Motor mount question

[Cragmor]

I have a 76 C10 that came with a 454 from the factory but now has a 350. Do the engine mounts attach at the same location on the truck regardless of engine, the difference being the mount itself? Just got the truck and peaked around. I don't see any other mount holes for the original mounts.

 

[AuroraGirl]

to my understanding you can interchange them but they were different. big blocks and 4wd sat lower in engine bay.
@bucket is the expert. i think he said something before about the forward / rear mounting distance may have been mildy different but that was drilled at factory not universal mayhaps

 

[bucket]

Lol, I'm no expert. The 350 is very likely bolted in on the original big block mounts and brackets. Even if that's not the case, a big block will bolt right in place of a small block.

Whenever GM had a different set of brackets for small/big blocks, only the installed heights were slightly different.

 

[dsteelejr]

I have a 76 C10 that came with a 454 from the factory but now has a 350. Do the engine mounts attach at the same location on the truck regardless of engine, the difference being the mount itself? Just got the truck and peaked around. I don't see any other mount holes for the original mounts.

My 1980 K25 came from the factory with a 350 according to the VIN. By the time my grandpa bought the truck in 1988 the previous owner swapped it with a 454 and I just put a reman 454 in it. When dropping it in I noticed that where the mounts bolt to the chassis the holes are elongated, which gives you some wiggle room to position the mounts and engine slightly more forward or back. Maybe this was done to accommodate both small blocks and big blocks.

The only instance I can think of where a mount would be different is on the medium duty trucks like the C65, C70, etc. These trucks had tall deck engines and they used one U shaped mount at the bottom front of the engine that mounted to a frame rail crossmember with the rest of support coming from being bolted to the tranny like on our light duty squares.

 

[bucket]

My 1980 K25 came from the factory with a 350 according to the VIN. By the time my grandpa bought the truck in 1988 the previous owner swapped it with a 454 and I just put a reman 454 in it. When dropping it in I noticed that where the mounts bolt to the chassis the holes are elongated, which gives you some wiggle room to position the mounts and engine slightly more forward or back. Maybe this was done to accommodate both small blocks and big blocks.

The only instance I can think of where a mount would be different is on the medium duty trucks like the C65, C70, etc. These trucks had tall deck engines and they used one U shaped mount at the bottom front of the engine that mounted to a frame rail crossmember with the rest of support coming from being bolted to the tranny like on our light duty squares.

Shouldn't be needed at all. Small blocks and big blocks share the same mount boss footprint and the distance from the mount bosses to the bellhousing flange is the same.

I can say with absolute certainty that both blocks can be swapped in these trucks with zero changes to the mounts.

 

[Dave M]

Different according to the workshop manual

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[Dave M]

Can anyone tell me how thick the rear transmission mount spacers are for the TH400, shown as above. I don't have those fitted to mine.

 

[bucket]

Different according to the workshop manual

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Yes, as I said, they are different. But you can remove a small block, replace it with a big block, or the other way around without changing ANYTHING about the mounts.

 

[Dave M]

I had an arm wrestle with mine when I had to replace them, ended up unbolting the chassis brackets also, to get all the bolts lined up.

 

[Blue Ox]

Yes, as I said, they are different. But you can remove a small block, replace it with a big block, or the other way around without changing ANYTHING about the mounts.

Correct. They will fit and the bolt patterns are the same, but the diesels and (I think) the big blocks used a heavier mount and different chassis bracket.

 

[Doppleganger]

I know they're 2 different mounts. Where else could they mount?

 

[custodian]

Correct. They will fit and the bolt patterns are the same, but the diesels and (I think) the big blocks used a heavier mount and different chassis bracket.

I had to use the diesel mounts when I switched to a 350 in my 85C10. The brackets that hold the motor mount, from the frame to the crossover, only has three mounting holes. The mounts that are used for the SBC, frame to crossover, has four mounting holes. I did keep the bolts loose when I dropped in the 350 for alignment.

 

[AuroraGirl]

i could see driveline heights like making the trans sit too low or high but within movement of the mnount, so not breaking anything but not putting it at its best angle perhaps?

 

[AuroraGirl]

Also on motor mounts, not to hijack thread,
it looks like my pads are fine and the cross support, but to my knowledge motor mounts are two pieces? Brand recommendations, idling and periodic clutch dumping to consider.

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I also need a tcase pad but that seems easier

 

[AuroraGirl]

@HotRodPC you knew a lot about motor mounts, yes?
my engine/trans/transfer case are mounted too far forward and my z bar is bent from it. I think if I unbolt the z bar, support engine, put new engine mounts in, move my crossmember to the right spot, it should all line up(maybe replace z bar..?)