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BMW 3-Series (E90 E92) Forum
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ZF6HP21 Shift Solenoids.....what issues can they cause when going bad?
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| 04-14-2020, 07:51 AM | #1 |
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Brigadier General
 
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ZF6HP21 Shift Solenoids.....what issues can they cause when going bad?
My 07' 335i has one of the ZF 6HP21 6-speed autos. The car has around 100K miles on it. When I bought it several months ago it had some rough down shifting issues.
I changed the fluid/filter, and replaced the four sleeve seals, and the D-seal under the valve body. That cured the rough down shifting issues. I went ahead and installed the xHP stage-3 flash on it...and it's been working good. Recently I've noticed that sometimes (not always), I'll get a sluggish/soft 1-2 shift......and sometimes a sluggish/soft 4-5 shift. Even at part throttle I'll notice it sometimes. The 3-4 shift is always nice and quick and firm. I'm wondering if these issues could be attributed to sticky/failing shift solenoids? Anyone?
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2007 335i, BMS DCI, BMS Chargepipe w/Tial BOV, ARM Catless Downpipes, silicone inlets, Bilstein B12 Prokit Suspension, Whiteline subframe bushings, Front/Rear M3 control arms, G-Plus FMIC, Stage 2 LPFP, Custom E40 tune by Justin (V8Bait), xHP stage 3 transmission flash, RB Two Turbos....10.90 @ 128mph
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