75HP Chrysler Lower Unit

[AaronJS]

I have a 1974 mod:757ha 75hp Chrysler that needs the Lower Unit seals replaced.
I took it out and it ran fine for about 30 i stopped and when I started the engine and put it in to gear it would not go it to drive all the way. I got it out the water and flushed it and checked the lower end gear oil and there was water and dark oil. I have separated the lower end from the engine and removed water pump and everything and now I am stuck. I have removed all the bolts possible and cant seem to separate the 2 or actually 3 different pieces. Can any one help me get to the next step in this process or should i pay some one to do a rebuild on it? I have ordered the seal kit and have gone this far and not broken any bolts or anything and think I could more than likely do it myself if assisted. Pictures posted below any suggestions would be greatly appreciated.
Thank you.


http://globalehosting.net/boat.JPG
http://globalehosting.net/boat2.JPG

 

[Frank Acampora]

Re: 75HP Chrysler Lower Unit

As you can see, that is a three bolt lower unit. The gearcase torpedo is held to the miid case by those three studs in the second photo. There is a small Oring around the bottom of the front stud but it is not efficient and frequently corrosion jams the front stud. It is about 8 inches long contained in the bolt hole in the front of the case. The rear two only go through about 1/2 to 1 inch of aluminum and they are bathed in gearcase oil so they never corrode. (that's why there are O rings under the washers on these two studs--to seal the gearcase.)

SO: if you have the time, keep spraying the top of the front bolt with penetrating oil.

However, even with oil, you will still need to rap it with a hammer and drive it out. How Much? Depends upon how corroded it is. Put an old 3/8 nut partway on it so you do not **** up the threads, and heat the case some with a propane torch.

When you get it a little loose, DO NOT PRY between the halves. there is not much metal there because an O ring is set into a groove to seal them and you will destroy that sealing surface.

When you reassemble it, coat the whole stud with anti-seize.

Yes, you can do it yourself and yes, it will be a little time consuming and frustrating to loosen the front stud.

For your next time, ALL seals in that unit are standard and can be purchased at your local bearing supply store. You probably will not save a lot of money but you may get then sooner.

When you go to install the shift rod seal, thread a lag screw into the old one and pull it out Then , lightly press in the new one metal side up. after installing the shift rod, take a socket of appropriate size and with a longer piece of pipe on top of it press down the seal until it is just snug around the shift rod. You want it tight enough to seal yet not so tight that it binds the shift rod. The rod should move smoothly through it.

At the rear gland, there is a tapered roller bearing with shims under the outside race. IF you need to remove the race to install the prop shaft seal, be certain that the outer race is tapped down firmly onto the shims when you re-install it. Failure to do so will drive you crazy. The engine willl "harden" to a stop. Then it will immediately start and run again until the lower heats again and the engine stops. The water cools it immediately and the cycle continues--and you don't know what the hell is going on.

 

[AaronJS]

Re: 75HP Chrysler Lower Unit

Thanks Frank for your help!
I heated that bolt like you said and with a few taps of the rubber mallet she broke loose. All the gears look good the gear/ Shift lever was a little tedious but all in all everything seems to be working properly when I turn the prop shaft. Is there anything in particular that i should be looking for? the bearings sound pretty good on one gear and the other sounds like it may need to be replaced soon. I have to wait on the gaskets but is there anything else I can do or is there anything I need to check before I seal it up?
I appreciate your help very much.
Aaron

 

[Frank Acampora]

Re: 75HP Chrysler Lower Unit

For insurance, use a little silicone RTV on the big O ring that seals the torpedo to the upper half. Also, be sure to tighten the nuts on the studs equally and tight enough to seal both the torpedo and the Orings under the back two nuts and washers. The back two washers are thick and the front one is regular.

To remove the top drive shaft seal, you must remove the pinion from the shaft and then pull up on the shaft, bending and removing the seal. Then re-install the drive shaft, replace the pinion and torque the nut to --My Clymers says 85 inch pounds but I think that is incorrect. Maybe someone else will either confirm or correct this. Install the seal over the drive shaft and tap into place with a large socket or other suitable tool. The drive shaft nut is a deformed thread locking nut and the manual calls for a new one to be installed BUT If you can "stake" the three punch marks again, you can re-use the nut. If the nut does not have three punch marks, look closely. It will be slightly oval. Take the narrow side and squeeze it SLIGHTLY in a vise and it will be reuasable. The object is to deform it just a little so it will start on the threads yet will need to be stretched a bit to continue to run onto them.

Other than that, there is nothing special to do -- Just be sure to install all the seals.

If you have the unit standing vertical in a vise, then refill the oil there. Pump it in the bottom hole'till it comes out the top. Then replace the top plug, pull out the fill tube and replace the bottom. Let it sit for about 1/2 hour to let any air rise, then top off the oil, again, through the bottom hole.

If the lower unit is on the engine, just have the engine in a vertical or nearly so poaition.