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1990 GMC 1500 Jimmy

scpaul

1/2 ton status
Joined
Oct 2, 2016
Posts
278
Reaction score
30
Location
central area of S.C.
Hello everybody, this is my first post on this forum and I'm not very good with a computer, so please over look any mistakes and tell me about them and I'll try not to do it again. I'm 60 yrs. old and have C.R.S.

My father-in -law died in late 1989 and just prior to his death he special ordered a loaded '90 GMC Jimmy 1500 and paid cash for it so my wife could carry my 2 daughters around in safety and not blow our budget. It was given to my wife with between 6 and 700 miles. She drove it for several years then gave it to me. It's almost perfect. The only wreck that it's been in was Thanksgiving about 15 yrs. or so years ago. It rolled a short distance across a grocery store parking lot and hit a yellow pole with the little blue sign on top that says handicapped only. It hit dead center front. The impact was at about 5-10 mph. so it didn't do too much damage (bumper, hood,radiator, trans. cooler, AC condenser(?)

I had to park it a few (8?) years ago because of the gas mileage. I had just put a set of 33-12.50-15's. They have less than 1000 miles on them. They cut my gear ratio to where it kept changing from drive to overdrive. I wound up parking it so I wouldn't tear the trans up. or have to file bankruptcy. It has about 130,000 miles on it and if washed and waxed it would look almost new.

It has the factory tow package on it, I think. It has a factory trans. cooler that looks to be about a foot square or larger. I put the 33's on it without any lift and they didn't rub, even on the front. I haven't messed with cars much since I used to drag race in the late 60's to early 70's, therefore I don't have the slightest idea of what it's worth and how much it would cost to put it back on the road. I would put up pics. but the only thing that I have is a flip phone and don't know/think that it will post pics.

I've thought about getting the motor (350, 4 bolt main?) and heads (pretty good?) rebuilt just a little more than stock. I figure that I'll probably have to have the trans. rebuilt pretty soon afterward.

Any info/suggestions would be a big help, thanks, Paul
 
A lot of people get tied up in having to have a four bolt main engine. With "just a little more than stock" power levels you'll be fine with just a two bolt main engine. hopefully you can get some pictures posted up of it, sounds like a nice clean ride!
 
Having driven vehicles with ridiculous highgears and lower axle gears, I can say 33s and 4.10 gears or in that area will help that transmission if it's still in good shape. I'd do that first if it runs and shifts well. That's a great vehicle to have around, especially since you've had it so long. most of us have to deal with previous owners.
 
Agreed, I read somewhere that you don't •need• 4 bolt mains until you're in the 600 hp ballpark.
 
I've had several 2 bolt main small blocks,including a 400 from a '78 Suburban,283's ,307's,350's--I never had any bottom end issues on any of them,or the few 4 bolt 350's I had...but I wasn't pegging the tach at 6000+ rpms a lot either..most all of them had well over 100,000 when I got them too,and were bone stock other than maybe a valve job,and a 4 bbl carb & intake I added myself..

4 bolt mains are better no doubt,but they aren't really a must for a street driven vehicle..
Trucks often got them because they see higher rpms and more abuse, especially in the 2 ton trucks with low gearing and multi speed transmissions,and some also had forged steel cranks and rods..for a daily driver you wont notice any difference..if you wanted to use nitrous a 4 bolt main is better...
I dont recall seeing any 2 bolt main motors ever have a bearing cap or block or bolt failure..just spun bearings..

The one thing I worry about on a high mileage chevy engine is the timing chain and gears..most had those crappy nylon coated cam sprockets that shed the nylon,and it ends up in the oil pan and pump screen,and other places nothing should go...seen them fail at 40,000 miles in some cars..

I replaced the chain and gears (and freeze plugs) when I was swapping an engine into my trucks from a donor vehicle,and I used a Cloyes double roller if it was a engine I planned to keep a long time,those rarely stretch--also the oil pan gasket and oil pump,if the screen had any nylon in it....doing the head gaskets would have been a good idea too,it really sucks pulling the heads off with the engine in the truck..especially if it has any lift,or is a big block or a diesel...bending over on a stepladder for a 2 day ordeal is no fun,but its easy as pie with the engine on a stand or bench..
 
