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! Ok guys I need to know at what level of horse power I need to worry about the rear end breaking?
2 How much H/P/torque can a stock 1330 U joints and a drive shaft take? (I have to shorten the stock one.)
3 Is there a aftermarket for the rear ends? What companys?
4 What parts fell? I/E the housing, ring and pinion, and such.
The car is a 1972, so it doesn't have the dana center section. I'm using a 4l80E trans so, no banging 2nd gear @8000. It will be street driven only, no track days for this one . Any help/stories wound be great. I want to here the good, the bad, and the ugly.Show pictures if you got um.
1-Ok guys I need to know at what level of horse power I need to worry about the rear end breaking? You can break a diff with 200hp and enough abuse. HP/TQ is only one factor of the equation.
2 How much H/P/torque can a stock 1330 U joints and a drive shaft take? (I have to shorten the stock one.) The driveshaft is less likely to break, than the 1/2 shafts with 1350- again same things apply as to the diff.
3 Is there a aftermarket for the rear ends? What companys? Yes, there are, some are very good conmen, others are dreamers with false claims, do your homework and learn about these diff's on your own. If you rely on inexperienced advice, names alone, or online claims you will most likely overpay for work that can be anywhere from plain bad to average stock, at best. If you are planning on doing the work yourself you can save money but to do the work right you need to have access to machinery, equipment, experience, and measuring tools. I have helped a LOT of people do this over the years. However, just a note for those doing this at home, some people are cheap and expect me to provide all my experience and knowledge for them after they buy parts/services elsewhere, so that killed the extent of time I pass along now. Please call those you buy parts from. Many things I do you will not get elsewhere, and those procedures are no longer given out. Hope all understand. This is not a solicitation, just an explanation and usually only affects those looking for the best work for the lowest price.
4 What parts fell? I/E the housing, ring and pinion, and such. Ring gear bolts, clutches, posi cases, cross shafts, axles, and gears- pretty much anything inside. How they are prepped and fit make a huge difference in the life of the parts.
How's this for a 375hp SB diff, 4 speed, and abuse?
NOTE- We ran those safety loops. They look good until needed, when a joint broke the loop broke at the weld. Look to Tom's for better loops or fab up your own and mount them in the center of the shaft not the ends.
NOTE- We ran those safety loops. They look good until needed, when a joint broke the loop broke at the weld. Look to Tom's for better loops or fab up your own and mount them in the center of the shaft not the ends.
No kidding? Maybe I could beef them up at the welds. Thanks for the info.
Thank you for the Very useful information. Keep it coming. Do they make a 1350 pinion yoke, and axle shafts with 1350's wheel side to. I would love to have 1350's everywhere. like a kit
Treat them right and they’ll last a long time. Though with big, sticky tires and hard launches, even a mild small block can do this:
This unit lasted me since ‘09, I’m pretty pleased with that.
Well thank god I dont have big sticky tires, a 4,5,or,6 speed. Or a transbake auto, just a 4L80E with a 3000 stall No hard launches just 40 to 50 mph rolling burns.
No kidding? Maybe I could beef them up at the welds. Thanks for the info.
No kidding
I don't have an axe to grind but after two such failures I stopped using them. Never had that with Tom's loops or those guys fabbed up. We have a 6 link as well, it is ok but the same type of loop was supplied. Take it for what it is, nothing more.
There are some interesting things in this picture, see them?
Traction is the key. If it spins a lot....things last a lot longer.
Funny story to illustrate....my buddy has a 4 speed '65 which has had several engine combos over the years...from mild 327's/350's to the current aluminum headed/solid roller 388". He flogs it every time he drives it.
He broke numerous diffs, halfshafts and outer stubs with the milder engines. He always told me how strong those engines were since he was breaking stuff on plain 'ole 255/60 BFG street radials. I told him it was just the opposite....he didn't have enough power to spin the tires!!
Since installing the 388" engine......he's pounded it constantly for 10+ years and hasn't broken anything since. But it smokes tires forever...which he enjoys!
It's only been to the track twice. First time it broke on the line on first launch with one of the mild engines. 2nd time out with the 388".... he spun the tires all the way into 3rd...and crossed the finish line in 3rd gear with 3.36 gears. It ran 12.0's@116 MPH....so definitely a low/mid 11 sec car with traction...if it didn't break anything!
Well thank god I dont have big sticky tires, a 4,5,or,6 speed. Or a transbake auto, just a 4L80E with a 3000 stall No hard launches just 40 to 50 mph rolling burns.
The damage I show is with street tires. A stock or stock rebuilt diff will not hold up with abuse. Same for the joints or stock outer axles.
No kidding
I don't have an axe to grind but after two such failures I stopped using them. Never had that with Tom's loops or those guys fabbed up. We have a 6 link as well, it is ok but the same type of loop was supplied. Take it for what it is, nothing more.
There are some interesting things in this picture, see them?
I see the loop is still intact, but holding bracket weld broken. Top holding bracket seems to be broken as well. It didn't contain the half shaft completely, looks like both ujoint's broke or did the outer break and then that broke the inner or visa versa?
However, I don't see damage to surrounding items from a flailing half shaft. So maybe a lot of the energy was dissipated through the loops, sacrificing the loops in the process? What kind of RPM or speed did this happen?
