Common Allison Transmission Shift Selector Problems with Solutions

Common Allison Transmission Shift Selector Problems with Solutions

If you drive a vehicle equipped with an Allison transmission, you’ve likely experienced some frustrating shift selector issues. Fear not – you’re not alone! Transmission selector problems are among the most common complaints of Allison owners.

In this special investigative report, we’ll unpack the top six shift selector gremlins and provide solutions to get you back on the road quickly. But first, some background on the world of automatic transmissions…

A Brief History of Automatic Transmissions

Automatic transmissions have come a long way since their debut in the late 1930s. Those early designs used a simple planetary gearset and a brake band to allow for two forward speeds – an improvement over the clunky, labor-intensive manual transmissions of the time.

In the post-war years, manufacturers added more gears and used progressively more complex hydraulics to achieve smooth shifting between them. By the 1960s, most family cars offered three-speed automatics. Torque converters also replaced the original fluid couplings for better acceleration and fuel efficiency.

No company has had a bigger influence on heavy-duty truck transmissions than Allison Transmission. Founded in 1946, Allison pioneered fully automatic transmissions for off-highway vehicles like construction equipment and military tanks. They introduced their 1000 series model for trucks in the early 1950s.

Allison’s innovative design uses a hydrokinetic torque converter and a planetary gear set instead of a wet multiple disc clutch pack like most passenger car autos. This “hydraulic” system is tougher and lasts far longer in grueling commercial applications. Today, Allison dominates the North American automatic truck transmission market.

Common Allison Transmission Shift Selector Problems with Solutions

So in summary – automatic transmissions have come a long way, but the core technology remains hydraulically-actuated planetary gearing. This allows for fully automatic shifts without a clutch pedal. Now let’s explore some common problems owners face with Allison shift selectors.

1. Delayed Shifting

One of the most aggravating shift selector issues is delayed shifting – when the transmission pauses noticeably before changing gears. This can happen for a few different reasons:

  • Worn shift solenoids – These electro-hydraulic valves direct fluid flow to engage the appropriate gear. Old solenoids may be sluggish.
  • Low transmission fluid level – Inadequate fluid means less pressure to shift smoothly.
  • Dirty fluid – Contaminated ATF can’t flow or change pressures as quickly.
  • Adjustment issues – Selector switch, linkage, or governor may need recalibration.

The solution is to check fluid level and condition, take a look at the shift solenoids, and have a technician evaluate any mechanical adjustments needed. Flush old fluid, top it off with the proper Allison type, and your shifts should feel quicker and more decisive again.

2. Limp Mode

Encountering the dreaded “Limp Mode” transmission is no fun at all. This occurs when the computer senses a problem and limits the transmission to only a few higher gears for safety until repairs can be made. This is usually the result of electrical or mechanical faults inside that the onboard computer detects.

Common causes include failed transmission temperature sensors, faulty pressure switches, worn clutches/bands, or electrical shorts. To escape Limp Mode, the root problem must be diagnosed and fixed. This often involves specialist transmission work beyond a regular fluid/filter service. Early intervention is best to avoid impending breakdown.

3. Mis-adjustment of Gears and Levers

Over time, linkages, cables, and suspension components can wear and go out of adjustment. This leads to issues selecting the proper gear or getting a solid engagement when shifting. The engine may even stall if a lever is misaligned enough.

To check for linkage problems, visually inspect for loose bolts, and worn cables/bushings, and measure specifications. Adjustments may help, but a transmission shop should verify everything is within factory service manual tolerances for long-term fixes. Replacing worn parts like Bowden cables before complete failure can prevent future problems.

4. Fluid Leakage

No one wants to find transmission fluid puddled under their vehicle. Leaks are never good but especially concerning on high mileage Allisons. External fluid seepage is normally from gaskets, o-rings or housing cracks, while internal wetness comes from leaky seals or valve body damage.

Have leaks located and immediately repaired to avoid fluid loss issues and potential transmission damage. Check housing, lines, cooler, and valve body areas. Gasket/oil seal replacement often fixes external seepage. However internal problems may require rebuilding or replacement depending on the extent of wear. Frequent fluid top-offs can temporarily mask small external leaks.

5. Stuck Gears

It’s never a good sign when the transmission gets “stuck” and refuses to shift out of gear. Whether during operation or even when attempting to manually select a gear, a stuck transmission needs professional diagnosis.

