Project Nomad: 1986 GMC Jimmy Sierra Classic

[Darkrider]

As you guys know i recently started a build on a 2015 Jeep Patriot. I also recently picked this truck up from a fellow car club member who needed a newer vehicle to get back and forth to work. So i traded him my '91 Sierra C1500 for this. I have a two part build plan well... Planned. The Jeep will be used for soft road type adventures and the Jimmy will be used places that the Jeep may not be able to handle. Ideally i would like to find a small tent trailer that is lightweight enough for both vehicles to pull. Ultimately i will not be surprised at this point if i end up building a lightweight teardrop style trailer that can be shared between them. Either way that particular component of the build will be sorted once the tow rigs are. Enough side tracking on the subject here is some info on the Jimmy.

Specs:

1986 GMC Jimmy Sierra classic (K5 full size)
305 High Output with Th700R4 trans
Np208 Transfer case
10 bolt front and rear diffs (3:08 with G80 rear)

It has an interesting mix of options in it from what i have seen so far.

Power Locks but manual windows. Did not know that was a thing with these trucks
Air conditioning
AM/FM Cassette deck with the corner speakers in the dash

Known repairs needed so far:

Front brakes
Fuel tank (has a leak in it possibly from mounting strap rub through)
Front and rear bumpers
Grille repaired or replaced
Rear window
Exhaust
Rocker panels replaced at some point most likely with square tubing rock slider style
May need an oil pressure and temp gauge. Though i seem to recall mention of the temp needing to be plugged in so will look into it in warmer weather.

and a couple pics for now.

Planned upgrades:

Hidden receiver hitch behind stock bumper (may change to the older 81-82 bumper with turn signals on it to relocate the signals to be easier to see with grille guard)
rocker panels replaced with rock sliders
stock rear bumper in place of step bumper
rear receiver hitch
Winch on receiver mount as it will allow me to use one winch for both ends of the truck
CUCV style front grille guard on stock bumper (may mount turn signals to guard if old style bumper is not used)

 

[jonnyquest]

Throttle body injection, right? Do you know about LMC Truck? They have all the restoration stuff for these.

 

[Darkrider]

Throttle body injection, right? Do you know about LMC Truck? They have all the restoration stuff for these.

4 barrel Quadrajet carb, They did not start with TBI till late '86 early '87. Very much familiar with LMC truck actually from previous projects.

 

[chilliwak]

Nice looking project there Mr Darkrider. I am looking forward to seeing where you go with this. Cheers, Chilli...

 

[Darkrider]

Nice looking project there Mr Darkrider. I am looking forward to seeing where you go with this. Cheers, Chilli...

Thanks Chilli, Def looking forward to working on it once the weather figures out what the hell it is doing. Ironically enough i thought of your truck when i seen that this Jimmy has the quad shocks up front.

Here is the spec list as best as i was able to decode from looking at the SPID tag in the glovebox and decoding via online searches. I will go back and revisit this later once i find the papers from when i had the Vin ran at the local GMC dealership.