So what I'm taking away from this is, the factory rear end is kinda weak. So what can you guys tell me about a 12 bolt IRS.Who sells parts to do this?..........What I have is a car with a 295 50 15 hankook 400 tread ware tire. A automatic with stall and, as the "I'm Screwed if it gets traction" we have the 750 hp the motor makes. Putting a straight axle in is not a option.
So what I'm taking away from this is, the factory rear end is kinda weak. So what can you guys tell me about a 12 bolt IRS.Who sells parts to do this?..........What I have is a car with a 295 50 15 hankook 400 tread ware tire. A automatic with stall and, as the "I'm Screwed if it gets traction" we have the 750 hp the motor makes. Putting a straight axle in is not a option.
750hp takes out the 10 bolt pretty much. I do have some 10 bolt I built in that power level, but I don't recommend it as abuse will break the case.
12 bolt vette conversions have been Tom's Differential setups for 40 years. Those, like myself, that build them use Tom's parts. I am building a 12 bolt 1480 now in fact. Unless you want 456 gears you're out of luck as there are no more 373 or 411's left, all been sucked up by some racers. It is unknown if anymore will be made, they are special grind. Not going to a solid 9", then the 12 was the one to use.
There are some 9" IRS conversions, I heard of some QC issues with them but can't confirm that. They are well over $10k now.
Finding a used Tom's diff is difficult, guys don't sell them typically.
I see the loop is still intact, but holding bracket weld broken. Top holding bracket seems to be broken as well. It didn't contain the half shaft completely, looks like both ujoint's broke or did the outer break and then that broke the inner or visa versa?
However, I don't see damage to surrounding items from a flailing half shaft. So maybe a lot of the energy was dissipated through the loops, sacrificing the loops in the process? What kind of RPM or speed did this happen?
Dead hook at the track, about 500-550hp, drag radials if I recall correctly, manual trans. I can only give my opinion on the loops. If I wasn't so busy, I would make my own. Since time is used for other things, Tom's would be my first choice given I have now used both styles. Luckily there was no glass damage, the car shut down right away. The loop failed in my opinion, sacrificial maybe. Both inner and outer joints sheared- solid Spicer joints. I think the shaft just dropped down but yes, the loop stopped it initially. The welds are not impressive at all, appears to have no penetration. Almost every time I go with someone else's work I regret it.
I see the loop is still intact, but holding bracket weld broken. Top holding bracket seems to be broken as well. It didn't contain the half shaft completely, looks like both ujoint's broke or did the outer break and then that broke the inner or visa versa?
However, I don't see damage to surrounding items from a flailing half shaft. So maybe a lot of the energy was dissipated through the loops, sacrificing the loops in the process? What kind of RPM or speed did this happen?
I would rather focus on making the weak links not weak anymore. so the straps should not be needed. If nothing is pushed to beyond the failure point. If this will always going to be a problem I will just build a set.......... GTR1999 You call the rear end a 10 bolt is it close to the 7.5 10 bolt chevy in strength? Is the toms 12 bolt, just a cast center section of the 12 bolt chevy rear end,,,, for the c3 vettes but with 12 bolt rear end internals, and stub shafts. Sorry for the newbie questions. I have a background in drag/street racing, heavy on the building/ fabbing what I part I need. Im new to the C3 thing and finding out the worries of making a high horse power C3 live. I'm lucky the car will never be raced. not drag raced, not auto crossed, maybe a 60 or 70 mph roll on the highway. This car will be a cruiser with the ability to do a long burnouts at maybe 40 mph or so.
Last edited by gearheadib; Sep 26, 2023 at 10:08 AM.
The 12 bolt conversion is a modified stock Vette carrier with 12 bolt guts installed. It takes some machining and the correctly made or modified gear set.
Tom learned the 12 bolt conversion back in the early 70's when he worked for Pepe Estrada at a gear shop in LA area. When he purchased the business in 1975 he really got into the development of the conversion and revised it several times over the years. I have rebuilt his early designs and they were still in good shape 40 years later. I know how to build them the old way, as those guys did 50 years ago. It takes more machine work and the cost goes up a lot more.
Tom had the gears made to his spec, they were a bolt in. The housing is a stock wide type, 67-79 only. It has to be opened up to clear the ring gear. The posi is an Eaton or a spool. The Eaton is not a stock 3 or 4, it is a 4 I have to machine. ALL the parts have to be hand fit and it takes me 55-60 hours to build one. There are some who offer lockers as well, it's not the case that is the issue it is getting the gears.
There are others, not a lot, out there that offer them. Some of those "works of art" I have seen. They failed in short order because "corners were cut" in the work. Some guys on here have them, they went cheap to save a few hundred and the conman builder took their money, cut corners inside, and the diff failed. I have the pictures of some of these failed 12's for the doubters out there.
These 12 bolts have a history of success for the past 50 years. However, all those you find online today - ebay, Drag Race vette vendors, known vette vendors, all used Tom's gears. If they know how to mod gears, then they might still offer them. Some of those places have called me for help on how to build them, kind of makes you wonder what they're selling? And no, if anyone wants to know how to cut the gears, I am not disclosing that information. I am tired of others copying my work, it's that simple.
You can call Tom's directly to get current status. Tom is gone now but his wife still runs the business. Maybe they will offer the gears again if there is enough interest but given the fact it is a specialty build, limited customer base, and very expensive overall, that might not be the case.
How Much Horse power
