Shim the K Member to modify driveline angles?

[XH29N0G]

I have a Tremec TKO 600 that is tail down.  I believe the correct fix would be to take the interior out to modify the tunnel more that than it has been modified and then shim the tailshaft.  I just ran across some other threads where people have shimmed the K Member by 1/2" to lower the engine.  I think that would also help my situation and am writing to ask members for their thoughts on the possibility.  I am aware that it will affect the suspension.   

[c00nhunterjoe]

Possible, yes, but i would modify the tunnel and raise the tail. Dropping the k frame 1/2" would PROBABLY still leave enough adjustment in the cams but will most likely put a bind on the torsion bars imo.

[XH29N0G]

Thanks.  Not what I hoped to hear, but the tunnel modification has been the suggested fix, and probably for a reason like you describe. 

[c00nhunterjoe]

Have you measured your driveline angles? How far off arr they? I assume you have a vibration problem?

[cdr]

I did it .5 inch, it works great!!!! i have an a518 overdrive & my drive line is where it should be now, car drives the same, the torsion bar adjuster is in about the same place as before. i used alum shims, shim it & do an alignment.  the bars are not in a bind,  a lot of others have done this. 

[Kern Dog]

The K member bolts are a tapered seat design. They properly locate the K member to the frame rails. If you use spacers, you effectively lose the self guiding feature of the taper in the bolts. Driven hard enough, the k member will shift around without the factory point of connection/location.

[cdr]

The K member bolts are a tapered seat design. They properly locate the K member to the frame rails. If you use spacers, you effectively lose the self guiding feature of the taper in the bolts. Driven hard enough, the k member will shift around without the factory point of connection/location.

so you have done this & the k frame moved ?

the factory hemi super stock dart had k frame spacers.

[Kern Dog]

Factory:
You think that they may have tooled up modified versions of the k member bolts? I bet they did. Did you? 

[firefighter3931]

I have 1in K Frame spacers on mine and it's been that way for several years now. From an alignment perspective ; dropping the K-frame actually improves bump steer. 

I did it for increased hood clearance to fit the 572 under the stock hood....the bump steer was an added bonus. Alignment is fine. The Black pig has been 130 mph down the track and runs straight as an arrow ! 


Ron

[cdr]

I have 1in K Frame spacers on mine and it's been that way for several years now. From an alignment perspective ; dropping the K-frame actually improves bump steer. 

I did it for increased hood clearance to fit the 572 under the stock hood....the bump steer was an added bonus. Alignment is fine. The Black pig has been 130 mph down the track and runs straight as an arrow ! 


Ron

& yes it also helped bump steer on mine.

[XH29N0G]

Thank you everyone.  I have some questions about the taper of the bolts. I interpret this to be a shoulder on the bolt. For those who have installed shims, is there advice for addressing this?  (I just scanned through the 1970 FSM and don't see where the K-member is described, but will continue looking).  I am not sure this is the fix I want to do, but am considering it since I am not driving the car and itching for the weather to get better.  What I read is that all four connecting points have been shimmed (1/2 inch to 1 inch) by those who have done it, and no shims are needed elsewhere to make things clear.


[C00nhunterjoe: I have a slight vibration at 70-80 mph when going down hill - no vibration on acceleration.  I measured my driveline angles a while ago.  If I recall correctly, the tail of the transmission is down by 4 degrees.  The vibration was very pronounced before I raised the nose of the differential to about 2 degrees up.  - I know in the nose is supposed to point down.]   

[Charger-Bodie]

If you try 1/4 shim similar to the 68 hemi dart , you can still use the original bolts. I've done this a few times now with zero negative results.

[cdr]

If you try 1/4 shim similar to the 68 hemi dart , you can still use the original bolts. I've done this a few times now with zero negative results.

when you drop the k down 1/4 it moves the end of the tail shaft UP a lot more than 1/4.

[cdr]

Thank you everyone.  I have some questions about the taper of the bolts. I interpret this to be a shoulder on the bolt. For those who have installed shims, is there advice for addressing this?  (I just scanned through the 1970 FSM and don't see where the K-member is described, but will continue looking).  I am not sure this is the fix I want to do, but am considering it since I am not driving the car and itching for the weather to get better.  What I read is that all four connecting points have been shimmed (1/2 inch to 1 inch) by those who have done it, and no shims are needed elsewhere to make things clear.


