Engineers and examples: 2 crossmembers needed with 4 speed Atlas or Titan and NP205

[nvrstuk]

So a buddy just bought an ibox and I'm thinking of going Titan... so with a Ford 4r70W, aTitan and 205... one or two rear crossmember (rear engine mounts)??

Atlas evenm for their 4 spd recommends a single crossmember (usually stock at the rear of the trans)

Do I need 2 cross members for running a Titan with my trans and 205 or is running just a beefy single transmission mount under the transmission tailshaft (stock mounting point) just fine? I really don't think the additional 20lbs or 205 weight determines if it needs an additional crossmember over an Atlas at 20lbs less... to me it's the extra 5.3" of ballast hanging out past the end of the rear mount and hanging on the tailshaft of a 4R70W.

I have 710ft lbs of torque and 40" tires. I don't bounce like crazy when rock crawling but I use my rig...

I've gotten some great suggestions for what I will have to do if I go with two crossmembers. If I have to go with 2 crossmembers: even weight on both, having the mounts designed as similar as possible so torque transferred thru each mount is as equal as possible...but do I need TWO?

I'm just concerned about another 5.33" extending the 205 out farther w/o an additional crossmember.

Here's my experience with them.

I ran a ZF/203/D20 for over 12 years and ate Dana 20's for lunch and used 2 cross members w/351W

I then ran a 4R70/KluneV/Atlas combo with 2 crossmembers w/o incident for about 6 yrs w/418 stroker

I've run a 4R70W/KluneV/205 combo with 2 crossmembers w/o incident for the past 2 yrs with 418 stroker

I now run a 4r70W/KluneV/205 same combo but with a 460 SBF


I plan on running a 4R70W/Titan/205 combo and thought I'd ask opinions and what HAS or HASN'T worked for wheelers... and why??

TIA

 

[nvrstuk]

Here's what Atlas says about "auxillary mounts"... this is off their website.

"There are some circumstances where an auxiliary mount may actually conflict with the primary support system and cause damage to the Atlas.

I heard an auxiliary mount will void my warranty, is that true? It is a question that really is impossible to answer. There are numerous factors in the design of vehicles. Typically vehicles that allow for more frame flex require less rigid mounting systems. An auxiliary mount under these circumstances may cause damage especially on the rear nose cone of the Atlas. Tube chassis vehicles that characteristically have rigid mounting systems and limited frame flex are unlikely to cause damage with an auxiliary mounting system. In these vehicles, the benefits may out way the risks of damage."

 

[gunnibronco]

Following. I've read similar opinions to run only one crossmember. I have a seriously stalled out upgrade to a ZF5 & 4 speed Atlas. I have 2 crossmembers built. But wonder if I should abandon the trans crossmember.

I'm finishing up a new garage, then I'll get back to work on my Bronco. Hope to have it back on the road by next spring.

 

[nvrstuk]

Got a very detailed response from Kris at NW Fab who builds/markets planetary gear reduction units...like the ibox, Titan, etc. His response was to definitely and without a doubt to use 2 crossmembers. He felt the weight and torque of the Titan (only 5.33" long) with the 205 (only weighs appr 20# more than an Atlas) is too much weight and torque hanging off the rear of the trans-whether it's an auto or manual.

He stressed the importance of making the two mounts as close to identical as possible. Meaning, they should be built with the same type and style of bushings, with them located in the same location. The weight on both cross members should be equal.

I'll post up what I end up with on my 14 bolt build thread... and will be asking for input...

https://classicbroncos.com/forums/showthread.php?t=297561

 

[lars]

Brian, I'm actually clueless about the exact gearboxes that you have in your combo because I haven't been paying attention for too dang long. But..

What your are dealing with is what a structural engineer would call a statically indeterminate problem. 3 point define a plane. With two crossmembers, you have more than that, and so the math becomes more complicated. That said, the math is, at least somewhat, probably unnecessary as long as you have an intuitive grasp of the problem.

Based on your description I can understand why you (or anyone) would want an extra crossmember. The design challenge is to assure that they don't fight each other. How simple! Except, as you know, not. Without knowing anything else, I'm thinking you might be able to mock the whole thing up, then get out your creeper (and if you are like me, a bottle or two of really good IPA) and stare at it for awhile. Then adjust as necessary before committing to metal.

 

[gunnibronco]

Got a very detailed response from Kris at NW Fab who builds/markets planetary gear reduction units...like the ibox, Titan, etc. His response was to definitely and without a doubt to use 2 crossmembers. He felt the weight and torque of the Titan (only 5.33" long) with the 205 (only weighs appr 20# more than an Atlas) is too much weight and torque hanging off the rear of the trans-whether it's an auto or manual.

He stressed the importance of making the two mounts as close to identical as possible. Meaning, they should be built with the same type and style of bushings, with them located in the same location. The weight on both cross members should be equal.

I'll post up what I end up with on my 14 bolt build thread... and will be asking for input...

https://classicbroncos.com/forums/showthread.php?t=297561

Thanks for the update.

 

[nvrstuk]

Yeah I think the creeper part is going to be critical part of my design!! lol

 

[73azbronco]

build a cage supporting both tranny and transfer, effectively making them one unit, then devise a mount from that to the frame. Walla. By cage I mean no poly bushings, use solid metal to metal on the cage, then poly or rubber from the cage to the frame. Walla again.

 

[nvrstuk]

Good idea...I will spend some creeper time today...

