Wheelhop with big power and T56 eating rear end gears

Hi all, it's been a while. Had 2 major surgeries last year and the Sleeperwagon sat for quite a while. Anyhoo, here's the issue- I stroked the LT1 and did some major upgrades. It now puts out approx 500+ hp NA, and I have a 550hp nitrous system with jets reduced to 250 that I haven't yet used because I keep breaking everything without it. I put a T56 trans in it with McLeod twin disc clutch and faceplated gears, a sedan rear end (poor man's narrowed axle), 4" aluminum driveshaft with oversize u joints, Moser chromoly axle shafts, Eaton posi, 4.11 gears, Wilwood rear discs, Camaro SS 20" wheels, and a bunch of other stuff. The issue is that when I do burnouts I get severe wheelhop, and the stress of slipping and grabbing repeatedly keeps grenading the ring and pinion gears. I blew up a set of 3.73s, went to 4.11s and the Eaton and then toasted the 4.11s. I put new Richmond performance racing gears in it but now I'm afraid to roast the tires. I'm not sure if the problem is the factory air shocks, flimsy OEM control arms, tired rear springs, etc. Where should I start to get rid of the problem? I also installed a line-loc on the front brakes but the gear failures have all happened without it. Any ideas?

Start with upgrading the rear control arms/bushings and go from there. Typically wheel hop is because of loose/soft connections that deflect under load, then when the tires break loose they move back because the load isn't there anymore, rinse, lather, repeat.

There are lots of control arm/bushing upgrades available, but with the GM 4 link in the rear it relies on the bushings being soft for the suspension to articulate properly. The best solution I've seen is a large spherical joint on the ends of the upper control arms.

For testing purposes and not blowing up more parts, start by trying to do burnouts in the rain/wet. If it starts to hop, get out of it. Just because it works well in the wet doesn't meant it will work in the dry but it's a good start.

Yep on the previous post, and especially the binding possibility of going to tight on the bushings.  

Also get a good look at your pinion  angle and transmission spline engagement depth.  Bad angle or pinion depth that bottoms out under axle wrap can make for bad hop. Especially with the trans and driveshaft changes, those things are really easy to have happen.

Also keep in mind that the sedan rear doesn't actually "fit" under the wagon. Control arms are in a bind and the springs aren't sitting correctly. It's one "mod" that I recommend everyone stay away from. The wagon uses a heavy duty rear end for a reason.

Proper wheel specs are a better option. Can also notch the frame on these cars to clear fat tires.

To be clearer, I relocated all the brackets to the position of the wagon axle and re-welded. The primary reason for swapping axles is that I couldn't find chromemoly axle shafts or a disc brake conversion that fit the outer bearings on the wagon axle. Maybe I didn't look hard enough

Sleeperwagon wrote:

To be clearer, I relocated all the brackets to the position of the wagon axle and re-welded. The primary reason for swapping axles is that I couldn't find chromemoly axle shafts or a disc brake conversion that fit the outer bearings on the wagon axle. Maybe I didn't look hard enough

Just have to do a little machine work to install the sedan disc backing plate on the wagon axle. The axles are of course a different story, though I know that Moser can build custom axles for these wagons.

For a very poor man's solution in past, at least on the leaf spring cars, was to put an adjustable or damped pinion snubber on them to prevent the axle from being able to wrap too much. Back then it was just an adjustable pin and tubes setup with a hard rubber stop on the top or bottom. They certainly weren't the best or anything like going to a true 4 link, track bar and coilovers, but was a tiny fraction of the cost and could make it so you could get down the strip without breaking anything most times. Staggered shocks also helped some cars.

I don't remember ever seeing snubbers on the GM cars, but I didn't deal much with them back then either so it certainly might have been done.

Intentional bushing binding and odd geometries must have been pretty common in the past as my 1970 Dodge challenger had one of the weirdest real leaf spring setup I have seen. They were asymmetrical with the spring ahead of the axle shorter than the rear to prevent spring wrap and they were also splayed out at the rear shackle compared the front spring mounts which was said the prevent axle side to side motion like a track bar, but of course the did bind and counted on the shackles to move a bit to accommodate the binding. Even with 600hp and torque that car never hopped, but I never had it on sticky slicks either.

