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HighwayThunder
12-07-2015, 05:20 PM
I'm converting the Ford 9" rear axle ratio from 3.0:1 to 3.7:1. Took the rear axle parts to a machine shop to have them remove old bearings and press on new ones. In the process they found a hairline crack in one of the ring carrier halves.

As far as I know the crack is not repairable. "You can't weld cast iron. After all, it's only one step up from dirt," said the machinist.

It's possible the crack has been there since the car left the factory and, given the way it's bolted together with its other half and the ring gear, there may be little danger it would cause the rear axle to fail. On the other hand, given the increased power due to engine mods, it could be a catastrophe waiting to happen.

Anybody know where I can get a new part without buying an entire rear end?

simplyconnected
12-07-2015, 06:23 PM
Around here, we have 'Trans & Gear' shops. Call your local transmission shop. The Ford 9" is very popular. If he doesn't have a good used one he can probably get one for you.

Your machine shop is right. By definition, cast iron is at least 2% carbon (graphite). That's why cast iron works so well in cylinder bores. - Dave

HighwayThunder
12-15-2015, 01:55 PM
I'm having trouble setting the pinion bearing pre-load. For a 9" with new bearings and a collapsible spacer, the manual says to torque the pinion nut to 175 ft/lb (minimum) and check that the rotation resistance is 17-32 in/lb. (First of all, don't have an in/lb torque indicator, but am able to estimate.) Rotation seemed way too resistive.

I took the assembly back to the machine shop and had them install a new collapsible spacer, but to leave the bearings a tad loose. I torqued the pinion nut to 145 ft/lb to start with, and measured the rotation. It seems to be about 7 ft/lbs by my reckoning. Tightening it to 175 ft/lb would only make it tighter.

Any advice as to what I'm doing wrong?

Cheers,

HighwayThunder
12-16-2015, 07:36 AM
The machinist confirmed that the spacer had been compressed.

It may be that the collapsible spacer is too ductile, causing it to compress at a lower pressure. Past a certain point you would be tightening the bearing rollers against the bearing cups, negating the purpose of the spacer.

(The Dorman spacers purchased from O'Reilly's came in a package of two, presumably an extra in case one over-tightens on the first go-round. Doesn't seem likely that one could fit both spacers on the pinion.)

simplyconnected
12-16-2015, 07:38 AM
Follow this YouTube video.. CLICK HERE (https://www.youtube.com/watch?v=IBih0TVtEto)
This is one of those jobs where you need a professional shop to do the work and to give you a warranty. WHY? Because they have experience, all the correct tools, a host of shims left over from previous installs and they can buy bearings and other parts cheaper because they order from a distributor.

Without seeing what parts you changed and your techniques used, I couldn't possibly know where you went wrong. The video demonstrates proper installation of both the crush washer and the solid. More importantly, it shows proper preparation of the castings. - Dave

HighwayThunder
12-16-2015, 08:06 AM
Thanks Dave!

That's the best video I've seen on the topic.

Will go to solid spacer/shims.

HighwayThunder
12-25-2015, 09:34 AM
My background is in electronics and, comparing electrical article testing to mechanical article testing, it seems that electrical testing is easier: precise parameters are visible using common test equipment. Mechanical testing can sometimes be ambiguous. A case-in-point is adjusting ring and pinion gears.

As previously posted, tightening the yoke nut to 175 ft/lb over-crushed the collapsible spacer resulting in too much preload drag on the pinion bearings. My machine shop advised me that common practice is to ignore the 175 ft/lb spec and just tighten the nut to the preload spec (the nut will not come loose under normal driving conditions). That’s what I did.

The next challenge is adjusting the pinion shims and ring gear backlash to achieve the “ideal” ring-pinion contact pattern. Again, there’s more to it than the factory manual lets on. Ring and Pinion Service, Inc. has an online paper (https://www.ringpinion.com/content/book/reading-and-adjusting-ring-and-pinion-tooth-patterns.pdf) on ring-pinion alignment Take-aways include:
Putting some drag on the ring gear during rotation will produce better pattern definition.
Pinion shim adjustment will be reflected in the pattern moving between ring gear face and ring gear flank.
Achieving an ideal ring drive side pattern is more important than the coast side. (Ever notice that your rear axle whines when you accelerate in reverse?)
“Ideal” can be a range of acceptable patterns, as pictured in the online document.However, after going through several iterations of shim and backlash adjustments without finding an acceptable contact pattern at the end of the rainbow, I took Dave’s advice and brought the assembly to a shop specializing in rear axle repair. They’ll have it ready by Monday.

Cheers,

simplyconnected
12-25-2015, 02:27 PM
Some jobs are better left to the guys who do it every day. I thought I could mud drywall, polish parts (in preparation for plating), spray paint a car, etc.

I ended up sanding off more drywall compound than I put on, I nearly ruined my classic car parts trying to polish them and I don't have a proper spray booth with filters. To me, all these jobs LOOK easy, like watching Michael Jordan shooting hoops. It's a different story when trying it for yourself.

I cannot afford to pay every professional that is needed for my car so I swap a lot of work. This practice produces more friends in the restoration business. We can never have too many.

Merry Christmas - Dave