You cannot even buy a 4-bolt replacement motor for a swirl-port TBI engine anymore...I know because I recently tried to buy one, and had to settle for a 2-bolt main instead even though my 1991 swirl-port TBI crew cab originally came with a 4-bolt. With only 130,000 miles on it, you should not have to do anything to get it back on the road. You may be able to re-program the trans to shift into over-drive at a higher MPH.
 
That's a great story! And welcome!
I think that you should simply get it back in service, and just use overdrive at higher speeds, when it doesn't downshift too much. Since the miles are so low, I would run it and see how things go. No sense in making plans without getting reacquainted.
 
I'd really like to keep all of the engine, etc. It's numbers matching. As far as the use that a 4 bolt will take, remember that I said that I used to drag race and it's probably not all out of me yet, I ain't dead! On the vin. # which places are the things like gear ratios, trans. models (think it's a 300r?), if it does have a tow pkg. etc. It has the hardtop that ends behind the fr. seats, it's NEVER been removed. The seats have zippers on them. Can I take the covers off and wash/dry clean them? It has 4 shocks on the fr.axle, does that mean anything as far as the suspension pkg?

I'll check back tomorrow, I really do appreciate the responses and answers, Paul
 
There is a options list in the glove box. It has everything listed by codes. I believe that someone on here has a online code book, but I can't remember who.
 
I looked at that, thinking that I'd copy it. There are 76 codes on that sticker. I quickly changed my mind about that.

There's a engine/transmission rebuilding business not too far from here that has a very good reputation and has been in business for many years. They build engines from showroom stock to local racetrack and give guarantees if the build is reasonable. They will build my engine to a low end torque mtr. and put the cam of my choice (within reason) for $895 to $1000 and do the heads including springs and 3 angle valve job and smoothing the runners for $3-400.

That being said, I know that I'd really need headers ASAP. How far will the original throttle body injection go? I'm guessing that the actual injectors in a throttle body can be changed. Isn't this the same basic throttle body as they put on the big blocks?

Being retired, this will take a while. I hope gas doesn't go back up in the mean time.

Again, thanks everybody for any advice. I'm probably going to ask some stupid things since engines had points the last time that I played with them. It's been so many years since I really messed with a vehicle other than tune-ups and oil changes.

Is there a way to post a pic from a fairly new flip phone. If so, please use the K.I.S.S method to explain it to me.

Paul
 
Again, thanks everybody for any advice. I'm probably going to ask some stupid things since engines had points the last time that I played with them. It's been so many years since I really messed with a vehicle other than tune-ups and oil changes.

Stupid questions are ok, as long as you keep learning. Welcome to CK5. If you don't feel like copying all of the RPO codes, you can look specifically for the axle ratio code. It will be the only code that starts with "GT" or "GU." GT4 = 3.73:1, GT3 = 3.42:1, GT2 = 3.23:1, GU4 = 3.08:1, etc. Post up what you have if it's not one of these common ratios. If you also have the G80 code it means that the rear axle has a "gov-lock" limited slip carrier (these are cool, but often cause problems when they get old).

As for transmissions, Chevy only made 2 automatic options in 1990. If you have a 4 speed O/D tranny it is a TH700R4 (which would be standard). A 3-speed direct drive tranny would be a TH400 (not normal for a K5).

You probably can get pictures from your phone, but I'm not sure how without actually looking at your phone. What model do you have?
 
It seems that it has a locking rear end and limited slip fr.axle. Can they put a limited slip in the fr. end? It seems that it had to be taken back to the dealer when it was young to have something adjusted. I think that the converter was engaging when it wasn't supposed to, early/late? That was probably around 1991/92+-. I do remember that in 4 low that first only went to about 5 mph. You could jog (no run) beside it with the motor turning as much as I felt comfortable. I'll probably go look at the tag in a few. Where is the code that tells me about the fr. axle, like is it a GM, Dana (not), etc. Thanks
 
It seems that it has a locking rear end and limited slip fr.axle. Can they put a limited slip in the fr. end? It seems that it had to be taken back to the dealer when it was young to have something adjusted. I think that the converter was engaging when it wasn't supposed to, early/late? That was probably around 1991/92+-. I do remember that in 4 low that first only went to about 5 mph. You could jog (no run) beside it with the motor turning as much as I felt comfortable. I'll probably go look at the tag in a few. Where is the code that tells me about the fr. axle, like is it a GM, Dana (not), etc. Thanks