⦁ AM7: SEAT,REAR FOLDING
⦁ A33: WINDOW,ELECTRIC CONTROL,TAILGATE OR BACK DOOR
⦁ CD4: WIPER SYSTEM,WINDSHIELD,PULSE
⦁ D45: MIRROR,OUTSIDE,BELOW EYELINE(STAINLESS STEEL)(9.5 X 6)
⦁ GU4: AXLE,REAR,3.08 RATIO
⦁ K05: HEATER,ENGINE BLOCK(CANADIAN)
⦁ LE9: High Output 305 (210 Hp)
⦁ NK7: FUEL TANK,117 LITER(31 GALLON)
⦁ N33: STEERING COLUMN,TILT TYPE
⦁ TT5: HEADLAMPS,HALOGEN 2
⦁ UA1: BATTERY,HEAVY DUTY
⦁ U35: CLOCK,ANALOG
⦁ V02:
⦁ XUZ: TIRE FRONT 31X10.50 R15LT/B WOL R/PE ST TL OOR (9591094)
⦁ YE9: CONVENIENCE PKG COMFORT & DECOR LEVEL #3
⦁ ZUZ: TIRE SPARE 31X10.50R15LT/B WOL R/PE ST TL OOR (9591094)
⦁ ZY5: EXTERIOR DECOR PACKAGE
⦁ Z75:
⦁ 90K:
⦁ A01: WINDOW,TINTED GLASS(ALL WINDOWS)
⦁ AU3: LOCK,SIDE DOOR,ELECTRIC(EXPORT,CANADA)
⦁ B32: COVERING,FLOOR MATS,FRONT AUXILIARY
⦁ C60: AIR CONDITIONER,FRONT,MANUAL CONTROLS
⦁ F60: SPRING,HEAVY DUTY,FRONT
⦁ G80: AXLE,REAR,POSITRACTION,LIMITED SLIP
⦁ K34: CRUISE CONTROL,AUTOMATIC,ELECTRONIC
⦁ MX0: TRANSMISSION,AUTOMATIC,OVERDRIVE
⦁ NY1: SHIELD,FUEL TANK
⦁ PA6: WHEEL,STYLED(PAINTED)
⦁ T63: WARNING SYSTEM,HEADLAMPS ON ALARM
⦁ UN3: RADIO AM/FM STEREO, CASSETTE
⦁ VE5: STRIP,FRONT AND REAR BUMPER IMPACT(BLACK)
⦁ V76: HOOK,FRONT TOW
⦁ X6W: HUB,LOCKING MANUAL
⦁ YUZ: TIRE REAR 31X10.50R15LT/B WOL R/PE ST TL OOR (9591094)
⦁ ZW9: BASE BODY OR CHASSIS
⦁ Z49: COUNTRY CANADA
⦁ 230:
⦁ 90U: EXTERIOR COLOR,PRIMARY,GRAY METALLIC

 

[Darkrider]

Have had a bit of time to think about where i want to be with this truck and got rethinking a couple details.. Namely the bumpers. As much as the rear step bumper makes no sense on a K5 in terms of what would be "correct" it makes sense for a build like this. Ultimately i think i will be taking the chrome one off and swapping it for the painted one on my '84 C10. At the same time i will more then likely end up adding a receiver hitch along with adding a swing out jerry can/hilift carrier to the step bumper. No need to have an external tire carrier as i have a factory one inside the truck and may just add a second to keep them inside out of the elements till they are actually needed. As for the front bumper...Well i have some thoughts on that as well keeping with the KISS rule here and going with one made out of 4x4 square tubing with a grille guard either welded or bolted to the top of it. Receiver tube in the center of it along with two shackle mounts. What i have in mind for the shackle mounts will be 1/2" steel plate which will go through the 4x4 tubing to both be the mount for the shackles as well as the mounts for the bumper itself. Ultimately i will end up drilling out the rivets holding the front rad support mounts on to bolt said plate to the inside of the chassis. More then likely laying some weld beads inside the chassis as well as a secondary means of making sure the bumper is secure and not putting all of the stress on the bolts holding it and the mounts under winch load situations. The reason for the receivers front and rear is simple: One winch for both ends of the truck.

 

[zoomad75]

Good to see another K5 around these parts. You've got a good game plan to start with. Here's a couple of questions that come to mind when looking at the plans.

You stated of keeping the spare and only have a swingout for fuel/water cans and the jack. Are you planning on going larger than stock on the tires or lifting it any? Reason I ask is the limit to the stock inside spare carrier is about 31" in diameter. That's pushing it too. A 31" tire will be rubbing on the rear seat and tight to the tailgate when closed. 31's are fairly small to what even a stock height suspension setup. 33" tires fit without a lift if you don't plan on flexing it a lot in off road situations. If you go bigger, you'll probably need to plan on dual swingouts.

The step bumper won't help get into the back any better than a stock one with the gate down. It will however, be much better for access to the roof with the gate up than stock though. Plus, adding the swingout much easier on that than a stock bumper. Make sure you brace/reinforce the inside/bottom of the bumper to support your hinge.

Receiver mounted winch. Good idea, just make sure you got a ton of support spreading out the load. A trailer hitch out back is easy and would work. I think Valley towing made a front receiver that bolted in. One thing to watch, keep the side pulls or high angle pulls down to a minumum. By mounting the winch to a receiver, you are concentrating the stress in a small center area. An extreme side pull will focus energy in a direction a bolt on receiver designed for. Receiver's are designed to pull in a straight line front to back, not at a sharp angle to the side. You can induce breakage pulling at an extreme angle.

