transmission crossmembers - The 1947 - Present Chevrolet & GMC Truck Message Board Network

454c10 · 03-14-2004, 10:44 PM

Hello everyone, my question is a simple one. Is there a difference in the tranny crossmembers between 1978 and 1979(no converter vs. converter)? Thanks for the help.

gchemist · 03-15-2004, 12:03 AM

What you mean by converter?
No the transmission crossmembers will interchange. The design might be different but the mounting holes are the same. Welcome to the board.

Stepsides 4Ever · 03-15-2004, 12:22 AM

Welcome to the board!

The short answer is, from what we saw today, yes..

The one that was for the catalytic converter had a dropped section just past the tranny mount area and below the drivers seat. It was obvious the converter should have mounted above the crossmember. Then it wrapped around the bottom of the drivers side frame rail and up the side. It bolted on the passenger side inside the frame rail - outside on the vertical section of the frame on the drivers side. Kinda weird looking.

The one that we bought was from an earlier truck (without the key in the column...not sure what year) and it went straight across, with a slight dropped section in the middle, p/n 3999964 stamped in it.

Hope this helps!

454c10 · 03-16-2004, 05:43 PM

Thanks for the welcome and the replies. Specifically, I need to know about exhaust clearance. It dosent look to me like an exhaust pipe will clear the top of the crossmember on the drivers side. This mount comes straight across to the trans and then dips to clear the catalytic converter on the passenger side. The exhaust splits out of the converter and becomes duals. I am installing headers and 3" pipes. You can understand my confusion.
I know that 78 had full duals, 79 did not. Thats why I wondered if the crossmember was different.
Thanks again for the warm welcome.

**swervin ervin** · 03-16-2004, 05:54 PM

Sounds like you have one for 88 up. Our trucks had the cat on the drivers side.

Stepsides 4Ever · 03-16-2004, 06:01 PM

Well, you can always do what we do, assuming you have a local pick-a-part yard nearby...just take your tape measure, get some measurements of what you need, and go crawl under some trucks.

There is something weirdly sexy about a woman with greasy hands, so if you can talk your wife/girlfriend/significant other into going with you, all the better!

454c10 · 03-16-2004, 06:19 PM

I suppose somewhere along the way somebody changed it. I never gave that athought since all the numbers match. I'm not fond of crawling under things out here, scorpions you know. But that is the easy way to find out Thanks for the help.

MylilBowTie · 03-16-2004, 10:21 PM

Does it look like this?

Or this?

454c10 · 03-16-2004, 10:59 PM

well of course at my age, brain death does begin to set in.it looks more like the first one but flatter on the passenger side( about 4" to the floor). Of course the converter is on the drivers side! I was looking to my right from the passenger side. what can I say. Anyway I see how u solved the problem, going over and under.
I should find a 78 or earlier, huh. Just to run straight?
Thanks for the help. Good place for the balance pipe too.

03-14-2004, 10:44 PM	#1
454c10 Registered User Join Date: Mar 2004 Location: Arizona Posts: 8	transmission crossmembers Hello everyone, my question is a simple one. Is there a difference in the tranny crossmembers between 1978 and 1979(no converter vs. converter)? Thanks for the help.

03-15-2004, 12:03 AM	#2
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	What you mean by converter? No the transmission crossmembers will interchange. The design might be different but the mounting holes are the same. Welcome to the board. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

03-15-2004, 12:22 AM	#3
Stepsides 4Ever Stepsides Are Bedder Join Date: Feb 2004 Location: Norco, CA Posts: 238	Tranny Crossmembers Welcome to the board! The short answer is, from what we saw today, yes.. The one that was for the catalytic converter had a dropped section just past the tranny mount area and below the drivers seat. It was obvious the converter should have mounted above the crossmember. Then it wrapped around the bottom of the drivers side frame rail and up the side. It bolted on the passenger side inside the frame rail - outside on the vertical section of the frame on the drivers side. Kinda weird looking. The one that we bought was from an earlier truck (without the key in the column...not sure what year) and it went straight across, with a slight dropped section in the middle, p/n 3999964 stamped in it. Hope this helps!

03-16-2004, 05:54 PM	#5
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Sounds like you have one for 88 up. Our trucks had the cat on the drivers side. __________________ Mike 1985 Chevy C-10

03-16-2004, 10:21 PM	#8
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	Does it look like this? Or this? __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

03-16-2004, 05:43 PM	#4
454c10 Registered User Join Date: Mar 2004 Location: Arizona Posts: 8	Thanks for the welcome and the replies. Specifically, I need to know about exhaust clearance. It dosent look to me like an exhaust pipe will clear the top of the crossmember on the drivers side. This mount comes straight across to the trans and then dips to clear the catalytic converter on the passenger side. The exhaust splits out of the converter and becomes duals. I am installing headers and 3" pipes. You can understand my confusion. I know that 78 had full duals, 79 did not. Thats why I wondered if the crossmember was different. Thanks again for the warm welcome.

03-16-2004, 06:01 PM	#6
Stepsides 4Ever Stepsides Are Bedder Join Date: Feb 2004 Location: Norco, CA Posts: 238	Well, you can always do what we do, assuming you have a local pick-a-part yard nearby...just take your tape measure, get some measurements of what you need, and go crawl under some trucks. There is something weirdly sexy about a woman with greasy hands, so if you can talk your wife/girlfriend/significant other into going with you, all the better!

03-16-2004, 06:19 PM	#7
454c10 Registered User Join Date: Mar 2004 Location: Arizona Posts: 8	I suppose somewhere along the way somebody changed it. I never gave that athought since all the numbers match. I'm not fond of crawling under things out here, scorpions you know. But that is the easy way to find out Thanks for the help.

03-16-2004, 10:59 PM	#9
454c10 Registered User Join Date: Mar 2004 Location: Arizona Posts: 8	well of course at my age, brain death does begin to set in.it looks more like the first one but flatter on the passenger side( about 4" to the floor). Of course the converter is on the drivers side! I was looking to my right from the passenger side. what can I say. Anyway I see how u solved the problem, going over and under. I should find a 78 or earlier, huh. Just to run straight? Thanks for the help. Good place for the balance pipe too.



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