78 105 Magnapower - Gear Box?

hello all. out doing some fishing last night and just buzzing along to hit another spot. heard a high reving sound as if i had knocked it into neuatral and came to a complete stop. enging still running and no drive gear. stopped and re-started and fired right up and runs normal without any engagement. no smells and no obvious noises when running. prop spins freelly in and out of gear. So what gives? an obvious lower unit problem but havn't had many boats and have been lucky so far with what i've had.....Thanks all for any input!

Re: 78 105 MAGNAPOWER - no engagement

Re: 78 105 MAGNAPOWER - no engagement

Well, that sounds too extreme to be a spun prop, though it is a possibility.

Seems more likely a broke drive train.

Re: 78 105 MAGNAPOWER - no engagement

Re: 78 105 MAGNAPOWER - no engagement

well just pulled the lower unit off and the cover that houses the drive shaft and visually it's all in great shape. the lower unit gear oil was a greenish color so some water penetration? when you engage the rod that goes into the back of the lower unit ( looking straight down and calling the prop end the front) and rotate the drive shaft it moves the prop shaft. But hold the prop shaft and spin the drive shaft it just clicks as if the splines where they meet have been sheered. there was no metal in the gear oil though so what else in there goes? is the lower unit re-buildable by the astute do-it-yourselfer?
it doesn't seem complicated, just gears driving gears.........oh well that's what i get for saying how great it was running . all input welcome and thanks ~ guess it's electic trolling for now.......

Re: 78 105 Magnapower - Gear Box?

DONE A LITTLE READING AND REALIZE I'M TALKING ABOUT THE GEARBOX.
what are my options? rebuild, used , any retro-fits? I only paid 200 for the whole boat and restored it somewhat. I'm bummed becasue this motor has run near perfect ( contrary to popular beleif it seems) since i bought it 2 yrs ago. Starts with a half click of the key and runs smooth and strong hot or cold with never a re-start. I was told the guy who owned the boat (it was donated by him with others to a church and I bought it at their auction) had a boat shop and rebuilt boats and motors then retired. I can send in some pics of this motor as it looks amazing for the year as if were all rebuit. Putting some money into it would not bother me at all so i'm open to suggestions. Thanks all.......

Re: 78 105 Magnapower - Gear Box?

Two piece or one piece lower, they all work the same, the only difference is in the prop shaft bearings and the drive shaft bearings.

Greenish colored oil is normal. Milky coloring indicates water contamination as does free water draining oit the drain screw before the oil does.

You may have worn or broken the shift yoke. It is not an expensive part and is not too terribly difficult to replace.

In front of the forward gear, which you do not need to remove, within the prop shaft is a second smaller shaft which slides back and forth to move the dog clutch on the splined internal portion of the prop shaft. There is a groove about 1/8 inch wide and deep cut into this shaft. In this groove rides a brass "U" shaped yoke. the linkage moves that yoke forward and backward to slide the dog clutch into engagement with either drive gear.

If that yoke has broken or fallen off the shaft, you will not be able to shift into either gear. If you remove the lower unit and tilt it either up or down, the weight of the dog clutch will move it into engagement with either gear.

So, you need to remove the rear gland if it is a two piece unit and pull out the prop shaft. If it is a one piece unit, you need to remove the anode, and the four bolts holding the spool in. then pull the rear gear bearing carrier and the prop shaft. Needless to say, oil must be drained first.

Then if the yoke is not on the shaft, tilt and shake the lower unit until it or its pieces fall out. Replace it and reassemble the lower unit. As In said, not really difficult, but slightly time consuming.

Re: 78 105 Magnapower - Gear Box?

THANKS FRANK, here are some photos of my lower unit. i've removed the four screws where the drive shaft goes in and the four screws where the prop shaft goes into the housing. what next? does the prop shaft pull out somehow? is there a retaining clip or the like? thanks a million! it appears this is my problem....where can i get the replacement parts once i get it out and determine what is broke?

Re: 78 105 Magnapower - Gear Box?

ok frank, i've realized that my motor does not have an anode. didn't know what the heck they were or did and just did some searching. my boat is fresh water and always gets dry docked in the garage. so that leaves me with just the four bolts i have removed. will the prop shaft come out or am i going to have to fight it? also you mentioned the carrier berrng; is that what i am looking at when staring down the drive shaft or is that part of the prop shaft assembly? thanks, getting there......

Re: 78 105 Magnapower - Gear Box?

That's a one piece lower unit. I thought Chrysler did not change to them until 1979 1/2.

