Engine mount holes- front or rear?

[jb4short]

We've put a SBC crate motor in our project along with a 700R4. I'm using the tubular motor mounts from Brother's and the ECE cross member. Somewhere it said to use the front set of mount holes on the frame but it looks like using the rear holes would line the trans cross with the frame holes for it. Has anyone used this setup? Should I use the front engine mount holes and drill the holes for the cross member?

[71Farmtruck]

I would not see a problem with that, you may need to look out for clearance issues with the trans hitting the floor pan on a low hump cab, if the new mounts raise the motor at all, there could be an issue. From what I have researched on this site, clearance issues can be hit and miss, some have them, some dont. I did because I used 73-87 motor stands with the clamshell mounts, which raised the motor about a half inch, giving me huge problems with my low hump cab. I am installing a high hump section as we speak. The only way to know for sure will to be to bite the bullet and mock it up to see if it works, if it does, you probably bypassed any driveshaft length issues using the original mounting holes and not moving the motor forward.

[fatboys69]

I have a set of tubular mounts from Performance Online and will look at the instructions tonite when I get home and see what they say and let you know.

[jb4short]

Originally Posted by fatboys69

I have a set of tubular mounts from Performance Online and will look at the instructions tonite when I get home and see what they say and let you know.

Thanks. I think that's where the "Use front holes" came from; but it really doesn't account for what trans you use

[jb4short]

Originally Posted by 71Farmtruck

I would not see a problem with that, you may need to look out for clearance issues with the trans hitting the floor pan on a low hump cab, if the new mounts raise the motor at all, there could be an issue. From what I have researched on this site, clearance issues can be hit and miss, some have them, some dont. I did because I used 73-87 motor stands with the clamshell mounts, which raised the motor about a half inch, giving me huge problems with my low hump cab. I am installing a high hump section as we speak. The only way to know for sure will to be to bite the bullet and mock it up to see if it works, if it does, you probably bypassed any driveshaft length issues using the original mounting holes and not moving the motor forward.

Thanks for the input Mike. We haven't ordered a driveshaft yet so there won't be an issue there. I think the "Mock up" will ultimately be the only way to know for sure but I thought there may be a member that had used the same setup.

[msgross]

wasn't the back holes for a 4wd? not that it matters in your case since you are using a newer tranny.

[fatboys69]

Yeah, I am running a 700R in mine.

[71Farmtruck]

That can be the problem with aftermarket and later model stands, the manufacturers don't know what trans you are using, and they probably haven't done the leg work on trying different combinations with the product, so it leaves many questions unanswered.

I didn't realize you were fabbing up a new drive shaft, sometimes I assume everyone is as cheap as me and modifies their existing one, if they have it. On my build I can already see that my drive shaft will have to be lengthened, I will have it done at a shaft shop, I have pole vaulted enough cars severing u-joints to know better.

[70rs/ss]

The SBC use the rear holes, if you are catting a DS it doesn't matter. The rear holes will give lots of room up front and can allow electric fans if you want, it also helps with weight distribution. The further rear the motor is the better the balance. BBC have to go in the front holes to clear the VC and dist. A SBC in the front holes leaves too much room behind the motor to me, but either way is OK. I think if you put the mount in the hole on the bottom that goes to the crossmember will only line up in one position, so if it isn't supposed to be in the rear holes the bottom mount hole won't line up with a hole in the crossmember, they usually only go in one position and the BBC mount goes in the other.

[jb4short]

Originally Posted by 70rs/ss

The SBC use the rear holes, if you are catting a DS it doesn't matter. The rear holes will give lots of room up front and can allow electric fans if you want, it also helps with weight distribution. The further rear the motor is the better the balance. BBC have to go in the front holes to clear the VC and dist. A SBC in the front holes leaves too much room behind the motor to me, but either way is OK. I think if you put the mount in the hole on the bottom that goes to the crossmember will only line up in one position, so if it isn't supposed to be in the rear holes the bottom mount hole won't line up with a hole in the crossmember, they usually only go in one position and the BBC mount goes in the other.

The lower hole doesn't line up- the mount had two holes in it and the upper one lined up. I think it should go in the back holes; but it does have an HEI dist.

[umwtnt]

I would try both setups. The kicker will be what distributor you use. With the big HEI you may have clearance problems. Also have your headers available to check for clearance.

[70GMCer]

Are these the mounts that you are going to use? If so, mine are mounted in the front holes. No clearance issues. My instructions didn't mention about which bolt holes to use. So, I used the same ones that the original tower mounts used. I also used the original driveshaft w/350 turbo.

[GMCPaul]

The factory used the front 2 holes for small and big block V-8's, they used the rear 2 holes for the 6cylinder's. You can install it in either the front or rear holes, I myself prefer the rear holes, I've never had a problem installing the HEI distributor with cap off after the motors in, it places the motor far enough back that you can have a 1 piece driveshaft without worrying about vibration problems caused by the difficulty in balancing a drive shaft thats longer ( All drive shaft shops I've spoken with would not build a 1pc driveshaft with motor in front holes as they says it to long to properly balance but in rear holes its just under their guidelines for max length ) it allows for better weight distribution mounted in rear position, and if your 5'9" and 145lbs you can climb in up front to do alot of your work that extra 2-3" makes a big difference.
But if your looking for factory correct its the 2 front holes.
GMCPaul

[jb4short]

Originally Posted by GMCPaul

The factory used the front 2 holes for small and big block V-8's, they used the rear 2 holes for the 6cylinder's. You can install it in either the front or rear holes, I myself prefer the rear holes, I've never had a problem installing the HEI distributor with cap off after the motors in, it places the motor far enough back that you can have a 1 piece driveshaft without worrying about vibration problems caused by the difficulty in balancing a drive shaft thats longer ( All drive shaft shops I've spoken with would not build a 1pc driveshaft with motor in front holes as they says it to long to properly balance but in rear holes its just under their guidelines for max length ) it allows for better weight distribution mounted in rear position, and if your 5'9" and 145lbs you can climb in up front to do alot of your work that extra 2-3" makes a big difference.
But if your looking for factory correct its the 2 front holes.
GMCPaul

Thanks Paul- that makes a lot of sense. I was concerned about the HEI and I want the work done before putting the cab on. This should also align the trans cross with the holes that are already in the frame. 145lbs? Pretty safe bet I won't be climbing in there...LOL

[67_C-30]

Originally Posted by GMCPaul

The factory used the front 2 holes for small and big block V-8's, they used the rear 2 holes for the 6cylinder's. You can install it in either the front or rear holes, I myself prefer the rear holes, I've never had a problem installing the HEI distributor with cap off after the motors in, it places the motor far enough back that you can have a 1 piece driveshaft without worrying about vibration problems caused by the difficulty in balancing a drive shaft thats longer ( All drive shaft shops I've spoken with would not build a 1pc driveshaft with motor in front holes as they says it to long to properly balance but in rear holes its just under their guidelines for max length ) it allows for better weight distribution mounted in rear position, and if your 5'9" and 145lbs you can climb in up front to do alot of your work that extra 2-3" makes a big difference.
But if your looking for factory correct its the 2 front holes.
GMCPaul

Agreed all my small block trucks use the front holes. I had a '69 stepside that had a small block swapped instead of the factory 6 cylinder and was real close.