Replacement Cab Crossmember

[cavalry]

I am looking for a replacement rear cab mount crossmemberr for my 87. GM shows is as no longer available. Is there a source, or will I need to rebuild existing?

 

[chengny]

I am in kind of the same situation as you. I am restoring my 86 K30 and have been looking for a rear crossmember. Mine is bent, not rotted ( I bent it while towing my van into the driveway this past winter - the bed and bumper were off) so I do have the option of returning it to it's original shape.

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Anyway to answer your question as to availability of NOS crossmembers (at least from what I have found) - they are NLA anywhere. Same goes for body mount brackets. I have one NOS bracket in hand and would like to replace both but have had no luck.

You didn't mention what the issue is with yours, but I am assuming it is wasted to the point of being unusable?

If that is the case, it is strange because my cab mount crossmember looks like it's almost brand new. I was amazed how clean it was. Same goes for the rear cross - other than the fact that it is bent.

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But the cross between the rear and cab mount crosses is a different story. It isn't hardly what you'd call wasted but does have a good amount of surface rust:

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I haven't given up my search yet. If I run across any possible source for these type of parts I will let you know. But - I hate to say it - these parts will probably be only available in junkyards.

What are you using for a part number? I show that particular cross (for an 87 V303) as being part number 15593955.

 

[MadOgre]

I am in kind of the same situation as you. I am restoring my 86 K30 and have been looking for a rear crossmember. Mine is bent, not rotted ( I bent it while towing my van into the driveway this past winter - the bed and bumper were off) so I do have the option of returning it to it's original shape.

You must be registered for see images attach

Anyway to answer your question as to availability of NOS crossmembers (at least from what I have found) - they are NLA anywhere. Same goes for body mount brackets. I have one NOS bracket in hand and would like to replace both but have had no luck.

You didn't mention what the issue is with yours, but I am assuming it is wasted to the point of being unusable?

If that is the case, it is strange because my cab mount crossmember looks like it's almost brand new. I was amazed how clean it was. Same goes for the rear cross - other than the fact that it is bent.

You must be registered for see images attach

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But the cross between the rear and cab mount crosses is a different story. It isn't hardly what you'd call wasted but does have a good amount of surface rust:

You must be registered for see images attach

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I haven't given up my search yet. If I run across any possible source for these type of parts I will let you know. But - I hate to say it - these parts will probably be only available in junkyards.

What are you using for a part number? I show that particular cross (for an 87 V303) as being part number 15593955.

Hey Jerry! What would be the best way to swap out that cab cross member? You would pretty much have to disassemble the entire frame rear of that cross member so that you could slide it in and out heh?

 

[cavalry]

You didn't mention what the issue is with yours, but I am assuming it is wasted to the point of being unusable?


What are you using for a part number? I show that particular cross (for an 87 V303) as being part number 15593955.

It has severe corrosion in the right body mount, The rest is not terrible. I have a parts truck that while does not have that particular part it has others that could be used as a filler piece to rebuild the rotten one.

I do not have access to the number as I just set the cab back on. It was prominently stamped on the cross member.

 

[cavalry]

Hey Jerry! What would be the best way to swap out that cab cross member? You would pretty much have to disassemble the entire frame rear of that cross member so that you could slide it in and out heh?

If it will not wiggle out, slice it in half and weld it back together in place. A lot easier than driving out all the rearward rivets.

 

[MadOgre]

If it will not wiggle out, slice it in half and weld it back together in place. A lot easier than driving out all the rearward rivets.

That does not sound like a very well thought out plan!

 

[MadOgre]

Just rebuild the rotten one. Do not cut it in half!

 

[cavalry]

Just rebuild the rotten one. Do not cut it in half!

Lol...and why not? I would rather do that that disassemble the frame to get it in. Its regular old mild steel, not like its HSLA. Bolt the ends in, fixture to establish straightness and go to town.

 

[chengny]

Hey Jerry! What would be the best way to swap out that cab cross member? You would pretty much have to disassemble the entire frame rear of that cross member so that you could slide it in and out heh?