Since it can be a royal witch with a "B" to get the yoke back in place, before you disassemble the lower unit move the shift rod to see if it will engage the gears. if it does not, then disassemble. The shift rod should be screwed all the way down into the Steel shift yoke inside the lower unit and backed off only enough to line up the holes with the holes in the upper shift rod (less than 1 turn)

Anyway, behind the prop there should be an anode --fresh water or not. It is held onto the spool by two screws. Beneath the anode there are four 5/16 bolts with 1/2 inch heads. You unscrew these bolts and using some all-thread 1/4 -20 screwed into the anode screw holes, you fabricate a puller. You pull out the spool. If it has not been removed in some time, it may be difficult.

Once you have removed the spool (called that because it is shaped like a thread spool) you will see an aluminum plate with the four holes for the 5/16 bolts and four other curved holes in it. Around the perimeter of this plate are two semi-circular clips that hold it in place. You reach in with a screwdriver and wedge it into the tapered ends of the clips, then pop them out.

Now, a good yank should remove the prop shaft, the bearing carrier, the dog clutch, and reverse gear as an assembly. The brass yoke should stay in the shaft groove if it was there to begin with and you have not been too rough with your handling. If you can't pull it out by hand, use some 5/16 all-thread and nuts to make a puller. Once the shaft is out, check the condition of the six dogs on the clutch and the three dogs on each drive gear. leading edges should be fairly sharp--within reason. If they are well rounded, they tend to pop out of engagement and will need to be repaired.

Forward gear and the drive shaft and pinion will stay in the housing --not necessary to remove them unless there are other problems--like repairing the drive dogs.

Clean residual oil out of the gear housing and then shake it around a bit to dislodge the brass yoke. It will come out the center hole in the forward gear.

Now, if it is broken, you will need to buy a new one--they used the exact same part for all three and four cylinder lower units since the late 1960s. Only difference was some came with a steel yoke (which I have never seen).

When you go to replace the yoke, use a good heavy grease to keep it in the slot. Then with the bearing carrier and reverse gear removed, slide it through the forward gear center hole. Here's the hard part. There is another steel "yoke" which is held in place by the famous side screw in the nose of the gearcase. pull up the shift rod all the way and you will be able to see the slots in this yoke. The two pins on the side of the brass yoke MUST engage these slots--It may take you several tries--and several references as to the parentage (or lack thereof) of the gearcase. Invocations and imprecations help your mental state.

After positioning the prop shaft in the forward gear move the shift rod and see if you can see the dog clutch moving forward and backward on the prop shaft. Do this with the lower unit horizontal since the steel yoke can move it up and gravity will move it down if the unit is vertical.

If it functions properly, replace rear gear, bearing carrier, circlips, spool and anode. Use some anti-seize on the O rings on both ends of the spool to help it come out easier next time. Buy new O rings--cheap insurance against leaks. Torque the four 5/16 bolts to 160 inch pounds. Be sure to not lose the small O rings under the washers. Better to buy new if any doubt exists about their condition.

Re: 78 105 Magnapower - Gear Box?

thanks frank for the very detailed response! I have read some of your other threads on various things to try to get to know this engine better. the anode must have been taken off and never reinstalled. i assume this must mean water was getting in behind that first wall since the anode holes were not filled. I know now the four bolts i took off around the the driveshaft housed the water pump and the impeller, good thing they came off without any fight. the shaft gleams like new and this engine had a great stream but i imagine since i have it all off i should do a new impeller and gasket. the clutch does engage when i move the rod up and down by hand and like i said when turning the drivshaft it in turn moves the prop as it should (all things working correctly). but apply pressure by holding the prop-shaft and turning the driveshaft it skips as if " worn gears" were the culprit. it's obvoius something in there wore past it's tollerance when the motor was buzzing along at wot.......will make a puller and yank it out. should I move the shift rod to a certain spot before pulling out the shaft unit? ie, neautral, up or down? i've never heard the term "all-thread" are we talking about a fine thread bolt that is thread from tip to toe? will wait till i hear back and thanks again frank for taking all of your time to respond to us boating neophites.......

Re: 78 105 Magnapower - Gear Box?

Since you also have her already apart, i would suggest buying a reseal kit. Its 40 bucks and easy to do, especially since you have her ripped apart already. Might be unneeded since your lower unit oil was green but a good piece of mind to know that all the seals are new and your good for another 5 to 10 yrs. Just a thought.

Re: 78 105 Magnapower - Gear Box?

All thread is a type of threading (like a screw but without the head) that can come in any lenght you want, from 1 ft to 5 ft. Its just the thread and not bolt or screw head attached. Your local lowes will have plenty and its cheap. Get yourself some and a few nuts that will fit it, you will use this multiple times.

Re: 78 105 Magnapower - Gear Box?

