Rear axle, in a '55 T-bird

[dmsfrr]

I will humbly plead ignorance on this question...
With the rear wheels blocked on the ground and the FoM trans in neutral, how much should the pinion shaft / drive shaft turn? How much overall backlash is too much?

The rear axle assembly may not be original to the car. If it's had previous work done I don't know.
There are no howling, clunking, clicking or grinding noises. Pinion shaft seal & cover gasket both drip.

A good front-end & suspension shop worked on the car a couple months ago and suggested rebuilding the differential, for a notable price.
There may(?) be excess wear in the ring/pinion & spider gears but I haven't taken the rear cover off because I wouldn't have a clue what to look for. (besides chipped teeth & filings in the gear lube)

 

[Sid]

It's hard to say how much it should turn. You have spider gear/axle play in there also. You would need to see the spider gears to see if hard face is worn. I do know that with the pinion held stationary about .005 to about .008 backlash ring/pinion is ideal. If it isn't howling or clunking just re seal/gasket it. I almost think before I spent a boat load of money on that old Dana I would consider hunting for a 57 bird rear end. 9" diff. and you can go with any gear ratio you wish.

 

[Daves55Sedan]

You have the original Dana integral housing type rearend which was typical of all '55 & '56 T-Birds and Wagon Models.
According to the '56 Ford Car Shop Manual, pinion backlash should be between .003 - .008 and pinion bearing pre-load should be between 10 - 30 inch/lbs torque.

 

[miker98038]

The Dana in the back of my bird came out of a truck. The bearings for the smaller bird axles didn’t fit, the truck bearings did. Mine was a T-86 O/D, and I assume someone found the 4:11 rear end in a wrecking yard. The welds on the spring perches were crude even by 55 Ford standards, as was a lot of the other work in my car.

If it’s not making any noise, just reseal it. You can eyeball the gears with the rear cover off. They’re a pretty bulletproof unit.

Due to transmission and other changes, I’ve had 3 gearsets, 4:11 open, and 3.3? and 3.7? limited slip. Had I looked far enough ahead, I could have put a 9” or more modern rearend under it and saved a lot of time and trouble. That would have included better rear brakes either disc or drums. When you add in the cost of two sets of rear disc before I found a setup that works, I should have just dropped the Dana on my foot.

 

[rotorwrench]

Ford used the Dana 44 for a long time so at least there are parts out there. If you go for a seal change, make sure you mark the nut so that it can be returned to its original location. Tightening preload on a used set of bearings will cause them to wear more rapidly. If you replace bearings then by all means set the preload to specs. With pinion to ring backlash, differential gear backlash and some slack in the axle splines, the drive shaft will move a fair amount but I wouldn't think that it would be more than a 1/8" or so unless there is a lot of wear.

All Dana 44 axles that Ford had back then use the same bearings but the Dana 45 had the oddball stuff. Dana 44 pinion seals did have variations from early to late and there are different axle splines for early and late. The Dana 45 is a good candidate for change to the 9-inch due to its rarity for parts. The Dana 44 is easy to find parts for a long as a person knows which parts to use.

That T-bird axle has a good set of gears for highway. 43/13 indicated 3.31:1 ratio. What to look for is the width of the gear pattern. The wider it gets, the more wear is going on. If there are any steps in the face of the gear teeth then it's time for a new set. Cracked or broken teeth are obvious. Spalling or abnormal wear of the gear teeth is also call for new stuff. It's mostly just common sense. If it looks like sh!t then it is. Chuck it & look for better. Spider gears can be somewhat loose. When setting up backlash on used gears, I leave them toward the upper limits. They will run cooler that way.

 

[dmsfrr]

... With pinion to ring backlash, differential gear backlash and some slack in the axle splines, the drive shaft will move a fair amount but I wouldn't think that it would be more than a 1/8" or so unless there is a lot of wear.
...

It looks to be rotating about 1/4 inch so it might be time for some repairs.

Thanks for the replies everyone.

 

[rotorwrench]

They do wear a good bit but can be used again if wear is even. It just has to make good backlash all the way around with a decent pattern marking if replacing bearings only. A good visual inspection of the gear teeth will tell you. I checked one of my 51 Mercury rear axles and it moves a bit more than 1/8" but not a lot more.

Some of the helicopter transmissions I work on run .014" on backlash now. They used to run .011" but the engineers decided they would run better with more backlash. They seem a bit loose to me but they work OK. The ring & pinion on these are a bit larger than a car but not by a lot. Maybe only 2.5-inches different in diameter on the ring gear.