Confirmation Needed - Trans Cross Member

[Steven R]

In order to pass safety I have been asked to replace my transmission mount and I thought this would be a good time to replace the cross member at this time as well. I have posted some pics and need to make sure that when I go and place an ad in the WTB area I will be asking for the right one. I am 95 % sure that I a crossmember that Fits a 1971 GMC 3/4 ton Longhorn. Just a direct factory replacement. I believe this trans is the factory trans and is the TH350, my glove box door tag say M49 turbo hydra matic.

so the question is... am I right in what I have and what I need?

I am wanting to replace the cross member due to a very bad twist and damage to the one side. At some point PO hit something and the cross member took the brunt of it.

Thanks in advance.

[SS Tim]

Its a TH350 and all the automatic crossmembers are the same. However from that picture (what I can see) it doesn't look like much of a problem and a couple on minutes on a press should take care of that little curl. Might want to consider resealing you speedo drive while you are under there too.

[Steven R]

I was going to try on the shop press to straighten it but wanted to have one as a spare if i just cant make it right. but here's a better pic of the damage. I wasn't really sure if i could get it right again.

thanks for you advise. noted - fix speedo seal @ trans

[SS Tim]

Looks a bit worse in that picture, so it sounds like a plan to get another. Make sure the Longhorn/C30-3500 specific crossmember riser/adapters are also good while its apart.

[michael bustamante]

im pretty sure a 3/4 frame is taller than a 1/2 ton frame, something to remember when looking for an auto trans crossmember.

[SS Tim]

Originally Posted by michael bustamante

im pretty sure a 3/4 frame is taller than a 1/2 ton frame, something to remember when looking for an auto trans crossmember.

Yes there is a difference in general published section height (6.04 vs 6.11") but also the frame thickness. So it pretty much cancels out. When you consider the crossmember assembly is three pieces (fitting between the upper and lower flanges) it can easily accommodate the minor variations between the C10 (105, 115 and 127"wb) and the heavier C20 (127"wb). But it only goes so far hence the adapters on the taller and thicker yet Longhorn and C30 frames.

[bobvilla67]

I have the trans crossmember from big block one ton with the correct spacers. Like the one shown in pic. Will be posting for sale soon as I have no use for it.

[Steven R]

1. My truck has a small block 350 in it with a th350 trans. is the crossmember the same for a 350 big block as for a 350 small block (the trans crossmember)?

this is were I just don't know enough and really wish dad was still alive so I could ask him.

2. I read this and see that I need to make sure it a "longhorn" or "C30" (aka 1 ton) crossmember. is this all I need to know when I start asking for one. or does motor size and trans size matter?

3. I would assume that a crossmember from a longhorn and a 3/4 ton are NOT the same? going by what is being said. why would they have used a different crossmember in a long horn 3/4 ton frame and a reg 3/4 ton frame different?

Sorry if these questions sound elementary to you guys, I was 12 years old when dad was trying to teach me this stuff. thanks for your time and interest guys.

[SS Tim]

Originally Posted by Steven R

1. My truck has a small block 350 in it with a th350 trans. is the crossmember the same for a 350 big block as for a 350 small block (the trans crossmember)?

this is were I just don't know enough and really wish dad was still alive so I could ask him.

2. I read this and see that I need to make sure it a "longhorn" or "C30" (aka 1 ton) crossmember. is this all I need to know when I start asking for one. or does motor size and trans size matter?

3. I would assume that a crossmember from a longhorn and a 3/4 ton are NOT the same? going by what is being said. why would they have used a different crossmember in a long horn 3/4 ton frame and a reg 3/4 ton frame different?

Sorry if these questions sound elementary to you guys, I was 12 years old when dad was trying to teach me this stuff. thanks for your time and interest guys.

All TH350/TH400 automatic crossmembers are the same for C10-30 trucks.

All Longhorns C20 and C30 are built on C30 frames with 133"wb but use different axles and springs as required for their weight rating.

Longhorns and C30's (133"wb 1-ton frames) have taller frames (almost an inch more) but use the same automatic crossmember as the C10-C20 trucks with an added riser bracket at each end. These brackets bolt to the frame and the crossmember.

[Steven R]

Ok i got it now. I see the riser block in the pic like your taking about. Thanks for making it clear. SS Tim

[SS Tim]

Since I have no idea where "Landmark" is this is more for the pictures if anyone wants them.
http://modesto.craigslist.org/pts/5108113236.html