Anyone see the new Mark Williams C2/C3 posi cases. A little pricey lol. Curious if anyone knows anybody using one. Love to hear what Gary thinks about them!


https://www.markwilliams.com/acg-030.html

 

Yeah.....not spending $3500 on a posi case, no matter how good it is. I am sure they are very high quality.

 

Saw a post on a vintage racing site that these will very likely be their go to units. The big blocks are making 800-900 horsepower now and even the best Tom’s units are not lasting. Anyway, no matter the price, nice to see someone stepping up to maybe fill the void Tom left. They have some nice looking axles as well.

Nice also that you can use the taller gears in it whereas the 12 bolt is limited to 3.70 and up.


Bill

 

A couple of guys sent me this link today as well. I have not seen one and probably don't expect to for $3500 but some thoughts

That looks a like nice case, no question 4340 steel is stronger than the nodular iron cases so I would say clear advantage to the steel case. The internals sound like stock Eaton pieces which are good parts but I don't know if they are using fiber or steel clutches. New Eatons use the fiber and they are not as good as the old solid steels. No mention of how the posi is setup that I saw- spring pack or tuned?

I think it comes down to application obviously.
If you are going to go out racing-road or drag, you should have a preventive maintenance program which would include regular service to the diff. Some guys will run through a season and go through the diff again in the off season. These steel cases will be idea for that usage and for that group the budget may allow for it.

I expect there are relatively small numbers of c2-c3 racing, as compared to street use. For street use there is a wide range of application which for engines spans from stock 200 hp to many custom built into 800-900hp. So you stuff a big power engine up front and many guys overlook everything south of the flywheel until something breaks and it usually will show up soon enough.

Tom Watt built plenty of nodular iron 12 bolts that were raced hard and sure some didn't make it but a lot have. I have worked on several of his older builds over the last year. These were 20-40 year old diff's and for the most part held up very well. They had some worn parts but the cases were intact and reused. Tom never cryo'd a diff, I asked him about that years ago. Tom's hasn't built a 12 bolt for years. Prior to his passing the last one was probably done 12-15+ years ago before Kenny died so if recent Tom's 12 bolts are failing is it the parts or the assembly? We can go back here on CF a year or so and see where one came apart with street use under 2500 miles. Was it the fault of the parts in that case? no it was the builder and his method used, lack of a press fit on the case, and the wrong setup of the ring gear bolts. One of our 12 bolts let go recently after 9 years of abusive driving, hard clutch dumps, and drag racing. Ripped a tooth off the pinion and in the process the tooth temporarily wedged between the R&P and bent the case flange 006". I would not call that a case failure but a gear failure and that type of gear impact probably would have affected even the 4340 steel case flange too. I think I am going to fit this one with a spool and test it, which is nothing new either.

So yes that is nice strong part. Do I expect they will sell a lot of them to corvette guys for $3500, no. Do the math, Summit sells a new loaded 12 bolt posi for about $625. Machine it for 12 bolt axles and ring gear- depending on if you have machines or sub it out I'll say $400 since it can be done in any 13+ inch lathe in a reasonable time. To compare the two use the same internals which come in the loaded Eaton- although I wouldn't use fiber for anything. Figure labor to polish and tune it- this will vary since most shops won't do either but we'll say they will at $100/hr so about $600 should cover it -if and this is a big if, they know what they're doing. Add $200 to cover cryo treating them, again this is subject to location. So for about $1800-$1900 or less you have a pretty stout posi case that will handle most of what guys are going to use them for on the street or down the track once in a while. Again, into real racing then these are subject to regular inspection and probably gear change over time. Is it bullet proof? That overused term is something I never use because working around these cars for the past 43 years I have seen some of what must have been some big bullets used. It is nothing more then a marketing tool for sales, same as one and done, Racers build, or anything else you can come up with that Johnny Gearhead will buy. Is the steel case bullet proof? I don't know but if the spiders are the same, they break too. I suppose the only real test would be to put them in the same application and see which breaks first and how long they go. I would expect the steel case to last longer but those 45 year old Tom's diff's have been out there still taking abuse.

Those with the budget and want them go for it, there's nothing wrong with them. Although I would look into the internals before I drop $3500. For those with mostly street use cars, a properly built nodular case will work and for about 1/2 the cost.

Overall usage
For some a 12 is not needed at all and a properly modified 10 will work, but I would say for most c2/c3 owners blueprinting their 10's for their level of use is all they need and the largest group overall. Then there is the common rebearing job some call a rebuild, those are the cheapest BUT for some that's all they need. Do you need a steel 12 bolt case for a 300hp street car with TH400, no. Would you use a common market type rebuild in a race car subjecting it to 800hp, I don't think so.

Tom's is still open, others have been trying to capture that market now that Tom is gone. I have seen some of the copies and where they improved one part they missed a larger issue with them. I do like the look of some of the newer axles I have seen though but even those will have a smaller market and that's what this is really all about right?

 

Gary, thanks for that. I have always been confused as to why 12 bolts are limited to 3.70 and up, and this case works for the taller gears. I surely wanted to go 12 bolt, but with my transmission choice, the 3.08 is perfect. Also liked the idea of the bigger pinion gear of the 3.08.


