tranny mount/crossmember- urgent help needed

Yes,no, maybe,lol. Just a retired mechanic here, worked mostly on foreign and GM over the years, by choice, 3 GM dealers.
On "untouched" older rigs, the spacers were "almost" always under the cross member. Never got a straight answer as to why, always assumed for frame flex. However, was taught always put them back the way you found them, by GM??
SO- a story, but true. Dealership, brand new suburban,4wd. Strange vibration, only at certain speeds and conditions. I watched this drag out over a 2 month period, as I was currently their Datsun mechanic. So, checks with the vibration analyzer. They send rear driveshaft out, to shaft shop. Still the same. Swapped shafts from other truck, the same, got a new shaft from GM, the same. GM Tech line contacted many times.
So after another month, as GM's traveling tech guy was very busy, he showed up. Goes for a ride, with the Vib, analyzer. Has them put it on a hoist, looks at the cross member, shakes his head, tells them to move the cross-member spacers from below to in-between member and frame. Ask him why he is shaking his head, his reply, "don't they teach this at the GM classes anymore??" So, after I'm done laughing, vehicle is road tested many times, him, GM mechanics, and shop foreman, it is perfect, vibration free. He is the one that told me put them back where you found them, as they may have been swapped for a problem, at the assembly line testing, or another dealer. SO take it for what it is worth.
BTY, from real experience, they do allw the bolts to come loose easier in sever off roading and such, as has happened to my plow truck several times, up here in the mountains, IF they are below or above the cross-member. I gave up, left them out, use bolts with lock-nuts, as in double nuts, no problems since.
Oh, the subby was a 90 or 91, best as I can recall.

I have never in my life even seen these so-called spacers. Every truck I have owned, crossmember went inside the frame channel and sat on top of the bottom lip. Drop bolts in from the top and used locknuts. Never, ever had a single problem. Maybe I'm missing something and haven't reached the bottom of the rabbit hole yet?

SquareRoot said:

I have never in my life even seen these so-called spacers. Every truck I have owned, crossmember went inside the frame channel and sat on top of the bottom lip. Drop bolts in from the top and used locknuts. Never, ever had a single problem. Maybe I'm missing something and haven't reached the bottom of he rabbit hole yet?

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Keep in mind besides the various transmissions used, there were half tons, 3/4 tons, 1 tons, 2 wheel and 4 wheel drive variations, short and long wheelbase too.
There were even inside the frame top mount (inside the frame, bolted to the top lip) ones. Most common under the frame was 4wd, 203 0r 205 t/cases, even into the 80's with the newer t/case. Then there was the 3 piece ones, also inside the frame, probably the strongest setup.

PrairieDrifter said:

I didn't say a k5 was long wheelbase? I also said exactly what the spacers are for?

Also no offense but how would you know if the nuts fell off or the bolts sheared?

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The way I read your post above was unclear (post#8) as to what you were putting inthe long wheelbase category, I was just clarifying.

the bolts were still in place. PO put the bolts down from inside the frame, and they did not fall out.

so you all have peaked my interest and Ive been trying to figure out what "normal" is from factory. Bolts,Sapcers on top of frame, frame, crossmember and then nut? Ive seen lots of pics with the spacers below the crossmember, which if I am understanding you all correctly, is wrong.

There is one squarebody in a junkyard within 100 miles that I can find. Im stuck on the couch after hip surgery, so Im sending the teenager trying to find them. I can make a spacer, thats not a bid deal. Just trying to understand if they have some purpose (obviously they do), its just very curious. I wheeled a 94 fullsize bronco for many years over all the california trails. It had a zf, doubler, 42" tires, one tons, etc. It too has a C channel frame. All crossmembers are either riveted or bolted to the frame from factory. The frame never cracked, though there was some concern when welding brackets to the frame, etc as it did not allow for any slippage. This is my first chevy, and Im trying to learn all the issues, problem areas.

Apparently, the 241 or tranny hit the botom of the floor when my son was jacking up the trans so he could pull the crossmember and mount. I guess my plan at this point is try to mount with crossmeber to frame if trans/tcase will clear floor. Ill check driveline angles. If that doesnt work, Ill just make a spacer from some 1" square unless I find the sleeves they used as I have that material on hand. Ill hard mount it, and keep an eye on it for cracking.

I have never in my life even seen these so-called spacers. Every truck I have owned, crossmember went inside the frame channel and sat on top of the bottom lip. Drop bolts in from the top and used locknuts. Never, ever had a single problem. Maybe I'm missing something and haven't reached the bottom of he rabbit hole yet?

plugugly said:

Ive been trying to figure out what "normal" is from factory.

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Don't assume that "normal" from the factory is the best way. If that were the case ORD would be out of business. They have built a company on doing what GM should have. Disclaimer: Mall Crawlers move along.

