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Remanufactured GMC G1500 Transmissions 

  • Learn about common GMC G1500transmission problems 
  • Everything you need to know when shopping for a GMC G1500transmission for sale 
  • How and when to buy a remanufactured GMC G1500transmission 

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Remanufactured GMC G1500 Transmissions 

One of the most influential GMC van models of all time was the GMC G1500. They were used as everything from passenger vans to work vans. However transmission problems with the 4L60, 4L80E, 6L90 or Allison 1000 can quickly bring this road warrior to its knees. So let’s find out if installing a remanufactured GMC G1500 transmission can more permanently solve some of the issues that you are experiencing. 


Common GMC G1500 Transmission Problems  


No Reverse 

One of the most common 4L60E transmission problems is the complete failure to engage reverse. There are many potential sources of this problem, which is ultimately brought on as the miles increase. The first culprit could be the low reverse clutch pack, where the disks are too worn out to engage reverse gear. 


If this is the case, you will likely see metal shavings in the transmission fluid when you remove the transmission pan. Or the problem could be coming from the valve body, which could mean that warping occurred due to excessive heat, or the reverse circuit has failed. 

Also, inspect the piston bore for scraping and score marks. This type of wear can lead to future reliability issues. So smooth out the bore with emery cloth, then remove the excess dust/debris with Brake Cleaner. 


Harsh or Delayed 12 Shift 

If your 4L60E transmission is pausing between first and second gear, it could be due to a worn or broken 24 transmission band. The steel 4L60E 2-4 transmission band is lined with a friction material that helps it to engage the clutch drum and execute the gear change. 

As that material wears away, the band will slip on the drum and delay the shift, or cause it to slip between the two gears. This is a common problem on higher mileage vehicles. 


This issue can also be caused by a faulty Throttle Position Sensor/TPS. With the ignition in the On’ position, you can test the 4L60E TPS using a voltmeter. If it is working, the voltage should increase/decrease in a smooth, linear line as you move the TPS. To find the correct voltage readings for your vehicle, refer to the shop manual. 


Shudder When Shifting From 1st to 2nd 

Another common problem is when it either slams’ into second gear, or doesnt seem to want to shift into second and the engine just revs. 


Take a look at the 1-2 accumulator. This little shock absorber-like device lives inside the valve body and dampens the excess fluid pressure that builds after a gear change. If the little plastic piston or the spring inside of it breaks, youll feel the fluid pressure buildup as the transmission sort of jerks itself into gear. 

If left un-repaired, this problem will eventually cause serious damage to the clutches and clutch drum assembly. 


Common GMC G1500 4L80 Transmission Problems  


Erratic Shifting 

Since this was an early electronically controlled transmission, many shift problems/Check Engine Lights can be attributed to a failed input/output speed sensor, or throttle position sensor. 


Slipping Between Gears/Failure to Shift 

The 4L80E uses a total of 8 solenoids to actuate gear changes, and activate the lockup torque converter. These little plungers are used to control the ATF fluid pressure, and theyre activated by an electric charge that passes through a coil of wire thats wrapped around the plunger mechanism. If excessive vibrations or an electrical surge causes the solenoid to short out, youll start to experience serious problems. 



The primary function of automatic transmission fluid is to remove heat from the moving parts inside. If youre towing/hauling a heavy load and the radiator cooler cant properly cool the ATF, the transmission will overheat, causing significant damage to the valve body, seals, clutches, bands, and other parts. 


Common GMC G1500 6L90 Transmission Problems  


Reverse Fails to Engage

If youve selected Reverse and your vehicle still wont move, then its possible the park prawl (the metal piece that stops your vehicle from rolling), or one of the clutches has become damaged. 

Slipping Between Gears

If you experience slipping in reverse, or between 2-3, then its very likely that the 1-2-3-3/5-R drum has developed a crack, which will require an entirely new drum and bearing. 

Slipping in First Gear

If you have difficulty getting your vehicle to move from a dead stop, then its possible that one of the solenoids is stuck in the off’ position, or theres a problem inside of the valve body. 


Common GMC G1500 Allison 1000 Transmission Problems  


The Allison 1000 works by the concept of adaptive learning. By comparing the average shift time against preprogrammed ideal benchmarks, the transmission can make shifting more efficient. However, rapid changes in speed or sporadic acceleration/deceleration prevent this process from occurring and the gear and valve assemblies cannot adapt to fluid pressure increases. 


Another key problem can be an improperly lubricated C3 clutch. The way the transmission is set up, this clutch does not get any fluid unless its done directly. It reduces performance due to wear on the clutch pad and can lead to failure. 


Five-speed Allison 1000 transmissions have problems with the C1 and C2 clutches. The pistons that cause these clutches to engage were designed slightly off center, leading to a lack of even pressure and in turn to uneven wear and early failure of the clutch plates. 


How to Solve GMC G1500 Transmission Problems 


Solution A: Buy a Used GMC G1500 Transmission  

Going to the local junkyard and picking up a used GMC G1500 transmission might seem like the cheapest and fastest option. But you need to consider the fact that you don’t know what the actual shape of the internal components are. It could very well be on the verge of transmission problems of its own, which would leave you in the exact same predicament that you’re in now. And that 30 – 90 day junkyard warranty probably won’t cover labor charges to install the replacement transmission if something goes wrong. 


Solution B: Buy a Rebuilt GMC G1500 Transmission  

Getting a rebuilt GMC G1500 transmission would probably seem like a better idea. However, a lot of mechanics and transmission shops will only rebuild your Buick Rendezvous transmission back to its original factory specifications. Which means that all of those factory design flaws are still going to be inplay. And that rebuilt transmission warranty might only be good at certain shops, which could do you no good if you have transmission problems while you’re traveling. 


Solution C: Buy a Remanufactured GMC G1500 Transmission  

If you want to get the most service life out of your little luxury SUV as possible, then you really should consider a remanufactured GMC G1500 transmission from Street Smart Transmission. Each one is completely disassembled and re-remanufactured, so nothing is left to chance. Theyre also modified to correct the factory design flaws, which will greatly extend the service life. Plus, you get a 3-Year/Unlimited Mile Nationwide Warranty. This will cover parts and labor charges at any licensed repair shop in the Continental United States, giving you a lot more flexibility and coverage.