1985 Autocar: we work on any truck
If it runs diesel and needs help, we'll show up. Age is not a barrier: classic, vintage, or modern.
Transmission Diagnosis & Repair
Truck Transmission Diagnosis & Repair in Charleston, SC
Shift fault on the dash, a slipping clutch or a CHECK TRANS light? We diagnose transmission problems where the truck is parked and give you clear direction before anything gets pulled.
- Automated manuals, manual transmissions and clutches, Allison automatics
- Fault codes, air supply, sensors, wiring and fluid checked at the truck
- Charleston, North Charleston, Summerville, Goose Creek, Mount Pleasant
Transmissions We Diagnose
Automated, manual and fully automatic
Automated manuals (AMTs)
Eaton Endurant and UltraShift PLUS, Detroit DT12, PACCAR TX-12, Volvo I-Shift and Mack mDRIVE. A control module shifts the gearbox and works the clutch with air, with no clutch pedal.
Manual transmissions & clutches
Slipping or dragging clutches, hard shifting, clutch adjustment and clutch brakes.
Allison automatics
Allison 1000, 2000 and 3000 Series in medium-duty trucks, school buses and transit buses.
Fluid & leaks
Low or burnt fluid, external leaks at lines and fittings, and fluid service.
Why Test Before Condemning
A shift fault isn't always a bad transmission
On an automated manual, the gearbox is shifted with air. Eaton lists low air pressure, contaminated air, air leaks and a failed filter-regulator among causes of UltraShift PLUS range and splitter faults, and a Detroit DT12 can warn "Low Air Pressure. Transmission may not shift." A truck that won't shift can have a healthy gearbox and a problem in the air supply or wiring.
On an Allison, when the control module detects a problem it can restrict shifting, turn on the CHECK TRANS light and store a code. Reading that code comes before anyone talks about pulling the transmission. Founder and lead technician Joseph Cufaude brings 13 years in the diesel trade to that process.
Why operators call us
- Mobile service where the truck is sitting
- Testing before parts replacement
- Clear written findings and next steps
- Commercial diesel and fleet-focused support
- 24/7 Charleston-area availability
Our Transmission Process
How we diagnose a transmission on-site
1. Codes and history
Active and inactive codes, plus when it happens: cold, hot, loaded or at a stop.
2. Air supply
Pressure, leaks, the filter-regulator and contamination in the air feeding the actuators.
3. Sensors and wiring
Speed and position sensors, chafed harnesses, corroded connectors, power and grounds.
4. Clutch check
Free pedal and clutch brake clearance on a manual clutch. Clutch data and actuator operation on an AMT.
5. Fluid
Level, condition and external leaks. Allisons with an oil level sensor allow an electronic level check.
6. Calibrate and verify
Calibrations or relearns after a repair, then a check that it shifts correctly.
Clutch Symptoms
Signs a clutch is going out
- Slipping: on a strong pull, engine rpm climbs but truck speed doesn't keep up.
- Hard shifting or grinding: gears clash going into first or reverse from a stop.
- Changing free pedal: free pedal travel is the guide to clutch and release condition.
- Sporadic engagement: a clutch that fails to engage now and then is often near the end.
- Clutch codes on an AMT: such as a code for a clutch unable to open fully.
Eaton Fuller Easy-Pedal and Angle-Spring clutches can be readjusted in the truck. The clutch brake stops the input shaft so gears go in cleanly at a stop, and is not meant to be used while moving.
Repairs At The Truck
What we fix on-site and when it has to come out
Many transmission problems are handled at the truck: air leaks and filter-regulators, sensors, wiring and connectors, clutch adjustment, fluid service, external leaks, and calibrations or relearns. On an Endurant or PACCAR TX-12, the linear clutch actuator can be replaced in the chassis, followed by a clutch calibration.
When testing shows the fault is inside the gearbox or the clutch itself is worn out, the transmission has to come out, and we don't rebuild transmissions. You get clear direction first, with the codes and test results, so you can decide where the work goes before anything gets pulled.
What to text us
- Year, make, transmission and unit number (or VIN)
- Where the truck is parked or broke down
- What it does: won't shift, stuck in gear, slips or grinds
- Photos of any dash message, warning light or code
- Any low air warning, air leak or fluid leak
Transmission trouble in the Charleston area?
Call or text Lowcountry Diagnostics and we'll diagnose it at the truck.
Common truck transmission questions
Why won't my automated transmission shift or go into gear?
Automated manuals shift with air, so low air pressure, leaks or a failed filter-regulator can cause shift faults, as can a bad sensor or connector. If the dash shows a low air warning, let the air build before driving. If the fault stays, text (843) 310-0995 with the codes and your location.
What are the signs a clutch is going out?
Engine rpm climbing on a pull without the truck speeding up, grinding into gear from a stop, changed free pedal travel, and sporadic engagement. We check and adjust a manual clutch at the truck when it has adjustment left. A worn-out clutch has to be replaced.
What does the CHECK TRANS light mean on an Allison?
The control module has detected a problem, may restrict shifting, and stores a code. We read it on-site and check fluid and wiring before anyone condemns the transmission.
Can you rebuild my transmission on-site?
No. We diagnose on-site and handle the repairs that are practical at the truck. When the transmission needs to come out or be rebuilt, you get clear direction first, so you can decide where the work goes.
Does a new clutch or clutch actuator need a calibration?
Often, yes. An Endurant or TX-12 needs a clutch calibration after an in-chassis clutch actuator replacement, and an I-Shift needs calibrating after a clutch replacement.
Request Transmission Diagnosis
Tell us where the truck is and what the transmission is doing. For a truck that is stuck or stranded now, calling or texting is fastest.
Truck won't go into gear? Call or text (843) 310-0995.
Recent Repair Photos
A look at the repairs we make
Real field photos from Lowcountry Diagnostics, from engine diagnostics and electrical to hydraulic, HVAC, and heavy-duty truck service, handled on-site across the Charleston area.
Reviews
What Charleston truck owners and fleets say
“Great team, personal and professional. These men were responsive and had great diagnostic equipment paired with experience…”
“These guys really know their stuff. Couldn't recommend em more.”