Can't find any info on this bolt needed

[Skittles]

Trying to help my son find all the parts needed to put a new engine and transmission into his frankin-square body (84 frame with an 87 cab). One bolt type we haven't been able to find any help in finding is the tailhousing connection to the crossmember. We have all the bushings, but they don't come with bolts. So we are looking for the length and size of the bolts needed for the bushings connection to crossmember AND the number of bolts, size, length, and pitch to mount to the crossmember. Hoping someone in the forums has a thought on how to find the information

 

[Radiohead]

⅜/16 x 1 seems to be in my head. Anyone else?

 

[bucket]

Is this a 2wd or a 4x4?

 

[Skittles]

It is 4 wd.

 

[Old Guy Bill]

How about a pic to help us out here?
I'm gonna guess it's a 7/16" diameter bolt...

 

[Skittles]

You must be registered for see images attach

This is the transmission mount that we ordered from Summit, they were unable to help with what hardware to use

 

[Ricko1966]

@Radiohead nailed it, 3/8 16 tpi unless it's metric then its 10mmx1.5 thread pitch.

 

[evren]

I had this issue, 3/8-16 and 10mmx1.5 are almost compatible. I didn't think anyone would put a metric thread on a GM transmission and couldn't believe they would put a bolt that almost works. When I torqued the 3/8 bolt it would tighten for a bit then slip. Finally realized it was metric. I ran a tap through it to clean the 10mmx1.5 thread a bit in case I messed them up when torquing down the English bolts.

 

[Rickf]

Why not bring it to a local hardware store and cruise the nuts and bolts aisle?

 

[Broken85]

I had this issue, 3/8-16 and 10mmx1.5 are almost compatible. I didn't think anyone would put a metric thread on a GM transmission and couldn't believe they would put a bolt that almost works. When I torqued the 3/8 bolt it would tighten for a bit then slip. Finally realized it was metric. I ran a tap through it to clean the 10mmx1.5 thread a bit in case I messed them up when torquing down the English bolts.

They are 15mm heads. Yep, metric bolts seem sacrilegious, but GM loves three things; 10mm bolts, 15mm bolts, and chrome plated plastic.

 

[evren]

They are 15mm heads. Yep, metric bolts seem sacrilegious, but GM loves three things; 10mm bolts, 15mm bolts, and chrome plated plastic.

It was the perfect storm - a lot of the bolts down there going the frame/corss member were all 3/8 coarse and so I assumed the transmission mounts to transmissions ones were as well. They threaded in there just fine, then as a torqued down on them they started to slip. What a mess.

 

[Radiohead]

I remember GM doing that in the 80's but didn't think it has affected new parts for earlier rigs. Now I need to go reef on mine and see if I have proper thread engagement. Great heads up

 

[Ricko1966]

I remember GM doing that in the 80's but didn't think it has affected new parts for earlier rigs. Now I need to go reef on mine and see if I have proper thread engagement. Great heads up

Turbo hydro 200s,700r4s,and 200r4s should be metric. Turbo 350s and 400s should not be metric. Beings he is using a 84 and 87 truck my 1st assumption is he is 700r4

 

[bucket]

They are 15mm heads. Yep, metric bolts seem sacrilegious, but GM loves three things; 10mm bolts, 15mm bolts, and chrome plated plastic.

Just to help find bolts in the future, head sizes are not bolt sizes. In most cases for GM, 10mm head is a 6mm bolt. 13mm head is usually an 8mm bolt, but often 10mm instead. 15mm head is often a 10mm bolt.

 

[Radiohead]

The big thing I remember from back in the day was that the Asian vehicles favored even number metric wrench size and north american vehicles favored odd number wrench sizes (with the exception of 10), probably holds true through today.