Common causes are worn bushings or bands, failed clutch packs, contaminated fluid, or software/mechanical issues. To remedy this, the transmission must be disassembled and the offending component(s) repaired or replaced. Rebuilds are usually necessary for stuck gears to fix the underlying mechanical problems. Early intervention avoids potentially more extensive repairs down the road.

6. Slipping Gears

Gear “slippage” happens gradually and feels like a hesitation, surge or lack of power between shifts. It’s the transmission’s way of showing internal wear is imminent if not already present.

Slipping is caused by worn friction material on clutch packs or bands no longer fully engaging or holding the gear. Contaminated fluid can accelerate this wear process too. The transmission may still be drivable depending on severity, but a rebuild is ultimately required to replace damaged components before a complete failure occurs.

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Component Estimated Lifespan Failure Symptoms
Clutches 150,000-300,000 miles Slipping, delayed shifts
Bands 150,000-250,000 miles Slipping, unable to shift
Solenoids 100,000-250,000 miles Delayed shifts, incorrect shifts
Governor 300,000+ miles Erratic shifting, limp mode
Pump 300,000+ miles Fluid loss, overheating

As you can see from this table comparing typical transmission component lifespans and failure modes, it’s important to address problems promptly. Delayed repairs often lead to complete component failures and higher repair bills down the road.

In summary – routine Allison transmission fluid services can catch small issues before they mushroom. But full rebuilds are sometimes necessary to remedy mechanical problems thoroughly. An experienced transmission shop can properly diagnose the root cause of any selector or shifting issues. Proactivity avoids costly breakdowns and gets you back cruising comfortably in no time.

With proper fluid changes, prompt repairs when symptoms arise, and gentle driving habits, Allison transmissions can easily last 300,000 miles or more even under heavy use. But like any precision mechanical system, things will eventually wear down over time and mileage.

The key is catching small problems before they escalate into far larger and more expensive failures. Hopefully, this special report has shed some light on common Allison shift selector gremlins and helped provide solutions. Saving a transmission before the total rebuild is needed is the name of the game.

The Inner Workings of an Allison Transmission

Now that we’ve covered the most common shift selector issues Allison owners face, let’s take a deeper dive into the ingenious hydraulic technology that powers these heavy-duty automatic transmissions. Understanding how all the moving parts work together can help explain problem areas and aid future troubleshooting.

At the core of every Allison transmission lies a precise planetary gear set. These consist of a Ring Gear bolted to the transmission housing, a set of Pinion Gears meshing with the Ring Gear, and a central Sun Gear. Different rotational speeds of these elements allow for multiple gear ratios.

Surrounding the planetary set are multiple clutch packs and brake bands that selectively engage or disengage components to achieve various forward and reverse gears. Sophisticated shifts between 1st, 2nd, 3rd, etc. are all carefully timed and smoothly executed thanks to precisely metered hydraulic pressure.

This pressurized automatic transmission fluid (ATF) originates from the transmission’s internal pump and is routed through dozens of channels machined into the cast aluminum valve body. Solenoids within this modular unit receive electrical signals to direct fluid to the appropriate clutch actuator or band servo.

By slipping or locking specific elements of the planetary gearset, different output shaft speeds relative to the input are possible. It’s nothing short of mechanical sorcery. Dirty or low fluid degrades this finely-tuned hydraulic ballet, leading to shifting issues.

Meanwhile, computers continuously monitor critical parameters like temperatures, pressures, and gear positions via onboard sensors. The transmission control module (TCM) coordinates solenoids, pumps, and filters utilizing a closed-loop control system. This smart prevents damage from errors like forced shifts due to limp mode.

In harsh commercial applications, all these components must function flawlessly through heat, shocks, extreme loads, and millions of shift cycles. It’s a testament to Allison Engineering that their transmissions achieve legendary reliability despite such brutal use.

Proper maintenance is equally crucial to longevity. Fluid acts as both a lubricant and a hydraulic medium, so contamination rapidly accelerates wear. Draining and refilling ATF according to the rebuild-recommended OEM specification is essential. Filters should likewise be changed based on hours of operation.

With the importance of precise fluid control and condition in shifting becoming clear, delaying needed services can grind an Allison transmission to a halt. Yet with regular fluid/filter upkeep, most examples will shift smoothly and seamlessly for over 300,000 miles of real-world use.