Bill

 

Bill
The 12 bolt R&P gears are special ground to fit the vette housing. When this was first started by Pepe Estrada in CA back in the early 70's and possibly by Henry's before that, they machined a stock 12 bolt gear set. Even though the gears are ground special there's only so much room in the housing to fit it all. With the larger pinion heads and gears it would push the RG too close to the inside and more material will have to be removed, making it too thin at the radius of the top of the housing. This is one area you have to be careful with. After all the years and 100's of these diff's I have worked on I have only seen 2 housings that were cracked. Neither one was a 12 bolt conversion but rather a stock diff pushed beyond their limit causing a very violent end to them. The impact from either the broken case or gear hitting the upper housing inside radius was enough to break it. That is why it is important to carefully fit these diffs. Now looking over past 12-bolt builds posted here one picture shows where the builder machine cut a clearance groove in that spot for the ring gear. The statement at the time was 030" was removed for a nice uniform cut, which it was. It was also touted that this was superior to way Tom or myself "gouged" them out by hand fitting. Most here thought that was great but it wasn't, was it just another flimflam to fool people or just inexperience. That area is already thin, under .250" on a radius, There is no reason to remove that much material and provide 030 clearance. The RG doesn't grow or heat expand 030 if it did it would be instant junk. Yet many were sold on it.

So that is why Tom offered just 373, 411, or 456 gears. He once had 355's but I recall him telling me that was a long time ago and he wasn't comfortable going that close. There are some out there probably 35-40 years old now but I never tried a 355 and if I did I would have to machine the gears and I don't have a cylindrical grinder. I do have the prints for doing it though.

Reminds me of a recent phone call I got from a Diff shop. The mechanic called me to ask how to fit the posi in the housing which I went over. A week later he called again saying he couldn't fit it. I assumed he was using Tom's gear set and 12 bolt parts but all he had was a stock 12 bolt gear set and posi- won't work like that. Not sure what happened after that.

As I said that is a nice case no doubt but the application is limited and based on my experience with corvette guys really not something a lot will want. I would have to see dimensions of it to see if a taller gear would fit, I don't think it would and you would still be faced with finding a 12 bolt 308 gear set that would need to be machined. That is why Tom was going to have a complete new center housing made that would accommodate the gears but that is a story for another day.

 

Wow, a lot of info to digest. Have to read it a few more times to get a better understanding.
thanks for the info.

Frank.

 

Bill,
The Mark Williams chrome moly case is now 4200 dollars. The Toms 12 bolt case is a modified 4 series eaton to center the ring gear to the housing.
The real answer would be a new housing that accepts standard 12 bolt gears which would solve the problem of not being able to find parts.
Another difference with the 12 bolt gears in stock housing is the 3.73 gears require more clearance then the 4 series. A better cover with some modifications for road racing would also help tremendously. If you want more details give me a call and we can discuss some ideas that I am going to be working on in the near future.
Dave

 

Price is now $4200, and notes say internals not included!

 

$4200 plus shipping- lol

Based on working on these cars for years there will be a very small window of buyers for this part.

Since Tom passed away there are some trying to capture his market, some with good parts others with smoke and mirrors. Prices continue to climb, some of the good parts are gone, witness the recent stop of US Gear production- although the 12 bolt gears made for Tom were not US Gear.

Tom spent time and a lot of money on coming up with a bolt in 12 bolt center. It never happened, not that it can't happen but there are limited buyers in that price range. Most of the restomods go with a newer vette diff setup and won't touch or look at an older unit. A lot of st/strip guys are still running Tom's 12 bolts after years of use or converted to 9" but most corvettes on the road are 10 bolt. All depends on the application.

 

I have trouble wondering why this exists.....who sat there and determined there was a market for this? At this level....you may as well just straight axle/four link the car.....
It would seem to me that this is way stronger than any half shaft could take......help me figure out why?
$700 markup in 2 months is crazy too......how many did there have on the shelf vs. people that buy them?

Jebby

 

That is insane for a diff. Depending on what I find on mine when I open it up. I maybe going a different route entirely for my resto mod. Based on that it is cheaper to switch to a 9" Ford IFS set up.

 

Am I missing something here? Wouldn't this be a better option than Mark Williams C2/C3 posi cases ?
https://www.vividracing.com/detroit-...152579010.html

 

That looks like a nice unit, I haven't seen one to check it but it looks like what Tom envisioned. 33 spline is cool and you would need their axles. Question is are they available? I heard there were some issue with some of the newer versions on the market, not sure if this was one or not. At that price it is less than an iron and if it offers the full line of rations available to the 12 bolts that would be an improvement but still most guys are not spending $5k for a street car under 500hp.

As to the other questions of why, knowing of some of the players, there are several reasons but as I said before some are out to capture Tom's market plus times have changed and will continue to change. Greed plays a big part.

 

Did all 427 have caps or only 435 HP?

 

Vivid Racing is about 5 miles from me, but have never been over there.