Hurth HSW 630 Leaking Tranny Fluid

[clseahorse]

I have a hurth zf hsw 630A transmission that has been leaking fluid which appears to be from the back or towards the prop area. It has been leaking for about a year. It looks like a lot but really only takes about 1/4 of a quart to fill it every couple months. Lately it seems to be increasing to about 1/2 quart. My boat is in the Bahamas so service is difficult at best. I'm wondering if I should try and get the seal replaced or just carry on topping up. I'm afraid of a catastrophic loss of fluid while underway that will wreck my whole transmission. Is this a real or unfounded fear?

[Laidback]

Originally Posted by clseahorse

I have a hurth zf hsw 630A transmission that has been leaking fluid which appears to be from the back or towards the prop area. It has been leaking for about a year. It looks like a lot but really only takes about 1/4 of a quart to fill it every couple months. Lately it seems to be increasing to about 1/2 quart. My boat is in the Bahamas so service is difficult at best. I'm wondering if I should try and get the seal replaced or just carry on topping up. I'm afraid of a catastrophic loss of fluid while underway that will wreck my whole transmission. Is this a real or unfounded fear?

Impossible to answer how it will be before the seal or the shaft wear allows
the transmission oil to leak fast enough to cause that transmission fail to operate.

The majority of seal replacements involve the following simple process:-

#1. disconnect the gearbox flange from the prop-shaft coupling
#2. move the prop-shaft back (aft) about 3<>4 inches (75<>100mm) IF Possible
#3. Remove the gearbox flange from the gearbox output shaft.
#4. Drain the gearbox (transmission) of its oil (fluid)
#5. Remove the rear section of the transmission outer case
#6. Remove the old seal and replace (if there is a bearing - replace it as well)
---------------
#7. Reinstall the rear section of the transmission outer case.
#8. Reinstall the gearbox flange.
#9. Recouple the prop-shaft coupling with the gearbox flange
#10. Refill the transmission (gearbox) with correct grade of transmission fluid)
----------------
The seal and bearing can be sourced at a non-marine establishment at a very low cost.
The single nut that connects the flange to the output shaft will probably need a large size socket - if not in one's tool kit : borrow for the occasion.
-------
Your gearbox schematic:-

[clseahorse]

Too cool!!!!!!!!!!!!!!!!Thank you SOOOO much!!!

[Boracay]

I had a small leak from a around couple of bolts on the back of my ZF63. Wasn't too bad (about the size of yours from the sound of it).

I got a couple of copper washers from the manufacturer (Free, thanks ZF) and put them in nice and snug. Still a very tiny weep, but nothing that I'd be going to worry about.

Note that one of the bolts has a ball and spring behind it. Serious care is needed that they stay in place and do not end up in the bilge.

I had factory backup a phone call away and it was a simple job. I would hesitate to do major surgery. The above sounds like send it off to the factory stuff.

From memory bolts nos 12 and 14 if that's any help. #12 is hex head on my trannie.

[Laidback]

Thanks for the info regarding copper washers on bolts on a ZF 63.

In this case the OP asked "I'm wondering if I should try and get the seal replaced or just carry on topping up." and it was in that regard that the (simple) steps were provided to remedy the problem. It is generally accepted that the rear output shaft seal on transmissions has a limited life in terms of time and usage - and in fact is one of the most common problems experienced.

[Laidback]

Originally Posted by Laidback

Impossible to answer how long it will be before the seal or the shaft wear allows the transmission oil to leak fast enough to cause that transmission to fail to operate.

#3. Remove the gearbox flange from the gearbox output shaft.

#8. Reinstall the gearbox flange.
#9. Recouple the prop-shaft coupling with the gearbox flange
----------------
"The single nut that connects the flange to the output shaft will probably need a large size socket"

Returning to step #s 3 and 8 -- Because some gearbox Flanges are fixed to the Output shaft by means of Circlip NOT a nut.
In this type, the output shaft is splined and fits inside the flange's splines. At the aft end of the shaft is a groove (all the way round) When the flange is pushed onto the shaft as far as it will go, then using circlip pliers, the circlip is opened to fit over the shaft and then the circlip is released into the groove. Once that is done the flange is properly fixed to the shaft.
To remove the Flange the reverse procedure is used.

Now to #9 again "Recouple the prop-shaft coupling with the gearbox flange"
The connection of these 2 components is very important in that the faces of both must be aligned with each so that a STRAIGHT line is achieved between the gearbox's output shaft and the propeller shaft (no more than 0.2mm - top <> bottom and 0.2mm - stb <> port) The aligning in a fiberglass boat should done in the water.
Illustrations of the Circlip and the correct Circlip Pliers :-

[clseahorse]

Thanks again. Do you by anychance know the number you called to get help with the washers?

[clseahorse]

Anyone know where or how to get a repair manual???? I've searched the web but?????

[FPNC]

Hello clseahorse,

I would try to seek out the source of the leak before I started removing parts from the transmission. ATF is pretty thin stuff. Your leak could be at the top of the gear or around the control head as suggested. Oil cooler lines are common sources for leaks.

If your output seal is leaking:

The output flange on the ZF 63 can be replaced in the boat and without separating case halves. Removing the rear case half in the boat would be an unpleasant experience at best.

The flange is fitted to the splined output shaft and held with a single bolt. The bolt is torqued to 100 nm/74 FT LBS.

Complications:

Breaking loose the bolt and retightening of said bolt to torque spec-- You will need pretty good access to the bolt with a big socket wrench and a method to secure the output flange from rotating.

Removing the flange from the splined shaft-- The flange is supposed to be sealed to the splines with locktite. Sometimes the flange will fall off. Other times you will have to use a puller. You will need room for the puller. A narrow puller can be made from flat bar and a hard bolt.

Note:

Drain the fluid before you remove the flange other wise all the fluid will be in your bilge.

The reseal on the ZF 63 output flange requires a new lip seal and a new o-ring.

E-mail me direct and I will get you a workshop manual with instructions and parts break down.

Good luck & best regards,

[Mark Zarley]

Most rear seal failures are due to a loose output shaft caused by an out of spec (worn) rear bearing. Putting a new seal in without replacing the bearing will probably not be a permanent fix.