Write Up: Building a True(er) Trac

[xjtrailrider]

Interesting and a good write up!

I'll add that my TT has around 35k on it and is still doing its job. I always run Lucas 85-140. I check it from time to time with the "one wheel on the hardtop, one wheel in the gravel" test. I did this the other day and got a little wheelspin then lock up and burnt BFG's

 

[O-Gauge Steamer]

In defence of the machine work...

Notice that the material removed is replaced with a radial roller bearing (aka thrust bearing). To install any radial bearing like this requires the "washers" called out in the parts list. These are not exactly washers, they are the hardened race that the bearing works against. So, the part of the TT that originally ran on the hardened case now runs on the hardened race.

The use of this bearing is the repair for the loss of the hardened material. The loss is what made machining the unit possible. Ever tried to lathe a hardened surface? If it is still present, you typically need to use a high speed grinder on it to cut of the surface. Once the surface has been breached, standard cutting tools can be used. The problem with relying on a hardened surface instead of a replacable bearing surface is what we see here. Once the hardening is breached, wear happen extremely quickly. The advantage (for Detroit) is that it simplifies the machining of the unit and reduces the number of parts used. In several of my lives, getting coest out of the manufacturing process is what I was dedicated to. Makes you look at all of the parts and processes involved. Could Detroit have used replacable races? Yes they could have but, it would add a ton of expense to the unit cost. Turns out it is usually the labour to install the "extra" parts that drives up costs.

I read this thread as a way to recover a worn beyond reasonable use TT, so it has value just for that. It is a clever and well thought out.

OK, defence off...

 

[Rod Knee]

I have seen Trutracs with 100,000 miles that show almost no where at all. .

I'm guessing that you mean you've seen TT's at that mileage with no wear at all. The way its written it roughly reads as though TT's are nowhere to found at 100K miles.

Not trying to be a smart @$$. That's the kind of writing mistake I could have easily made.

 

[Boostwerks.com]

First off I would like to say very nice job on the machine work and thinking outside the box to fix the problem. Everything looks very well done. However I do not reccomend these modifications.

The case in a Trutrac is heat treated steel and has a very hard surface. While the case being worn does show it has been highly used the gear is still riding on a hard surface designed for wear. By machining the case 0.150" you have machined away the entire hard surface of the case. You now have a bearing wearing on the soft core of the material. Bearings are not designed to wear on soft material.

Along with the wear issue the Trutrac's design works on friction between the gears and case. You have removed nearly all friction between the case and the side geasr by adding a bearing in this application. While you have increased the belleville springs force back to the original design you have eliminated a good portion of some of the overriding forces.

I would also like to note that a good majority of the Trutrac models do not have any belleville washers in the assembly. These units work very well without this feature. The bellevilles are only added to produce some amount of pre-load on the unit.

I have seen Trutracs with 100,000 miles that show almost no where at all. I would say the unit in this thread is not the norm.

As already mentioned by 0 gauge, and right above the picture int he write up...the thrust bearing requires the use of hardened bearing races with the correct C64 rockwell value for it's rated load of 5,600lbs.

You are correct about the friction design. However, the friction needs to be created by the components that can handle it IE: the inner gear face and cam bearings. While the friction surface area has been reduced, shiming the bellevilles or removing them for slightly thicker ones will gain back some of the lost friction. I would honestly rather sacrafice less preload if it meant the gear isn't going to wear into the casing.

Do the units your talking about without bellevilles have any form of preload? If not, the diff will and does operate like any open differential.

Your findings of no wear are NOT what I have found to be true. How many have you cracked open? Do you have pictures to support your findings? If the casing is surface hardened, their methods still need revising. The whole issue could be solved by using a harder gear steel for the casing ends, but that would definetly increase cost.

 

[Ty2003K]

I missed the second thrust washer on the first pictures. Thats my mistake. But again I have to say that you have significantly reduced a friction surface that is designed for friction.

Every Trutrac design built for a C-clip rear end does not have any form of preload. The preload is only there to increase friction at the static or near static state. The great part of a Trutrac design is that as one wheel spins faster it bias's more torque to the other side and exponentially increases the friction of the unit. The unit will only operate as an open differential when there is no torque to bias whatsoever. Similar to a tire in the air. Most people running Trutracs have most likely seen this. The preload was added to reduce this affet. Others have designed a cam action into the side gear to also combat this.

Every Trutrac I have seen does in fact use case hardened gear steel for both caps of the case and the center body. If your case was not hardened in the first place thats something that has already changed. All the D30 Trutracs I have seen also use 6 bolts for each side of the case half.

Next time I see one I can snap a few pictures, but I have seen plenty. SAE 8620 case hardened roughly 0.040" on all of them. Oh and using a lathe on a hard surface is no problem at all. You just have to be prepared for it.

 

[Ty2003K]

Double post.

 

[tbburg]

I'm not an expert on TTs, but I do own two of them. When I first started looking into the TTs, I recall reading specifically the Dana-30 model has pre-load built into it. When I got mine, I was curious, so I stuck a pair of axle shafts into the uninstalled unit and turned it with a pipe wrench. The D-30 model(bought used) required significantly more force to spin one side gear then the D-44 model(NIB) Based on that, it wouldn't surprise me if some models don't have the belleview spring, or at least a much lower pre-load.

I don't think the TT requires friction on the back of the side gear to operate properly. As I understand the engineering, the torque transfer is due to the inhearent load/friction in the worm gears similar to(exactly the same as?)the Gleason Tor-sen differential.

 

[Ty2003K]

The friction on the back side (the side next to the end caps) is not as critical as the friction on the internal center block, the middle of the case, due to the helix angle and direction of the gears. Ill agree that it is a secondary friction surface but it is also has very large surface area and does experiance some significant forces.