SquareRoot said:

I have never in my life even seen these so-called spacers. Every truck I have owned, crossmember went inside the frame channel and sat on top of the bottom lip. Drop bolts in from the top and used locknuts. Never, ever had a single problem. Maybe I'm missing something and haven't reached the bottom of he rabbit hole yet?

Don't assume that "normal" from the factory is the best way. If that were the case ORD would be out of business. They have built a company on doing what GM should have. Disclaimer: Mall Crawlers move along.

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For reference this is what those sleeves/spacers look like:

SquareRoot said:

I don't know, they gave us the infamous 305.

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305s made gm money
people paid to not have them, and they increased CAFE when that became a factor, because if you didnt give them money for the better enine, you got the engine which kept them competitive on the emissions front. mind you, in the same years as these, fords were doing far worse on horsepower, had a lot off casting reliability issues with heads and blocks and they were struggling to get above 305 chevy hp out of their fuel hog 351s.


as they got EST and engines were picking up and trending to HP again and more reliability, the 305s became pretty valuable options able to produce power and keep the mpg higher with the new 4 speed autos.

The bolts thing? Either that or using rivets and/or using crossmemers which "build in" the spacer, so it has longer bolts without using that machined spacer but just a slightly more complex stamping, im sure that added up to some savings over time as well

less people leaving them out, putting them in wrong that way too

plugugly said:

The way I read your post above was unclear (post#8) as to what you were putting inthe long wheelbase category, I was just clarifying.

the bolts were still in place. PO put the bolts down from inside the frame, and they did not fall out.

so you all have peaked my interest and Ive been trying to figure out what "normal" is from factory. Bolts,Sapcers on top of frame, frame, crossmember and then nut? Ive seen lots of pics with the spacers below the crossmember, which if I am understanding you all correctly, is wrong.

There is one squarebody in a junkyard within 100 miles that I can find. Im stuck on the couch after hip surgery, so Im sending the teenager trying to find them. I can make a spacer, thats not a bid deal. Just trying to understand if they have some purpose (obviously they do), its just very curious. I wheeled a 94 fullsize bronco for many years over all the california trails. It had a zf, doubler, 42" tires, one tons, etc. It too has a C channel frame. All crossmembers are either riveted or bolted to the frame from factory. The frame never cracked, though there was some concern when welding brackets to the frame, etc as it did not allow for any slippage. This is my first chevy, and Im trying to learn all the issues, problem areas.

Apparently, the 241 or tranny hit the botom of the floor when my son was jacking up the trans so he could pull the crossmember and mount. I guess my plan at this point is try to mount with crossmeber to frame if trans/tcase will clear floor. Ill check driveline angles. If that doesnt work, Ill just make a spacer from some 1" square unless I find the sleeves they used as I have that material on hand. Ill hard mount it, and keep an eye on it for cracking.

Click to expand...

It doesn't matter if the spacers are on top or below, as long as they aren't between the frame and the crossmember.

SquareRoot said:

I have never in my life even seen these so-called spacers. Every truck I have owned, crossmember went inside the frame channel and sat on top of the bottom lip. Drop bolts in from the top and used locknuts. Never, ever had a single problem. Maybe I'm missing something and haven't reached the bottom of the rabbit hole yet?

Click to expand...

Have you only had 1 ton frames?

bucket said:

Have you only had 1 ton frames?

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3/4

74 2wd 4 speed 3/4

73 2wd auto 3/4

mid 80's 4wd, goes under frame

83-85 2wd auto, yes, one side goes above bottom frame lip, one under.
So many choices!!

AuroraGirl said:

305s made gm money
people paid to not have them, and they increased CAFE when that became a factor, because if you didnt give them money for the better enine, you got the engine which kept them competitive on the emissions front. mind you, in the same years as these, fords were doing far worse on horsepower, had a lot off casting reliability issues with heads and blocks and they were struggling to get above 305 chevy hp out of their fuel hog 351s.


as they got EST and engines were picking up and trending to HP again and more reliability, the 305s became pretty valuable options able to produce power and keep the mpg higher with the new 4 speed autos.

The bolts thing? Either that or using rivets and/or using crossmemers which "build in" the spacer, so it has longer bolts without using that machined spacer but just a slightly more complex stamping, im sure that added up to some savings over time as well

less people leaving them out, putting them in wrong that way too

Click to expand...

CAFE stood for corporate average fuel economy, people tend to forget about this.The trucks had to average x mpg across the line. So without the hated 250s. 4.3s. and 305s to bring the average up no one would get a 350. And the 305s do just fine for everyday people doing average truck things just like the 283 2v did and save a few bucks on gas at the same time.