Crossmember bolts

[Frankenchevy]

I am laying under my truck this afternoon after work contemplating on whether or not I am even going to paint the rest of the frame now or wait until I have my lift to pull the cab off with ease. If I decide to not finish fully painting the frame now, I am definitely going to hit the parts that need a little paint just for temporary protection.

As I am going crazy with a brillo pad I started to wonder why the bolts on my crossmember are longer than necessary... is this a factory thing or was it whatever was laying around when they put this crossmember in last? Also, notice in the picture how deep the serial number stamping is in the frame. Seems a little overzealous to me with the stamping, but what do I know?

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[rpcraft]

It is a factory thing. I have heard a lot of BS about why they did that but never anything from a gm engineer. Two working theories are that for one, gm did that so that the bolts would flex or wiggle some and allow some to allow for if you impact the skid plate but I think that is not the case because in an impact situation they would still sheer off easily enough. The other theory is they put the on there to allow people to adjust for lift kits, but I don't believe that either. I'm sure someone on here will pipe in to something that sounds more like truth than black magix, lol.

 

[idahovette]

On the 79 K-10 I built for my grandson those spacers were between the frame and the crossmember because of the dimensions of the 203 transfer case. In other words they dropped the crossmember.

 

[rpcraft]

On the 79 K-10 I built for my grandson those spacers were between the frame and the crossmember because of the dimensions of the 203 transfer case. In other words they dropped the crossmember.

Someone did that after factory more than likely. OEM position was for it to be above the frame, just usually people use them to space the transmission down after a lift kit to help eliminate dirvetrain vibration created by the angle changing slightly on the rear pinion/driveshaft.

 

[idahovette]

My 75 K-20 is the same way and unless some fairy moved them ,they came from GM factory that way cause I have NOT changed them.

 

[rpcraft]

See, that is why there is confusion as to why they exist and what their intended use is, lol...

 

[Jrgunn5150]

They are factory, my K5 is the same way, I'm not sure why, maybe @Keith Seymore could tell us why.

My suspicion is the same bolts are used elsewhere and it was cheaper/easier to source a bunch of the same.

 

[Craig 85]

On my '79 K15 with a 203 case, the crossmember was below the frame similar to this.

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[Frankenchevy]

Seems like they did the same with the steering box.

 

[Blue Ox]

No manufacturer puts "extra" parts in a vehicle, especially not as a consideration in case the owner wants to modify it later. Here's some quick math. According to Jane Pauley and NBC who did the smear piece on the side saddle fuel tanks, GM made 5 million of these trucks. So, say half of them are Ks (I don't know if the Cs use the spacers too) but if they cost 10¢ each that turns in to $1,000,000 over the production run. GM isn't going to give up that kind of money unless there is a necessity. Kind of like those front support brackets on starters the dealer technicians throw away ("You don't need that.") because it cuts the time they can make on a job.

I've seen at least one other application where a similar system is used. On Caterpillar 3208 engines the injection pump is only locked in place by two bolts on the back of the pump. That mounting flange was often prone to cracking. CAT came out with a revised mounting system using longer bolts with a spacer and a higher torque specification to "increase bolt stretch and improve joint clamp loading."

As to the question of orientation, my truck has the collars below the crossmember like Craig 85's. To the best of my recollection that's the way it came from the factory, but the truck has also had about six transmissions in it, so anything is possible.

 

[Keith Seymore]

It's factory.

The additional length allows for more "bolt stretch", which helps them maintain torque and clamp load over the life of the vehicle.

K

 

[Blue Ox]

Told ya'.

 

[Keith Seymore]

According to Jane Pauley and NBC who did the smear piece on the side saddle fuel tanks, GM made 5 million of these trucks...

Actually - that number needs to be closer to 15 million, according to GM and to NHTSA (that includes pickup, cab/chassis, Blazer and Suburban).

K

 

[Blue Ox]

Maybe they did say 15 mil. They say the memory is the second thing to go.

 

[idahovette]

Hey BlueOx speak for yourself LOL