New to me truck/ what should i go through and look at

[gotamotor74]

Hi all, I'm new to the forum here.
Also new to chevy/gmc trucks.
I picked up myself a 1974 gmc k25 about a month ago. Its got a 350 block, and sm465 transmision and an NP203 transfer case, not sure whats in the diffs. Again I'm very new to trucks. Most of my experience has been on my grandpa's 64' volkswagen and my 77' harley, both are a little different than trucks.
The truck seems to me to be in good condition I picked it up 2 hours away and drove it home that day with no issues and no over heating.
I plan on just going over the whole thing, change fluids and doing the wiring because.. oh yeah, no wiring... it has a "painless" wiring kit that the seller gave to me. But other than that.
My question is, what should I look for on this new to me truck? And what should I service/do before really driving it?
Thanks all, hope to get some wisdom on this site.

 

[Radiohead]

Rubber articles. I mean that to include things like fuel line rubber, where the steel lines transition to short hoses for the win. Flexible brake lines are another as well as brake caliper/wheel cylinder/master cylinder units for seepage. Vacuum lines are another fun place for a leak, including but not limited to the line feeding the brake booster from the engine. Pretty much any original rubber is going to be suspect by age alone by this time, much like how tire date codes work. Suspension bushings are another rubber component to inspect as well, and something else overlooked too often are exhaust hanger insulators. Window seals aren't exempt from any of this either. Seals of all stripes are included. Don't forget hoses.
Have I forgotten any rubbery on a square?

You get the picture.
Then you need to consider not just the actual rubber hitting the actual road, but the hard spinny parts that give that road rubbing rubber a place to rub from. Like wheel bearings, u-joints, those spindly things that hold the steering and front suspension together as well as any areas where movement is part of the normally engineered function. Another oddball thing to check, or at least be aware of, is that the frame area where the steering gear mounts to the frame can crack out around the fastening locations.

The forums here are good for seeing what others are doing about the problems they're encountering and what the resolutions are. Many things are quite common and we all get to share in most of them. One pre-requisite of GMSB you will discover is the need for photos.

You will see. Like every one here grew up 'reading' Playboy or something.

 

[CalSgt]

Check all fluids of course, including trans and transfer case plus both differentials.

Check steering parts, look for worn tie rod ends Etc.

Check Frame near steering box bolts - commonly cracked on 4x4 and more so if it’s lifted with oversized tires

Check frame at rear shock mount holes - cracks near there too

Check, clean, and repack front hub bearings, don’t forget the roller bearings under the hub spindle (lots of people over look these) If any of the bearings have pitting or aren’t able to look clean and shiny when the old grease gets cleaned out be sure to replace them. set hub bearing preload & lightly grease 4x4 locking hubs on reassembly. Since you have a 203 tc it may or may not have locking hubs.

Check front brakes while it’s apart for bearing service. Service them if they are worn out or worn in an odd way.

Check driveshaft u-joints replace if there’s any play, grease if not (if they are grease able). Be sure to give the front shaft double cardan joint some attention, lots of people don’t know how to rebuild them and they get overlooked often.

Check rear brakes, rears last a long while in these trucks but well worth putting eyes on them. If there’s any grease flung inside the drums plan on rear axle seals.

you say it has no wiring but also that you drove it two hours home? Many people assume old car wiring is junk but that’s not always the case. Only issue with ‘74 wiring is glass fuses which isn’t really a problem. If it’s been hacked up by tweekers, been on fire/melted, or chewed up by mice or rats then the painless kit is probably a good idea. Otherwise, just make whatever smaller repairs the electrical needs and swap to the painless eventually or never… your call there.

 

[75gmck25]

Coqngratulations!

I’ll assume your ‘74 is very similar to my ‘75 K25, but the option label on the inside of the glove box door will tell you more detail. For example, mine has Silverado trim, so that adds some convenience items. I also have the camper special package and 8400 lb GVW, G80 locker, and A/C with HD cooling. Most of theses options make a difference when you are looking for parts.

