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Fixing Factory Mistakes - 1988-1998 GM 1500 trouble spots

Posted in How To on August 23, 2013 Comment (0)
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Fixing Factory Mistakes - 1988-1998 GM 1500 trouble spots

The used truck market is alive and well. With the high cost of new pickups these days, more people are keeping their trucks longer and trading up to a pre-owned ride. The ’88-’98 GMC and Chevy 1500 trucks were a huge hit for GM and still wildly popular today. We know many of you are looking to purchase a new-to-you version of the first-gen IFS GM trucks (or simply trying to make your own last longer). That’s why we put together a list of the truck’s most notorious trouble spots and ways to upgrade and fix the problems.

Don’t worry—we are not singling out just GMs. There will be future articles like this one that span everything from import, domestic, and military 4x4s.

The Problem: Idler Arm
We would classify the ’88-’98 steering system as adequate at best. The tie-rod endlinks are small (more on that later), the idler and pitman arm swing set is problematic, and when you toss larger tires and a lift into the equation the wear is accelerated even more. One of the most common failing points is the bronze bushings that the idler arm uses to pivot. As the idler arm deteriorates so will the pitman arm.

The Fix: Cognito Bracing
There is no magic replace-all cure for the first-gen IFS GM trucks, but Cognito Motorsports (www.cognitomotorsports.com) offers an idler pivot assembly that will help. The system works by replacing the stock idler arm with a beefier version that uses roller bearings instead of the troublesome bushings. Depending on the year, a weld-in gusset is included as well to brace the idler arm. If the pitman arm is bad, a parts-store replacement will have to do.

The Problem: Tie-rod Endlinks
When it comes to a fullsize truck, size does matter. The factory tie-rod endlinks are small and known to bend and/or fail when mixed with rough terrain and large tires.

4x4 ifs suspension

The Fix: DIY Sleeves
The ’99-present GM 1500 trucks have a host of tie-rod endlink upgrades, but there isn’t much for the ’88-’98 trucks. A creative solution is to grab a new set of endlinks from your local parts store and sleeve them with DOM tubing. For a more extreme fix, you can craft your own endlinks using rod ends and DOM tubing. This will require more work and modification to the knuckles, pitman and idler arms.

The Problem: Front Diff Actuator
The front differential actuator (technically known as the thermal linear actuator) is a problematic piece. It’s affixed to the long side of the differential housing and is what engages the intermediate shaft inside of the front differential. While the cast-differential housings have been known to crack (especially when fitted with a locker), the actuator is the most common front differential-related issue for the ’88-’98 trucks.

front diff actuator

The Fix: Posi-Lock
A stock replacement unit from your local parts house will get you going again, and it’s very easy to replace. If you plan to use your 4x4 frequently, we suggest upgrading to a more reliable cable-actuated shifter from 4x4 Posi-Lok (www.4x4posi-lok.com). The 4x4 Posi-Lok bolts in place of the stock actuator and only requires a small cable and mount to be installed inside of the cab. When you are ready to engage four-wheel drive, you simply shift the transfer case into 4-Hi or 4-Lo and pull the Posi-Lock cable-actuation knob about an inch. Another added feature of the 4x4 Posi-Lok is that you now have the ability to operate in low range, with the front disengaged.

The Problem: 10-Bolt Rear
GM’s 8.5-inch, 10-bolt rear axle is one of our least favorite ½-ton axles. The 30-spline (some have 28-spline) C-clip axles work OK in stock form, but don’t mix well with large tires or big power. If you’re planning on a larger set of cleats and wheeling, a rear axle upgrade should be on your radar.

The Fix: Semi-float 14-bolt
Although not overly common, the semi-float 9.5-inch 14-bolt rear axle was offered in some ’88-’98 GM trucks. This makes the heavy-duty rear axle one of the easiest axle upgrades to perform. The 14-bolts massive 9.5-inch ring gear is big improvement over the 10-bolt and the 1.34-inch axleshafts are a nice upgrade as well. While 33 splines are better than 30, the semi-float 14-bolt is still a C-clip axle. Since the semi-float 14-bolt retains the factory six-lug pattern, you won’t have to swap out your wheels either. You’ll have to do some junkyard digging and online shopping to source one. The limited application base has kept the prices down low, so you shouldn’t have to fork out more than a few hundred bucks.