Dana axles were phased out long before 1990, you should have 8.5" GM ten-bolt axles front and rear. If you do have the G80 rear, do some research into the 8.5" "gov-lock" unit, it has a nasty habit of fragmenting the carrier and leaving people stranded on the side of the road. It's a neat idea, but that rendition has been known to fail even under light-duty street driving (and I'm owner of two trucks that failed that way). The 9.5" and 10.5" versions don't have such a bad rap. As for limited slip, I know there are some trucks with Eaton Posi units in the front, but I'm not sure if that was a factory option or not. If you take the time to look up each of the 76 codes you will know for sure. Your truck might be new enough that the RPO sheet can be looked up from the VIN, saving you the headache of copying down each code. We have 3 or 4 dealer guys around here that have offered to look up VINs for folks (I don't have that ability). My '83 is too old.

If you have a torque converter lockup it is almost certainly a 4-speed TH700R4 (very few TH400 units had that feature).
 
I really want to chime in here, however I feel like the information I will be providing will likely be incomplete.

As for building up your engine, certain modifications will also require changes to the engine computer to allow them to work. Simple changes like headers and exhaust should be ok as long as they still allow for the O2 sensor. Cam and compression changes would likely require computer changes.

I don't think that the front axle should have a limited slip, unless somebody put one in somewhere along the way, and the front axle should be a corporate 10 bolt, unless of course it was changed out some where along the way.

The trans SHOULD be a TH700R4, unless it was changed...

Transfer case should be a NP241C, unless it was changed, and it should be noted that the 241c is worth keeping...

Gear ratios can vary, gotta check the codes as mentioned or while servicing the differentials you could count teeth and do the math...
 
Should, should, should. We all know how that works out... :rolleyes: :haha:

But if this is a one-owner truck there shouldn't be very many surprises.

:popcorn:
 
I went outside and got the original sticker that was in the window. It's got a 4 speed auto w/overdrive, locking Differential 3.42 gears, H.D. Trailering Special Equip, H.D.Front Springs (explains why it's always set high in the front), Front quad shocks, auto locking hubs. There's alot more, but my finger is tired. If there's anything else that I should look at let me know. I tried to take a pic of that sticker but couldn't get anything readable. I might be able to use a flashlight.

I'm in S.C. What area is most of the membership from or just everywhere?

Paul
 
I went outside and got the original sticker that was in the window. It's got a 4 speed auto w/overdrive, locking Differential 3.42 gears, H.D. Trailering Special Equip, H.D.Front Springs (explains why it's always set high in the front), Front quad shocks, auto locking hubs. There's alot more, but my finger is tired. If there's anything else that I should look at let me know. I tried to take a pic of that sticker but couldn't get anything readable. I might be able to use a flashlight.

I'm in S.C. What area is most of the membership from or just everywhere?

Paul

All over the US & Canada. There are pockets of members scattered around, you're not the only one in SC. Sounds like you have pretty common options (though quad shocks have gone out of favor over the years). If you do have the factory G80 gov-lock, keep in mind that at some point it will probably fragment into pieces and cause axle failure. You might be fine for years, you might not. Otherwise it sounds like a pretty nice starting point. What is it that you are planning on doing with it? If drag racing is really in your future you might want to plan some upgrades. :D
 
Also, 700R4 failures commonly involve excessive heat or rapid shifting back and forth between the gears. Your oversized cooler is a really good thing, but you were wise in grounding the truck when the larger tires threw off the shifting points. You can adjust the shifting points, the gearing, or the tire size, but one way or the other that tranny needs to avoid hunting and pecking.
 
Sounds like you have a great k5 to work with...If it was me I would clean it up get it tuned and running good and leave it alone.
Nice one owner trucks In stock condition are hard to find and worth a ton of money!

Upgrades are nice but nothing you have listed is a ticking time bomb! JMO.

Welcome to the sight its a fun place to hang out!

https://www.google.com/maps/d/viewe...&ll=48.63246103618516,-112.45511094999997&z=3
BTW If you look it this link it will show you some of the members on the map...pretty cool!
 
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