Does anybody have any experience based recommendations for aftermarket control arm brands? I see that there are several but I'm not sure if they are all still in production. Also, are sedan lower control arms interchangeable, or are they different? I had to install a 1/4" spacer between engine and transmission to accommodate the hydraulic throw out bearing and twin disc clutch, so I'm not averse to using longer control arms to regain driveshaft travel

What is your rear sway bar situation? This will narrow things down for what your rear control arm options are.

Rear control arms are the same between wagon and sedan. Placement is different as noted above.

No sway bar in the rear. The car is built for drag racing, not cornering. If I eventually add one, I have a full manual/ cnc machine shop, so I can modify brackets or control arms as necessary

In that case with your machining/fabrication capabilities, I'd recommend making your own rear control arms with "spherical" joints.

See this thread for more info...

https://www.impalassforum.com/threads/bmr-vs-umi-rear-lcas-with-roto-joint-modifier.1319010/#post-12125547

Wow, that thread has a wealth of cool ideas in it! I think I may indeed make my own. I like the idea of adding a watts link but don't enjoy the thought of all the added weight doing that AND a sway bar. A frame to axle sway bar system seems better than mounting to the control arms as well

Sleeperwagon wrote:

Does anybody have any experience based recommendations for aftermarket control arm brands? I see that there are several but I'm not sure if they are all still in production. Also, are sedan lower control arms interchangeable, or are they different? I had to install a 1/4" spacer between engine and transmission to accommodate the hydraulic throw out bearing and twin disc clutch, so I'm not averse to using longer control arms to regain driveshaft travel

The distance between the trans and rear is further at the compressed position of the suspension than at ride height.

Stock rear arms , bushings , theres a place start. As you are a fab shop building them should not be an issue for you
Nothing wrong with big rear bars at the drag strip.
Being you have done a T56 how is you crank angle vs pinion angle.
While I do not make the power you do on power adders I have never had a wheel hop issue .
The car will twist 30 axles at will though.
To that end I have gone to 33s.
Good luck with your project.

Sleeperwagon wrote:

Does anybody have any experience based recommendations for aftermarket control arm brands? I see that there are several but I'm not sure if they are all still in production. Also, are sedan lower control arms interchangeable, or are they different? I had to install a 1/4" spacer between engine and transmission to accommodate the hydraulic throw out bearing and twin disc clutch, so I'm not averse to using longer control arms to regain driveshaft travel

a low budget mod would be to weld the stock arms up with a plate on the bottom to box them.  would definitely stiffen them up, but for the amount of power you are making, I'd look to the aftermarket as you've already spent a ton of $$$ lol.

I don't think it would apply here, but my sisters 5.0 Fox body mustang had a kicker shock to help dampen axle wind up, but If I recall that had leaf springs in the rear. I just recall the horizontally mounted shocks over the rear axle...

94Woody wrote:

Also keep in mind that the sedan rear doesn't actually "fit" under the wagon. Control arms are in a bind and the springs aren't sitting correctly. It's one "mod" that I recommend everyone stay away from. The wagon uses a heavy duty rear end for a reason.

Proper wheel specs are a better option. Can also notch the frame on these cars to clear fat tires.

Looking at a wagon this weekend. How is the wagon rear more “HD” than the sedan rear? Are the component mounts the same and a different width?

Thanks!

ShgnWgn wrote:

94Woody wrote:

Also keep in mind that the sedan rear doesn't actually "fit" under the wagon. Control arms are in a bind and the springs aren't sitting correctly. It's one "mod" that I recommend everyone stay away from. The wagon uses a heavy duty rear end for a reason.

Proper wheel specs are a better option. Can also notch the frame on these cars to clear fat tires.

Looking at a wagon this weekend. How is the wagon rear more “HD” than the sedan rear? Are the component mounts the same and a different width?

Thanks!

The sedan rear end is a small rear end designed with the lighter car in mind. The wagon is heavier and basically has a pick up truck rear end under it. Larger axles, wheel bearings. Spring perches and control arm mounts are in different places because the wagon frame is wider in the back than the sedans are. I've cut these cars up and there is a LOT of sheet metal back there that doesn't exist on sedans, not to mention all the glass, seat, carpet, trim, etc. These things are heavy back there and have a rear end intended for it.

That said, do people shove sedan rears in these wagons and never have an issue? They sure do. I would never do it though because rear discs aren't that important to me. Sedan discs can be adapted to the wagon rear anyways. Not everyone does it for that reason but the majority of them do.