Differential pinion depth

[seniorchristo]

I am rebuilding my diff and replacing all the bearings. From the manual, the correct way to set pinion depth is to use a special tool which measures from the carrier bearing seats to a dummy pinion after setting pinion bearing preload. Not having this equipment, I measured from differential mounting face, down to the end of the pinion gear before removing the pinion. After replacing the bearings and setting the preload I plan to duplicate this measurement by inserting the correct shim. Would this be an acceptable method of setting the pinion depth?
thanks
Chris

The photo shows how depth was measured however it was taken after I removed pinion. The actual space between pinion and straightedge was actually .460"

[2cams70]

I'm in the same boat as you rebuilding a diff without special tools! Since you are retaining the original crown wheel and pinion set and carrier housing the method you are proposing should be fine. In fact in your case you don't really need to measure at all because the manufacturing tolerances across bearings are close and so the shim thickness is quite unlikely to change assuming it was correct in the first place. It will all show up in final tooth contact pattern checking anyway whether the setting is correct. In my case I also did a tooth contact pattern check BEFORE disassembly and photographed it for reference.
In my case I am swapping crown wheel and pinion sets and carrier housings so it's likely the shim thickness will change a bit because the manufacturing tolerances on these components are loose by comparison. I purchased 2 new sets of pinion bearings of the same brand. One set reserved for final assembly and one set reserved for shim selection and setting up. On the set reserved for setting up I bored out the ID using a brake cylinder hone in an electric drill such that they became a hand slip fit on the pinion. This enabled them to be removed multiple times without having to use a press during a trial and error process of selecting the correct shim by tooth contact pattern checking.
Note the company below is a good source of parts and they also have some very handy tools for setting the pinion bearing preload. In my case they would not ship direct to Australia but I used UK based freight forwarder Forward2Me who sent all the bits and pieces to me at very reasonable cost.

https://www.bearingkits.co.uk/FORD-ESCO ... L/1445.htm

You'll also need to set the carrier bearing preload (cap spread) during assembly. I have some ways for this too which I can discuss also when you get to that stage.

Note I also use a second pinion nut for trial assembly that has the crimped bit that creates thread interference ground away. Just makes it a bit easier and also less wear on the pinion threads.

Oh I see Forward2Me don't ship to USA unfortunately. You can get around the flange adapter of course but it's something that's nice to have. If you want some dimensions to make your own let me know.

[Elan45]

Chris,

I agree w/ 2 cams that as long as all you're replacing is the bearings, you needn't check the pinion height. The bearings are made so accurately that the new bearings will go back in same as the old ones.

Roger

[seniorchristo]

Thanks for your replies,

Yesterday I removed the old bearings and replaced with new ones. The next step will be setting the pinion bearing preload. I have to research the setting of carrier bearing preload, cap spread and CW / pinion backlash but I think this can be accomplished with a dial indicator and/or large calipers. I am also interested in your method 2cams. I also checked the pattern before disassembly and saw it was off center a bit. I was told the fore and aft location on the tooth is not as critical.



Roger
I missed you at LOG 38. Were you there?

Regards
Chris Herr

[Elan45]

I was there on Saturday only. Sorry I missed you.

My diff set-up was different, because I was around BMC cars so much, I threw out the crush sleeve and replaced it w/ a solid spacer and shims that I made from scratch. Then I set the pre-load w/ a torque screw-driver that reads in in-oz. This was done before installing the pinion seal so that its drag did not affect the preload reading. I made 3 of those spacers in 1984, used one on my SS I was restoring and can't understand why I only have one left to use on my coupe restoration.

Roger

[RichardHawkins]

2Cams,

May I offer a word of warning. As the pinion shaft bearing is an interference fit on the pinion shaft, when it is pressed into place it changes shape, as the bearing is a taper roller type it effectively moves axially as well as radially, altering your depth of crown wheel to pinion engagement compared to your "setup" bearing. I found this out the hard way, but found on final blueing of the teeth the error was small, and hope I will not notice when driving.

Richard Hawkins

[promotor]

2Cams,

May I offer a word of warning. As the pinion shaft bearing is an interference fit on the pinion shaft, when it is pressed into place it changes shape, as the bearing is a taper roller type it effectively moves axially as well as radially, altering your depth of crown wheel to pinion engagement compared to your "setup" bearing. I found this out the hard way, but found on final blueing of the teeth the error was small, and hope I will not notice when driving.

