you do use them, pick up a car magazine like Hot Rod or something, there's usually always Harbor Frieght one or two page ads near the back. 20% off minimum on any single item and often multiple free stuff (rags, lights, magnet trays, etc).

On a side note, have you simply tried calling LMC and explaining they may have sent you the wrong parts. Verify part numbers, make/model with them on the phone, and they may just send you a new kit since they possibly screwed up.

**GMCPaul** · 05-06-2018, 06:15 AM

Quote:

Originally Posted by Damien8086

Maybe someone else who has ordered a kit can confirm if the rear hardware is a smaller diameter.

1/2 ton 2wd Front Mount bolts- 9/16"-12 x 6" hex head cap bolt
1/2 ton Rear cab mount bolts, 7/16-14 x 6", hex head bolt
Core support bolts, 7/16-14 x 4", carriage head bolt
Bed Bolts 67-72 8- carriage bolts 3/8-16 x 4"

**Longhorn 69** · 05-06-2018, 08:19 AM

You probably already did this, but did you try the bolt in the nut to see if it fit? the hole in the cab mount brackets are sized for the actual bushings, not the diameter of the bolt, also make sure that if you by a larger bolt to fit the nut that it fits through the bushings also. It might be hard to get to the rivets with a grinder with the cab on, so you may have to center punch the rivets and drill the head of them then chisel the head off and use a punch to punch them out. Not to easy anyway you do it.

Damien8086 · 05-06-2018, 10:28 AM

Thank you for all of the suggestions and information.

Yes, the larger bolt that is meant for the front (I guess the 9/16 one) fits in the nut in the rear on the inside floor (near the underside of the fuel tank). It also fits through the bushings fine, but it does not fit through the washer or the shim that comes with the kit so I'll just swap those out.

I guess the nuts on the inside floor aren't the original ones since the bolt meant for the rear is 7/16, but it's funny because they sure look like they've always been there. I don't suppose it is possible that some of these trucks came with 9/16 bolts in the front and back?

Damien8086 · 05-06-2018, 10:45 AM

I see that Brothers charges about $99.95 for the pair of rear cab mount brackets here: https://www.brotherstrucks.com/67-72...tinfo/FM72CMR/

...and that LMC only charges $29.95 each for them here: http://www.lmctruck.com/icatalog/cb/full.aspx?Page=17

Anyone know if there is a difference in quality that warrants the extra $40 for the pair from Brothers?

Artofdeath · 05-07-2018, 01:38 PM

Not sure about the Brother's, I purchased the LMC's and they are skookum.

**Longhorn 69** · 05-07-2018, 10:08 PM

Brothers is priced for a pair, and LMC is $30. each. Why Brothers is $40. more is unknown.
Good Luck with your project!

**Longhorn 69** · 05-07-2018, 10:11 PM

Reread your post. $40. is exactly what you said! I don't know either.

Damien8086 · 05-21-2018, 08:23 PM

So an update:

I was unable to get the damaged bracket off. The cab is attached and so I had very little room to work. I tried to drill it out, but it would not budge.

I ended up just trying to repair it with some POR-15 epoxy. After applying the epoxy I let it sit for about 24 hours and then drilled a hole in it for the bolt and spacer. I then painted it with the POR-15 rust paint, let that sit for 24 hours, then sanded, then applied one coat of the top coat spray-on.

Getting the top bushing and the shim that goes on top of that on was a pain. I just managed to squeeze it in.

It seems stronger than before, but time will tell I guess how it holds up. Now on to the other 3 corners

Attached pictures.

Artofdeath · 05-22-2018, 07:49 AM

Looks good partner! As long as the frame bracket holds I think you are golden. Having access to the rivets to replace the frame brackets is why I removed my cab. I can't imagine doing it with the cab on, without a lift, laying flat on my back. Yah, I'd rather you punch me in the face, lol!

05-05-2018, 06:53 PM	#1
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	How to replace the rear cab mount brackets Hello, I have a 1970 C10 CST and I had ordered the cab mounting kit from LMC in hopes to replace the worn out hardware and cushions on my truck. Unfortunately once I got in there I found that the hex bolts that I took off of the rear appear to actually be the same size as the larger hex bolts that come with the kit that are meant for the front of the cab. Also the upper cushion does not really resemble the replacement upper cushion that I got with the kit. Worst of all the driver side rear bracket is completely rusted out. At some point someone appears to have put a couple of metal plates on the top of the cab mount bracket attached to the frame to (I guess) work as shims and to make up for the rusted out bolt hole in the bracket. I have attached some pictures. My question is how do I replace the brackets themselves? I see a lot of posts about doing the cab mount kit job, but very little about the brackets. Is this a job that requires welding experience (I have none nor the tools)? Thanks for any help that you can provide.