Your plans have you going off road into places the soft roader Jeep can go. I can probably bet, the Jimmy stock can go way more places than the Patriot can go. Not saying that to upset anybody, but it just struck me funny. Still that being said, how much harder of off road fun were you thinking? Rough and unimproved forest roads? More difficuilt passes with some crawling required? Knowing that will aid in direction on how to build. Here's an example. Going onto a little more rougher terrain where say a short lift (2-3 inches) would help clear say 33's with flexing. Problem is, going to 33's with the stock 3.08 gearing and 700r4 is a guarantee of a future trans problem. It's happened time and time again (see CK5.com for more details of this type) where the tall gearing combined with taller than stock tires causes the trans to shuttle back and forth between OD and drive due to the added load of taller tires with less mechanical advantage of steeper (higher numerically) gears. Typically, one can get away with 31's without much issue, but going to 33's or 35's would have negative impact on the trans shifting in an out of OD at speed. Regearing is the option here. The other issue going to larger tires is the added strain on the engine. A 305 even in good tune/condition is going to be a dog under acceleration if you go to larger tires with stock gearing.


There's a natural snowball effect when you start changing things up. Keep that in mind as you go. Good start to the build!

 

[chilliwak]

Good to see you online posting again Mr Darkrider. I am looking forward to see what you do with this old beauty of a truck. You can have a look at the bumper I made. Maybe something like that would be right for you? Keep us updated with lots of pics. Cheers, Chilli...

 

[Darkrider]

Good to see another K5 around these parts. You've got a good game plan to start with. Here's a couple of questions that come to mind when looking at the plans.

You stated of keeping the spare and only have a swingout for fuel/water cans and the jack. Are you planning on going larger than stock on the tires or lifting it any? Reason I ask is the limit to the stock inside spare carrier is about 31" in diameter. That's pushing it too. A 31" tire will be rubbing on the rear seat and tight to the tailgate when closed. 31's are fairly small to what even a stock height suspension setup. 33" tires fit without a lift if you don't plan on flexing it a lot in off road situations. If you go bigger, you'll probably need to plan on dual swingouts.

The step bumper won't help get into the back any better than a stock one with the gate down. It will however, be much better for access to the roof with the gate up than stock though. Plus, adding the swingout much easier on that than a stock bumper. Make sure you brace/reinforce the inside/bottom of the bumper to support your hinge.

Receiver mounted winch. Good idea, just make sure you got a ton of support spreading out the load. A trailer hitch out back is easy and would work. I think Valley towing made a front receiver that bolted in. One thing to watch, keep the side pulls or high angle pulls down to a minumum. By mounting the winch to a receiver, you are concentrating the stress in a small center area. An extreme side pull will focus energy in a direction a bolt on receiver designed for. Receiver's are designed to pull in a straight line front to back, not at a sharp angle to the side. You can induce breakage pulling at an extreme angle.

Your plans have you going off road into places the soft roader Jeep can go. I can probably bet, the Jimmy stock can go way more places than the Patriot can go. Not saying that to upset anybody, but it just struck me funny. Still that being said, how much harder of off road fun were you thinking? Rough and unimproved forest roads? More difficult passes with some crawling required? Knowing that will aid in direction on how to build. Here's an example. Going onto a little more rougher terrain where say a short lift (2-3 inches) would help clear say 33's with flexing. Problem is, going to 33's with the stock 3.08 gearing and 700r4 is a guarantee of a future trans problem. It's happened time and time again (see CK5.com for more details of this type) where the tall gearing combined with taller than stock tires causes the trans to shuttle back and forth between OD and drive due to the added load of taller tires with less mechanical advantage of steeper (higher numerically) gears. Typically, one can get away with 31's without much issue, but going to 33's or 35's would have negative impact on the trans shifting in an out of OD at speed. Regearing is the option here. The other issue going to larger tires is the added strain on the engine. A 305 even in good tune/condition is going to be a dog under acceleration if you go to larger tires with stock gearing.


There's a natural snowball effect when you start changing things up. Keep that in mind as you go. Good start to the build!

Thanks! and Thanks for the info!

To answer your questions about the tires first. The plan is to keep it on 31s for a few reasons. One being cost to keep it easier to maintain in the long run plus coupled with this it is much easier to find a 31 at a tire shop or at least one close in size to it. I will be running two different sets of tires on this truck. 31x10.5R 15s and 215/85R16. The purpose of this is to have different options depending on terrain. Most of the time it will be running the 15s but come winter and mud conditions i would be running the narrower 16 which is pretty much the same height but close to 2" narrower.