Thanks JD, I spend my life in Lowe's and the Depot so I'll grab some (we are in real estate and in this market I have to repair or re-build everything myself). Havn't really had to do anything to this motor so what's a good resource for parts since i might as well put in new seals and an impeller. (how can u tell wear on the impeller it looks like plenty of rubber left on the little nubs). The plate also looks very clean so I have a feeling, the deeper I get into this motor, most of this stuff was done but since the boat was trashed it never got to the puddle ( our resivoirs are tiny) to get wet.
How readily available are the internal parts to the gear box? once i pull it out i'll post some pics. In all honesty I had the whole lower end out and seperated in about 30 min so i'm happy to see they are fairly simple in design but i'm sure the gear box won't be that easy. Thanks for chiming in!

Re: 78 105 Magnapower - Gear Box?

That lower unit was used for about ten years with no internal changes so parts should be readily available. Here's the problem: The dog clutch costs about 150, and each gear only comes as a set with its associated bearing. They cost 250 or more each. AND--if you replace the gears, you must re-shim the driveshaft and propshaft.

Because of this, if the drive dogs are worn beyond use (rounded), it is a much better option to re-grind the faces square again. You can do it yourself or pay a machine shop. The drive dogs are massive enough that you could grind off 1/4 inch from the face and still have more than you need to handle the horsepower.

The center of the spool is part of the water intake so a leak or holes in the face nearest the prop will have almost no effect. The critical seal is the slightly smaller O ring further inside the gearcase and the four small O rings under the bolt heads and washers.

Re: 78 105 Magnapower - Gear Box?

Just interupting for a second as something i noticed regarding one of Franks comments. Frank as you know i just resealed my lower unit but after taking her out the other day i still had milky lower unit oil. I noticed that in your above comment that the spool has two different size O rings, i think i installed them incorrectly, the outside O ring fit snug and the inside O ring was loose. I installed it that way anyway, do you think thats the issue with still getttin water intrusion. I must say though its milky lower unit oil but it doesnt have free water in it like it used too. Once again sorry for the hijack of the thread, i just saw something in a comment that started making me think. Thanks again

Re: 78 105 Magnapower - Gear Box?

bump!!!

Re: 78 105 Magnapower - Gear Box?

The gearcase is stepped to two different sizes with the larger bore nearest the prop. Thus when you replace the spool, the inner O-ring will be loose until it contacts the inner, smaller bore just behind the bearing carrier.

I don't know if it is possible to assemble it with the O-rings in the incorrect grooves--the larger O-ring is only about 1/8 inch in diameter more and it probably will fit in the groove in the small end of the spool. It may compress and seal, or it may kink, or it may tear--I don't know--I never tried it.

However, since the four 5/16 bolts communicate directly into the oil chamber of the gearcase, if the 5/16 ID O-rings are worn or cut or have taken a set, it is highly likely to have a water leak there. Replacing those O-rings and the washers (if they are bent) on top of them is cheap and they are standard--Get 'em at Lowes or Home Depot.

BTW---While we are on this subject, the bearing carrier can only go in one way since it is relieved for a hardened thrust washer on the reverse gear side. The other side has a bevel as does the small end of the spool, and when you torque the four 5/16 bolts, it squeezes the bearing carrier and spool on the two half circlips---thus positively locating the reverse gear with respect to the pinion. The factory went to a lot of trouble to locate the circlip grooves with respect to the pinion. So, it is important to torque these bolts to the recommended value--160 inch pounds. This also ensures adequate compression of the small O-ring seals without deforming the washers.

Re: 78 105 Magnapower - Gear Box?

Well frank, i think i didnt torque the bolts correctly. I was to scared one would snap off like the water pump bolt. Do you think i need to drain and tear it apart again or can i just losen the bolts and retorque. Right now im leaning toward tearing into it and just putting new O Rings on everythign again just so i can sleep at night. I dont plan on removing the lower unit again, is it acceptable reseal he prop side O Rings while its on the boat? THanks

Re: 78 105 Magnapower - Gear Box?

bump-hopefully last time.

Re: 78 105 Magnapower - Gear Box?

There's no need to remove it from the engine to do that small job. All you will be doing is to remove the spool. Shaft and gears will stay inside the unit.

160 inch pounds is standard torque for a 5/16 bolt. You will not strip or shear them. Especially since they are always in a lubricated non-corroded part (bearing and reverse gear carrier).

BTW: Did you replace the prop shaft seal inside the spool? The spool has a needle bearing to carry the prop shaft and a seal. The reverse gear never touches the prop shaft--there is quite a bit of clearance to eliminate drag at that point.

All told, the one piece lower unit is a vast improvement over the two piece earlier units.

Re: 78 105 Magnapower - Gear Box?

Yep replaced the prop shaft seal, i think my problem is improper torqing and the bad O Ring on the spool. Ill tear her apart and put a new orings and torque the bots to 160 inch pounds. Thanks again frank