Richard Hawkins

It's a good point to raise and interestingly the Lotus manuals (and early Fords such as Anglia/Corsair/Mk1 Cortina etc) do not use any adjustment for the bearing expansion when pressed on. However, the later mk2 cortina and all mk1 escort manuals advise to a use a shim 0.001" thinner than measured with dummy pinion gauge due to this expansion.
As the shim range increments went from 0.001" in early cars to 0.0005" in later cars it shows how accurate Ford intended the set-up to be.

Chris, with that in mind if you may well find it useful to know that the tolerances in bearings do differ - for example a Koyo bearing is thicker/taller so requires - on average - a 0.002-0.003" thinner shim than with a Timken bearing for the same pinion depth setting. Timken bearings - in my opinion - are better than Koyo as they don't have any stiction which interferes with setting the pre-load when using the lb in weight gauge as shown in the manual. If using an alternative such as a rotational torque gauge this isn't so much of a problem.

With the figures in mind it is clear that accuracy of measurement in terms of your pinion height is your best bet to help you setting the diff up correctly. .

Your contact patch doesn't look very clear to me (even when I have a diff in front of me it is sometimes so vague it really takes a while to see the patch) and from what I can make out I think you need a thinner pinion shim. I would recommend adding a slight bit of oil to your engineers' blue to give you a bit better contact mark to really see where it is contacting. You also need to try to load the crownwheel while you do the mesh check.
Worn gears don't show a pattern as per the book - it's usually more towards the toe of the teeth. A lot of the time it is not possible to obtain the "picture perfect" contact patch and it's knowing when you've got to a point that you can't do any better and won't ever get a mesh like the book shows.

You can set the side bearing preload by using the lb in or torque gauge once you've set the pinion preload - I usually see an approx figure of 4-5 lb in on top of the pinion pre-load figure. I use a proper capspread gauge as per the manual and set my diffs using the 0.005-0.007" figure but I also check the total running torque as it's a very quick check just after doing the final torquing of the cap bolts.

[2cams70]

Accepted that the interference fit of the bearing on the pinion shaft will expand the bearing slightly and bring the pinion slightly closer to the crown wheel than the set up case of using bearings without interference. Using bored out bearings for setup however is still a very useful method of getting shims sized within the correct ballpark if you don't have the correct tools - dummy pinion, gauge block's etc. All will be revealed in the final tooth contact pattern check anyway. If the shim thickness needs to be reduced slightly (perhaps 0.0005 - 0.001") you can still do it. I find that it can be a real pain to press off the bearing closest to the pinion because there is not much space for a press plate between the pinion head and the bearing and it's easy to damage the bearing. Using bored out bearings for set up makes it much easier and reduces the risk of damaging bearings. Once we get a figure for the bearing interference compensation factor (if required) it all becomes easy and repeatable in any case.
For measuring cap spread I'm using a large outside micrometer and two installed hex socket head countersunk screws in the bearing caps where the locking tab screws go. The countersunk screws have a nice round head that make it easy and repeatable to find the widest measuring point with the micrometer. Suitably large micrometers can be found quite cheaply on Ebay. I've forgotten the size I bought but can advise if necessary.
Another thing I would mention is that it's not unknown for the crown wheel bolts to come loose and shear off. I'd therefore recommend removing the crown wheel from it's carrier and thoroughly cleaning everything especially the bolts and the threads in the crown wheel. Be sure to torque them correctly on reassembly and use some high strength Loctite on the threads. Most manufacturers stipulate high strength Loctite on these threads even though Ford back in the day did not.

[Elan45]

I find it hard to see the pattern too. Chris, I don't know if you knew, but there are two different engineers blue products, one that is put on a surface such as sheet steel and is used prior to making scribe marks on the surface. It is usually a liquid or aerosol spray. The other material is a paste and is for checking bearing and gear patterns. This is what you should be using.