If it hasn’t been switched to HEI ignition (‘74 was the last year for points) that would be a very good upgrade. If it still has 16 1/2” rims and tires, getting a junkyard set of 16” rims would make it much easier and cheaper for new tires. 245/75R16 load range E tires should be about the same height and width as the original tires, and they are easy to find.

The standard axle gearing should be 4.10, but 4.56 was an option on the K25. At a certain GVW rating you get the full floating rear axle, and it’s easy to see the hubs sticking out in back. FF axle rear brakes are a PIA to service- they may need some work.

The stock 350 is pretty lame, but it helps if you increase base timing. There are no catalytic converters required with HD emissions, and in the 49 states version there is no EGR, smog pump, etc. Not sure about California.

Stock truck had fixed front hubs, but 203 may have been converted and then a switch to locking hubs. NP203 is a boat anchor, but extremely durable. Everyone seems to want to convert to the 205, but I’ve never heard of anyone actually breaking an unconverted 203.

 

[PeteJr]

As well as the above suggestions.........

Check wiring and/or connections. Be sure the fuse panel is safe and not a bungled mess.
IF you go as far as an extensive "redo" I vote to install a new wiring harness...........

 

[gotamotor74]

Rubber articles. I mean that to include things like fuel line rubber, where the steel lines transition to short hoses for the win. Flexible brake lines are another as well as brake caliper/wheel cylinder/master cylinder units for seepage. Vacuum lines are another fun place for a leak, including but not limited to the line feeding the brake booster from the engine. Pretty much any original rubber is going to be suspect by age alone by this time, much like how tire date codes work. Suspension bushings are another rubber component to inspect as well, and something else overlooked too often are exhaust hanger insulators. Window seals aren't exempt from any of this either. Seals of all stripes are included. Don't forget hoses.
Have I forgotten any rubbery on a square?

You get the picture.
Then you need to consider not just the actual rubber hitting the actual road, but the hard spinny parts that give that road rubbing rubber a place to rub from. Like wheel bearings, u-joints, those spindly things that hold the steering and front suspension together as well as any areas where movement is part of the normally engineered function. Another oddball thing to check, or at least be aware of, is that the frame area where the steering gear mounts to the frame can crack out around the fastening locations.

The forums here are good for seeing what others are doing about the problems they're encountering and what the resolutions are. Many things are quite common and we all get to share in most of them. One pre-requisite of GMSB you will discover is the need for photos.

You will see. Like every one here grew up 'reading' Playboy or something.

Okay, rubbers will be added to the list... important to have good rubbers....on a the truck!
My master cylinder I believe it is... it's a big red thing that's connected to the also big red booster i think..is certainly leaking. The cap and seal seems worn out so I'm gonna try that first hopefully solves that one.
I am also leaking an immense amount of power steering fluid I noticed. I filled it up, drove the truck for a solid day probably about 80 miles or so, drove it to the store the next day and heard a squeak in the wheel. Checked the fluid and it was all gone, just gone. I had filled it to the mark prior to driving. There is also a puddle under that location...hmm don't know much about power steering stuff.
so I'll plan on doing all rubbers.
I did look at the steering box mount and shook the truck around and stuff to see if it was broken or cracked, saw it on a video I watched, that seems to be good.

 

[gotamotor74]

Check all fluids of course, including trans and transfer case plus both differentials.

Check steering parts, look for worn tie rod ends Etc.

Check Frame near steering box bolts - commonly cracked on 4x4 and more so if it’s lifted with oversized tires

Check frame at rear shock mount holes - cracks near there too

Check, clean, and repack front hub bearings, don’t forget the roller bearings under the hub spindle (lots of people over look these) If any of the bearings have pitting or aren’t able to look clean and shiny when the old grease gets cleaned out be sure to replace them. set hub bearing preload & lightly grease 4x4 locking hubs on reassembly. Since you have a 203 tc it may or may not have locking hubs.

Check front brakes while it’s apart for bearing service. Service them if they are worn out or worn in an odd way.

Check driveshaft u-joints replace if there’s any play, grease if not (if they are grease able). Be sure to give the front shaft double cardan joint some attention, lots of people don’t know how to rebuild them and they get overlooked often.

