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Thread: Pinion shimming

  1. #1

    Pinion shimming

    Hello all.... I am in the middle of my dana 25 rebuild. The gears are all mint and I am just replacing seals, bearings and bearing cups. Iíve seen a million videos on the importance of setting rotational torque. My question- If I duplicate the exact shims that came out and change nothing else, will it not return to the exact location and rotational torque as previously set? If this Jeep, when finished, will only see light duty show/parade use, does this torque thing really matter?
    Thank you
    Tom

  2. #2
    Super Moderator LarrBeard's Avatar
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    Dana 25 Rebuild

    Quote Originally Posted by Toms51 View Post
    Hello all.... I am in the middle of my dana 25 rebuild. The gears are all mint and I am just replacing seals, bearings and bearing cups. Iíve seen a million videos on the importance of setting rotational torque. My question- If I duplicate the exact shims that came out and change nothing else, will it not return to the exact location and rotational torque as previously set? If this Jeep, when finished, will only see light duty show/parade use, does this torque thing really matter?
    Thank you
    Tom
    BMorgil is the expert on all things Dana/Spicer. He will give you more info that you thought you needed about setting up shim packs and all of the ins and outs or rotational torque.

  3. #3
    Super Moderator bmorgil's Avatar
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    LarryBeard... what a build up!

    Tom, setting the correct pinion bearing preload is imperative to the life and durability of a few things. When you are going through the axle your thought process is fairly good. Sticking with the original shim pack thicknesses will always keep things close.

    We are looking at the dimensional tolerances between bearing dimensions. You are changing the bearings. They can't be made to the exact same dimensions. You shim it after a rebuild if those tolerances affect the build up. That being said, modern bearings are very, very close. Changes of more than a few thousands of an inch would be unheard of in a quality bearing. If we were going racing I would say proper tools, processes and specifications prevail. Since we are not doing that, You will get great results the way you are going. The shims initially make up for all the manufacturing tolerances. On the pinion depth, if it is not within 2 thousands or so of its original depth, it will begin to get noisy and generate heat. If the ring gear backlash gets too tight or loose, again with the noise and strength becomes an issue. I have set up MANY axles using the original shims and gears with new bearings. The carrier position (backlash) controlled by the shims under the carrier bearings and the pinion position will be just fine reusing or exactly replacing the shims.

    So noise is the biggest concern with the position of the gears controlled by the pinion and carrier shims. Way off and it's noisy, runs hotter and is weaker in general. The preload of the bearings is a bit different story. You do need to check and adjust it if needed. The chances are it will be good.

    Assemble the carrier into the housing with no pinion in the housing. I am going to assume you don't have a case spreader to drop in the differential assembly. The assembly when shimmed correctly is about a .015" press fit into the housing. This provides the critical carrier bearing preload. Too much and the races may spin out. Too loose and a lot of bad things happen. You should have to VERY carefully slightly cock the races and drive the carrier into the housing. Lube the bearings and use a SOFT dead-blow. This is how outer races get scratched. Do not draw it in with the bearing caps. They will break in half. Drive the carrier all the way in (you will hear it hit home). Torque the caps and pull on the carrier and you should feel a good smooth resistance to rotate. It should take a few foot lbs to rotate it. Incorrect carrier bearing preload is a majior contributor to axle failures.

    On to the equally important Pinion bearing preload. Remove the carrier and install the pinion with no seal. Torque the pinion nut to spec (use the old nut). This preload most likely will change. A .001" change in the bearing pack can run the pinion too loose or too tight. Too loose is worse than too tight. The specification to rotate the pinion is 10 to 25 inch lbs. I have no fear running them up to 35 inch lbs. I never run them under 20 inch lbs. If the pinion bearing preload is insufficient, the pinion looses its critical position. The force on a pinion under load is tremendous. It is trying to force the pinion out the front. With no preload everything moves too much.

    I hope this helps you! To answer your question in a shorter format, yes it's important!

    Bob

    I hope this helps you. I have taught a lot of classes on rebuilding the Dana axles. I haven't seen it all but I saw a few. I do know that in every class I ever held, someone would say " I just bang em' in and out and back together with my air gun, I've never had any problems"!
    Last edited by bmorgil; 12-03-2019 at 01:21 PM.

  4. #4
    Thank you very much Bob. That is the most comprehensive answer I’ve gotten on any topic. Between you and the OCD gentlemen in Connecticut that’s rebuilding the engine, I’ve got the same answer. I will use your directions and put this axle together correctly. Is it a regular inch pound torque wrench that is needed? I could use one anyway.
    Thanks again
    Tom

  5. #5
    Super Moderator LarrBeard's Avatar
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    We're going to start calling you Dr. Dana!

  6. #6
    Super Moderator bmorgil's Avatar
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    Quote Originally Posted by Toms51 View Post
    Is it a regular inch pound torque wrench that is needed? I could use one anyway
    You are welcome Tom!

    This is easiest with a good old fashioned "beam style" inch pound wrench.

    https://www.homedepot.com/p/Presa-1-...B&gclsrc=aw.ds

    This isn't a real precise measurement. You are going to rotate the pinion with the wrench, floating the handle while trying to read the scale. It will take a torque spike to get it moving. Once you have it rotating you should see it cruising along at a fairly steady reading plus or minus 5 inch pounds or so. An average around 25 inch pounds would be just great! Be sure to use gear lube lightly on the bearings.

  7. #7
    Super Moderator gmwillys's Avatar
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    It is almost a lost art to setting pinions. Dr. Dana has done an excellent job in explaining the process so even I can follow.

  8. #8
    You can say that again! Thanks again Bob, I go into this with a renewed confidence.

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