Ernie's diff....iculties

Ernie, Plugzit and I had a fun day on Ernie's gearbox. Today Ernie became a 348 differential mechanic. He will tell you the rest of the story.
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With a tounge like that,i thought it was Gene Simmons with a haircut

 

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Is that all the parts laid out on the white sheet. Doesnt look like too big a job FBB?? Which bearing did you guys have to cut off?

 

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Cool! I can see a brand new 348 Brotherhood page being added to the Primer...

 

Yeah we did tear appart and rebuild the differential today.

The bearing race you see was a BEEEEOTCH to get off. That damn thing did NOT want to come off via a puller. We tried everything. We tried to cut bigger groves in the old bearing race so that we could pull it off. We even sacrificed a puller and welded it to the race. Did that work, NO! The dang thing busted the race. I then tired to cut the race off, and that wasn't working either. So finally we did it the way we should have in the first place, and took the diff appart.

The pics you see are of most of the insides layed out. But that is pretty much it. Not really a big deal once you remove the 12 bolts that hold it together, it comes right appart.

To get the diff out of the tranny case you do need to remove the bearing on the passenger side, and then rotate the differential so that the big ring gear is facing the front of the tranny, then you can take it out. Other wise your gonna have to dissasemble the differential inside the case, and that will be a big time pain.

 

Im a little lost here ernie. Where was that bearing located? And is that why you did the re-build?? Is it your box that FBB has apart rebuilding?

 

Looks interesting, but why did you wear White trainers they wernt that white as the pics went down.

Andy.

 

If you look at the last picture, the one where I'm holding the diff in my lap, the bearing goes on there, just over the splined shaft. You will see 12 holes around the outside, and then 4 holes on the inside. The reason I had to take the diff apart was to get the bearing race off the flange. The only way to get to the back of the race is through the 4 holes. You can only get to the back of the hole by taking appart the diff, the ring gear is in the way. We did get the bearing off of the right side because there is a lip that allowed the puller fingers to get into the 4 holes. But on the left side we couldn't because the lip that the bearing rests on was not as high as the one on the right side. In order to get the puller finger in the holes we had to grind it down some. Well that grinding weakens the fingers. So one of the fingers broke. So the diff had to come appart to get at the race from behind.

The reason I did the rebuild was because the pinion gear was destroyed. I am changing the bearings because of all the metal that was in the tranny. We don't have pictures of the bearing race, but it is pretty pitted.

 

Those are my old shoes that I really don't care if I get dirty.

 

FYI, you're supposed to replace the crownwheel bolts for new every time.

While it's out, check the torque required to turn it statically (use a torque wrench and find the slip point).

Check the 348 manuals, but I don't think you'll find a number anyway.

Then set it to at least 40 lb/ft, maybe 50 lb/ft using extra (0.10"?)shim material behind the cone washer or thicker flat cross plates.

A tighter static slip on track improves traction a little, with no negative. Dont go mad with it though, ideally it's the ramp angles you need to change.

 

I do not know much about diffs...do you mean 50 IN/LBS? the 348 manual says 4kg but with the special ferrari pully tool so without knowing the radius or diameter of that pully I can't calculate the rolling torque. If I guess at a 10" wheel then we are close at 88 in/lbs.

Also, I'm helping a guy do T-belts on a 360 which has hydralic tensioners. The manual does not tell you how to set them. Is there a particular technique or is there a spring in the tensioner for static tension and then the oil pressure brings the true tension up to operational spec?

 

Thanks for the info Phil.

Do you know what size the wheel is for the torque dial, and how long the string is that attatches to the weight? The manual also doesn't give the rate and distance at which the weight needs to fall for the specified torque?

 

I was wondering about shiming it to get the correct preload. Because nothing was mentioned in the write up about it from ernie.

 

That's because we haven't gotten to that part yet. But in general the thicker the shim the less drag it will cause, the thinner the shim the more drag it will cause. That is were you get the preload.

 

Oops,sorry man. Yeah,thats right. I know all about shiming and pre-load brother. Shimmed me up some hub bearings on a Caterpillar Tele-handler at work the other night actually

 

No, I'm talking about static slip of the diff, not bearing preload.

My figures are written as intended.

Keep bearing pre load to book specs... set it on the upper (tight) tolerance for new bearings, and the lower one if re-using old ones.

 

It will be on the tight side as I'm putting on new bearings.

So when I go to shim it, is it better to put the shim behind the crown washer (I assume your talking about the on in the 3rd pic from the bottom, with the index on it), or is it better to put them behind the cross plates (5th pic from the bottom)?

I'm guessing that it would be better to ad to the cross plate/s?

 

hmmmm. I think you're misunderstanding me...

Shimming the bearing preload has NOTHING to do with static slip, or the crown washer and cross plates inside the diff itself.

Bearing preload is set by shims in the gearbox casing. Not even shown in your photo's.

I started talking about static slip because I thought you were "racy"....

Static slip is the resistance you feel when trying to turn one wheel, while the other is held still. Bearing preload is the resistance you feel when trying to turn the diff in the gearbox casing (with crownwheel removed).

 

I think your right, I am misunderstanding what your talking about.

It's not "racy" it's "crazy" lol.

Okay so were is it that I adjust this then? You said for me to check this while I had the diff out. I looked in my shop manual, and it only talks about adjusting the preload on the pinion gear (D37-39), and thrust bearings (D44-45). I can't find anywhere explaining how to adjust the static slip in the diff. Heck it doesn't even have anything in it explaining the proceedure for rebuilding the differential either. So the only way I can see to adjust it is by altering the cross plates or washer inside the diff? What am I missing hear?

 

The manual will definitely say about bearing preload, but it wont tell you much about static slip, unless the 348Challenge manual has some extra info perhaps. Haven't got or seen either.

Bearing preload will be the same, regardless of what you do inside the diff regarding static slip.

To measure static slip... set up an output shaft flange and hold it in a vice with a couple of bolts through the CV holes. Then sit the assembled diff on top, and put the other out put shaft flange on the other side. Then use a torque wrench to turn the free output shaft while the other is clamped still in the vice.

Adjust the torque wrench until it clicks at the point of slip..... You have just measured your static slip.... probably about 25-35 lb/ft on an old diff.

Now, strip the diff again and add shims (home made is fine) to a non moving surface (behind the cone washer or first cross plate), reassemble and repeat the test to re-measure the static slip.

Set it to between 40 and 50 lb/ft and it'll feel great on the road, give better traction with no ill handling effects.

Remember to oil it while testing this.

 

I think I was the one who confused you. That is my 348 race car in the pictures but that is Ernie's gearbox apart in my garage. I understand what you are saying. I also am glad to know it is an easy shim to get more lock-up. I have never done that so I was thinking there are extra shims available just to do this job. Anyway look at my picture. If I understand you correctly shimming any non-moving part the best place is the Cross plates. I think the factory says OEM diffs are set for 60% lock-up. So if you go for 80% lock is that 50lb/ft. For a full race never see the street how tight can I make this before driveablity goes the wrong way? Is there a relation between say 0.10" shim = 10 ft/lbs to kind of take out so much trial and error? I also assume I can shim just one side? At what point does the extra lock-up fry the clutch plates. Are you changing those out say every year on the 360 challenge cars? Thanks for taking the time to enlighten us. This is cool stuff.
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