As for gearing I am already considering moving up to 3:42s or 3:54s with a drop in locker in the rear diff. If i go this route i will swap the G80 LSD carrier into my '84 C10 2wd and use the open carrier from that truck for the locker upgrade with a drop in kit like a Spartan. The gearing change will help later on if i do end up going larger in tires.

I may still change the plan when it comes to the swingout to add a secondary spare tire but i will cross that bridge when i get to that point.

As for the use vs the Patriot. The overall goal with both this rig and the Jeep is to go exploring old ghost towns and similar areas all over the country. Now a lot of these places can be accessed with a prepped 2wd or an AWD vehicle like the Jeep but some of them will require more dedicated 4x4 hardware like the K5.

So basically Jeep for areas that can be accessed with a 2wd in ideal conditions but may require the AWD at a moments notice such as mud or sand or snow.

The K5 for forest/unimproved roads that may require the ability to crawl as well. Of course as pointed out it could easily snowball at a given moment.

The eventual goal is to possibly have two K5s. This one and one converted to a Half Cab. The Half Cab will more then likely end up on 33s or 35s and possibly on 8 lug axles.

Good way of looking at it is the Good/Better/Best system here. Good (Jeep)/Better (this K5)/Best (Half Cab K5)

Good to see you online posting again Mr Darkrider. I am looking forward to see what you do with this old beauty of a truck. You can have a look at the bumper I made. Maybe something like that would be right for you? Keep us updated with lots of pics. Cheers, Chilli...

Will def take a look Chilli. I am assuming this bumper is shown in your canopy thread for your square?

 

[zoomad75]

Good plans so far. Gearing for 10 bolt axles is going to be limited to 3.42's or 3.73's. I'd say for no more than the size of tire you plan on running, 3.42's would be good. 3.73's would give the little 305 some extra grunt down low but will cause a higher RPM at a given speed than the 3.42's.

Going with a drop in locker is a good idea too, but that will put the weak link in at the c-clip retained axle shafts. Again for your plans you probably aren't going to stress the shafts by more hard core terrain so this may not be an issue.

 

[Darkrider]

Good plans so far. Gearing for 10 bolt axles is going to be limited to 3.42's or 3.73's. I'd say for no more than the size of tire you plan on running, 3.42's would be good. 3.73's would give the little 305 some extra grunt down low but will cause a higher RPM at a given speed than the 3.42's.

Going with a drop in locker is a good idea too, but that will put the weak link in at the c-clip retained axle shafts. Again for your plans you probably aren't going to stress the shafts by more hard core terrain so this may not be an issue.

Good to know! If i do get concerned about the c clips i may handle it the same way i will be doing so in the 2wd i am swapping diffs with and that is a C clip eliminator kit. Just that added bit of insurance to help keep it in one piece.

 

[chilliwak]

Lets see some more pics of this wicked ride Mr Darkrider....

 

[Darkrider]

Lets see some more pics of this wicked ride Mr Darkrider....

No new pics as of yet as it is in the storage yard. However i did get a short vid clip of it that i am uploading to Youtube atm. Now to touch upon what i was mentioning about picking up a second K5...There is one other direction i may go with it if i am getting it with the full intent of Half cab or at the very least it donating its tailgate to this one along with its hard top as a spare. And that is building a scaled down version of your canopy on it. Still deciding on that particular point however. If i do so i may go about the half cab a different way and that is with a simple flat panel that bolts to the back of the cab when the canopy is not in place. But when it is however it would be more like a Blazer Chalet/Jimmy Casa Grande and that is the front wall of the canopy bolting to the back of the cab. I also know where i can lay my hands on a camperette from a long box pick up that i could use for a similar idea. But building my own unit allows me to do the pick up tailgate swap as well.

It is a bit loud due to no mufflers but here is a brief walk around..

 

[chilliwak]

That truck sounds wicked! I love the cutout in the passenger side running board for the exhaust. So ghetto! The rear bumper extension looks funky too. If you do make a camper thing for the other K5 let me know. I can give you some light weight options that could work for you. Thanks for posting that vid. Cheers, Chilli...

 

[Smileyshaun]

A much simpler solution then putting in a c-clip Eliminator kit would be just a switch to three quarter ton axles their dime a dozen they can be found most anywhere the only thing you really need is a conversion U-joint for the rear end