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Thread: Another Differential Question

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    Another Differential Question

    Just how critical is the pinion shaft depth setting? The book I have says it should be set with 3.4375" from the machined bearing surface on the forward side of the pinion gear to the center line of the axle shafts. I've done the math half a dozen times and measured it 3 times, and I get a measurement of 3.3865" with no shims installed, which puts the end of the shaft .051" too close to the axle shaft center line. Am I correct in thinking that the side-to-side adjustment made to the ring gear will accommodate this difference?
    Thanks, Phil

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    Re: Another Differential Question

    2018-12-29 13.47.29-1.jpg2019-01-05 13.58.59.jpgI made a jig to hold a dial indicator . I used a cad drawing to do the math and dimensions . The actual dimension that I used was from the axle datum to the face of the pinion . I measured the thickness of the pinion gear and factored that into the calculation the dial indicator measurement on mine was dependant on the flat reference surface that I machined on the centre shaft of my measuring tool / The outer drums were machined to the same size as the bearings and the jig clamped in with the bearing holders tightened up to take the measurements pinion setting gauge v1 Drawing v1.pdf

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    Re: Another Differential Question

    The big red factory service manual has a good explanation of the pinion depth gauge. Its purpose to replicate the relationship of the ring gear/pinion when they were lapped at the factory. This position will produce the minimum noise in use. However, the contact picture will determine the final setting and it may be necessary to deviate from the ideal 3.4375" dimension. At least, that is my understanding.
    Berry

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    Re: Another Differential Question

    I like Berry’s method. Set the pinion using the same shims that came out. Then read the contact pattern and adjust from the reading. Setting the gears cannot be done in one shot unless you are using the original bearings and shims.
    John

    1955 TR2

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    Re: Another Differential Question

    TR2 Pinion Shaft Depth.jpg
    Thanks for the replies!
    Since this is a new ring and pinion, I had compared gear measurements from the original to the new one and found them identical. So I initially installed the same measure of spacers that I had taken out, knowing I would likely have to adjust them. Going by the 3.4375" spec in the book, the shaft is .076" too close to the axle center line now. Removing all the shims currently installed will leave me .051" too close to axle center line, with no further adjustment away from center line possible.

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    Re: Another Differential Question

    Your initial thought is correct. Install what came out. Now go ahead and install your pumpkin and use white grease to take some mesh patterns in drive and coast. Do not worry about the "theoretical" position specified in the manual. Without the special Churchill tool that measurement is virtual at best, and difficult or impossible to measure at worst.
    John

    1955 TR2

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    Re: Another Differential Question

    I went back over everything, figuring that I must have missed something. Sure enough I found that the pinion head bearing was not fully seated, and I measured .023" of gap there. (Must have been at night without my eyeglasses on to miss that one!) With that corrected I was still too close to the axle center line, so I removed the shims I had put behind the bearing race and ended up much closer to spec. Now, though, I have more endplay in the pinion shaft than shims at the forward bearing. So it looks like I'll either need to shim out the front bearing race, or shorten the collar to be able to re-adjust the pinion shaft preload. Although an easier option would be to re-install just enough shim at the head bearing race to give me the pre-load adjustment I need, then install the pumpkin and adjust for correct pattern as John suggests.
    Thank You!

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    Re: Another Differential Question

    Are you aware that the front pinion bearing currently supplied is thicker than the original? This article is for a TR6, but the diff internals are mostly the same as TR3. http://bullfire.net/TR6/TR6-38/TR6-38.html
    Berry

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    Re: Another Differential Question

    Thanks Berry,
    I had come across that article while poking around the internet for tips and suggestions on the diff rebuild. The spacing I needed to get the correct pinion pre-load was different than what had been in there, and I figured that was do to the new parts. I had set that pre-load before checking the shaft depth, thinking it would have an effect on the overall setting.
    Phil

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    Re: Another Differential Question

    You might want to look at my experience doing this, where I address some of the issues you raise:

    http://www.nonlintec.com/tr4a/differential/

    The only thing I'd do differently, now, is to use a depth micrometer (which I now have) instead of a dial micrometer.