Check rear brakes, rears last a long while in these trucks but well worth putting eyes on them. If there’s any grease flung inside the drums plan on rear axle seals.

you say it has no wiring but also that you drove it two hours home? Many people assume old car wiring is junk but that’s not always the case. Only issue with ‘74 wiring is glass fuses which isn’t really a problem. If it’s been hacked up by tweekers, been on fire/melted, or chewed up by mice or rats then the painless kit is probably a good idea. Otherwise, just make whatever smaller repairs the electrical needs and swap to the painless eventually or never… your call there.

I will have to learn how to do all that wheel bearing stuff hub stuff you speak of... never done it before but sounds important. Any links or videos or manuals you recommend for learning that stuff?
I believe I do not have locking hubs.
What's a double cardan joint?
I have seen many grease zerk fitting thinngys on the u joints and near the brakes... maybe some other places can't remember.
Not sure what to look for as far as the play you mentioned. I planned on just going through and putting grease everywhere I can find a fitting.... any grease type you reccomend?

So the wiring has all been torn out, the original stuff atleast. I failed to mention it's a "74" gmc.. atleast I believe the frame to be, and is what is on the title. But the cab has been changed to a 78' cab during its life and has a flatbed. And the owner before the owner I got it from had big plans for it. Including the painless wiring kit. But he only got as far as just wiring it to drive. So basically the whole kit is in the truck just budled up on the floorboard. The rest of it in a box I have.

 

[gotamotor74]

Coqngratulations!

I’ll assume your ‘74 is very similar to my ‘75 K25, but the option label on the inside of the glove box door will tell you more detail. For example, mine has Silverado trim, so that adds some convenience items. I also have the camper special package and 8400 lb GVW, G80 locker, and A/C with HD cooling. Most of theses options make a difference when you are looking for parts.

If it hasn’t been switched to HEI ignition (‘74 was the last year for points) that would be a very good upgrade. If it still has 16 1/2” rims and tires, getting a junkyard set of 16” rims would make it much easier and cheaper for new tires. 245/75R16 load range E tires should be about the same height and width as the original tires, and they are easy to find.

The standard axle gearing should be 4.10, but 4.56 was an option on the K25. At a certain GVW rating you get the full floating rear axle, and it’s easy to see the hubs sticking out in back. FF axle rear brakes are a PIA to service- they may need some work.

The stock 350 is pretty lame, but it helps if you increase base timing. There are no catalytic converters required with HD emissions, and in the 49 states version there is no EGR, smog pump, etc. Not sure about California.

Stock truck had fixed front hubs, but 203 may have been converted and then a switch to locking hubs. NP203 is a boat anchor, but extremely durable. Everyone seems to want to convert to the 205, but I’ve never heard of anyone actually breaking an unconverted 203.

Thanks!! I'm super excited about this, have always wanted a truck but for some reason just never looked to hard for one untill i saw this one, fell in love and it just happend!
So the tire situation on it is certainly not stock, as well as the suspension I would imagine. Its got 37" tires and it has a 6" rough country suspension lift. The rims do look to be about 16" still I'm not sure, don't know much about tire sizes and rims and stuff... but I do know these suckers are not stock.
I will take a look around and see if I have full floating axels.. not sure what thoes are but maybe i can take a picture and you can tell me what I got.

350 is supposedly rebuilt and it does seem so, I've always heard good things about them? I don't need to go fast I just cruise. No smog here in California on pre-75 vehicles so we're all good there!

I do not see locking hubs so I don't believe the 203 has been converted. And I don't plan on doing so after some research on it. However!! Maybe you can help me on this one......

So...not knowing much of anything when I got this truck, *cough* noob....it appears that for the period that I was driving it.. not too long of a period but..some decent driving.... I had the transfer case in 4Hi LOCK.... I didn't know what the other little stick did... I mean I knew what it did but I thought it was just 4hi and 4 low... because I had heard about the whole "Chevy all time 4wheel drive" thing, I figured oh its just in 4 wheel drive... all the time? However turning was a reall..really... well it's was really Jerky in slow maneuvers. So I did some reaserch and discovered there is.. shifting from top to bottom--- 4low lock---4low--neutral--4Hi--4hi lock.... how much damage you think I did driving in 4hi lock for an amount of time?
Just been on my mind for a bit.... woops!

