Whats a stronger (than stock) rearend , for a 1970 BB ??

[SwaveDave]

Id like to select a stronger rearend to get, for when i need work done on the existing factory one. What do u suggest ?

Thanks, Dave

 

[Tom73]

That rearend ran behind the L88 and the LS6. Unless you are running ten inch slicks and doing 5K rpm clutch dumps you should be okay.

tom...

 

[iron cross]

That rearend ran behind the L88 and the LS6. Unless you are running ten inch slicks and doing 5K rpm clutch dumps you should be okay.

tom...

great answer!

 

[WayneLBurnham]

My First High-End Upgrade...12 bolt

No monster disrespect intended, but this is one of the weaknesses in the vette. The reason those rearends held up to 550+ hp engines was simple: lack of decent tires. They also do grenade. They are quick-acting, lower-rotating mass units, with good limited slip set-ups, but one part that is less robust from a power-input concern than even the units going in other Chevy products.

Dana 36 and Dana 44's are only capable of taking so much power, and that's in essence what vette rearends are.

A strong modern power level big block with grabby modern tires may easily overwhelm these well-balanced but lighter units.

Since the only reason I bought my vette was to be a decent platform for a monster stroker big block I am obsessed with building, I needed to improve this part early, and I did.

It cost a small fortune - about $4K installed for JUST the center section, but I had a custom built 12 bolt differential from
Tom's Differentials in California. They are rated to nominally
1250 ft lbs of torque.

They also off a set of HUGE half shafts to go with it (the 1480 series), which I had to wait on. I couldn't even afford the normal high-strength ones (1350 series), so just had mine checked out and new u-joints put on it. (I will actually have to have part of the new unit changed to use the 1480's later...bummer. I can use their 1350's (or other mfg's 1350-type) without change though.)

I wore out my rear end early and so made this big leap. I only have a weak SB in there now. So this was mainly due to previous owners and age of the unit. In your case, if you drive it hard, you may be looking at a $1K normal rearend every few years or even sooner.

$2800-3500 material cost for an ultimate "bullet proof" answer may be for you too.

 

[woobie1966]

is there a big weight difference between the stock/modified differential? is the modified unit a "bolt in" replacement, or are there other modifications necessary ?
thank
mike

 

[SwaveDave]

Wayne,

What do u think of Crygenically (super cold ) treating the parts in a differential and driveline.??

Dave

 

[woobie1966]

dave, super cooling the parts will increase their strength by changing the makeup of the metal, how much of a difference....im not sure. have you heard of a place doing this work with auto motive parts?
mike

 

[SwaveDave]

Mike,

www.deepfreezecryo.com . Looks real interesting. Dont know his prices though.

Dave

 

[sscam69]

Swavedave

What exactly are you planning on doing with the car. It seems your looking into doing something pretty heavy.

IRS suspensions aren't the best for drag racing for several reasons. One being there are to many weak links.

You can build a strong IRS but its going to cost you a small fortune.

I had looked into this already.

 

[SwaveDave]

The car is used for high performance street useage , primarily. Up here in Northern Illinois., we have some nice country roads where you can see what your car is capable of doing without fear of radar or pedestrians . While i realize that my 255x60 tires are sort of a 'safety valve' from damaging the drivetrain with the h.p/tq im generating...its been a long time since the rearend has been rebuilt plus im way over the limits of the stock rearend and M21 gearbox, im told. I simply want to do some investigating , so i can have a plan when the gearbox, driveline, half shafts, rearend...need repairing/replacing. If i can beef up these components , id like to do so. Does this sound like a sensible plan ??

Dave

 

[KANE]

Sure Dave- you can do it!

I would recommend ordering a Vette Brakes catalog. They have some neat stuff that takes the some of the weaker componets out of load bearing postions in the IRS. Special tie rods, control arms, the like.

Or, you could go with a Ford 9" rear end conversion. Those are BULLET PROOF. If I had a 1200Hp small block I'd do it!

 

[SwaveDave]

Ok, thanks. Ill see what vette brakes has to offer.

Dave

 

[WayneLBurnham]

Externally the TD 12bolt unit is the same

It does seem to be heavier, just from moving it and another one laying nearby around on the floor, but I would imagine this is a matter of a few pounds - possibly up to 5-10, which is tiny on a vette IRS, since that's sprung weight (bolted straight to the chassis). It uses all normal parts except the ujoints hooking up to the inner half-shafts I believe are different, since these become a flange type mount (I guess you call it, rather than the ubolt type deal - well, it changes anyhow )

I would have LOVED a Ford 9" conversion! Couldn't find one. TD was supposedly developing one, but all the others I found were
non-IRS conversions. I understand giving up the enormous advantages of the IRS if you want to do 7 and 8 sec monster drag classes, but not for anything else. There ARE some custom houses who could alter an aftermarket 9" case and the spring mounts and whatnot to make a 9" IRS feasible, but they all apparently are "one-of's" and you could expect $10K+ for such an effort (and possibly months in R&D/testing time from a big specialist.)