But that could also lead to another discussion. The Trutracs design is meant to have both side gears push into the center of the case when tires are slipping. I believe they also designed there cases to be diiassembled and the center gears switched from one side to another to change between front and rear differentials. If this is an older case and possibly before this change it could be operating in the opposite direction and wearing more predominately on the end caps thus also the need for the extra preload.

 

[Boostwerks.com]

It might be possible the design has changed but the d30 true tracs ive seen look exactly like the one i have. And the fact the case halves have worn and not the gears is an obvious sign it is not the same material. Hard evidence doesnt lie. And also there has to be some form of preload unless the physical gear design is different. I might have to disassemble this diff again if you dont beleive me. Without the preload i can spin the diff by hand just like any open diff. IE the load is entirely transfered to the wheel with the least resistance.

 

[Ty2003K]

Please dont disassemble the unit again unless you have other reasons too. The inherent problem with the helical gear design is the fact that it needs some available torque to bias. As you mention with no preload the unit will spin by hand. That same unit will also let you down offroad when one tire is in the air. I can't be the only person to witness this offroad? Trutrac added preload to help this issue in some of the differentials. Others like Wavetrac, added a cam mechanism and additional friction surfaces to help the problem. Again these mechanisms only work at static or near static load. The units without the belleville springs in the middle work just fine. I have driven GM8.5's, Chy9.25's, and F9.75's non of which had any sort of spring in the middle. All work just fine and are even too aggressive for some people.

Like all limited slips get a tire off the ground and your wishing you had a locker.

 

[BlueCuda]

I was told that if you had a tru-trac unit that held together with 3 large bolts that they were the "good" ones. The same person said if I had one with more smaller bolts that they were junk. Someone told me this as I planned on purchasing one that was used.

I ended up with a 3 bolt one and IMO it was terrible addition to my jeep. It failed offroad anytime a tire got light. It also had enough friction in it to ruin the winter performance. When on ice it wouldn't let the tires slip so it just didn't steer worth a flip, and you can't get away from that even in 2wd.

I ended up with a locker in the front(already was locked in the rear) and couldn't be happier. Its still quirky in the snow and ice but its controllable as I can just let off the throttle to return to having a differential. And since it doesn't typicly snow but once or twice a year I hear I am always wide open doing powerslides anyways .

Just my .02 but in my mind I can't see how a tru-trac is a good option for anyone that plans to get off the pavement at all. For the rear maybe I could see that working well, the front is a no go though.

 

[tbburg]

The "3-bolt" TTs have 3 sets of worm gears, with one bolt between each set. The "4-bolt" TTs have 2 sets of worm gears, with 2 bolts between each set. I believe all C-clip style TTs have the 2 gear set/4 bolt arrangement, to allow the locking system to be installed.
The 2 gear set diffs may be somewhat weaker then the 3 gear setups, but they're all the same quality.

'Never driven mine in snow since I put the TT up front, but I haven't noticed any strange low-traction issues yet. I have used it in several situations where I had to hang a tire, and haven't had any problems that a little left foot braking didn't solve. TTs are not lockers, but I wouldn't call them junk. They DO have very specific operational modes. As stated earlier, they can only transfer a percentage of the available torque. With one wheel off the ground, it's basically an open dif. When this happens you have to apply braking to slow the free(spinning)wheel in order to get any torque transfer.
A clutch style LS will actually work better without any other driver input, but in my experience, the TT will "lock" harder then a clutch style LS under braking load.

 

[ChiXJeff]

<shrug> I have a D30 TrueTrac in my 94 XJ, it's been in there for something like 12 years and maybe 150k miles. It was my daily driver outside of Chicago for several years. BlueCuda, I suspect that you had something else going on there, I've had zero problems with my TT, and for a DD, I'd have no trouble doing it again.

If I get ambitious this summer, I may it out just for grins to see what sort of wear I've got on it.

 

[BlueCuda]

I very well could have had something wrong. Either way, I didn't like the way it acted. I had this stigma in my head that if I locked the front I would be in trouble in snow and ice(got that from here lol). But in reallity I should have gone straight to the locker but hindsight is 20/20. I believe i sold that TT to Cal for $20 shipped to CA .

 

[Boostwerks.com]

I've seen the true trac work like it should in the front of several rigs, and have no doubt it'll do it's job in my DD. If by chance it doesn't however, I'll swap it out for a full detroit. The fact I picked it up for cheap and the fix is cheap and easy I'm still happy I did it.

I'll have a report on how it works here soon.

 

[Koosza]

Final Assembly:
It's getting installed within the next couple weeks, and I'll be able to give a ful report on it's performance. Ideally I'd like to test it to find it's slip load value but I'm not exactly sure how accurate or relevant the info would be.
Total Cost: About $26 :cheers:
Enjoi.

Hi there Boostwerks.

Any feedback on this mod?

Cheers

 

[Boostwerks.com]

2 years of daily commuting and still going strong. Figured this needed a bump.

The only downside I've noticed is that it tends to push the front in tight turns in the snow. Otherwise it's been working great on and offroad.

 

[kastein]

Not sure how I missed this when you posted it, but damn that's neat.

PS - saw you tried to PM me a while ago, cleared a few out. I swear one of these days I am going to actually clear out my inbox completely :dunce:

 

[notamos]

Did you ever contact Eaton about this? If so, interested to hear their response.

 

[Boostwerks.com]

Not sure how I missed this when you posted it, but damn that's neat.

PS - saw you tried to PM me a while ago, cleared a few out. I swear one of these days I am going to actually clear out my inbox completely :dunce:

:cheers:

Did you ever contact Eaton about this? If so, interested to hear their response.

I had sent an email at one point, but never heard back. Other than that I haven't tried very hard honestly.