05-05-2018, 06:55 PM	#2
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets Pictures... Attached Images

05-05-2018, 07:03 PM	#3
bob8619 Registered User Join Date: Jan 2014 Location: Ft Myers Florida Posts: 571	Re: How to replace the rear cab mount brackets Grind off those rivets holding it to the frame and use bolts to install some new used ones. __________________ 1968 C10

05-05-2018, 07:21 PM	#4
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets Does that upper cushion that I removed look correct? It appears to have metal in it around the hole whereas the new one is just rubber. I don't have a grinder, is there a specific one I should get and certain type of cutting wheel? My other concern is that if I replace the bracket on the frame then the hex bolt will no longer fit in the nut welded to the inside cab floor. Would it make sense to replace the rusted out rear bracket with a new front bracket so that the bolt still fits? Attached Images

05-05-2018, 07:29 PM	#5
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: How to replace the rear cab mount brackets any metal shop can duplicate those frame brackets exactly or even rebuild yours __________________ I BELIEVE IN JOHN 3:16

05-05-2018, 07:35 PM	#6
Artofdeath Registered User Join Date: Jul 2017 Location: Sandusky, Ohio USA Posts: 104	Re: How to replace the rear cab mount brackets I ordered front and rear brackets from LMC. Taking those rivets out isn't to bad. Grind them flat, drill them and use a heavy hammer and a punch to push em out. I feel your pain brother. Doing this job myself.

05-05-2018, 07:41 PM	#7
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets Thank you for the replies. Should I also grind off the nut on the inside of the cab (on the floor under the gas tank), otherwise the hex bolt that goes with the new rear cab mount bracket won't fit. What kind of bolts did you use on the bracket?

05-05-2018, 07:45 PM	#8
Artofdeath Registered User Join Date: Jul 2017 Location: Sandusky, Ohio USA Posts: 104	Re: How to replace the rear cab mount brackets Not sure about your budget. Harbor Freight has cheap grinders that will work but I recommend dewalt. The adjustable guard is the way to go. http://tinyurl.com/y9frhlcu Cut off wheel http://tinyurl.com/yadtscpe Grinding wheel https://www.harborfreight.com/4-12-i...eel-61152.html

05-05-2018, 07:49 PM	#9
Artofdeath Registered User Join Date: Jul 2017 Location: Sandusky, Ohio USA Posts: 104	Re: How to replace the rear cab mount brackets I haven't gotten that far yet. Did you get a mount kit with new bolts? I am bolting, then welding my brackets on. I will use the bolts that came with my mount kit, if the nut doesn't fit I will grind it off and replace it.

05-05-2018, 08:06 PM	#10
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets Yeah i got the mount kit, but the rear mount bolt is smaller than the nut attached to the inside floor. It looks like the larger bolts that are in the front were also used in the rear on this truck.

05-05-2018, 08:15 PM	#11
MQUnlimited Registered User Join Date: Jul 2017 Location: Socal Posts: 48	Re: How to replace the rear cab mount brackets What's the reason why you can't reuse the old bolt that was removed or get the correct pitch/diameter bolt? That would be simpler than grinding the nut off because then you'll either have to weld on a new nut or you'll just have to hold it as you're tightening the hardware. Only reason I see being beneficial to grind it off is if it was strip IMO.

05-05-2018, 08:24 PM	#12
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets The bolt and washers that came with the kit and I am assuming the hole in the new bracket (haven't bought that yet) are a smaller diameter

05-05-2018, 08:54 PM	#13
Smitty Senior Member Join Date: Dec 1999 Location: Spring Valley, Ca. Posts: 1,100	Re: How to replace the rear cab mount brackets Rather than grinding the not off the cab floor to make the wrong size bolt work doesn't make sense. Just buy a bolt that is the correct diameter and length. Not sure but common sense tells me that they would be the same diameter bolt front and rear. __________________ Smitty '71 Short Fleetside Spring Valley, Ca.

05-05-2018, 10:19 PM	#14
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets The bolt, washer, and shim for the rear that came in the kit that I received is definitely a smaller diameter than the bolt, washer, and square shaped shim that came in the kit for the front of the cab. The kit I received could have been packed wrong, but I doubt it since the bolts are also listed individually at different prices ($7.95 for the front and $4.95 for the rear). Maybe someone else who has ordered a kit can confirm if the rear hardware is a smaller diameter. I agree though, if the hole in the rear bracket will accept the larger bolt then I'd just get a new bolt, washer, and shim rather than mess with the nut on the inside floor.