Pretty much any time you can do some fancy heat treating and cryo processing, you are as far ahead as when using an untempered cutting edge on a tool versus one well tempered and stress relieved. It's ALWAYS a good idea. I'm more used to cryo treatments in the gun world and they deliver some remarkable improvements there. Peppy Estrada developed early higher-temp single step cryo treatment for his monster axles in the '70's just using dry ice and made them considerably stronger, provided he started with quality stock.

Some have apparently tried the sort-of Porsche/Jag custom conversions made new for street rods by company's like Heidt's, which are usually built around Ford 9". One street rod shop in El Paso I talked to about that, before I found Tom's Differentials, iterally BEGGED me not to do that to a vette though. They are apparently much longer, fore-to-aft, than the vette suspension and you have to do major body and frame surgery to install one of these impressive designs.

VBP has some outstanding driveline upgrades to make the structure capable of much more long term high horse power use without incident than the best stock ever was. They also make excellent front suspensions. Today I just got in their transverse leaf and tubular lower a-frame conversion for mine, to go along with my tubular upppers I installed last year.

That, and reinstalling my all-new PS system, will make a "fun" weekend...

I may go with Guldstrand's 5 link conversion for the rear though, although it's abouyt $2500 and a fair amount of surgery to install over the VBP upgrade set, which is only about $1100 for everything. I am still debating the upper rear control arm addition Tom's (and others) market as that REALLY is just a "disaster containment measure" and NOT a controlling mechanism under normal use and may even limit articualtion a little. I will go with Tom's 1480 half shafts.

You apparently CAN save money on driveshafts somewhat. Vette driveshafts from most authorities are about the last piece to fail since, well, unlike most designs, they don't really DO much - very little movement compared to a "normal" non-IRS suspension with constantly changing main driveshaft geometry.

Whatever you do, look at ALL options first and make wish lists.
Suspension and drivetrain can easily exceed $15K on a jsut decent effort.

Gotta run to work - no chance to proof read! Sorry!

 

[SwaveDave]

Thanks for the info.

Which direction would you go, if, the car was used only on the street , to make it a heavier duty rear ??

Dave

 

[WayneLBurnham]

Sorry for the delay!

BTW, the VBP transverse front spring conversion is GREAT!

I ended up finding a local shop that installed it for me for fairly cheap ($250) so I didn't have to scare myself silly under the car in the driveway on "might-make-it" jackstands. (Yes, I'm a COWARD! )

I had located all the links and everything for you on these items and then LOST it!

From what I can piece together, vette drivelines have the following weak parts, in DECREASING importance:

• Outter Axle U-Joint
• Inner Axle U-Joint
• Outter Axle
• Inner Axle
• Half-Shafts
• Differential Cover, Mounting Bolts and Bushing
• Differential
• Strut (Adjuster) Rods
• Trailing Arms
• Spring
• DriveShaft U-Joints
• Driveshaft

The last five items are either stronger in duration than their counterparts on a "normal" non-IRS suspension or play a support role in not allowing the drivetrain to flex too much under a load and thus placing undue stress on the differential and other key parts.

With your engine specs, you are already well past nearly every engine combination that ever came on a vette. With decent modern tires that have twice the traction of their late 60's and early 70's counterparts, you are already putting far more strain on the drivetrain than the most awesome, under-rated, only-650-ever-actually-built big blocks ever did.

You need maximum effort stuff!

All I can recommend is what I'm putting on mine, which is 1/3 done, although over 60% of the expensive part is complete.

I'd go with the following in order of decreasing immediate need:

