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Second Series 05-06-2019 06:05 PM

1988 gmc k2500
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I have a 1988 K2500 that doesnít get much use. I bought it a few years ago from a shady used car dealer. They had the truck on their lot, but had to meet me at a grocery store parking lot. I thought it would be a good donor for a frame swap for an older truck, and stick shifts are rare around here. I use it for work around the house, getting a load of gravel, or making a dump run.
I have had it for about six years. When I got it, it had an intermittent starting issue. I found that if I push on the fuse block, it would allow it to start. The ECM fuse is shared with the Temperature sender, oil sender, and fuel pump. If the engine overheats, or looses oil pressure, the circuit draws excessive current and blows the fuse, shutting off the system. It looks like a new radiator, so it may have overheated. The fuse was 30A, should be 20A, and the fuse socket had lost itís tension-the fuse was loose. I picked up a used fuse block and replaced several loose fuse sockets to fix that.
The speedometer was broken, so I also picked up a gauge cluster. The gauge cluster in the truck was broken at the odometer, so it was probably rolled back. The new to me gauge cluster works, but Iíll never know how many miles are on this truck. It mostly sits. A couple years ago, I was having difficulty starting. It would try to start, and eventually go. I looked at the injectors, replaced one, but it still had problems. I measured the resistance of the temperature sender cold, ran the engine awhile and measured it again hot. It did change, but the range was shifted from what it should have been. I replaced the temp sender and it starts right up now.
At some point I did a brake job, pads and rotors turned, shoes and drums turned on the back. The right front rotor got hot on a trip back from the hardware store, so I replace the caliper. That was easy enough, so I replaced the driver side too.
This spring I decided to start driving it. I got a load of gravel and the right front rotor got hot, I was smelling burning brake pad on the way home. Iím working through this problem now.Iím ready to start the frame swap project, so I want to fix this first. Iím also ready to continue on projects around the house, so I needed a replacement truck.

mingoman 05-06-2019 07:49 PM

Re: 1988 gmc k2500
You may want to replace the rubber hose going from the hard line to the caliper. They're pretty notorious for separating on the inside and letting fluid go to the caliper, but not back.

Second Series 05-09-2019 01:28 PM

Re: 1988 gmc k2500
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Thanks for the tip Mingoman, I have read about that in my on-line search, and itís even listed in the manual as one of the culprits. Iím trying not to throw parts at this, instead learning how systems work and troubleshooting to determine the fix.

I was going to put the two trucks in the same thread, but decided it might get even more confusing. Hereís my new truck:

I have been reading on-line and in manuals about the brake system.
I tested the master and booster first because it was easy following this procedure:
With the engine stopped, press the brake pedal several times to deplete the vacuum reservoir, then press the pedal hard and hold it for15 seconds . If the pedal sinks, either the master cylinder is bypassing internally, or the brake system (master cylinder, lines, modulator, proportioning valve, calipers, or wheel cylinders) is leaking.
Start the engine with the brake pedal pressed. If the pedal sinks slightly, the vacuum booster is operating normally. If the pedal height does not vary, the booster or check valve is faulty.
With the engine running, press the brake pedal lightly. If the brake pedal sinks more than 10 mm (3/8 inch) in 3 minutes , the master cylinder is faulty. A slight change in pedal height when the A/C compressor cycles on and off is normal. (The A/C compressor load changes the vacuum available to the booster.) Leak Test
Press the brake pedal with the engine running, then stop the engine. If the pedal height does not vary while pressed for30 seconds , the vacuum booster is OK. If the pedal rises, the booster is faulty.
Turn the engine off and wait 30 seconds . Press the brake pedal several times using normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.
That all checks good.

There is a long hill that I was riding the brakes down when I got the gravel before, I thought maybe that caused the burning. I went for another load of gravel, and changed my technique. When I got home and found the wheels hot, I jacked up the front and put it on jack stands. I rushed around gathering the jackstands, droplight and wrench. I finally opened the bleeder on each side and the fluid did not squirt out. I also tried to turn the wheels with the bleeder open and it was difficult.
This weekend I took off the calipers and lubed the pins, but they looked new. I also compressed the pads. When I bled the brakes before, I didnít do anything with the distribution block, or the isolation/dump valve. I read some more and found something about clearance between caliper and bracket. I had to hammer and pry to get the calipers off and on, so there was no clearance. I read about different kinds of calipers, floating and fixed, these are floating. I tried to file the edge of the caliper, but the file wasnít even getting the paint off. I dug out my grinder, but couldnít find a grinding wheel. I put 80 grit sandpaper and it worked great, took off enough and not too much. I put some sil-glyde on the edge, and the calipers went on easy. I pumped the brake pedal up and the wheels spin now. Iím still unloading gravel, but Iíll get it on the road next week.

Second Series 06-06-2019 12:04 PM

Re: 1988 gmc k2500
I went for a drive around town this week. The brake issue seems to be resolved. Sometimes when I'm driving the truck starts to shake violently, usually around 40mph. I think it may be a wheel bouncing. Awhile ago I picked up a set of 8 lug rims with tires for my '47 truck for $100. those tires had good tread, so I had them mounted on this truck's rims. I don't know if they were balanced then. When I drove it this week, I may have hit a pot hole as I was getting up to speed, but it started shaking, wheel hop? I plan on replacing the shocks first. I think if a wheel was out of balance it would be consistent, but I later got it up to 50mph with no shakes. The shocks look crusty too. I can take off pretty hard without issue, it shakes while I'm already moving. I've read about axle wrap and pinion angle causing wheel hop, I don't think that's going on here. I did grab the driveshaft and it didn't seem loose, I do need to hit every zerk with the grease gun though.

Second Series 07-26-2019 11:38 AM

Re: 1988 gmc k2500
I replaced the shocks. When I took out the first one, it collapsed. The rest were toast as well. I had known about the test that you push down on a corner of the vehicle to test the shocks. When I did this test there wasnít much movement with the old shocks, I jump on the end of the bumper and the truck goes down and returns. With new shocks, it goes up and down a few times before settling. I didnít know it should do that, now I know.
The ride is better, but still shakes when I hit a pothole. The maypop tires are load range D and I had 30lbs in them. I aired up to 60 and that helped some. They may need to be ballanced, but Iíll probably get new tires instead.
Truck is running good and strong, itís fun to driveÖLast time I went out on errands, the idle would not kick down. Actually it did that a week before and after I got home, I started it up and let it idle awhile and it did go down. This time I made several stops, but it stayed high.
I compiled a list of things to check including the IAC and vacuum leaks, but I have been focused on another issue. My knuckles hit the dashboard when I was shifting. I started a thread about that when it happened before:

Second Series 09-05-2019 11:21 AM

Re: 1988 gmc k2500
I put some helicoils in the top of the transmission, now the stick doesnít flop around so bad. For the high idle, I tried to test the AIC. I checked the signal at the connector with volt meter and saw pulsing. I shorted the ALDL pins A and B, turned the key, and disconnected the AIC after a minute. I pulled the short, and started the engine, but the idle remained high. I sprayed starting fluid around looking for vacuum leaks. I replaced the AIC, but the idle remained high. I took the truck to a repair shop. They replaced the AIC, said the one I put in was bad. Itís running good now and Iím ready to start the frame swap.

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