'98 SL500 R129. Soft-top stops half-way through opening cycle, can't go further up or back down. Reservoir is full. Pump runs.
What's the pressure test point and whats the spec?
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09-01-2023 11:18 AM
#1
09-01-2023 02:14 PM
#2
Vasilios_Billy
Lifetime Benzer
Join Date: Mar 2008
Location: Campbelltown NSW
Posts: 1,864
Club: M.A.L.A.K.A.S.
Car: 2020 AMG GT C
Location: Campbelltown NSW
Posts: 1,864
Club: M.A.L.A.K.A.S.
Car: 2020 AMG GT C
Henry - the R129 hydraulic top stopping mid-cycle with full reservoir and running pump is a pressure-too-low fault, almost always due to one of the 6 cylinders bypassing internally past a worn seal. The pump is delivering oil but the system can't hold pressure to complete the cycle.
Diagnosis sequence:
- Pressure test point: theres a Schrader-style port on the pump housing. Connect a hydraulic gauge (Repco or similar, 0-200 bar). Spec: 165 bar minimum during top operation.
- If you see 165 bar but the top still stops: the fault diagnostic codes via STAR system will identify which cylinder is bypassing.
- If pressure is below 165 bar: pump regulator is faulty or pump itself worn.
R129 hydraulic top cylinders are $480 each genuine MB. There are 6 cylinders total. Don't shotgun all 6 - identify the failed one(s) via STAR.
Best NSW specialist for this specific job: ACHMLA member Marco at Drummoyne Auto Specialists (02 9181 4400). He has done over 60 R129 top systems. $380 diagnostic + parts at cost + $850 labour for typical 2-cylinder replacement.
09-01-2023 07:42 PM
#3
Billy - booking with Marco next week. Cheers..