Tom Talks About Diff Carrier Tuning

68/70Vette

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[ame]http://www.youtube.com/watch?v=CGq15JBBUQw[/ame]

This is Part 1. This shows Tom setting up the differential carrier unit. Look at the work that goes into setting up the unit. How are these things made on an assembly line? You couldn't spend this much time on mass produced differentials.

This is part 2.
[ame]http://www.youtube.com/watch?v=UwxLHFZq6QA[/ame]

There's only a brief glance of Tom's face in one of the videos. Looks to me like he's lost a little weight. Also, he looks a little older, but don't we all. His voice is still the same.

There's another video also. Just dial up youtube.com and search on toms differentials.

ENJOY
 
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Thanks for posting this video, very interesting. BTW...Tom's is mentioned in the latest edition of VETTE magazine Oct 2011, in a story titled BIG-BLOCK Party: part 3, prepping our 69 for the installation of a modern, EFI Big Block. Upgrading the C-3 differential is part of their program, in case anyone is interested.
 
There is indeed a lot of time required to tune and polish a posi. Takes me about 5 hours to do both. I also have a "machine" I'm building to aid in tuning but the old tried and true hand method still works.
 
Nice, i should have seen this before, would have made the assesment of the force to turn a tuned posi a whole lot easier.

What got my attention, was that he didn't pay any attention to the amount of spider gear backlash. I was bit weary about that.

Seen i was not trusting my own feeling when turning the posi, i measured torque and checked backlash on the gears. What I got on my unit was that when i got backlash in the correct .001-.008 zone (.006' to be exact when putting a little force on the gears with a screwdriver as per workshop manual) that the force on to turn the posi (with a bolt welded to an old side yoke was around 25-30 lb/ft. However I never turned it around 50 times in each direction :confused:
I have to add, that when i did a trial assembly with a loose shim setup (no preload) and then put in a spring pack, that the preload with the springs was exactly 25 lb/ft.

Maybe it's to tight but anyway, seen the fact that i didn't turn it 50 times, it will probably loosen up a little.

IMO there must be a better way to determine the amount of torque to turn the carrier after putting shims in. To me it seems best to measure torque to do this.
The workshop manual calls for a 70 lb/ft of torque on the wheel when new clutches are used and 40 lb/ft when worn. I'm still a far cry away from the 40 lb/ft mark.

I even put gear paste on the spider gears to see if the pinion was not sitting to deep in them...

Well, i will see in a short while if I did a good job. Hopefully i do not have to take it apart again because it's frankly a PIA job.
 
What got my attention, was that he didn't pay any attention to the amount of spider gear backlash. I was bit weary about that.

Belgian,
It seems to me the backlash would be zero. Since the side gears are preloaded into the spider gears. Or am I wrong?

Also do you polish the rough cast areas such as inside the posi case?

Great video's anyhow!
 
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I polished the case also.

When having the carrier on a stand, and the side gear locked to the stand and a wooden wedge between the pinion shaft and side gears, you can point a micrometer at the pinions and try to move them with a screwdriver. This is the way i measured it. I got .006.

The thing is the clutches get preloaded more with the gear seperation forces that are created when the pinions are turning and when there is more torque input. Tom mentioned it briefly in the vid.

I would like to add, that today I had my car back on the wheels again. I put one wheel on the ground and used a breaker bar to turn the hub on the other side. The frame is unloaded (no body, no engine, no trans) Seen the floor is rather slippery I would have expected the wheel that was on the ground to slip if i preloaded the clutches too much when tuning them. With both wheels of the ground, they both turned.

What this means is that even on a rather slippery surface you get differential action (no locking)
When applying engine torque to the rear, you get more gear seperation forces and the clutches are preloaded more, so more torque is transferred to the other wheel.

I even rolled out the frame an made a turn, no binding, or anything, it rolled out perfectly.

The only thing that bothers me, was the bumpiness (you can also see and hear it in the vid when tom turns the carrier) of the cut gears i bought from Tom. When turning the carrier, you can feel that. I even felt it when turning the hub. However I didn't feel anything when pushing the frame out.
 
