johannesschauss
New User
Hi everyone,
I’m working on a 1975 Volvo BM 850 (Canadian market version of the BM 800) and running into issues with the Shift-On-the-Go (SOTG) high/low range system.
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The Issue:
Tractor drives fine in low range.
When I try to shift into high range, nothing happens — no sound, no engagement.
If I really try to force it, I can hear a slight grinding, which makes me think it’s almost trying to shift.
My guess is the hydraulic cylinder or actuator that shifts the planetary clutch isn’t getting pressure or isn’t working at all.
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What I’ve Checked:
Hydraulic fluid level is good and clean.
SOTG lever in cab appears connected and moving something below.
Linkages appear intact.
No external shift cylinder visible, so I suspect it’s an internal piston activated by a hydraulic valve.
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What I Need Help With:
1. Where exactly is the hydraulic cylinder or shift actuator located? Internal? Side-mounted?
3. Has anyone rebuilt or unjammed one of these? Tips for testing or confirming failure?
3. Any diagrams, photos, or manual pages showing how this SOTG system works?
5. Can the actuator be manually shifted for testing?
---
Any insight would be greatly appreciated — trying to avoid splitting the tractor if this is something simple like a stuck valve or blown O-ring. This is my first time working with a Volvo BM of this vintage, and resources are tough to find.
Thanks in advance for your help!
— Johannes
I’m working on a 1975 Volvo BM 850 (Canadian market version of the BM 800) and running into issues with the Shift-On-the-Go (SOTG) high/low range system.
---
The Issue:
Tractor drives fine in low range.
When I try to shift into high range, nothing happens — no sound, no engagement.
If I really try to force it, I can hear a slight grinding, which makes me think it’s almost trying to shift.
My guess is the hydraulic cylinder or actuator that shifts the planetary clutch isn’t getting pressure or isn’t working at all.
---
What I’ve Checked:
Hydraulic fluid level is good and clean.
SOTG lever in cab appears connected and moving something below.
Linkages appear intact.
No external shift cylinder visible, so I suspect it’s an internal piston activated by a hydraulic valve.
---
What I Need Help With:
1. Where exactly is the hydraulic cylinder or shift actuator located? Internal? Side-mounted?
3. Has anyone rebuilt or unjammed one of these? Tips for testing or confirming failure?
3. Any diagrams, photos, or manual pages showing how this SOTG system works?
5. Can the actuator be manually shifted for testing?
---
Any insight would be greatly appreciated — trying to avoid splitting the tractor if this is something simple like a stuck valve or blown O-ring. This is my first time working with a Volvo BM of this vintage, and resources are tough to find.
Thanks in advance for your help!
— Johannes
