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Old 06-29-2017, 12:25 PM
mspring135 mspring135 is offline
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ZF Hurth Transmission Rebuild/Replacement

I may be looking at a transmission rebuild/replacement on my HSW 450D transmission. I am thinking about undertaking a rebuild on myself (preferably at the end of the season). I am good with cars and general mechanical/maintenance type jobs, however, I have not worked on transmissions before, so I am a little hesitant. What are the approximate costs and good places to source a replacement? Looking around the prices that I have found varied widely. Also where would be the best place to get a rebuild kit? I'm in the middle of troubleshooting right now so I'll post updates as it goes and if I do in fact take on a rebuild I'll make a DIY thread. Below are the symptoms and steps that I have taken.

Initial symptom: Low speed compared to RPM for a direct drive (2000 rpm - ~10mph, 3000 rpm - 18mph, 4000 rpm - ~30 mph, 4800 rpm - 35mph, all GPS verified)
Suspected cause: Transmission Slipping
Steps Taken:
-Changed fluid, no improvement.
-Swapped with new prop to verify it wasn't a prop issue.
-Checked oil level/color/smell: correct level, looks like used ATF (darker than new but no brown tinge present when put on a white oil absorbent), does not look milky, smells the same as new oil.
-Ran it and monitored temperature, got into the low 100F's. From what I saw in the manual that is below the upper limit.
Next steps:
-Check shifting pressure and verify in spec for the rpm range. (If the shifting pressure is in spec can I still have clutch slippage?)
-I ordered a photo tach (mine is permanently 'borrowed') to verify engine rpm vs. shaft rpm to validate that it is slipping (hoping for a faulty tachometer).
-Cleaning the filter in the transmission (just found out about that little guy).

If the filter is good and the tachometer confirms slipping I think that I will be into a rebuild/new tranny at some point in the near future. If I am missing anything let me know, this is my first direct drive setup and I'm still learning.

Thanks in advance, looking around the forum it seems like a good group!

Last edited by mspring135; 06-29-2017 at 02:50 PM.
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Old 06-29-2017, 12:31 PM
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CantRepeat CantRepeat is offline
 
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The very first thing you ahould do is change the trans fluid and clean the filter if your model has one.

I got two more years on mine with fluid change and then I rebuilt it over the winter.
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Old 06-29-2017, 01:04 PM
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Dylan Dylan is offline
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I replaced my 450D in a previous boat. No one locally wanted to touch it. Pricing a rebuild was $1000 plus shipping (two ways), two weeks minimum for downtime. I bought a completely new one for $1400 from a local Marina direct from ZF, and had it in 2 days. Be aware you need a special socket for output side. I was fortunate that my local marina was able to source the socket through the distributor and did the swap for me.
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Old 06-29-2017, 01:05 PM
NatesGr8 NatesGr8 is offline
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I agree, start easy, change fluid and clean filter. Ensure proper level too obviously. How many hours on the boat and what would you say most of those hours were spent doing?
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Old 06-29-2017, 02:49 PM
mspring135 mspring135 is offline
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Boat: 2000 Prostar
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Sorry I forgot to mention I started with changing the fluid in the spring. I started noticing the lower top end at the end of last season. I also put a new ACME 13x12 prop on the boat to rule out the original prop which had a small ding in it. There are around 500 hours on the boat (it's a 2000) and most of it spent skiing and barefooting.
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Old 07-03-2017, 08:14 AM
mspring135 mspring135 is offline
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Fixed! Turns out it was a bad tachometer.

I verified that I had no slippage by comparing shaft rpm to engine rpm with a photo tach and it was exactly the same. I checked shifting pressure just to make sure and it was over 200psi which was in spec. I'm still going to clean the filter at some point, it's just under the transmission and I'm not sure that I'll be able to get it out/in without lifting the transmission up. Thanks for the replies!
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