I understand how the bearing height could change slightly between slipper toleranced set-up bearings and actual installed bearing, but this is not really a concern here, as Chris doesn't need to replace the shim under the pinion head, just replace the bearings and the tolerance on the bearings is so close that there is no need to worry about pinion height setting at all. I agree about the desirability of the Timken product

Roger

[promotor]

I understand how the bearing height could change slightly between slipper toleranced set-up bearings and actual installed bearing, but this is not really a concern here, as Chris doesn't need to replace the shim under the pinion head, just replace the bearings and the tolerance on the bearings is so close that there is no need to worry about pinion height setting at all. I agree about the desirability of the Timken product

Roger

Unless I've misunderstood you here the shim may need replacing due to different bearing heights as I mentioned in my post - I've measured these differences between manufacturers consistently using a proper dummy pinion. There is a constant difference in pinion height of 0.002-0.003" between Koyo and Timken - that is to say that Koyo usually require a 0.130" or 0.131" thick shim and the Timken usually require a 0.133" or 0.134" in a good cast iron nose that was accurately machined from the factory. Of the last ten diffs I've done approx 7 required a 0.133" shim after a dummy pinion check with Timken bearings (this is not necessarily the final shim I use due to a correction for tooth wear but does show the tolerances of different manufacturers bearings). The cases are usually machined so accurately that those figures play out time and time again, and that it is the bearings that do show a measurable difference.

Despite the repeatable accuracy of a brand of bearings it has to be considered that the manufacturer will recommend any checks done should be with the actual bearings to be used in final assembly to do away with "hope" that the bearings are exactly the same height.

I'm not saying here to not use another bearing, just be prepared that it may not work out how you hope.

Additionally, in my experience the whole point of changing the bearings is to have a nicely set-up diff with correctly preloaded bearings and the best contact patch possible - it is sometimes required to change the shim (from the recommended dummy pinion figure) if the diff has worn in such a way that the only way to adjust the contact is by using a thicker or thinner shim.

Of course, the final say of whether the shim is correct is the contact patch - as long as you have a way to obtain this then method used to get there is irrelevant. If you can't get there with any number of different shims it may be that the teeth are simply worn out.

[2cams70]

That's why it's important to check the contact patch BEFORE disassembly. If the diff was quiet prior to disassembly (i.e no whines under drive or coast conditions or backlash clonks) then that same contact patch will still be OK after replacing the bearings even if it may not appear ideal. Worn bearings generally create an "airey" sound that is quite distinct from an incorrectly set up or worn crown wheel and pinion.

[seniorchristo]

Difficult to see but the wear pattern in my photo was centered longitudinally, and closer to the crown wheel (heel) by about 2/3 the tooth width. I think bearings removed were British while new ones are Japanese.

Promotor, Will .001" difference in shim make a noticeable difference in wear pattern?

Thanks,
Chris

[promotor]

Difficult to see but the wear pattern in my photo was centered longitudinally, and closer to the crown wheel (heel) by about 2/3 the tooth width. I think bearings removed were British while new ones are Japanese.

Promotor, Will .001" difference in shim make a noticeable difference in wear pattern?

Thanks,
Chris

With an excellent condition genuine Ford CWP or with the new replacement ones available usually 0.001" will make a difference - that is the sign of a good CWP set when you can make the contact patch move around noticeably.
With a worn crown wheel and pinion it is generally much harder to be able to see the contact moving with 0.001" change as the pattern tends to be vague and it's hard to see the change. As suggested try adding a small amount of oil to the blue and try again to be really sure what is contacting. I use plenty of engineers blue and rotate the diff a few times to spread the engineers blue nicely.
Also, to get an idea of correct pinion height you should look at the contact patch of the coast-side of the teeth - this will indicate if you are at the right pinion height.

Meshing used diffs is a lot about compromise unfortunately.

I've got one in at the moment that has a backlash variation of 0.006" - the book spec is 0.002" variation! Basically that means I've got to set the minimum at around 0.004" to give a max of 0.010". That diff will be going through a lot of mesh change each time it rotates in the car. I'm not confident it will be quiet!

As for your 0.001"? You should be OK in that you aren't moving the contact patch too far, it's just not optimised as per book specs. The aim is to get into the strong part of the teeth while not contacting the peak of the teeth (potentially weak as the power is in a smaller area) or in the valley of the teeth where you can get a situation where the pinion is contacting the drive and coast sides simultaneously which makes the diff go tight and also stresses the teeth. Between those two is where you want to be.

[Hawksfield]

Hi seniorchristo
I have found yellow ochre to be a better paste for viewing contact patch
Better for me anyway
Good luck l

[2cams70]

Yes that yellow stuff is really good. I obtained mine from Ebay. See link:

https://www.ebay.com.au/itm/Crown-Wheel ... ctupt=true

For reference I have attached the contact pattern pictures from my diff pulled from a grandma driven Mk2 Escort automatic before I dismantled it. I'm swapping the 3.77 gears into a period correct carrier casting for an Mk1 Escort Twin Cam together with new bearings.