1. The legacy of the SL range

2. The overlooked gearbox

3. Expert insight

4. Common issues with Mercedes gearboxes

5. The 722 series gearbox

The legacy of the SL range

The SL range, birthed by the 1954 300SL Gullwing and Roadster, didn’t necessarily need the 300SLR’s popularity boost. Sales figures and retail values of not only the rare and expensive 300SLs but also the W121 190SL and the W113 Pagoda have been on the rise for some time. Building on this momentum, the R107, produced from 1971 to 1989, is now enjoying increased popularity with good examples growing in value. SLs have always been the best-engineered two-seat sports cars money can buy. While not always the fastest or most track-focused, an SL has almost always been better built, serving as a peerless cruiser with ample power and a solid investment, not to mention its beauty, exclusivity, and desirability.

The overlooked gearbox

Despite the high build quality – the exacting engineering and class-leading quality control – mechanical problems do arise. All machines have a lifespan and require maintenance. The gearbox, however, is often overlooked during annual services. While most motorists and classic car enthusiasts understand the need for regular engine oil and filter changes, the gearbox often remains ‘out of sight, out of mind.’

Expert insight

Mercedes automatic gearbox specialist, trained by Mercedes-Benz with a focus on pre-electronic models, has spent nearly three decades immersed in gearbox repair and maintenance. He has encountered a variety of gearbox issues and believes that the fundamental components of these gearboxes are super-solid. With appropriate servicing and a reminder that your SL is not an F1 car, many trouble-free miles can be enjoyed.

Common issues with Mercedes gearboxes

Seized or Sticking Double-Acting Solenoid

• When a solenoid is seized, the three fundamental pressures in the transmission cannot be regulated. Applying lubricant can usually restore movement.

Poorly Adjusted Control Rod Between Double-Acting Solenoid and Modulating Pressure Transmitter

• If the basic pressure in the transmission does not increase from 0.9 bar to 2.8 when the throttle is moved off idle, the transmission will slip. A pressure test can indicate if the control rod is poorly adjusted. Poor adjustment can also prevent the gearbox from kicking down.

Faulty or Poorly Adjusted Throttle Position Switch

• The throttle position is transmitted to the solenoid via a switch on the throttle body. A faulty or poorly adjusted switch can cause similar symptoms to a poorly adjusted control rod. Replacing the switch can be expensive, costing up to £1,000 for an original component.

General Shifting Issues

• Problems such as engine racing during upshifts, irregular shifting, and loss of gears are generally caused by contamination. Draining the oil and inspecting it for black debris or burnt oil can indicate a burnt-out clutch pack, necessitating a complete transmission refurbishment.

The 722 series gearbox

The discussion also covers issues specific to the 722 series gearboxes fitted to the R107, including models 722.0, 722.1, and 722.2. Similar to the GA (Pagoda) type transmission, the main culprits are lack of maintenance and driver misuse.

Transmission Slipping Due to Low Oil Level

• Low oil, often caused by an unrectified leak, can burn out the clutch pack, resulting in a slipping transmission. Inspecting the sump pan for abrasive dust and stripping the transmission is necessary.

Slipping When Pulling Away

• Issues such as a delay in kickdown or power can be caused by a faulty valve chest gasket. Inspecting the valve chest and replacing the gasket with a modified one is required if faults are found.

Slipping 2nd to 3rd Gear

• Incorrectly adjusted modulating pressure can cause slipping. This can be checked by monitoring the valves while driving. Fitting a modified modulatory valve or friction plates may be necessary.

Are you already a proud owner of a Mercedes? If so, check out our selection of parts for this car at the following link:

https://octoclassic.com/product-category/mercedes-benz

Photos sources: Pinterest, SLSHOP, mercedes-enthusiasts.co.uk