[C00nhunterjoe: I have a slight vibration at 70-80 mph when going down hill - no vibration on acceleration.  I measured my driveline angles a while ago.  If I recall correctly, the tail of the transmission is down by 4 degrees.  The vibration was very pronounced before I raised the nose of the differential to about 2 degrees up.  - I know in the nose is supposed to point down.]   

on a street driven car the trans & pinion should be parallel, up to 2 deg down from the trans

[c00nhunterjoe]

I have 1in K Frame spacers on mine and it's been that way for several years now. From an alignment perspective ; dropping the K-frame actually improves bump steer. 

I did it for increased hood clearance to fit the 572 under the stock hood....the bump steer was an added bonus. Alignment is fine. The Black pig has been 130 mph down the track and runs straight as an arrow ! 


Ron

A full inch? Wow, thats impressive. What did it do to the tailshaft? Did you have to modify to lower it as well?

[Kern Dog]

I don't see how this can affect bump steer since everything is bolted to the K member anyway. Bump steer is  the result of differing arcs of travel between the control arms and the steering linkage. Maybe the spacing had the effect of using a taller spindle?

[cdr]

I don't see how this can affect bump steer since everything is bolted to the K member anyway. Bump steer is  the result of differing arcs of travel between the control arms and the steering linkage. Maybe the spacing had the effect of using a taller spindle?

the distance between the fulcrum points of upper & lower control arms is changed & so is the arc is different, it is like the old direct connection cure for really bad bump steer, heating up & bending the lower balljoint arm where the tie rod hooks to.

[RallyeMike]

Glad to read this thread. There was a discussion on shimming the K awhile back to correct driveline angle.... where were you guys then?!

[Mike DC]

     
How are you guys getting these massive height changes accomplished?  Using the OEM K-frame bolts, with an inch less of the bolt threaded through the nut?  That doesn't strike me as being particularly safe. 



BTW, does anyone sell the K-frame nuts these days?  (Not the bolts, but rather the nuts that the factory welded inside the framerails.) 

I'm pretty sure the bolts are being repopped by now.

[XH29N0G]

This will sound lame.... but I did try to search, (honest) and was outsmarted by the search protocol.  I also appreciate the feedback from all.

I am still interested in knowing whether different bolts have been used, or whether there are some spacers to deal with the taper (shoulder?) on the bolts.  I am gathering that my steering linkage will move with the K member because there isn't much space between it and the headers.

[cdr]

I used my stock bolts.

[RallyeMike]

Using the OEM K-frame bolts, with an inch less of the bolt threaded through the nut?  That doesn't strike me as being particularly safe. 

A lot of things are designed where it is the friction of the mating steel that is created by the tension in the bolt giving the connection strength. As long as you have full thread engagement and correct torque on the bolt, strength of the connection is achieved.  This can be stronger than the shear strength of the bolt.

[HPP]

I don't see how this can affect bump steer since everything is bolted to the K member anyway. Bump steer is  the result of differing arcs of travel between the control arms and the steering linkage. Maybe the spacing had the effect of using a taller spindle?

the distance between the fulcrum points of upper & lower control arms is changed & so is the arc is different, it is like the old direct connection cure for really bad bump steer, heating up & bending the lower balljoint arm where the tie rod hooks to.

It impacts more than bump steer as spreading the control arm mounting points apart also changes instant centers which then alter roll center height.  Just swagging it, I'd say it raises the roll pivot line slightly. This could reduce the leverage of body roll while cornering. Sometimes a benefit, but depends on the location of the rear roll point compared to the change induced with the front roll point.

[Mike DC]

  
What the K-frame drop would do to the IFS geometry . . . that would depend on how the ride height is set when all is said & done.  

Are the wheels ending up in the same place in relation to the unibody, and just the K-frame/drivetrain is hanging an inch lower to the ground?  That would affect the LCA geometry like you lowered the car's front end (cranked down the torsion bars), but it would keep the UCA angles the same.  




If you combined a small K-frame drop + slightly taller spindles (and/or taller upper BJs), then you might actually lower the roll center.  IMO that might be a good thing for muscle Mopars (in moderation, with swaybars to fit the change).  It's one of the only practical ways to lower the front RC without lowering the whole car in a big way.


But with stuff like this, you can end up doing a lot of running in circles unless you want one factor improved and you plan it out well.  

Lowering the K & drivertrain for handling purposes probably isn't worthwhile because you would be better off just cranking down the torsion bars & lowering the whole front end of the car.  Either way you get limited by the same ground clearance drawbacks.  At least lowering the whole car moves ALL the weight down, it's a lot easier, no geometry goofs, etc.    

[HPP]

In my car I raised the engine, driveline, and exhaust up into the car further, then dropped the car down as a whole.

Dropping the car down does lower both roll centers. Depending on how far you go, it can drop the front roll center to a position underground. Using taller spindles will raise the roll center back up to a reasonable location.