Near Miss on my differential

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Model T Ford Forum: Forum 2014: Near Miss on my differential
Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Sunday, November 02, 2014 - 08:57 am:

I bought a new ring an pinion gear for my 26 back in march and am just now getting around to putting them in. The ring and pinion were well worn when I went through the rear end 4000 miles ago and I had to shim the ring gear to get the right gear lash. When I pulled the guts out of the cases yesterday I found the below situation. All but two of the ring gear mounting bolts were sheered off. I used new steel thrust washers and new bronze thrust washers when I rebuilt the rear end 4 years ago. I miked the washers now and the bronze is still at 0.200, I forgot to check the steel washers. I read a bunch of past threads last night about ring and pinion gear installation and getting the contact surface and gear lash right. I was having difficulty getting the contact between the pinion and ring right. I'm getting contact on the inner 1/3 of the pinion only. In the course of reading these threads, it was debated several times that ring gear shims are dangerous because they can cause the ring gear mounting bolts to sheer during panic (hard) braking. Some said this was nonsense and others insisted it was the worst thing you could do. The recommendation was to shim the thrust washers. I will add that I'm using the adjustable pinion gear bearing and have all the pinion gear shims that cam with the kit. One other good piece of advice I picked up was that you should get the contact pattern right then shim to set gear lash. I have the three volumes of T tips for rebuilding the differential on CD and have watched them several times but they don't discuss the new style pinion bearing or how to set contact patch. Maybe this is an opportunity to update the material? I think this also shows the value of safety wire versus lock washers. The safety wire held the bolt heads from rolling around in the case and doing more damage or casing an accident. I think you can guess my preference for shimming method going forward. I'm not saying who's right on that subject but I will follow my personal experience on this one and order the thrust washer shims.



Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Sunday, November 02, 2014 - 09:29 am:

Thanks for posting about your experience :-)
And it's great you found the problem before anything bad happened. Did you use original ring gear bolts?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Tomaso - Milton,WA on Sunday, November 02, 2014 - 09:59 am:

How thick is that shim ???????


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Sunday, November 02, 2014 - 10:46 am:

I've seen loose diff gear bolts on rear ends I've opened up, locking wire present or not. I can see the problem with steel shims shearing off the bolts under such circumstances. I know Ford ring gear bolts are soft. I suspect the threads stretch under the stress of acceleration and braking. When this occurs I can see the shims acting like knife blades on the bolts as the ring gear shifts on the carrier. Perhaps the remedy is to purchase new harder bolts that won't stretch. I think the new bolts sold by the vendors are harder than the originals.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Sunday, November 02, 2014 - 12:19 pm:

I had one 0.010 and one 0.015 under the ring gear. Ring gear bolts were new when I rebuilt the rear end 4 years/4000 miles ago. I buy 99% of my parts from Langs. Only time I don't buy from them is if they don't have what I need in stock.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Sunday, November 02, 2014 - 02:04 pm:

I bet you won't have that problem with a new ring and pinion using new bolts. On one Perfecto rebuild, I had to shim the ring gear 50 thou. I used new gears and bolts. No problem thus far but, admittedly haven't opened it up to look and see.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Sunday, November 02, 2014 - 05:38 pm:

what do you have under the hood? we had a member who had an early T with a Rajo or other type overhead valve head on his engine. He also had a Model A crank and early V8 transmission with a Ruckstell. He had too much power ahead of the differential and on several occasions he broke off the bolts holding the ring gear. Once time it happened on the San Diego Coronado bridge while he was carrying the Governor of California. Another time he passed everyone on a tour when we were going up in the mountains to Julian. He just laughed as he passed the other T's. Later in the day I saw him by the side of the road and others were just passing him and laughing. I took him home to get his truck and trailer. Same problem The bolts were sheared off.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Sunday, November 02, 2014 - 08:07 pm:

I had my short block rebuilt about 1000 miles ago but only 0.040 over on the pistons with a stock reconditioned crank and stock cam. Stock head and regular aluminum pistons with one piece replacement valves. I run a distributor and water pump. Maybe it was the water pump that pushed things over the edge(LOL). I wonder though, if shimming the ring gear is such a bad idea and causes this type failure then why do the parts suppliers still offer them?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Monday, November 03, 2014 - 01:19 am:

I've seen it happen several times. The parts vendors sell them because people don't believe there is a problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Monday, November 03, 2014 - 04:47 am:

It might only be momentary, but I'm pretty sure that a hard stop with the brake pedal, or, a "panic stop" where several pedals including the brake pedal are used to lock up the rear end will put considerable more strain on the differential ring & pinion than the engine can! Don't misunderstand, I certainly don't recommend "stomping" on all pedals, however, I firmly believe it has been done in desparation, and to shear those bolts, I'm thinking that it only takes once!

Also, come to think of it, just think what happens when an engine throws a rod or brakes a crankshaft!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Monday, November 03, 2014 - 07:23 am:

That's one advantage to safety wiring all the way around, rather than in pairs.

It's still early and I'm still on my first cup of coffee, but I'm not sure I understand the theory of the shims cutting the bolts. Can someone give me a quick explanation of the theory?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Monday, November 03, 2014 - 08:56 am:

I've re watched the T tips videos from MTFCOA again and I didn't see mention of a torque spec for the ring gear bolts. I will be using new bolts from Langs. Also, they mention centering the pinion on the ring gear but don't show very well what that looks like. Do you go by contact pattern or some other measurement? Any advice will be appreciated.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Monday, November 03, 2014 - 09:12 am:

The T-Tips video also recommended a gear lash of 0.004 to0.006. The latest threads I've read here suggest about twice that much and range anywhere from 0.010 to 0.015 What is a fella to believe?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Monday, November 03, 2014 - 09:30 am:

I'd go with Glen's numbers in the axle book. Page 28.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Monday, November 03, 2014 - 11:17 am:

Hal, the ring gear should not be driving on the bolts. It should be driving from friction between the carrier and the ring gear. Each shim you use reduces that friction.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Monday, November 03, 2014 - 12:19 pm:

Thanks Tom.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve McClelland on Monday, November 03, 2014 - 12:44 pm:

OlHenry was pretty smart, he knew this was a high torque or high stress area, that's why he used the safety wire....
I've seen a lot of things taken apart over the years on these old T's and some of the fellows I've came across working on them that swear by loctite doesn't see a need for the safety wire. They just don't get it...!
I sure hope they see this thread, maybe they'll have a new outlook on why the wire is needed. And what it's purpose is.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Smith on Monday, November 03, 2014 - 12:51 pm:

I'd replace that ring gear too. It looks pretty bad.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Tuesday, November 04, 2014 - 08:52 am:

I have a new ring gear, pinion gear, steel and bronze thrust washers going in it. I had intended to install them back in March but got side tracked and when I opened the cases this week, I discovered the above issues. I finally got the contact patch between the ring and pinion set yesterday and ended up with the thickest spacer in the kit plus a 0.005" spacer. I currently have 0.040" gear lash with no shims under the ring gear or thrust washer. My thrust washer shims should be here today or tomorrow so when they arrive, I'll set the gear lash then recheck the contact patch. What is a good torque spec on the new from Lang's ring gear mounting bolts?


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