Author Topic: Hard Auto Box Upshift between 2nd and 3rd gears  (Read 1308 times)

Nicolas Aristodemou

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  • 280SL Auto 1970 W113, 380SL Auto 1982 R107
Hard Auto Box Upshift between 2nd and 3rd gears
« on: October 19, 2019, 15:35:09 »
My 1970 US spec 280SL seems to be managing all the upshifts and downshifts extremely well (almost like a modern car) apart from the upshift between 2nd and third gear (during normal driving with shifter in position 4, taking place  at around 2500 rpm when starting from a standstill) which is not smooth like all the other gear-changes. This particular gear change is not accompanied by any noise it is just jerky. When I press the car harder from standstill so that this first gear change happens at just under 4000rpm, things are much smoother.

I have changed the gearbox oil and filter but so significant change.

Any ideas as to what could be causing it?
Nicolas Aristodemou
Nicosia - CYPRUS
280SL Auto 1970 US spec (W113), 380SL 1982 R107, Citroen DS23 Pallas 1973, Triumph TR4 1963, Triumph Stag 1973, Mini Cooper S Mk1
1965, Jaguar 3.8 Mk2 1962, VW Beetle 1978 Karman Converible, 1987 Ferrari 328GTS

teahead

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Re: Hard Auto Box Upshift between 2nd and 3rd gears
« Reply #1 on: October 19, 2019, 17:08:19 »
probably need to lower the pressure.

Facing the modulator adjustment thing, loosen the 10mm nut, and turn with a pair of pliers counter clockwise some.  PITA to get under there and w/that heat shield almost in the way, but can be done.
1970 280SL auto, AC - aka "Edelweiss"

Nicolas Aristodemou

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  • 280SL Auto 1970 W113, 380SL Auto 1982 R107
Re: Hard Auto Box Upshift between 2nd and 3rd gears
« Reply #2 on: October 19, 2019, 17:37:49 »
Thanks for the suggestion. Will take the car to my mechanic to lift it up for me and will try this adjustment..... see the result....next week.....
Nicolas Aristodemou
Nicosia - CYPRUS
280SL Auto 1970 US spec (W113), 380SL 1982 R107, Citroen DS23 Pallas 1973, Triumph TR4 1963, Triumph Stag 1973, Mini Cooper S Mk1
1965, Jaguar 3.8 Mk2 1962, VW Beetle 1978 Karman Converible, 1987 Ferrari 328GTS

Nicolas Aristodemou

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  • Cyprus, Lefkosia, NICOSIA
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  • 280SL Auto 1970 W113, 380SL Auto 1982 R107
Re: Hard Auto Box Upshift between 2nd and 3rd gears
« Reply #3 on: November 08, 2019, 10:32:24 »
I had a chance to lift up the car today and adjust the modulator pressure on the assumption that the hard shift between 2nd and 3rd gears was due to a high gearbox operating pressure (>40psi). I don't have the banjo fitting with the pressure gauge to see what the actual pressure was and didn't want to bother sourcing the parts to fabricate such a set.

As per teahed's suggestion I unscrewed the 10mm locknut on the modulator and turned with a pair of pointed pliers the adjusting screw anti-clockwise by 180 degrees (half a turn).

Result was a much a smoother gearchange from 2nd to 3rd, to the point that I am now happy. Remaining upshifts and downshifts have not been affected since they were initially spot on.

Thanks for the useful advice.
Nicolas Aristodemou
Nicosia - CYPRUS
280SL Auto 1970 US spec (W113), 380SL 1982 R107, Citroen DS23 Pallas 1973, Triumph TR4 1963, Triumph Stag 1973, Mini Cooper S Mk1
1965, Jaguar 3.8 Mk2 1962, VW Beetle 1978 Karman Converible, 1987 Ferrari 328GTS