    The spec for the pinion depth gives a range of only 3 mils, and it's tricky to get it centered in that range. It's absolutely essential to press the bearing races ALL the way home, and that takes a lot of force. I used my hydraulic press for everything, and made some special tools as well. If you're not careful about this, you'll have the experience where you make a measurement, figure out what spacers you need to add or remove, change the spacers, put it back together, and you're still several mils away from what you expected.

    There's a note at the end of my page describing the problem with the outer pinion bearing, which regularly blindsides people doing diff rebuilds. The right bearing is the Timken 15100 SR, but suppliers invariably provide the 15100, since it's more readily available. But it's NOT the same bearing! If you have a lathe, it's not a big deal, as you can take a couple mils off the spacer to compensate. I was able to find the 15100 SR, but it took some looking.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: Another Differential Question

    Here's a follow-up, with another question. I looked over the thread from Sarastro (thanks for the tip), and noticed no reference to the contact pattern check. I have the differential assembled, with a couple exceptions to specs I've read in the book. Pinion gear pre-load measures 10-12 inch-pounds instead of 18, with no shims behind the front bearing. Crown gear-to-pinion backlash is .005", using white grease I have a nice, even pattern on both faces of the crown gear teeth. There is zero side play in the carrier, but it went together without having to spread the case, just a little push in. In the experience of the more experienced, is this OK to run, or would I need to add .003 shims tp each side of the carrier to force pre-load?
    Thanks, Phil

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    Re: Another Differential Question

    I might be wrong, but I think you would add .0015" shims to each side of the carrier to maintain the contact picture and increase the pre-load. Also, increase the pinion pre-load to 15-18"lbs by removing material (try .001"and recheck) from the spacer.
    Berry

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    Re: Another Differential Question

    I've seen that number(.003") a couple different places for pre-load on bearings. Is that per bearing, or per assembly as you suggest. The thinnest shims I can find anywhere are .003" thick. On the pinion pre-load, just how much of a difference, from an operational view, does that 5-8 additional inch-lbs make?
    Thanks!

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    Re: Another Differential Question

    The spec for the carrier bearings is .002"-.004" "pinch over both bearings", so .003" would be in the middle. Maybe you could find some .0015-.002" shim stock and make your own.
    Just my opinion, but I would try get the pinion pre-load to at least the minium, since it will probably decrease with use.
    Berry

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    Re: Another Differential Question

    +1 to the pre-load. You can avoid spreading the case by simply supporting the axles and rotating the rear opening downward when installing the pumpkin. This naturally spreads the case.

    Also, no shims on the pinion is rare. Are you sure your even pattern is not biased to the outside edge of the crown teeth? It’s not just even, but location that you are looking for.
    John

    1955 TR2

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    Re: Another Differential Question

    Another follow-up: I took it back apart, took some length off of the pinion spacer, and got the pre-load on the pinion shaft to 18 inch/pounds. Re-set the carrier bearing spacing and have a real nice pattern on the ring gear, with added shims to get the pre-load there in spec also. I'd have it all back together, but the spider gear shims are on back-order. I have the axle bearings on the axles, the seals in the hubs and axle housing, so when those shims get here it's ready to go back together and get hung. (New springs and bushings are already here). Thank You for all the tips!
    Phil

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    Re: Another Differential Question

    hi Windsor
    Noticed you are using a diff spreader. Do you have any idea where i can source one ??
    Thanks
    Steve

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    Re: Another Differential Question

    If you have a welder, it's pretty easy just to make one. I think that's what most of us do.

    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: Another Differential Question

    A welder is the one thing I'm short of .. I did have a Churchill diff spreader in the 80's but sold it when my GT6 went .. so regret that move
    cheers
    Steve

    Quote Originally Posted by Sarastro View Post
    If you have a welder, it's pretty easy just to make one. I think that's what most of us do.


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    Re: Another Differential Question

    I would be very surprised if you can't get it apart and back together without a diff spreader I did with no problems.

    Graham
    [SIGPIC][/SIGPIC]

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