The Problem: Steering Column Tilt Assembly
This issue is more prevalent on early-model trucks. If you only take one piece of advice away from this article, let it be this: do not use your steering wheel as a hoist to pull yourself into your truck! On GM’s part, the issue of the loose steering column is largely to blame on the lack of thread lock on the four screws that secure the tilt assembly.

gm 1500 steering wheel

The Fix: Tighten Up
Plan to spend an afternoon breaking down the tilt assembly. Un-bolt the four screws that secure the main mechanism, add Loctite or the equivalent of, and tighten everything back in place.

The Problem: Gov-Loc
Found in the back of thousands of GM pickups, the Gov-Loc is a somewhat unconventional limited-slip/pseudo-locker. The Gov-Loc garners its name from how the traction aid works. As the differential accelerates, a governor is thrust outward and up a slanted side gear. As the rpms increase, the governor forces pressure onto a thrust block, which allows a small cam gear to force the limited-slip clutches in place. The idea is that the faster the carrier rotates, the more the governor applies pressure. This action is supposed to “lock” both axleshafts together so they can spin at the same speed. While the design and theory behind the Gov-Loc may appear sound, we rarely see them function consistently.

gm gov loc diagram

The Fix: Open or Lock
Your two best options when a Gov-Loc fails are to either replace it with a full-carrier locker or an open differential carrier. The open carrier will be a cheaper route, but the locker will provide better performance off-road. We would shy away from rebuilding the Gov-Loc as well.

The Problem: Saggy Doors
The old saying of they don’t build them like they used to rings very true in some ways. With the launch of the new K1500 in 1988 came the start of some new problems. It seems the “like a rock” mantra was taken seriously at GM, as the heavy doors caused the hinges to wear more rapidly. This is more noticeable in higher mileage trucks and 4x4 models that are lifted (don’t use your door as a lift aid!).

The Fix: Replacement Parts
Depending on your autobody skillset, you may choose to sub this job out to a pro. New hinge-pins and bushings can be purchased at your local GM dealership or local autobody shop. Companies such as LMC Truck (www.lmctruck.com) also offer replacement body parts, including hard to find pieces that often disappear over the years. The job isn’t terribly difficult, but an extra set of hands (or an engine hoist) will make it go a lot smoother.

The Problem: Intake Gasket
The 5.7L V-8 engines were a great power source for the GM truck platform. It is a very reliable pushrod V-8, although it doesn’t quite make the power as the newer 5.3L engines. A common issue we’ve seen with the 5.7L is a leaky intake manifold gasket. This causes the engine to run rough and inefficiently.

gm 5 7l v8 engine

The Fix: New Gasket
It will take a little time under the hood, but you can grab everything you need from your local parts house. The intake manifold gasket swap is a little involved, but very straightforward.

The Problem: Worn Suspension
As trucks go, the suspension and bed always take a beating. Rear springs are easy to replace, but you may notice that your front end won’t stay level. This may be due to the fact that the torsion bars have worn out. Another place to check is the torsion bar mount. Specifically, look for cracks around the frame mounts and bolt tabs.

The Fix: R&R
A replacement set of torsion bars is definitely a great option, but may be expensive and hard to find in like-new condition. You might be able to get a little more life out of the springs by simply adding a set of leveling torsion keys from companies like Zone Offroad Products (www.zoneoffroad.com). These can easily be installed at home, but you will need a professional alignment post-install.

The Problem: CV Axles
Independent front suspensions get a bad rap for a host of reasons, but none more so than the often problematic and weak CV front axles. Typically, the ’shafts will live fine under a unmodified truck, but cranking up the torsion bars and/or changing the operating angles is a recipe for disaster. Adding a larger tire and a front locker to the equation will only aggravate the problem.

rcv performance axles

The Fix: Performance ’Shafts
There are a few ways to save your front ’shafts from certain death. The first thing you should do is to make certain that the ’shafts are nearly level- the less operating angle, the better. Second, understand that the stock frontend is only good for about a 35-inch tire. That’s it. The strongest fix for the stock GM front axleshafts come via RCV Performance (www.rcvperformance.com). RCV uses massive chromoly CVs and ’shafts that are backed by a lifetime warranty. While you may never break a front ’shaft again, the upgrade doesn’t come cheap. If the price doesn’t have you worried, then you should be aware that you are transmitting your weak link further inboard to the less-than-par IFS centersection. An open diff will help keep the frontend living longer. For those looking to simply replace the stock CV ’shafts a set can usually be had for cheap from your local parts store.

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