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Discussion Starter #1
Folks,

I have searched this forum seeking the correct answer to the following question:

Which of the 69 big block tranny crossmembers may be used to correctly install a 2 speed powerglide?

Thanks,
Bill.B
 

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Is it behind a big block? If so, the big block "4-speed" crossmember should work for Glide and TH350. It is the same style as the crossmember used for all transmissions available behind the small block, just with the trans mount holes offset to the passenger side of the car to account for the engine offset. The BB "automatic" crossmember won't work, the only available automatic was the TH400 which mounts further back.
 

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If you are using the correct big block motor mounts, you may have clearance issues with the front crank pulley and crossmember because I believe the trans sits a little higher at the rear and tilts the engine forward and down.
That's what happened to me. My pulley was right on the crossmember.
I had to switch back to using small block motor mounts with my big block/Powerglide.

A side note is that I do not have the BB/4sp crossmember.

How does it differ from the sb/4sp/th350 one?
 

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If you are using the correct big block motor mounts, you may have clearance issues with the front crank pulley and crossmember because I believe the trans sits a little higher at the rear and tilts the engine forward and down.
That's what happened to me. My pulley was right on the crossmember.
I had to switch back to using small block motor mounts with my big block/Powerglide.

A side note is that I do not have the BB/4sp crossmember.

How does it differ from the sb/4sp/th350 one?

The bb crossmembers have the trans pad offset app. 1" to the passenger side instead of centered like the small blocks. This was due to the bb engine frame mounts moving the engine the same 1" over for steering box clearance.

Jody
 

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Discussion Starter #6
Guys,

Thanks for your input. It sounds like a big block crossmember must be used to mount the powerglide and big block combo in order to acheive correct engine offset and trans alignment . I do have access to a BBC crossmember that I believe is for a TH400. It appears somewhat tubular in design with the mounting pad being being square (offset to passenger side) and the bolt or stud holes are oblonged. Can any one confirm that this is a TH400 crossmember?

I would consider fabricating whatever is required to adapt the powerglide to the TH400 mount, or is there any aftermarket crossmembers available?

Thanks,
Bill.B
 

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i think only the 1969 is offset ,the 1967 & 1968 are still on center . in the AIM on page L35 A12 the crossmember is 3912570 can someone check a 1967, 1968 AIM and see what the part number is ?
 

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Folks,

I have searched this forum seeking the correct answer to the following question:

Which of the 69 big block tranny crossmembers may be used to correctly install a 2 speed powerglide?

Thanks,
Bill.B
I am going to say a BB/4spd crossmember is needed to mount the Powerglide, because on a small block, which is centered, the PG and 4 speed use the same centered cross member, so logic dictates that on the offset BB, they would need the same offset cross member.
But I have never gone BB/PG, so real world may be different.
 

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Bill -

Your last question got lost a little.

Yes, the TH400 crossmember is tubular, with the mount pad offset to the passenger side. If I remember correctly, the main issue with the TH400 corss is that the mount pad is on the back, so you'd have to cut it off and re-weld it to the front of the tube.

Do you have a smallblock crossmember? If so, a lot of guys swapping in a BB run a poly transmount (has three holes on the side toward the crossmember) and just secure it with one bolt through the passenger side-most hole on the SB cross.
 

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Discussion Starter #13
Eric,

Thanks for the clarification. I think I will go ahead and install the powerglide/bbc combo and then have a look at how things like up with both the tubular TH400 crossmember and the small block crossmember. I like the idea of fabricating an adapter to utilize the big block crossmember to ensure correct alignment. I will post any results at a later date.

Thanks,
Bill.B
 

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Discussion Starter #14
Folks,

A quick update on the correct crossmember for a big block/powerglide combo. Last weekend I was able to view an original big block Nova that had a Turbo 400 big block crossmember modified for a powerglide. The owner had the correct mounting tab fabricated and welded to the front of the TH400 crossmember to make up the difference in length from the TH400 to the powerglide. This insured that the transmission was installed with the correct alignment and height. It was done very nicely and powder coated black for an factory appearing piece.

Bill.B
 
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