• Tom's Differential 12 or MAYBE 10 bolt differential:
  Parts Cost: $2600/$1700?
• Muskegon Brake or Similar Strengthened Rear Cover:
  PC: $150? (might be included in the TD assy, I don't recall)
• Tom's Differential's "1480" 0.135" Axle Kit or Drag Vettes (or
  many vendors) "1350" heavy duty axle kit: PC $2100 or $800??
  (These whole kits include inner and outter 30&31 spline axles, max sized halfshafts and ujoints. I have MOST of the 1350 version, except the halfshafts themselves. I'll have my differential operated on slightly to accomodate the full 1480 kit.)
• VBP "Smart Struts" rear control arms PC: $250?
• VBP Dual Mount Fiber Spring w/ max spring rate (460#?)
  PC: $700 (Also usefull for drag set up - can be raised/lowered)
• VBP Offset Trailing Arms PC: $300
  (These may not work with standard model springs, and the 1480 Axle kit may actually require them to be altered)
• VBP/other 0.875+" Rear Sway Bar PC: $125
  (This is handling, not driveline, but stiffens the whole driveline as well, resisting odd wheel motions. Drags often disconnect these for better "wheel wrap" but that is rough on differentials. I got one only listed in one place in the VBP book - heavier than all their recommendations, but it helped save my car when my rear wheel blew off at 80. These may not work well with the dual rear mount springs or offset trailing arms - or you may need a different model.)
• Drive shaft U-Joints PC: $75 (Probably never need replacing)
• Half Shaft Safety Loops: PC: $200
  (Several designs exist and this is a critical danger in vettes.)
• Drive Shaft Safety Loop: PC: $50
  (Not critical on vettes, but cheap)
• Quality High Strength DriveShaft: PC: $300 (Least Needed)

See why I said you really need to decide early and plan it out?
A LOT of money can go back there where the BEST you will ever know is NO PROBLEMS! Not hardly a SMIDGEN of performance gain, for the price of a high-end crate motor!

I would also consider rigging a differential fluid temp sensor and a cooler due to the price of these pieces and that they lack the circulating fluid of a non-IRS rearend, even though they bolt directly to a huge mass of metal to act as a heat sink (which is lessened considerably with fibersprings.) Just a sensor could probably be welded or epoxied to some piece of the differential casing, but a cooler would require using the drain holes or access points and would best use a pump of some kind, requiring power and making the system more prone to catestrophic fluid loss.

After having the inner bearing on my right rear seize at 80 with NO WARNING and thus lose the entire wheel assembly, I am also concerned with bearing life, grease and temperature control. I might like the whole non-taper system changed, but have found no solid answer to this yet - hopefully it was just a fluke.

 

[SwaveDave]

Great info. Thanks.

Dont think im going to pop for the entire full blown buildup of the rear just yet...but im going to print off what youve told me here. Do u have any experience on Eatons Differentials , with thier carbon fiber internal ??? $470 PC .

Dave

 

[WayneLBurnham]

Eaton C Fiber Guts?

Wow.

No I hadn't heard of them until now.

They sound very interesting. On the other hand C-fiber (and kevlar, fiberglass, ceramics and even high strength aluminum and titanium) structures are remarkable for their tensile strength, elasticity and this and other properties per unit weight. For ultimate volumetric strength, hardness and toughness, ferrous alloys are really the ultimate (at least in commercially available materials.) Also more ferrous materials have failure modes less catastrophic than some of these new high strength ones - twisting and deforming rather than shattering, for example.

Some of those nifty new materials get used in places they really aren't suitable, but in other areas both increase strength and reduce mass - including rotational mass. I would think the external parts, like the case, would be more suited to fiber replacement - or large rotating masses like driveshafts and halfshafts, but Eaton is a great name and this may be a major step forward.

I have had Eaton differentials and misc. gears and such in several vehicles, but never ones made of carbon fiber, and this is my only vette so far.

 

[SwaveDave]

Yes...i learned this info on the carbon fiber from the Eaton Techline. Go to thier website and take a look. Tell me what you think after you do. Thanks for your input. Looking forward to hearing what y ou think .

Dave

 

[Jack]

There's an IRS setup being produced using Ford 9" center. I believe the company is called "Dutchman" or "Dutchman's". I recall it goes for about $4K. Someone at Tom's diffs probably has lowdown on it.
JACK:gap

 

[WayneLBurnham]

I bought too early then!!!

Damn! I would ABSOLUTELY go with the 9" Ford over the 12 Bolt!!! Those things are nearly indestructable in anything that weighs under 5 tons!!! Well, I guess I bought early....if I ever get to build my "oberstfrankenbigundblocken" that was the whole reason I ever bought the vette in the first place and I blow up the 12 bolt with it, I'll replace it with that 9"!

I'll have to go search for that and look at the Eaton C-fiber 'site.

Tom's was definitely mute about this product as of last November - obviously because they either it wasn't out yet or more likely because they weren't selling it. They did mention they had been playing with one themselves in part because strangely the small but steady demand for their high-strength 10 bolt and mutant 12 bolt units, although both available for 20+ years, was actually increasing in recent years, despite the vastly fewer modified C2-C3's that are out there now in high-end racing.

There is a "Dutchman" Fabricators who make frame and suspension sections for streetrodders, like Heidt's and FatMan. They don't list this item in their ads in Rod and Custom and StreetRodder, but maybe have just developed it. I'll have to look just because I hate myself and like to measure how much milk I spilled...

.