05-05-2018, 11:05 PM	#15
TXGreaseMonkey Registered User Join Date: Feb 2017 Location: San Antonio, Texas Posts: 10	Re: How to replace the rear cab mount brackets Ive been using Harbor Freight tools as a hobby mechanic (not professional) for years. Grinders, drills, sawzall, miter saw, air compressor, torque wrenches, shop press, etc. Very rarely do i have issues, and if i do i take it back and they swap it. They're at least a good option to get started in welding/grinding/etc for tools you might only periodically use. If you do use them, pick up a car magazine like Hot Rod or something, there's usually always Harbor Frieght one or two page ads near the back. 20% off minimum on any single item and often multiple free stuff (rags, lights, magnet trays, etc). On a side note, have you simply tried calling LMC and explaining they may have sent you the wrong parts. Verify part numbers, make/model with them on the phone, and they may just send you a new kit since they possibly screwed up. __________________ 1970 C10 Longbed - new project to annoy the wife with...



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05-06-2018, 08:19 AM	#17
Longhorn 69 Junior Member Join Date: Oct 2017 Location: Oregon, Ill. Posts: 62	Re: How to replace the rear cab mount brackets You probably already did this, but did you try the bolt in the nut to see if it fit? the hole in the cab mount brackets are sized for the actual bushings, not the diameter of the bolt, also make sure that if you by a larger bolt to fit the nut that it fits through the bushings also. It might be hard to get to the rivets with a grinder with the cab on, so you may have to center punch the rivets and drill the head of them then chisel the head off and use a punch to punch them out. Not to easy anyway you do it. __________________ Greg 69 Longhorn 396, 4 Speed SM 465, PS, PB, No Air

05-06-2018, 10:28 AM	#18
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets Thank you for all of the suggestions and information. Yes, the larger bolt that is meant for the front (I guess the 9/16 one) fits in the nut in the rear on the inside floor (near the underside of the fuel tank). It also fits through the bushings fine, but it does not fit through the washer or the shim that comes with the kit so I'll just swap those out. I guess the nuts on the inside floor aren't the original ones since the bolt meant for the rear is 7/16, but it's funny because they sure look like they've always been there. I don't suppose it is possible that some of these trucks came with 9/16 bolts in the front and back?

05-06-2018, 10:45 AM	#19
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets I see that Brothers charges about $99.95 for the pair of rear cab mount brackets here: https://www.brotherstrucks.com/67-72...tinfo/FM72CMR/ ...and that LMC only charges $29.95 each for them here: http://www.lmctruck.com/icatalog/cb/full.aspx?Page=17 Anyone know if there is a difference in quality that warrants the extra $40 for the pair from Brothers?

05-07-2018, 01:38 PM	#20
Artofdeath Registered User Join Date: Jul 2017 Location: Sandusky, Ohio USA Posts: 104	Re: How to replace the rear cab mount brackets Not sure about the Brother's, I purchased the LMC's and they are skookum. Attached Images

05-07-2018, 10:08 PM	#21
Longhorn 69 Junior Member Join Date: Oct 2017 Location: Oregon, Ill. Posts: 62	Re: How to replace the rear cab mount brackets Brothers is priced for a pair, and LMC is $30. each. Why Brothers is $40. more is unknown. Good Luck with your project! __________________ Greg 69 Longhorn 396, 4 Speed SM 465, PS, PB, No Air

05-07-2018, 10:11 PM	#22
Longhorn 69 Junior Member Join Date: Oct 2017 Location: Oregon, Ill. Posts: 62	Re: How to replace the rear cab mount brackets Reread your post. $40. is exactly what you said! I don't know either. __________________ Greg 69 Longhorn 396, 4 Speed SM 465, PS, PB, No Air

05-21-2018, 08:23 PM	#23
Damien8086 Registered User Join Date: Mar 2018 Location: Virginia Posts: 45	Re: How to replace the rear cab mount brackets So an update: I was unable to get the damaged bracket off. The cab is attached and so I had very little room to work. I tried to drill it out, but it would not budge. I ended up just trying to repair it with some POR-15 epoxy. After applying the epoxy I let it sit for about 24 hours and then drilled a hole in it for the bolt and spacer. I then painted it with the POR-15 rust paint, let that sit for 24 hours, then sanded, then applied one coat of the top coat spray-on. Getting the top bushing and the shim that goes on top of that on was a pain. I just managed to squeeze it in. It seems stronger than before, but time will tell I guess how it holds up. Now on to the other 3 corners Attached pictures. Attached Images

05-22-2018, 07:49 AM	#24
Artofdeath Registered User Join Date: Jul 2017 Location: Sandusky, Ohio USA Posts: 104	Re: How to replace the rear cab mount brackets Looks good partner! As long as the frame bracket holds I think you are golden. Having access to the rivets to replace the frame brackets is why I removed my cab. I can't imagine doing it with the cab on, without a lift, laying flat on my back. Yah, I'd rather you punch me in the face, lol!

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