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You shouldn't get any posi hammering with it properly tuned. 006 lash is a bit high in my opinion but the checking methods could be different. I have my little way of doing these, developed after doing a lot of them.

I've found some new spiders cause a tight spot at times, most times I found the face of the 10 tooth gear stamped and that sometimes distorts the tooth and gives the high spot. I have to dress them with a dremel at times to correct this. Not much as to be removed , it's kind of like scraping machine ways to remove the high spots.
 
Belgian,
Yes I noticed the uneven gears also in Tom's video. GTR1999, a suggestion next time. Instead of using a dremel, if you have access to a glass beader. Mask the gear areas off you don't want to remove the material and bead the areas you do. This will give you even removal. And if the variations are not that much it will not take that long. We use yellow plastic tape for masking beaded parts.

One more question, has anyone ever polished the entire rear housing? Will it remove possible fracture areas?
 
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You shouldn't get any posi hammering with it properly tuned. 006 lash is a bit high in my opinion but the checking methods could be different. I have my little way of doing these, developed after doing a lot of them.

I've found some new spiders cause a tight spot at times, most times I found the face of the 10 tooth gear stamped and that sometimes distorts the tooth and gives the high spot. I have to dress them with a dremel at times to correct this. Not much as to be removed , it's kind of like scraping machine ways to remove the high spots.

Checking methods play a big role indeed. The amount of pressure on the screwdriver is something that plays a big role. After a couple of rounds, i managed to get a 'feel' for it.
I'm a bit in the dark what you mean with a stamped gear (die formed maybe ?). The gears I used were the cut heat treated ones. When going over the net for info, i found out that a lot of guys had the 'bumpiness' in the gears when turning the carrier around on a stand.

I was always intrigued about what exactly they mean with a 'hammering diff'. If i'm not mistaken this is not the same as a diff that doesn't have 'differential action' and thus causes the inside tire to grab/slipping on the surface. I always suppose, with hammering the meant subsequently grabbing and loosening of the clutches in the diff, mainly caused by the spring setup.

Anyway, to make sure the gears were not binding i put marking past on them. If i'm not mistaken, when they bind, the top edge will be running close tot the valley in the spider gears, maybe even touching the valley. This was certainly not the case.
I even slightly filed the edges of the teeth, to make things smoother, but it only helped marginally.

BTW : even with a loose setup the 'bumpiness' in the gears was still there, so this is certainly not caused by 'gear bind'

Must admit, interesting subject, but as I pm'd to Gary before, a diff is not an easy job.
 
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I just realized that Toms "tuned" units don't have spring packs in them. Trying to rationalize this, it looks like hand tuning the differential cases allows the pinion gears to be tigtly installed without springs. However, what happens when you drive one of the springless cases after say 20,000, 60,000, etc miles? Don't the shims wear and then does the differential case pinion gears get sloppy without the springs? I can already guess that for stressful situations (drag racing) the springless cases must have an advantage, or Tom wouldn't be selling them at premium prices. Can someone comment about the tradeoffs of diff cases wihtout springs and those with springs?
 
I just realized that Toms "tuned" units don't have spring packs in them. Trying to rationalize this, it looks like hand tuning the differential cases allows the pinion gears to be tigtly installed without springs. However, what happens when you drive one of the springless cases after say 20,000, 60,000, etc miles? Don't the shims wear and then does the differential case pinion gears get sloppy without the springs? I can already guess that for stressful situations (drag racing) the springless cases must have an advantage, or Tom wouldn't be selling them at premium prices. Can someone comment about the tradeoffs of diff cases wihtout springs and those with springs?

I had a hard time believing this too. The fact is that the posi-action doesn't come from the springs, it comes from the forces that try to separate the gears in the posi. Since the pinions cannot go sideways, only the side gears can...doing so they compress the clutches more, providing torque input for the wheel that has traction.
The more torque input, the greater the separation forces, the more torque transfer.

What the springs do is provide preloading the shims and helping a sloppy setup. Like Tom mentioned, the less distance the gears have to travel, the faster/better the clutch action.
However the springs can cause the hammering action.

The big question we're talking about here is how much preload there should be on the clutches to start with. Like you can see in the vid, Tom's doing it by feeling. Its hard to tell how much 'resistance' he feels of course. This resistance is the preload setting.