 

[Digger556]

A single mount is ideal, however it needs to be close to the transfercase. Best case, you find a way to attach it to the range box between the trans and transfercase.

The problem many people fail to understand (not saying this is you) is that adding more than 3 discrete mounts over-constrains the drivetrain and opens the potential for frame flex to damage the drivetrain.

I like the idea of making a sub-frame that the range box and t-case sit on, but it will need to be pretty rigid. Steel is still flexible, albeit much stiffer than rubber. This is also a case where soft isolators will help prevent drivetrain damage. OE type mounts are best.

 

[Yeller]

^^^^ Digger is right on target. Single crossmember with a central mount. No matter how well matched 2 crossmembers are it’s all out the window when you twist up the suspension which does flex the chassis. That flex will find the weak link and break it. Can’t count the number of broken bell housings, adapters, motor mounts and adapters that were directly caused by the mounting being too rigid that I’ve witnessed

 

[nvrstuk]

Exo-cage I think is out... lack of space. I think it's the best but I just don't see how to make it all fit/work yet.

I think I can catch 5 of the bolts that wrap around the rear output shaft housing to the main case on the 205. IF I do this I will have both mtr mounts centered directly under the center line of the crank/trans/doubler/t-case.

I'm thinking then I'd make an identical cross-member to my current trans mount with the same durometer rating bushing on each end (or in the middle). A buddy mounted twin cases with mounts under the centerline of the trans-tcase for the same reason.

I've run dual crossmembers for decades and will implement the new design into place hopefully to avoid problems in the future.

Having problems coming up with an exo- "cage" heavy duty enough to not flex but still fit in the contraints of a Bronco... lol

 

[Montoya]

Having problems coming up with an exo- "cage" heavy duty enough to not flex but still fit in the contraints of a Bronco... lol

Maybe the IPA isn't the right drink...;D

 

[WILDHORSES]

Both of our 4 speed Atlas run single cross member.

NV 4500 with 4 speed Atlas (stuck in 5th gear right now) in the Mare many years, many trails.

Reveres valve body C4 with Atlas 4 speed in the Bling has worked great less time, less trails. Under the knife fixing fuel rail leak.

Always check for loose hardware pre and post trail inspection. Saved us when we did and cost us when we didn't.;D

Jim

 

[gunnibronco]

Both of our 4 speed Atlas run single cross member.

NV 4500 with 4 speed Atlas (stuck in 5th gear right now) in the Mare many years, many trails.

Reveres valve body C4 with Atlas 4 speed in the Bling has worked great less time, less trails. Under the knife fixing fuel rail leak.

Always check for loose hardware pre and post trail inspection. Saved us when we did and cost us when we didn't.;D

Jim

Where does the cross member support the drive line? At the back of the Atlas or farther forward? Thanks

 

[toddz69]

Where does the cross member support the drive line? At the back of the Atlas or farther forward? Thanks

In front of the Atlas underneath the adapter between the trans and t-case. My single mount crossmember has been doing fine since early 2007 (I have 4 speed Atlas #21). I don't have a ton of horsepower or do hardcore crawling but mine bounces down a lot more rough dirt roads than most rigs do.

Todd Z.

 

[CW72]

I’m in the process of building a SBF 302/6R80/Magnum/205. It was advised by ORD to use just the single built in and supplied mounting parts on the bottom side of the magnum box. (It’s at the rear of the case right where it meets the input of the 205. The mount they give you is a few pieces of steel and some factory 205 bushings. You’re to assemble it in whatever configuration fits your truck.


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[nvrstuk]

CW72...have you checked into the Titan/205? Just curious if you've noticed the Titan doubler is only 5.3" long w/o any adapters needed and a 34 spline output shaft.

Seems like most run a single crossmember...

I don't think I would just run one at the back of the 4r70w but even at the back of the 205... L O O O O N G span from the frt engine mount to the middle of the 205... 45" ???between them? (Very rough guess).

KluneV comes with a 1/4" thick mounting ring with a "foot" to use as a rear mount... I would feel comfortable mounting where Todd mounted his or where the Klune has a "foot mount"...but not at the back of the 205 or at the end of the trans...

I need to refresh how the 205 mounts stock again.

 

[nvrstuk]

Todd- so you are saying the adapter btw the Atlas and your trans has a mount?

 

[CW72]

CW72...have you checked into the Titan/205? Just curious if you've noticed the Titan doubler is only 5.3" long w/o any adapters needed and a 34 spline output shaft.

Seems like most run a single crossmember...

I don't think I would just run one at the back of the 4r70w but even at the back of the 205... L O O O O N G span from the frt engine mount to the middle of the 205... 45-50" between them? (Very rough guess).

KluneV comes with a 1/4" thick mounting ring with a "foot" to use as a rear mount... I would feel comfortable mounting where Todd mounted his or where the Klune has a "foot mount"...but not at the back of the 205 or at the end of the trans...

I need to refresh how the 205 mounts stock again.

I’ve seen it yeah, the magnum is a little less than an inch longer with the same shaft. I needed to run an adapter behind the 6R because it’s not a standard 6 bolt round. It’s the mount advance adapters makes for the atlas, and does have its own mounting holes. I may or may not tie this into together, the spacing between the mounts is roughly 7-8”.

It’s what I’ll be trying first and seeing how it goes, using the magnums mount. Sounds very similar in style to the “foot” you’re talking about on the Klune. There’s a pretty good picture on their website of the breakdown of parts that shows it.


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