71 C10 auto crossmembers - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Charlie71C10 · 03-04-2021, 06:02 PM

Doing a frame off on a 71 shortbed. The original truck is a 250 with a 3 on the tree. Because of the condition of the frame I bought another 71 frame and it had what I believe to be an auto trans crossmember. The new truck will have a 292 and auto in it. So my question is are there different auto crossmembers? And how would I tell which is which? Thanks guys
Posted via Mobile Device

**Palf70Step** · 03-05-2021, 08:01 AM

Far as I know, you can use the same cross-member for various transmissions. Just slide it (back normally), drill mounting holes if they don all exist and you are good. I would get the proper tranny mount, bolt it to the cross-member and adjust, then drill

**MikeB** · 03-06-2021, 09:45 PM

Six or V-8, 3-speed or automatic, cross members are the same and in the same location. And drive shafts are the same length.

At least that's the case with a TH350 and 3-speed Saginaw, as well as Muncie 4-speed.

**HO455** · 03-06-2021, 09:50 PM

I swapped the factory Th400 for a th350 using the same crossmember just moved forward and bolted in a different set of factory holes.

**BigBird05** · 03-06-2021, 10:18 PM

Isn't the 3 speed manual trans cross member riveted to the frame and the bell housing bolts to it.

**MikeB** · 03-06-2021, 11:01 PM

Quote:

Originally Posted by BigBird05

Isn't the 3 speed manual trans cross member riveted to the frame and the bell housing bolts to it.

I thought it was only pre-1958 vehicles that used front engine mounts, and bellhousing mounts. At least that was the case with Chevy cars.

Like this:

Accelo · 03-07-2021, 02:30 AM

Quote:

Originally Posted by BigBird05

Isn't the 3 speed manual trans cross member riveted to the frame and the bell housing bolts to it.

I just took a 3 speed out of a 70. And yes it had the forward cross member with the mounts on the bell-housing.

**MikeB** · 03-07-2021, 10:19 AM

Quote:

Originally Posted by Accelo

I just took a 3 speed out of a 70. And yes it had the forward cross member with the mounts on the bell-housing.

Wow! I'm very surprised. I stand corrected.

Did it use front or side motor mounts?

Was the trans supported, or just hanging out there like pre-1958 cars?

**Grumpy old man** · 03-07-2021, 10:43 AM

For the 67-72 trucks there are auto cross members 6 manual and V8 manual trans cross members and 4 wd are their own animals , Depending on each application determines where they are mounted in the frame. The stock cast iron manual bell housings are rubber mounted to the cross member with the cast iron trans 3/4 speed hanging off the back with NO tail shaft mounts . The frames are all drilled for the different stock cross members . There are multiple drive shaft lengths be it 1 piece , 2 piece , long bed /short bed . There are no front engine mounts used on the 67-72 trucks

Charlie71C10 · 03-07-2021, 12:08 PM

The old frame has a bell housing mounted crossmember for the 3 on the tree. The new frame has one mounted much farther back, I’m assuming it’s an automatic crossmember. So depending on the location it should fit whatever automatic I choose?

**Grumpy old man** · 03-07-2021, 12:22 PM

This is a pic of the V8 and 6 manual trans cross members , V8 on the bottom .

Charlie71C10 · 03-07-2021, 01:29 PM

Grumpy old man I’m trying to post a photo of what I have but being unsuccessful. It looks as though it’s the V8. Will this work with the 292? It’s that a manual crossmember?

**old51sedan** · 03-07-2021, 01:41 PM

Quote:

Originally Posted by Charlie71C10

Doing a frame off on a 71 shortbed. The original truck is a 250 with a 3 on the tree. Because of the condition of the frame I bought another 71 frame and it had what I believe to be an auto trans crossmember. The new truck will have a 292 and auto in it. So my question is are there different auto crossmembers? And how would I tell which is which? Thanks guys
Posted via Mobile Device

I have a 69 SB which had an original 250 with automatic. I installed a 292 with a 200-4R automatic. To go from the 350 turbo to the overdrive I had to move the trans member backwards to the last set of holes, the 1 piece driveshaft also fit with no problems. I take it that you know that the left motor mount has to be changed and moved forward to install the 292. Mine went from an automatic to an automatic so I'm not sure about the cross member.

**Palf70Step** · 03-07-2021, 01:41 PM

I had a 6 cylinder I used with a V*, just had to drill 2 holes in frame for mounting that didn't line up, so I would assume it works the other way also.

Charlie71C10 · 03-07-2021, 02:07 PM

Thank you old51sedan I have the 292 mounts and perches. How does it do with the 200? What gears are you running?

**old51sedan** · 03-08-2021, 10:13 AM

Quote:

Originally Posted by Charlie71C10

Thank you old51sedan I have the 292 mounts and perches. How does it do with the 200? What gears are you running?