FWIW, the stock spring provides 25 lb/ft preload.

Like is said in the vid also, the preload is controlled by the amount of shims behind the packs, the more shims, the more preload. However, sometimes you need to go in between the shims to get the exact setting. When i was tuning, one step down, was too loose, the step i used now, might be a tad to much for Gary. I do not have a surface grinder to grind the shims in between.

As for the wear on the clutches : they do wear. What happens is they wear of untill there is no preload anymore. This doesn't mean you don't have posi-action anymore, since they get compressed when you get torque input/separation forces pushing the side gears out. But the clutch action without torque input or at small input, will be non. However, you could of course put your foot down...
 
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I'm getting close to pulling the trigger on some Tom's stuff. (Stuff is also a German word that I thinks that means the same as the English word.) I'll ask him about this (the diff spring pack issue). One thing I don't know about my plans to buy his "stuff" is, what current prices are? His prices are in a 2009 webpage catalog. I think I'm going to go for the 1350 rear end parts with 30 splines. I'd really like to buy the 14XX stuff, but it's a lot more expensive and I don't think I need it. What's great about the 14XX stuff is it's appearance. Those U joints look like that came off of a heavy duty truck!!!!!!!I'm restricted to a 10 series diff with a 3.08:1 rear end. I have a Richmond 5 speed, so in first gear, I'll be the same as a Muncie car with 4.11:1. Anyhow...I'll be interested in knowing what today's prices are.
 
Just call him up, he'll tell you pricing. If you're thinking 1350 inner axles,you're going to have to replace the spiders too unless you're staying with 17 splines. In that case it doesn't make it worth it just to replace the stock 17's with a flanged 17 spline axle.
 
I just realized that Toms "tuned" units don't have spring packs in them. Trying to rationalize this, it looks like hand tuning the differential cases allows the pinion gears to be tigtly installed without springs. However, what happens when you drive one of the springless cases after say 20,000, 60,000, etc miles? Don't the shims wear and then does the differential case pinion gears get sloppy without the springs? I can already guess that for stressful situations (drag racing) the springless cases must have an advantage, or Tom wouldn't be selling them at premium prices. Can someone comment about the tradeoffs of diff cases wihtout springs and those with springs?

I had a hard time believing this too. The fact is that the posi-action doesn't come from the springs, it comes from the forces that try to separate the gears in the posi. Since the pinions cannot go sideways, only the side gears can...doing so they compress the clutches more, providing torque input for the wheel that has traction.
The more torque input, the greater the separation forces, the more torque transfer.

What the springs do is provide preloading the shims and helping a sloppy setup. Like Tom mentioned, the less distance the gears have to travel, the faster/better the clutch action.
However the springs can cause the hammering action.

The big question we're talking about here is how much preload there should be on the clutches to start with. Like you can see in the vid, Tom's doing it by feeling. Its hard to tell how much 'resistance' he feels of course. This resistance is the preload setting.

FWIW, the stock spring provides 25 lb/ft preload.

Like is said in the vid also, the preload is controlled by the amount of shims behind the packs, the more shims, the more preload. However, sometimes you need to go in between the shims to get the exact setting. When i was tuning, one step down, was too loose, the step i used now, might be a tad to much for Gary. I do not have a surface grinder to grind the shims in between.

As for the wear on the clutches : they do wear. What happens is they wear of untill there is no preload anymore. This doesn't mean you don't have posi-action anymore, since they get compressed when you get torque input/separation forces pushing the side gears out. But the clutch action without torque input or at small input, will be non. However, you could of course put your foot down...

You're going to get less wear with a tuned posi over a stock spring setup. I've taken apart 40 year old stock posi's and the mic'd the clutches and they only had 001-003" wear on each, however the sideplay and lash were lousy.

I took apart a new loaded Eaton last winter, with those huge springs out there was 030" endplay in the side gears- terrible. They weren't precision units in 1965 nor are they today. They work, they're simple, but in my opinion can be made better. Sounds like you have yours setup pretty good, and I suspect it's better then any one you're going to find in a catalog.
 
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