 

[CalSgt]

I will have to learn how to do all that wheel bearing stuff hub stuff you speak of... never done it before but sounds important. Any links or videos or manuals you recommend for learning that stuff?

There's probably lots of videos on it, I learned when I was a kid so I've never looked to see what's out there for instructional material. Its a messy job and kinda a PIA but not too complicated if you have any mechanical aptitude. Only special tools I can think of would be a GM spindle nut socket, maybe snap ring pliers...

I believe I do not have locking hubs.

That will probably make the job a bit simpler, all the ones I've dealt with had the locking style.

What's a double cardan joint?

Two U-joints connected to each other at the same end of a driveshaft, some people call them a CV joint. It would be on the front shaft where it mates to the TC. Each u-joint should be greaseable and theres a grease fitting in the housing for the centering ball, that one probably requires a grease needle and may not have a regular zerk.

I have seen many grease zerk fitting thinngys on the u joints and near the brakes... maybe some other places can't remember.
Not sure what to look for as far as the play you mentioned. I planned on just going through and putting grease everywhere I can find a fitting.... any grease type you reccomend?

The ones near the brakes are not grease zerks! Those are brake bleeder valves, do not pump grease in them.

Look at the joints for cracks and damage, also look for rust bleeding out of the caps. Grab the driveshaft next to each joint and forcefully wiggle it left, right up, down, it should not move at all if it does replace it. Before you grease them you can squirt some WD-40 on each cap where it seals to the cross then take a short lap around the block or so. Crawl back under there and look for orange rusty oil leaking out of any of the caps, if there is replace them.

I just put high temp, disc brake, wheel bearing grease in most everything, its the red stuff that looks kinda like strawberry jelly.

So the wiring has all been torn out, the original stuff atleast. I failed to mention it's a "74" gmc.. atleast I believe the frame to be, and is what is on the title. But the cab has been changed to a 78' cab during its life and has a flatbed. And the owner before the owner I got it from had big plans for it. Including the painless wiring kit. But he only got as far as just wiring it to drive. So basically the whole kit is in the truck just budled up on the floorboard. The rest of it in a box I have.

Well, at least you have the kit!

 

[85K304SPD]

It sounds like the power steering pump may need to be re sealed to the reservoir, or the steering gear box is leaking and either needs new seals or just remove and replace with one from the parts store.

 

[waterpirate]

Put it on a lift, or better yet. Jack it up, put it on jack stands, take the wheels off, and look at everything. Lie on your back on a creeper, have a couple cold ones, look at everything. Look at everything and learn stuff. If its greasy oily or dirty, clean it. If it leaks fix it. If it looks hanky, it prolly is. Wheels back on, and on the ground will start another round of " what's up with my 74 K25 " LOL
Eric

 

[AZ Highlander]

We need pics Tyler!

 

[gotamotor74]

It sounds like the power steering pump may need to be re sealed to the reservoir, or the steering gear box is leaking and either needs new seals or just remove and replace with one from the parts store.

It does leak right from what I think is the steering gearbox, all oily and has drips. If I'm lookin at the right part they don't seem to expensive? May just replace. Maybe also repair this one and have two

 

[gotamotor74]

Put it on a lift, or better yet. Jack it up, put it on jack stands, take the wheels off, and look at everything. Lie on your back on a creeper, have a couple cold ones, look at everything. Look at everything and learn stuff. If its greasy oily or dirty, clean it. If it leaks fix it. If it looks hanky, it prolly is. Wheels back on, and on the ground will start another round of " what's up with my 74 K25 " LOL
Eric

I like your methods of inspection, I think I can do that. Atleast, I know I can definantly Crack a few cold ones that's forsure! Lol

 

[gotamotor74]

We need pics Tyler!

I'll try an get some on here!