Transmission Troubles on the 1972 Allis-Chalmers 816 Backhoe

[MikePhua]

The Legacy of the Allis-Chalmers 816
The Allis-Chalmers 816 backhoe, introduced in the early 1970s, was part of a broader push by Allis-Chalmers to compete in the compact construction equipment market. Known for its rugged build and straightforward mechanical systems, the 816 was powered by a diesel engine mated to a shuttle-type transmission designed for frequent directional changes in trenching and loading operations.
Allis-Chalmers, founded in Milwaukee in 1901, had a long history in agricultural and industrial machinery. By the 1970s, the company was producing a range of construction equipment, including wheel loaders, graders, and backhoes. The 816 was not a high-volume seller compared to competitors like Case or John Deere, but it earned a loyal following among operators who appreciated its simplicity and durability.
Understanding the Reverser Transmission
The 816 backhoe used a shuttle transmission system, commonly referred to as a “reverser.” This system allows the operator to shift between forward and reverse without using the clutch, ideal for repetitive tasks like backfilling or trenching. The reverser consists of a hydraulic clutch pack, directional control valve, and a fluid reservoir. When functioning properly, it provides smooth directional changes with minimal lag.
Key terminology:

• Reverser: A hydraulic shuttle mechanism that enables clutchless shifting between forward and reverse.
  
• Clutch Pack: A set of friction discs and steel plates that engage or disengage power flow.
  
• Hydraulic Fluid: The medium used to actuate the clutch pack and lubricate internal components.
  
• Pickup Screen: A mesh filter that prevents debris from entering the hydraulic pump.
  

Symptoms and Initial Diagnosis
One common issue with aging 816 units is loss of forward drive while reverse remains functional. This symptom often points to contamination or wear within the forward clutch pack. In one case, the machine had been operated without a dipstick on the reverser, allowing dirt and moisture to enter the system. After multiple flushes, the pickup screen began to clear, and the machine regained forward motion—temporarily.
Eventually, the forward gear began slipping again, requiring high RPMs to engage. After switching from Dexron ATF to Hy-Tran hydraulic fluid, the machine ran well for 30–40 minutes before losing forward drive entirely. Reverse continued to function, suggesting that the issue was isolated to the forward clutch circuit.
Fluid Selection and Compatibility
Using the correct hydraulic fluid is critical. Dexron, while suitable for some automatic transmissions, lacks the anti-wear additives and viscosity stability required for older hydraulic shuttle systems. Hy-Tran, developed by International Harvester and widely adopted across brands, offers better thermal stability and friction characteristics.
Operators should consider:

• Using Hy-Tran or equivalent high-quality hydraulic fluid
  
• Avoiding multi-purpose fluids unless specifically rated for wet clutch systems
  
• Flushing the system thoroughly before switching fluid types
  
• Inspecting for water contamination, which can degrade clutch material
  

Thermal Behavior and Clutch Engagement
The behavior of the transmission after warm-up suggests thermal expansion is temporarily improving clutch engagement. As fluid warms, its viscosity decreases, allowing better flow and pressure. However, if seals are worn or clutch discs are glazed, the system may fail once cooled.
In one anecdote, an operator ran the machine for half an hour spreading millings, then shut it down for lunch. Upon return, the machine refused to move forward. After cooling overnight, the issue persisted. This pattern points to marginal clutch engagement that fails under cold fluid conditions.
Mechanical Inspection and Rebuild Considerations
If fluid changes and flushing do not restore function, mechanical inspection is necessary. Steps include:

• Checking clutch pack wear using pressure gauges at test ports
  
• Inspecting directional control valve for sticking or internal leakage
  
• Verifying pump output pressure and flow rate
  
• Removing and inspecting clutch discs for glazing, warping, or delamination
  
• Replacing seals and gaskets to restore hydraulic integrity
  

Rebuilding the reverser is labor-intensive but often more cost-effective than sourcing a replacement unit. Parts availability may be limited, but some components are interchangeable with other Allis-Chalmers or Fiat-Allis models.
Historical Context and Operator Stories
During the 1970s, Allis-Chalmers supplied equipment to municipal fleets and small contractors. One retired operator recalled using an 816 to dig utility trenches in Connecticut, praising its torque and visibility but lamenting its finicky transmission. Another technician in Missouri described rebuilding a reverser using salvaged parts from a Fiat-Allis loader, noting that the clutch packs were nearly identical.
These stories highlight the machine’s adaptability and the ingenuity of field mechanics who kept them running long after factory support faded.
Preventive Measures and Long-Term Solutions
To extend the life of the 816’s transmission:

• Always use a dipstick and maintain fluid level
  
• Replace suction screens and filters annually
  
• Avoid prolonged idling in gear, which can overheat clutch packs
  
• Use block heaters in winter to pre-warm fluid
  
• Monitor for signs of slipping, delayed engagement, or fluid discoloration
  
• Document fluid changes and pressure readings for future reference
  

Conclusion
The transmission issues on the 1972 Allis-Chalmers 816 backhoe reflect the challenges of maintaining vintage machinery. While fluid changes and flushing may offer temporary relief, underlying mechanical wear often requires deeper intervention. With careful diagnostics, proper fluid selection, and a willingness to rebuild, operators can restore these machines to reliable service. The 816 may not be common today, but its legacy lives on in the hands of those who understand its quirks and keep it working against the odds.