I.D. The difference in LA to B body K Member

[Kern Dog]

Mopar Action magazine had an article awhile back featuring a 1978 Magnum with a defective k member. The factory shipped a small block unit to the dealer, the customer installed it himself having great difficulty. He realized that he was given The wrong one since he had a 400 in his car.

 

[Shorty Thompson]

The biggest give away on big block vs small block is the passenger mount has a triangle bracket on the big block and an L shaped bracket on the small block.

View attachment 1712091

I see what your saying now.

 

[YY1]

DC made a set of motor mounts to swap a BB into a SB K frame.

IIRC the BB K frame moves the engine back about an inch to help with F/R weight distribution.

I believe the pre- 1966 cars did the same thing.

 

[Shorty Thompson]

DC made a set of motor mounts to swap a BB into a SB K frame.

IIRC the BB K frame moves the engine back about an inch to help with F/R weight distribution.

I believe the pre- 1966 cars did the same thing.

Needing clarification for 1973 & 1974 though.

 

[YY1]

On what?

 

[YY1]

DC made a set of BB motor mounts for use in 73-79 SB K frames.

They are different from BB motor mounts for BB K frames.

Hard to find, but I found a set a few years ago.

 

[Kern Dog]

DC made a set of motor mounts to swap a BB into a SB K frame.

IIRC the BB K frame moves the engine back about an inch to help with F/R weight distribution.

I believe the pre- 1966 cars did the same thing.

Again, I don’t think this is correct. Do you actually think that one inch would make any difference at all in weight distribution? Three gallons of gas would accomplish the same thing.
Moving the engine back also moves the transmission. This would require a different transmission crossmember.
They would have to extend the ears on crossmembers like these:

 

[YY1]

Again, I don’t think this is correct.
Moving the engine back also moves the transmission. This would require a different transmission crossmember.

So they used different transmissions.

...but not transmission mounts?

 

[Shorty Thompson]

On what?

which 1 is which. I'm pretty sure what I'm being told is correct. However I look at what's being said the K-Members I have that are close to what's being showed are all 318-360 LA K-Members. I think I have 1 that like the 7/slanted shape. Yet it's supposedly small block also.

 

[Kern Dog]

Again, I don’t think this is correct.
Moving the engine back also moves the transmission. This would require a different transmission crossmember.

So they used different transmissions.

...but not transmission mounts?

The 400/440 always had a 727 if it was an automatic. The 318/340/360 could have been a 727 or 904. The mounting point for those transmissions is the same. To move the engine back, it would also affect the shifter linkage, drive shaft length, transmission cooler lines, etc.
I really doubt the engine fore/aft placement would have been different.

 

[Shorty Thompson]

Again, I don’t think this is correct.
Moving the engine back also moves the transmission. This would require a different transmission crossmember.

It shouldn't logically.

 

[Kern Dog]

Uhh, have you actually worked on any of these cars?
If you move the engine back, the transmission and it's mount move back too. These cars had a crossmember that supported the transmission. It was welded to the floor so it couldn't move back to match any fictional engine setback. The removable section of the transmission crossmember would have to be different to accommodate this setback.
Explain how I am wrong on this.

 

[Shorty Thompson]

On what?

I got it. " How to tell 1 from the other

 

[YY1]

I thought I remembered that being the case.

Perhaps not.


Big block 727 and small block 727 are in fact different, none the less.

 

[Kern Dog]

They are only different at the bell housing and mounting pattern. The rest of the dimensions are the same.

 

[T2R9]

This thread has really gone down a rabbit hole. As Kern said the transmission is positioned the same regardless of what engine is in front of it. The K frame differences are only there to position the engine correctly.

 

[YY1]

Well, there you go.