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Is anyone here a transmission mechanic, need help?

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Before I hand my boat over to a transmission shop (since the Malibu dealers don't work on transmissions. Two dealers told me they do nothing on trans except for measure fluid level, change fluid) I could really use some help.

I have the 2007 Waksetter Hammerhead 383 with ZF Hurth 45 IV (which is the 45C plus AFT Vee-drive.) and 170 hours. Got tune up 2 months ago at dealer. Went wakeboarding one day and after 3 hours checked bilge (for heck of it) and saw all my trans fluid. My dipstick showed nothing. After 3 hours of debug found out my stop screw which holds the spool valve in place was halfway out. So tightened up and filled with 2 liters and then it started coming out vent. Measured dipstick and saw it was 1/2 inch over max mark. (so I learned to not assume completely empty just cause dipstick shows nothing !!!) Suctioned out and went for drive. Still kept coming out vent. Trans mechanic suggested to flush system as there's probably bad trans fluid in there. So emptied trans fluid completely (got about 1.75 liters out) and put in a fresh 1.75 liters and now it measures correctly to max mark. I measure by turning on engine for a few minutes and move from reverse to forward to neutral then shut off and wait 30 seconds then measure. And its at the max mark. Now when I go 3500 RPMs at 35 mph nothing comes out vent. But when I go 4-5000 RPMs and 40-45mph it comes out vent after 3 minutes. I can go an hour doing 3000 RPMs at 30 knots and nothing comes out vent. Checked all water cooling system and no clogs. My engine stays at 160 degrees. I have been told by 2 dealers there's no trans temp sensor or error code. I took off the breather and could blow thru it and ATF goes out it anyways so breather should not bet causing pressure build up.

I have not checked my trans filter yet or checked if there's any clog in trans lines from trans to cooler. I dont know if the trans fluid is overheating and coming out vent or if there's excess pressure or excess air getting in and causing to go out vent. Or maybe running it very low caused some other issue. Could my spool valve or some-else else have broken and cause this symptom? Maybe I should have the fluid at the min mark and see if anything comes out of vent at 45 mph

I dont get any slippage or anything. The trans runs awesome but leaks at breather.

When I open the trans dipstick and turn engine on I see the trans fluid spraying inside and can feel it. I assume this is normal and shows that pump is working?

Any suggestions or help?

FYI the ZF45C manual show the following

  • Plug behind the neutral safety switch. Nothing connected. What is this for?
  • (On top port side) Neutral safety switch/microswitch
  • (On Top middle) Trans fluid connection
  • (On top starboard side) Plug with wires. What is this for?
  • (Facing bow) )Stop screw (for spool valve) which was halfway out on my 2007 with only 150 hours on it AND what caused my transmission to leak 100% dry). Maybe this should have had Loctite??? Dealer told me he has seen this before.
  • (Facing bow) Second plug with ball that screws into spool valve,
  • Second trans fluid connection.
  • the spool valve
  • Breather
  • Dipstick

Edited by JoeMama
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There is a trans temp sensor on your transmission. This would be a sensor with two spade connectors, top middle of the transmission. Neutral safety switch has two screw connections.

I would check to make sure the trans cooler and lines are not blocked, and the transmission is not overheating. Aside from temperature, typically overfilling is the other cause of ATF coming out the breather vent. You should be able to fill the trans to the proper mark on the dipstick with engine off, and without screwing in.

There is no pressure sensor.


Edited by SmoothWaterMan
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I had 2 dealers (Malibu service managers) tell me there's no trans temp sensor and the trans manuals dont talk about one. But I finally see in the Malibu Manual the following "The ECM uses the engine oil pressure, engine temp and trans temp switches for input and parameters are stored in the ECM." I checked an ECM Diagnostics manual (not sure if its for mine) and it mentioned an auxiliary switch for trans temp. I do see two electrical connectors on top of transmission, one for neutral switch and the other must be for temp.

Is the temp switch just open or closed for overheat or does it give a variable resistance?

Is there a way or device to connect to the trans to measure the exact temp? As my boat is not beeping or giving any error codes even when my trans fluid was basically empty.

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Before I hand my boat over to a transmission shop (since the Malibu dealers don't work on transmissions. Two dealers told me they do nothing on trans except for measure fluid level, change fluid) I could really use some help.

That seems very wrong that they cannot service the boat fully and completely... I would expect a transmission shop to be dumfounded if you drop a boat off.... Your dealer should at a minimum be engaging Indmar on resolving.

I unfortunately can't help technically.. just moral support.. I would really challenge your dealers to step up.

Edited by G-Mack
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Well let me say that ZF is a great company.

I contacted one of their execs and got a call back within 24 hours. They mentioned they recommend a new dipstick which will actually lower the transmission fluid level. Said some installs require lower trans level, maybe its my boat. Believes if I leave it at the min mark then I would have no issues. Also said they are getting lots of calls of similar issue from the wakesurfers (I don't do wakesurfing yet) since the boat is so tipped it causes the trans to come out breather. Solution is a lower trans level. Seems its a very fine line between correct level and coming out your breather.

Also confirmed there is a plug behind neutral switch which I could add a pressure sensor (0-400PSI) to and then that could be a good monitor to determine if my levels are getting too low. He also confirmed that the plug (starboard side) next to the trans fluid cooler can be used for temp sensing and its up to the boat manufacturers to determine what to put in there. So that confirms what Indmar had told me. However the temp switch that Malibu/Indmar use is only an open/closed switch. Is that good enough ?

ZF suggested I can add temp sensor with a "T" in the trans fluid cooler line.

If I did not check my bilge for shaft leak, I would never had seen my transmission fluid basically empty. There must have been only 4 ounces of ATF left and the temp sens error never went off. So I wonder when would it have gone off, after I damaged my transmission? I would love to see a trans temp vs trans fluid volume chart and see what happens when you start to run a trans dry and when my sensor would actually tell me the trans is too hot. Will it tell me before I get any damage?

I will most likely add my own ATF temp sensor and pressure sensor later on this year. And probably get in the habit of checking my bilge at the end of my day. Will post another one after I get my level down to min and do 45 mph for 20 minutes and ensure nothing comes out breather. This debug work has cost me a lot of money in gas but its better than working and I have learned a lot !!!

Edited by JoeMama
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