Preload

eatonaxle

eatonaxle

Junior Member
What is the approved method of preloading the pinion bearing and then the carrier bearings to the axle housings? What is the recommended preload and how is it measured?
In the past I have used fishing scales and I pull the banjo or crown wheel over with suitable string wound around to get 4lb pull (or preload.) This is preloading each item separately. It takes time, but I have never had any problems. The whole method is pretty crude and there must be a better way, say with the aid of a torque wrench measuring foot pounds.
If using really good second hand bearings, (double taper and carrier bearings) is the preload still the same?
An old engineer friend of mine (now deceased) told me that Model 'A' diffs were made to go together without any real adjustment. He meant the meshing of the pinion to crown wheel teeth, but to use different banjo housing gaskets to gain the correct preload for the carrier bearings. Does this make sense? If the teeth do not mesh or give a good pattern when blued, what happens to the carrier bearing preload when you add more gaskets one side to mesh correctly? You would be running round in ever decreasing circles, or am I barking up the wrong tree?
 
Yes and no, The Model a diffs, and many other assemblies, were machined and used parts that when assembled made fine adjustments unnecessary.

Today with 80+ year old parts, non uniform new parts from several off shore vendors, it is next to impossible to get the exacting machining that Ford demanded. It can take hours to get a rear end done correctly today. There was no way Ford could allow that to happen back then.

Take a look here;

Tom Endy's Seminar
 
I am in the middle of this also. Recently, I sent the pinion out to have the front (smaller)bearing dia reduced to allow the NEW bearing to slip on. But when I snugged up the pinion nut, which forced the pinion bore against the tapered shaft, the dia of the front race swelled up about .0015". Now the front bearing has to be tapped on in a press fit which I think will give me false torque readings when I set the preload. When I disassembled the pinion the new bearing will no longer go over the ground dia but the OLD bearing will. The old bearing appears to be in exellent shape. Good rollers, no marks at all. So I reassembled the pinion to the banjo without the shaft and torqued up the nuts to establish preload at 12 IN lb. Then I assembled the shaft and tightened the nut to 50 FTlb. Now I have one old bearing and one new bearing at 12 in lb. Have I got a mess or will I be OK to finish putting it all together? Thanks Bill G
 
Preload is basically the same for good-quality new & used bearings.

Bill, I think you will be alright with new & used together however I do agree that you finding yourself tapping on the front bearing is possibly giving you a false reading. That would concern me too but I think you have a handle on it. I sometimes think people over-agonize with rebuilding rear ends.

.
 
I was reading the Tom Endy seminar 5 or 6 times when restore my rear end axle, before begining to understand!! cost me a lot understand a tecnical words in english!!
This seminar really explain how function the rear axle!!
 
Some comments for Bill Goddard:

If you are using new Timkin bearings you should not have a problem. The bearing that goes nearest the pinion gear should be an interference press fit. The forward bearing should not be a press fit. It should be a tight fit, usually such that you cannot move it by hand. As long as it is not so tight you can't knock it back by tapping on the end of the drive shaft with a brass hammer in the event you get the pre-load too tight and have to start over.

It is a given that when I rebuild a rear end all the bearings, races, and seals are replaced with new. I have had custemers ask me to reuse the old bearings if they look ok. I don't take the job in unless new bearings are installed. I tell the customer that up front. I would put the new bearing back in if I was you.

I also torque the the pinion nut a little tighter. I set my wrench at 90 lbs and torque, then I go looking for the cotter pin hole. I may end up with 120 lbs when done, but it has worked for me all these years. It is best to torque the nut before you set the pre-load because the pinion sleeve will swell and if you previously set the pre-load, it will increase.

When setting pinion pre-load I am trying to obtain 20 in lbs. And if you work at it you can get it there. However, anything between 14 and 22 in lbs will be acceptable. With new bearings and races I measure the pre-load with an inch pound torque wrench and the tool I made as shown in my disertation.

When adjusting the pre-load with used bearings you generally cannot set them at 18-20 in lbs. I don't even try to measure them. I do the adjustment by feel and get as close as I can before feeling the bearing binding.

The only time I do this is when I am installing an overdrive and the task is to just pull the pinion assembly and replace the drive shaft with the stub shaft. Often the two bearings and the race are so bad I replace them. But if they are reasonable, they are probably the same as the two carrier bearings and races, and since I am not doing an overhaul I set them the best I can.

Tom Endy
 
Comments for Mr.Ratamahata:

Thank you for the compliment. Your written English is by far better than my written Spanish.

Tom Endy
 
Tom I have been using your directions. They are easy to follow. Thanks for posting the link. The one tool I need to add to my collection is a dial read inch pound torque wrench that reads in the 0 to 30 or 60 lbs range. The one I am using goes to 120 and is the swing arm type, very hard to read. Every one that I have seen so far, is 1/4 inch or if 3/8 goes for the way big bucks.
 
Redmodelt:

My foot pound torque wrench is a half inch drive Proto. It reads from 30 to 150 and is the type that goes "click". It handles just about everything on a Model A except setting the pre-loads. For that you need a dial indicator inch pound torque wrench. The one I have is also a Proto and is a 1\4" drive that reads 0 to 75. And they are expensive. This one was about $250 20 years ago. Sometimes the used tool vendors at the big swap meets have them at a reasonable price.

Tom Endy
 
thanks also Tom ,i have read your article over and over as i am doing my A diff now ,i have done the carrier preload and am happy with that ,we pressed in the pinion cup and installed the new bearings ,as i dont have a dial tool so i took it to our local diff man to set it he checked by feel and considered it ok he even gave me some proper paste to do the gears ,he has confidence in my ability ,i am determined to get it right ,its enjoyable to have a go a something like this and hopefully it will be good ,my son is a mechanic ,i am a plumber so between us we can make something run out of the diff,,,,,
 
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