Lets face it! Diesel automatic transmissions can be troublesome, particularly those models that use vacuum to control shifts. This is largely due to the fact that diesel engines don't produce vacuum naturally. It has to be artificially manufactured. This is what makes diesel transmission tuning difficult. The numerous vacuum and pressure controls that were added to make it shift properly can create all kinds of problems when they fail or get out of adjustment. The big challenge in writing the manual was to clearly explain how to get all these controls working in harmony for the transmission to operate at peak efficiency.
Many problems related to poor or improper shifting can be solved without repairing or replacing the transmission. Can you imagine how many Mercedes diesel transmissions have been replaced over the years that most likely did not need replacing! From my own experience, I know the numbers would be shocking. I will never forget one particular customer bringing me his 300D for a second opinion on an abrupt shifting problem. He had been told his transmission needed a complete overhaul and it would cost $1800. Upon close inspection, I found the rubber hose connector at the vacuum modulator had failed. After replacing the hose the transmission performed as new. The total cost of repair including labor = $22.00. Stories like this are what motivated me to complete this manual.
The manual is broken down into phases (rather than chapters). These phases have to be followed in order to achieve success. Note that the first phase starts with the engine. That's right! If your engine is not tuned properly or developing full power, forget about trying to tune the jerks and flairs out of shifts! Next comes the vacuum system. Why is that so important? Since 1978 vacuum became the key shift control in diesel automatics. That whole system has to be dealt with next. From there the manual progresses through the phases of repairing key vacuum controls, adjusting mechanical controls, dealing with internal hydraulics, testing and adjusting the mysterious VCV, and finally tuning them all together for the final performance.
If you are a diesel owner or diesel enthusiast you won't want to put this manual down once you start reading! Even if you don't plan on doing the work yourself, the information in this manual could save you big $$ by preventing an unnecessary transmission overhaul or replacement.
ATTENTION 1985 OWNERS: Mercedes made some MAJOR CHANGES to all the vacuum routing and to the controls that shift the transmission in most 1985 model years. There are no more 3/2 valves and there are other vacuum controls and extra lines that you don't see on the earlier models. Example: If you see a blue vacuum disk like the one pictured here - then you have the model that this manual will not cover. We are sorry we do not have any specific troubleshooting and repair information on these 1985 models. Try to obtain the factory engine manual that covers this system.
1985 Model diesels like this NOT COVERED!
This manual does not cover removing the transmission, opening the transmission, or repairing transmission internals. We have other manuals/kits that only cover the following.
- Transmission removal and replacement guide
- Early automatic transmission front reseal kit
- Late automatic transmission kit
We do NOT have any manuals that deal with opening up or overhauling an automatic transmission.
61x Diesel Automatic Transmission Tuning for Peak Performance
Application: 61x refers to the diesel engine. These include the 615 and 616 four-cylinder diesels and the 617 five-cylinder diesel automatic transmissions from 1969 to 1984 with the exception of the 201 chassis 190D. Some troubleshooting and adjustment are specific to the older non-vacuum regulated transmissions. But due to the complexity of vacuum controls, most of the material in the manual relates to transmissions with vacuum modulators installed. Vacuum controls first appeared on the 1978 300SD and then in 1980 on the 240D, 300D, 300CD, and 300TD.
Table of contents:
Phase 1: Diesel Engine Repair and Tuning
Phase 2: Vacuum System Inspection and Repair
Phase 3: 3/2 Switchover Valve Assembly Overhaul
Phase 4; Mechanical Shift Controls Inspection and Adjustment
Phase 5: Hydraulic Shift Controls Diagnosis and Tuning
Phase 6: VCV Testing and adjustment
Phase 7: Vacuum Supply Throttling
Phase 8: The Final Performance
Use of transmission additives
Vacuum shift control diagrams
NOTE: Proper testing and tuning will require vacuum and hydraulic gauges along with the proper connection hose and fittings. Kent has put together two new test kits (LISTED BELOW) that will allow you to properly tune the transmission yourself. These kits are available separately and can be purchased along with or even after reading the manual.
Diesel Automatic Transmission Vacuum Controls Testing Kit
All diesel Automatic Transmissions with Vacuum Modulator Fitted 1978 to 1993
61x Diesel Automatic Transmission Modulating Pressure Test Kit
1969 to 1985 220D 240D 300D 300CD 300TD 300SD
TESTIMONIALS: Here is what some of our customers are saying about this new manual
Hi Kent, just wanted to say your new trans manual was really worth the
wait! What a terrific job explaining the workings of the trans as only you
can do. Nowhere else can you find this kind of info laid out in such an
orderly & easy to understand way. I will have my trans shifting like new in
no time, thanks again for the great job! sincerely your friend George R.