Maybe not. Notice the construction of that middle cross. Unlike the cab mount cross and the rear cross, the middle one is made up of three parts. Two support gussets and the actual cross member. If the rivets were removed as shown below, the main cross beam could be slid back away from the gussets. Then, if one end were tilted all the way down to the lower flange of the frame channel, the other end might be able to clear the top flange on the other side. I haven't measured carefully or done the math yet.

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If that method alone doesn't allow it to be removed, removal of the rear cross would be necessary. At that point, the frame could be spread slightly (or the middle cross could be finagled all the way out from the back of the frame channels).

 

[Old77]

^^^^good ideas here

 

[MadOgre]

Hey Jerry! What would be the best way to swap out that cab cross member? You would pretty much have to disassemble the entire frame rear of that cross member so that you could slide it in and out heh?

Maybe not. Notice the construction of that middle cross. Unlike the cab mount cross and the rear cross, the middle one is made up of three parts. Two support gussets and the actual cross member. If the rivets were removed as shown below, the main cross beam could be slid back away from the gussets. Then, if one end were tilted all the way down to the lower flange of the frame channel, the other end might be able to clear the top flange on the other side. I haven't measured carefully or done the math yet.

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If that method alone doesn't allow it to be removed, removal of the rear cross would be necessary. At that point, the frame could be spread slightly (or the middle cross could be finagled all the way out from the back of the frame channels).

But that's not the cab cross member. I have entertained the idea of removing the cab support I have with the extra support brackets which seem to be an 85' and newer thing and swapping it into a different frame, but I cant envision any way of getting it in and out with out having to take the whole frame apart.

Ya the cross member that goes from rear hanger to hanger could be taken out by itself for sure. I have actually done that before. But I don't know about the cab support one?

 

[MadOgre]

Lol...and why not? I would rather do that that disassemble the frame to get it in. Its regular old mild steel, not like its HSLA. Bolt the ends in, fixture to establish straightness and go to town.

Nope! They are high tensile carbon steel and not the best metal for welding with. Technically your not even supposed to weld the stuff. As far as I know. I know yes you can weld it but a non welded piece will far outlast a welded piece. So yes you can weld it but it would be much stronger if you didn't.

 

[cavalry]

Nope! They are high tensile carbon steel and not the best metal for welding with. Technically your not even supposed to weld the stuff. As far as I know. I know yes you can weld it but a non welded piece will far outlast a welded piece. So yes you can weld it but it would be much stronger if you didn't.

Please reference this manual on page 6.
https://www.gmheritagecenter.com/do...its/Chevrolet-Trucks/1986-Chevrolet-Truck.pdf

Frame steel is 36-39K PSI. This puts it smack in the middle of low carbon steel. High carbon would have a much higher tensile strength. GM could have used any one of many alloys but A36 is very likely. Regardless of the alloy I can verify that a competent weldor can weld this vintage of frame with zero issues.

 

[chengny]

The 36,000-39,000 designation refers to the yield strength as a function of psi (determined by a standardized testing method). A 36K-39K rating would classify structural steel at the very upper limit of mild steel:

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I would imagine a simple SMAW (arc welding) procedure using a small diameter 6011 rod would be acceptable. The first two digits of a rod's code indicate the yield strength of the finished weld joint. So a weld made with a 60XX rod has a yield strength of 60,000 psi - which exceeds the strength of the base material. Allow cool down between passes and no pre-heat required (if the steel is less than 1/4").

Just some general notes on crack repair/frame welding - from the 1986 GMC Light Truck Service Manual:

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[Old77]

The 36,000-39,000 designation refers to the yield strength as a function of psi (determined by a standardized testing method). A 36K-39K rating would classify structural steel at the very upper limit of mild steel:

You must be registered for see images attach

I would imagine a simple SMAW (arc welding) procedure using a small diameter 6011 rod would be acceptable. The first two digits of a rod's code indicate the yield strength of the finished weld joint. So a weld made with a 60XX rod has a yield strength of 60,000 psi - which exceeds the strength of the base material. Allow cool down between passes and no pre-heat required (if the steel is less than 1/4").

Just some general notes on crack repair/frame welding - from the 1986 GMC Light Truck Service Manual:

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