79 GMC Street Coupe - Stock Drivetrain

[Keith Seymore]

Now we enter the unknown I was trying to solve, or was overthinking, simply for consistency's sake. As for the LS9 RPO, the 350 engine part is confirmed from the RPO, but not all of the engine info like 2 or 4 bolt is given ( I was wondering if the 4 in the RPO description sheet I provided might give a clue to the trained eye). Same with MX1 for Transmission, and some of what I read indicated the engine 2 or 4 bolt designation accompanying an F44 often received the 400 as a more HD 3 speed in those configurations. the 400 replacing the Might explain the Yellow arrow on the transmission side drive shaft, might be a giveaway. Figuring out what other people did and why is hard.

I'll drop the oil pan tomorrow to make sure of 2/4 bolt. It came from Hi-Tech Engines in Spokane, and I spoke with A person who used to work in that company.

Keep in mind "HD" in the truck world means "better durability", not "high performance/race car stuff".

For trucks heavy duty applications will use lower compression ratios and other design features to facilitate long life, not going fast.

Re: yellow arrow - no - that is not a marking we used in the vehicle assembly plant. We would use circumferential stripes of different colors to represent part pick codes, but not arrows. Somebody out in the world added that mark.

K

 

[Keith Seymore]

Dug out the sticker nothing about rearend. But I'm almost positive it had 3:45 stamped in the ring gear, may have been changed.

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Quick sidebar on this SPID:

note that the front and rear tires are different.

XLB = front tires, hwy
YLC = rear tires OOR
ZLC = spare OOR

That's why we released them that way (X = front, Y = rear, Z= spare) so that the customer could have different tires front, rear and spare (or no spare).

K

 

[legopnuematic]

If it was a 454 truck it would have a TH400, a 350/305 should be a TH350. However the RPO for automatic transmission (MX1) does not make that distinction.

AFAIK in a half ton a big block was the only way to get a TH400.

 

[KCJim]

Dug out the sticker nothing about rearend. But I'm almost positive it had 3:45 stamped in the ring gear, may have been changed.

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Thank you, and thank everyone. I'm more confident now on the configuration it should be.
350 4 BBL 2 Bolt Main
TH350 3 Speed Automatic Transmission
12 Bolt Rear End
Heavy-Half/F44 HD Chassis/Suspension Front and Rear

 

[KCJim]

Thank you everyone.

I'm much more confident now on the configuration it should be.
350 4 BBL 2 Bolt Main
TH350 3 Speed Automatic Transmission
12 Bolt Rear End
Heavy-Half/F44 HD Chassis/Suspension Front and Rear

I was able to get access to the transmission tag. If the tag (attached) means what i think it means, the TH400 is a 1987. I can't find a decoder for these tags. I'll drop the pan this week and now I'm expecting a 2 bolt main. Maybe I'll get a pleasant surprise. I feel committed to putting it back to the way it was mechanically when it was original. It was gifted to me, and I want to show my appreciation by respecting the norms.

I just started the disassembly. I'm sure we'll be talking again.

 

[DoubleDingo]

Nothing wrong with 2 bolt mains.

Post a pic of trans pan.

 

[KCJim]

Nothing wrong with 2 bolt mains.

Post a pic of trans pan.

I can't load the file. I get an error file too large. I tried several ways for resizing. It's a TH400 by visual inspection with info I got from the following website.

How to Identify GM Transmissions | 700R4, TH350, 4L60, TH400, 4L80e, Powerglide, & More

This resource contains a transmission pan shape ID chart and other tips to help with identifying GM transmissions.

www.speedwaymotors.com

 

[Keith Seymore]

Nothing wrong with 2 bolt mains.

Agree. I've never seen a crankshaft laying on the dragstrip.















Except for this guy (and I think we can all agree there is something extenuating going on there).

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[Ricko1966]

Wow over 40 years have passed. Over 40 years ago my friend Dennis ran an asphalt modified at Lakeside we learned lots of tricks to go faster. But 2 things learned and remembered. Oldsmobile rods don't like sustained high RPM and 4 bolt blocks were more likely to crack in the main webs than a 2 bolt with sustained high RPMS we attributed it to 4 bolts being more rigid. A 2 bolt block in most cases,especially for just a truck doing truck stuff is more than adequate. If you don't have a blower or nitrous you will never know the difference.

 

[KCJim]

Wow over 40 years have passed. Over 40 years ago my friend Dennis ran an asphalt modified at Lakeside we learned lots of tricks to go faster. But 2 things learned and remembered. Oldsmobile rods don't like sustained high RPM and 4 bolt blocks were more likely to crack in the main webs than a 2 bolt with sustained high RPMS we attributed it to 4 bolts being more rigid. A 2 bolt block in most cases,especially for just a truck doing truck stuff is more than adequate. If you don't have a blower or nitrous you will never know the difference.

I grew up at Lakeside, and I-70. Back when it was by the Lake. Before the Dog Track. You might know my cousin, John Dempsey. Thanks for the info too. Appreciate it.

 

[Scruffy49]

If it was a 454 truck it would have a TH400, a 350/305 should be a TH350. However the RPO for automatic transmission (MX1) does not make that distinction.

AFAIK in a half ton a big block was the only way to get a TH400.

Our 85 shipped new with a Qjet equipped 4.3L V6 and a Th400… Special order number on the spid.

 

[KCJim]

Tried to add a link to rpo codes here. The link didn't work and there wasn't much on the sticker that needed looking up any way. Sorry.

Thanks. Added to my collection.