“The dealership told me it would take 6 weeks before they could even look at it…”
“I really appreciate the effort you guys put into getting my truck fixed and back to me so quickly. I need that truck to make a living and couldn’t afford to have it down for very long. The dealership told me it would take 6 weeks before they could look at it and they had no idea how long it would take to get a transmission. Thanks to the ATC team for making this as painless as possible!”
— Mike P., GMC Sierra Owner & Contractor
8L90 Transmission Rebuild: How We Got Mike Back on the Road in 5 Days
The Situation: A Work Truck in Trouble
Mike P. works in construction and relies on his 2017 GMC Sierra 1500 to make a living. When he began noticing issues with how the truck drove, he didn’t waste time:
- Shuddered hard above 40 mph
- Shifts were erratic and unpredictable
- Some shifts felt like being rear-ended
- No warning lights appeared, but something was off
Mike knew something was wrong and he needed answers—fast. That’s where our Free TrueTest™ Diagnostic came in. More than just a quick scan or fluid check, it’s a thorough, step-by-step process designed to uncover the root cause of transmission issues and give our customers the clarity they need.
What’s Included in a TrueTest™ Diagnostic?
Our TrueTest™ Diagnostic is a comprehensive, multi-step process designed to get an accurate diagnosis the first time:
✅ 1. Visual Inspection
- Transmission case and mounts
- Leaks or mechanical damage
- Signs of heat or wear around the pan and housing
✅ 2. Road Test with Diagnostic Scanner
- Check for active or stored error codes
- Monitor real-time data from control modules
- Observe shifting behavior, RPM ranges, and temperatures
✅ 3. Fluid Condition Check
Mike’s transmission fluid was blackened and burnt, indicating extreme internal heat and advanced wear.
⚠️ The Diagnosis: 8L90 Transmission Failure in Progress
Even without transmission codes, our inspection confirmed that the 8L90 transmission was already in a state of failure. Immediate attention was needed to prevent a complete breakdown.
What’s Wrong with the 8L90 Transmission?
The 8L90 transmission, introduced by GM in 2014, is known for its performance issues despite being marketed for improved fuel efficiency and smooth shifting.
Common Complaints:
- Shuddering during acceleration
- Harsh or delayed shifting
- Overheating and fluid breakdown
- Premature internal wear
Two Major Weak Points:
1. Chain-Driven Pump Failure – The pump is driven by a chain that stretches over time, leading to pressure loss and overheating.
2. Undersized Valve Body Accumulators – Small, wear-prone pistons cause erratic shifting and poor hydraulic regulation.
GM has faced class action lawsuits over these issues. OEM replacement transmissions are often on nationwide backorder.
The Fix: Our 8L90 Rebuild Process
We’ve rebuilt dozens of 8L90 transmissions and understand how to address both common failures and less obvious issues.
Step-by-Step Rebuild:
- Full teardown and inspection of all clutches, electronics, sensors, valve body, and torque converter
- Valve body modification to install larger accumulator pistons for better performance
- Replacement of internal wiring harnesses and damaged electronics
- New torque converter to prevent contamination from the old system
️ Fast Turnaround: From Diagnosis to Delivery in 5 Days
Day |
Work Completed |
|---|---|
| Monday | TrueTest™ Inspection & Diagnosis |
| Tuesday | Transmission removed and inspected |
| Wednesday | Parts delivered and rebuild completed |
| Thursday | Reinstallation and reprogramming |
| Friday | Final road test, quality control, and pickup |
What’s the Cost of an 8L90 Rebuild?
A full 8L90 rebuild typically costs between $7,000–$8,000 plus tax, depending on damage. While not inexpensive, it’s far more cost-effective than replacing the entire truck, especially one valued at $50,000–$70,000.
Serving Lakewood & Westminster, CO
If you’re experiencing:
- Shuddering on acceleration
- Harsh or delayed shifting
- Transmission overheating or fluid issues
Don’t wait. Get a Free TrueTest™ Diagnostic from the most experienced transmission team in Colorado.
Contact Us Today
Advanced Transmission Center
Denver Colorado’s Most Trusted Transmission Shop Since 1986
Lakewood Location:
1194 S. Pierce St.
Lakewood, CO 80232
303-816-3856
Westminster Location:
3686 W. 72nd Ave
Westminster, CO 80030
(303) 647-5257
With over 10 years of hands-on experience in the automotive industry, including serving as General Manager for a high-volume transmission shop, Tom Christy brings deep operational and technical expertise to every facet of auto repair and service management. Having overseen multi-million-dollar operations, led national teams, and improved shop performance across sales, staffing, and customer service, Tom has a proven track record of growing revenue while reducing costs. Tom's real-world experience in transmission diagnostics, repair workflows, and customer satisfaction makes them a trusted voice in the field.
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