305 Mystery engine and GMC mystery axle

[JonnyTechMech]

JonnyTechMech in the house and new to this list. I’ve been cruzin this site for a week now and I’m impressed that there’s so much knowledge sharing on every level. I felt it was time to become part of it all. I’ll keep the babble to a minimal, cause I still have a lot to learn about this site. Don’t claim to know everything and plan to learn all I can from you all. As well as share, what I can. Glad you’re here and glad to be here from DFW by way of the Capital City “Austin”.

If it’s ok, I’ll dive right in.

I own an 87 GMC Fleetside recently purchased. It’s running a 305, th400 tranny. I have a few questions that maybe some of you can help me.
Have any of you seen some engines that have a dummy cavity for the mechanical fuel pump? No doubt, it’s EFI, but a mechanical fuel pump can never be installed. It’s the original engine of the truck. Is there anything special about it? It also has the four bolts that run though the valve covers.
Haven't popped the covers to check the ID yet.
The ID on the front of the block is THJ509139 and K1029FAZ.

In addition, I have a ID# on the drive axle which is BR36298 for a corporate 10 bolt. My guess, it's a 2.73. Anyone know what it could be. I’ve not found any other #'s on it. I was going to pop the Diff cover and verify the #, but the Diff bleed plug is impossible to move. I’ll start with this for now. I’ve checked 73-87.com, mortec.com and branch sites from these pages with no luck.

Thanks.

JonnnyTM

[skeet85silverado]

all chevrolet engine 87 and up have the center bolt heads and that dummy fuel pump area is for if you were to install a carbutrator on it you can run a mechecinal fuel pump

[Truckstuff]

The THJ code on the engine block, I think means its a 350. As far as the axle code, check for a Service Parts ID Sheet (RPOs). The gear ratios are G codes. Eg. GU2 = 2.73 The engines are L codes.

[Slonaker]

My '86 lists the gear ratio on the label in the glove compartment. Most of the later trucks have 2.73s from what I have seen on this site. Mine has 3.08s for some reason.

Are you sure it is a 305 and a TH400? Most 305s had either a TH350 (TH350C in later trucks...) or a 700R4. I guess someone could have swapped in anything they wanted, though.

Slonaker

[JonnyTechMech]

I was thinking the same on the THJ code. (That It’s a 350). It matches the VIN and the VIN tells me it’s a 305. Mighty Strange!!! It’s a pain to get behind the engine to get the cast#. Let alone reach back there. According to the VIN the “50” in the ID is a 305 and a “57” is a 350. I really don’t care what’s in there. I just would like to know what I’m working with. (350 would be nice ;-)
I’ve called machine shop and no one so far can give a straight answer.


I also looked at the label in the glove compartment and it has “GU2” for a standard rear axle. Bumm deal !!! I’m contemplating changing it out for a lower geared rear end when I convert the Drums to Discs.

Regarding the tranny, I looked at the pan and identified it as a th400. I’m the third owner of the truck and the elderly man who owned it before met rarely drove and only really added water and oil. It’s been setting for 4 years. He wasn’t a mechanic by any means and told me hasn’t had to changed anything. It still has the original shocks. So I’m on a journey to update and renew the whole suspension. I suspected that the owner before him might have changed some things like the tranny and such. I’ve noticed that there’s only 4 leafs on the rear springs.

For my next trick, I’ll be change out the timing chain since the gasket is leaking oil. I spent last weekend change out a corroded leaking freeze plug.

I’ll keep at it.

Thanks to all.

[1FaastC10]

Originally Posted by JonnyTechMech

According to the VIN the “50” in the ID is a 305 and a “57” is a 350.

incorrect, the engine displacement is indicated by a single letter in the VIN, its the 8th character or the vin if i remember correctly. my 86 has an "H" in that position i do believe.

[JonnyTechMech]

RIGHT! you are 1FaastC10! I must have gotten that mix up with some else I read online or title record check I did before buying it. My Badd. Thanks for the correction. "H" as the 8th character is a Chevy 305

JonnyTM

[jfrank133]

Hello Johnny, welcome to this site. Im a rookie to all this and this site has been very helpful to me with all my questions. I owe many beers to guys that have helped me. At times i wish i could shake their hand for the information they have provided me. I have found a site that talks about ID numbers on trucks you can check it out, maybe you can find what your looking for, the site is: http://www.chuckschevytruckpages.com/. good luck and welcome to the site.

[dons454s]

The code you want to use on the block is the faz that makes it an 87 305.

Originally Posted by JonnyTechMech

JonnyTechMech in the house and new to this list. I’ve been cruzin this site for a week now and I’m impressed that there’s so much knowledge sharing on every level. I felt it was time to become part of it all. I’ll keep the babble to a minimal, cause I still have a lot to learn about this site. Don’t claim to know everything and plan to learn all I can from you all. As well as share, what I can. Glad you’re here and glad to be here from DFW by way of the Capital City “Austin”.

If it’s ok, I’ll dive right in.

I own an 87 GMC Fleetside recently purchased. It’s running a 305, th400 tranny. I have a few questions that maybe some of you can help me.
Have any of you seen some engines that have a dummy cavity for the mechanical fuel pump? No doubt, it’s EFI, but a mechanical fuel pump can never be installed. It’s the original engine of the truck. Is there anything special about it? It also has the four bolts that run though the valve covers.
Haven't popped the covers to check the ID yet.
The ID on the front of the block is THJ509139 and K1029FAZ.

In addition, I have a ID# on the drive axle which is BR36298 for a corporate 10 bolt. My guess, it's a 2.73. Anyone know what it could be. I’ve not found any other #'s on it. I was going to pop the Diff cover and verify the #, but the Diff bleed plug is impossible to move. I’ll start with this for now. I’ve checked 73-87.com, mortec.com and branch sites from these pages with no luck.

Thanks.

JonnnyTM

[1972]

I’ve noticed that there’s only 4 leafs on the rear springs.

4 leafs and an overload came stock on many 1/2 ton trucks. I scrapped an '86 that had them. It also had a 4.3 V-6 and a TH400. It was explained to me that GM no longer made a TH350 in these years so that's why it got a TH400, and the gutless 4.3 couldn't pull an OD tranny.

[JonnyTechMech]

Thanks jfrank133, dons454s, and 1972 for all your replies. I've found something useful in all you've posted. It puts many of my thoughts to rest.

Thanks,

JonnyTM

[Slonaker]

Originally Posted by 1972

4 leafs and an overload came stock on many 1/2 ton trucks. I scrapped an '86 that had them. It also had a 4.3 V-6 and a TH400. It was explained to me that GM no longer made a TH350 in these years so that's why it got a TH400, and the gutless 4.3 couldn't pull an OD tranny.

My '86 has a TH350C that is factory. They are not common in the later trucks, but they were available.

Slonaker