That's a good question. It has a 3.73 rear end which should be fine. I'm currently in Florida for the winter. I have it all together, running, but haven't had in on the road because of no exhaust. Since I've been hear I have bought a 4 barrel intake and a 550 Holley for it. Also have a new set of cast iron headers, so I will be installing all of that when I get back, then the exhaust. Hopefully it will run out fairly well. Good luck with your project.

Charlie71C10 · 03-08-2021, 10:23 AM

Thank you. You as well.

03-04-2021, 06:02 PM	#1
Charlie71C10 Registered User Join Date: Oct 2020 Location: Western Massachusetts Posts: 22	71 C10 auto crossmembers Doing a frame off on a 71 shortbed. The original truck is a 250 with a 3 on the tree. Because of the condition of the frame I bought another 71 frame and it had what I believe to be an auto trans crossmember. The new truck will have a 292 and auto in it. So my question is are there different auto crossmembers? And how would I tell which is which? Thanks guys Posted via Mobile Device

03-05-2021, 08:01 AM	#2
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,609	Re: 71 C10 auto crossmembers Far as I know, you can use the same cross-member for various transmissions. Just slide it (back normally), drill mounting holes if they don all exist and you are good. I would get the proper tranny mount, bolt it to the cross-member and adjust, then drill __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

03-06-2021, 09:45 PM	#3
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,408	Re: 71 C10 auto crossmembers Six or V-8, 3-speed or automatic, cross members are the same and in the same location. And drive shafts are the same length. At least that's the case with a TH350 and 3-speed Saginaw, as well as Muncie 4-speed. __________________ Mike 1969 C10 LWB -- owned for 34 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 23 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 03-06-2021 at 09:55 PM.

03-06-2021, 09:50 PM	#4
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 10,787	Re: 71 C10 auto crossmembers I swapped the factory Th400 for a th350 using the same crossmember just moved forward and bolted in a different set of factory holes. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

03-06-2021, 10:18 PM	#5
BigBird05 Senior Member Join Date: Aug 2019 Location: Cheraw Posts: 1,305	Re: 71 C10 auto crossmembers Isn't the 3 speed manual trans cross member riveted to the frame and the bell housing bolts to it.

03-07-2021, 10:43 AM	#9
Grumpy old man Senior Member Join Date: Dec 2013 Location: Gods country East,Tn Posts: 8,545	Re: 71 C10 auto crossmembers For the 67-72 trucks there are auto cross members 6 manual and V8 manual trans cross members and 4 wd are their own animals , Depending on each application determines where they are mounted in the frame. The stock cast iron manual bell housings are rubber mounted to the cross member with the cast iron trans 3/4 speed hanging off the back with NO tail shaft mounts . The frames are all drilled for the different stock cross members . There are multiple drive shaft lengths be it 1 piece , 2 piece , long bed /short bed . There are no front engine mounts used on the 67-72 trucks __________________ 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop

03-07-2021, 12:08 PM	#10
Charlie71C10 Registered User Join Date: Oct 2020 Location: Western Massachusetts Posts: 22	Re: 71 C10 auto crossmembers The old frame has a bell housing mounted crossmember for the 3 on the tree. The new frame has one mounted much farther back, I’m assuming it’s an automatic crossmember. So depending on the location it should fit whatever automatic I choose?

03-07-2021, 12:22 PM	#11
Grumpy old man Senior Member Join Date: Dec 2013 Location: Gods country East,Tn Posts: 8,545	Re: 71 C10 auto crossmembers This is a pic of the V8 and 6 manual trans cross members , V8 on the bottom . Attached Images __________________ 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop

03-07-2021, 01:29 PM	#12
Charlie71C10 Registered User Join Date: Oct 2020 Location: Western Massachusetts Posts: 22	Re: 71 C10 auto crossmembers Grumpy old man I’m trying to post a photo of what I have but being unsuccessful. It looks as though it’s the V8. Will this work with the 292? It’s that a manual crossmember?

03-07-2021, 01:41 PM	#14
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 46,609	Re: 71 C10 auto crossmembers I had a 6 cylinder I used with a V, just had to drill 2 holes in frame for mounting that didn't line up, so I would assume it works the other way also. __________________ Bill* 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

03-07-2021, 02:07 PM	#15
Charlie71C10 Registered User Join Date: Oct 2020 Location: Western Massachusetts Posts: 22	Re: 71 C10 auto crossmembers Thank you old51sedan I have the 292 mounts and perches. How does it do with the 200? What gears are you running?

03-08-2021, 10:23 AM	#17
Charlie71C10 Registered User Join Date: Oct 2020 Location: Western Massachusetts Posts: 22	Re: 71 C10 auto crossmembers Thank you. You as well.



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