[michaelfbush]

OK I've read alot of addvice about shim tools and omc procedures. I've never used the shim tools so I'm looking for clarification on there use. From all that I've read in repair manuals The tool only measures the driveshaft, thrust bearing, pinion gear assy. with no reguard for the tolerances of the rest of the gearcase. Is this true? If it is true it assumes that the rest of the gearcase and all of its parts are predictably perfect. Shouldn't the entire gearcase be assembled and the gear lash/thrust bearing clearence be determined by gear inking or by drive shaft axial end play?

[Marc J.]

My manual reads the same Rude. I questioned the procedure myself. There's gotta be an alternative to using the OMC tool. I've seen rear differentials checked with the ink/grease, and it looks like the same principle. I've read that undertorquing the pinion nut would reduce pinion life. Wouldn't the thrust bearing be affected too? Maybe one of the pros will comment soon.

[clanton]

However you choose to do the shimming, there were changes made in the procedures,and specs see the service bulletins for the years affected.

[michaelfbush]

Claton: I'd love to see the sb's. where should i look? Also check my brain cell activity below. The shims do only one thing. They set the distance the pinion/thrust bearing/shaft assy. can 'unscrew' in the up derection as force is applied to the spirial cut rack set. Slop is needed for only two reasons 1)room for expansion 2)proper mesh registration under power. In the down direction gravity rules ( unless to much shim forces it down). Since no shims exist to position the fwd. / rev. gears and there is no prevention of exsessive down force (no drive shaft lower thrust bearing), the gear mesh will be sloppy and imperfect no mater what. So all we can hope to do is prevent excesive down force due to expansion diferentials. Like with auto rears and wheel bearings and power transmision gear boxes; don't assume a shim based on the messurement of a few parts. Put all the parts together and measure.OK, OK, mill$? What should the slop be? I was thinking 0.010 to 0.015 inch. Maybe a Mech E. with power trans exp. would like to comment?

[michaelfbush]

CLANTON sorry for miss spell

[michaelfbush]

73BAJA: any part not torqued right is in for trouble

[clanton]

My books are packed again, may take 2/3 weeks.

[michaelfbush]

Any other self help source for SB's?

[DHPMARINE]

You might find Service Bulletins at Johnson.com, They will let you look up parts.On the shim thing ... BRP uses a machined area in the 'nose' of the gearcase to position the forward gear.They also use a machined area to position the bearing carrier and reverse gear.So they only have to position the pinion gear in the correct place.That is why they use that driveshaft/shim tool.Mercs seem to need shimming all over the place..and you need a lot more special tools .Then you tighten the nut that holds the bearing carrier in,and recheck.DHPDHP

[dafox99]

Hey Rude .. I'm no expert, but it seems like DHPMARINE has a point. Ring gears are not shimmed, they are positioned along the centerline of their bearings (like the fwd/rev in this gearcase). I believe the pinion on a car differential is shimmed much like this gearcase. I think the only situation we care about is when everything is spinning .. and if the pinion is spinning, to your point, the pinion is forced upward against the shim. So, I think the sloppy, imperfect mesh you are talking about is when nothing is moving. If the fwd/rev gears are positioned by machined surfaces (like the ring gear), the mesh and backlash should only be controlled by the depth of the the pinion. I'd think some book would tell you the gearlash spec. I would have guessed .006 - .010, but it's just a guess.I've only torn into a couple of mercs .. yup .. shims, measurements and shim gauges everywhere (ugh). Good luck!

[rodbolt]

while ringears are not shimmed on certain GM eaton and dana units some other ringears are, the pinion depth is the one that is set standard. goes for most power transmissions, also the auto differential is a hypoid spiral and most outbards are just spiral beval type gear cuts. most use the force of the power transmission to force the pinon and thus the shft upwards into the thrust bearing, some of the others cut the spiral the opposite way and actually pull the pinion down under a load into a tapered bearing. I have never seen a backlash spec on a halyway moderen OMC unit. would be a pain to rig a tensioning device on the fwd gear to backlash check and lead gear paint check the tooth contact pattern. I love OMC cases, takes 3-4 hours to dissasemble and reassemble, try a volvo DP if ya like shimming,backlash checking and gear contact marking. volvo and suzuki found places to put shims that merc forgot . but follow the manual, use a new pinion nut on reassembly with the correct torque and all will be happy

[michaelfbush]

DHPMARINE: Not to beat this to death, well just once more. All the parts for the drive shaft are machined as well but we still shim it. Shimming helps acomidate for machining and assy. tolerences as well as predictions such as expansion. The fwd. gear relies on 5 parts and ten machined sufaces to set its axial posision and its still free to float aft. Thats 10 prayers for perfection. The rev. gear is worse it relies on unmachined parts such as 2 snap ring, retaining ring and the prop shaft bearing housing and its free to float fwd.But thats life. No way to shim that set up. The only thing we can control is the axial play in the drive shaft. And I was thinking we should shim the unit fully assemled. I guess I was looking for a vote on this more inclusive method and a consensus on a value. I was thinking in the 0.010 range. Last jab at OMC method: Who among us doesnt gab the shaft after its fully assembled and check for end play and too much shim down force and turn it to feel and listen for indications of shimming success. I know I do

[michaelfbush]

To all: We're working on these things for a reason. And many times its due to gear ingestion. And as we all have seen, the aluminum parts that set the posistion of things gets impregnated with tuff to see, find and or remove gear bits. And if any parts change posision due to gear chips or scratches and ultimatly my reluctance to buy new parts (like the gear housing itself) I think the fully assembled approach might take more of the new imperfections into account. ???????