Let this technical overview of Allison’s transmission anatomy serve as further motivation for proactive fluid services and prompt repairs. Preventing problems is exponentially more affordable than wholesale rebuilds in the long run. Staying ahead of any lurking gremlins contributes majorly to maximizing Allison’s incredible lifespan.

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Transmission Rebuild: Pulling Back the Curtain

For those facing more extensive Allison transmission repairs like a rebuild, the process may seem daunting. But pulling back the curtain reveals how straightforward the work truly is for a skilled mechanic. Let’s take a look at the step-by-step procedures involved.

The first crucial task is to carefully disassemble the entire transmission while keeping all parts organized and labeled. Wash down components to remove residual debris before inspection. Transtech’s rebuild specialists utilize customized trays that neatly arrange each unique piece intuitively for reassembly later.

Once fully separated, each clutch, band, gear, and housing is meticulously examined under magnification. Technicians take measurements, check clearances, and assess wear with micrometers to ensure all dimensions conform to factory specifications. Parts exceeding service limits are replaced with genuine Allison OEM replacements.

The valve body assembly comes completely disassembled for cleaning each small passageway and solenoid bore. An ultrasonic tank lifts away varnish and deposits that can disrupt precision hydraulic control. New filters and gaskets are then installed to restore like-new functionality.

Reconditioning focuses next on replacing all seals, o-rings, and bushings throughout with new premium components. Housings and castings get scoured of carbon buildup before treatment with a high-lubricity coating. This protects metal alloys from friction and corrosion for maximum part life.

Finally, the process goes into reverse – reinstalling each component according to the factory service manual procedures. This precise rebuilding verifies correct assembly torques are applied in the proper sequence. Only then does filling and bleeding of the transmission with new proprietary Allison ATF fluid occur.

Rigorous quality assurance testing puts the rebuilt transmission through its full operational paces. Only after passing these benchmarks at the factory level of quality control does the unit leave Transmission Technologies to be remated back in the customer’s vehicle.

A full Allison rebuild takes time but restores like-new durability, smoothness, and efficiency. This increases resale values as well as safety by removing any risks from excessively worn internals. Consider it preventative vehicle maintenance at its finest.

So in summary – don’t be intimidated by transmission rebuilds. Experienced technicians have performed countless and made the process methodical and meticulous to ensure lasting results for worry-free driving enjoyment.

The Future of Allison Transmissions

While the core technology has remained largely unchanged for decades, Allison is continually innovating to push boundaries and boost efficiency. Let’s take a glimpse into what the next generation may bring:

Electric Hybrids – Allison introduced their H 40/50 EP hybrid-electric propulsion system in 2020 for medium-duty trucks and buses. Its ability to recover energy from braking to charge batteries makes it over 30% more efficient than conventional diesel alone.

eGen Flex – Their plug-in electric axle can deliver 120kW continuously or 240kW peak power. It’s compatible with any vehicle configuration and helps commercial fleets meet tightening emissions rules globally.

Fully Automatic eAxle – This single assembly combines an electric motor, single-speed transmission, and power electronics. Pre-integrated eAxle modules simplify vehicle design and integration complexities for OEM partners.

Enhanced TCMs – Next-level transmission control modules will refine shifting strategies through machine learning algorithms and over-the-air software updates. This “digital twin” digitally models transmissions to optimize performance.

Integrated Safety Systems – Allison foresees transmissions actively controlling braking and traction applications in the future. This could assist commercial vehicles with features like stability control, automatic braking, and preventative collision avoidance.

Beyond internal combustion, hydrogen fuel cells may one day replace diesels to repower heavy trucks through Allison’s HT series transmissions. With green hydrogen produced from renewable sources, this opens the door to truly zero-emission commercial transports.

The quest for increased productivity, efficiency, and driver experience will remain constant themes. Allison’s legacy of leadership in medium and heavy-duty automatic transmission innovation ensures they will help power the transportation industry into a new era. Stay tuned for increasing electrification and autonomy ahead!

In Conclusion

This special report has provided an in-depth look into the superb technology that is Allison transmissions, as well as troubleshooting guidance for common shift selector issues owners face. Understanding proper maintenance habits and being proactive with any symptoms can save thousands in repair bills down the road.

With transmissions now achieving operational lifespans over 300,000 miles routinely, it’s clear Allison has mastered precision powertrain engineering like no other. Their future innovations promise to dramatically reduce emissions and optimize vehicle performance. Commercial drivers worldwide are fortunate to have such a reliable partner shifting them smoothly into tomorrow.