Gear Vendors and pinion angles

[RECHRGD]

I got a new aluminum drive shaft and now my, always questionable, pig up pinion angle is causing problems.  Ron suggests a two degree downward angle at the pig. To accomplish that, I will need to raise my GV unit over an 1 1/2".  That would entail an unacceptable amount of beating up on the driveshaft tunnel to make room.  What have you guys used for angles that worked for you and how did you accomplish it.  Thanks, Bob.....

[Kern Dog]

I think that it is common for some "dimpling" to the trans tunnel for the GV install. I have one in my 70 Charger. The problem for me is the speedo housing. To get the GV up higher I'd have to really beat up the floor there to get the cable to clear.
I had some vibration awhile back but it was due to the trans mount resting on the  crossmember.

[XH29N0G]

Partly related - not intended to hijaak - how difficult is it to dimple the tunnel, and what are the preferred methods of figuring out where and how to resculpture the tunnel?

[charger Downunder]

Cant you just  shim the diff down or up with a mopar shim kit to get the angle and leave the GV unit alone.

[RECHRGD]

Cant you just  shim the diff down or up with a mopar shim kit to get the angle and leave the GV unit alone.

Having both the pig and the tailpiece pointing down goes against everything I've read on the subject.  Ideally, they should be parallel but opposite....

[MSRacing89]

Cant you just  shim the diff down or up with a mopar shim kit to get the angle and leave the GV unit alone.

Having both the pig and the tailpiece pointing down goes against everything I've read on the subject.  Ideally, they should be parallel but opposite....

This is how we run it.  Tail down, 3rd member down.  For me its all about working angles as the u-joints don't know if they are in parallel or not, the angles are the only important thing. Secondly, I want to know what is going on with the pinion under acceleration.  No way I am running positive pinion angle with nearly 600 HP. What the books say don't always work when your tailshaft is lower then your 3rd member.   

[RECHRGD]

Cant you just  shim the diff down or up with a mopar shim kit to get the angle and leave the GV unit alone.

Having both the pig and the tailpiece pointing down goes against everything I've read on the subject.  Ideally, they should be parallel but opposite....

This is how we run it.  Tail down, 3rd member down.  For me its all about working angles as the u-joints don't know if they are in parallel or not, the angles are the only important thing. Secondly, I want to know what is going on with the pinion under acceleration.  No way I am running positive pinion angle with nearly 600 HP. What the books say don't always work when your tailshaft is lower then your 3rd member.   

Yea, it's been running for years with the pig up with no real problem.  With the lighter aluminum DS the pig went crazy under hard acceleration and beat the heck out of my new aluminum yoke.  It's going in as you described now.

[Kern Dog]

Up until sometime last year, I ran the SS leaf spring hangers in my car. I drilled holes higher up to put the spring eyes closer to the body. This was done to lower the car without modifying the springs. I didn't know it but it affected the pinion angle by making it "nose-up" at rest. Of course it only gets worse under acceleration. Maybe I got lucky with it because It never seemed to vibrate or give me any trouble until I installed the Gear Vendors unit. Maybe it was because the driveshaft was now shorter?
Anyhow, I put stock spring hangers back in but the vibration remained. Digging further, I found a point of contact at the trans case and crossmember. I little clearancing and all is well now.

[RallyeMike]

The pig angle has to be set relative to the trans and driveshaft. I find it hard to believe the trans needs to raise 1-1/2 inches. Wow! Is this at the mount or end of the OD tailshaft?


Relative to the driveshaft, shoot for 2-3 degrees down angle on the trans, and 2-3 degrees up angle on the pig. Best results come by keeping the angles as equal as possible (within 1/2 degree).

You can increase up angle of the trans by shimming down the k-member if you need to get drastic.

[XH29N0G]

You can increase up angle of the trans by shimming down the k-member if you need to get drastic.

Can you elaborate on how this is done? and whether there are drawbacks for doing this? 

[RallyeMike]

The k-member bolts on at four locations. Install a steel shim here. As long as the shim is not radical, the suspension geometry, shock lengths, torsion bars, steering gear, sway bar mounting, etc. will be able to handle it within tolerances. This effectively lowers the engine relative to the trans mount, raising up the tailshaft. It has less impact to the trans tunnel clearance (compared to simply raising the trans at the trans mount).

I have not done this personally, but I considered it as an option at one point. 

Coincidentally I just read an article where an owner shimmed his k-member to increase hood clearance for aftermarket induction so he didnt have to cut his hood. Clever!

[XH29N0G]

As long as the shim is not radical

I hope it is OK to ask for further clarification and still think this is relevant to this thread.  What do you consider radical?  The tail on my transmission is down by 3.5 degrees.  I set up a spreadsheet and  my calculations show a significant shim on the front would be needed (like 1.18") to cut that in half.  My guess is this would qualify as radical.

[RECHRGD]

Played with it some more today.  Got the pig set at 2.5* down, the tail shaft at about 4* down and the DS is sitting at about dead zero with the suspension loaded.  I jacked up the rear end to get the wheels off the ground and ran it up to speed while on the lift.  From zero to 70 it's smooth, between 70 and 80 there's a slight vibration, but not enough to make the rear view mirror fuzzy.  After 80 on up to over 100 it's smooth.  It's the same whether in OD or not.  I'll have to get it out on the road in a few days when the rain stops, and see how it behaves in the real world.  At least the pig is now pointing down, so I should be able to accelerate without the drama.  To get the tail shaft any further up will require a lot more surgery on the tunnel or Mike's K-Frame shim.  Wish me luck.......

[Kern Dog]

Remember that the mount is forward of the tailshaft. Any addition to the mount is extropolated. An inch at the mount can be 1 1/2" at the end of the tailshaft, etc.

[RallyeMike]

As long as the shim is not radical


I hope it is OK to ask for further clarification and still think this is relevant to this thread.  What do you consider radical?  The tail on my transmission is down by 3.5 degrees.  I set up a spreadsheet and  my calculations show a significant shim on the front would be needed (like 1.18") to cut that in half.  My guess is this would qualify as radical.

I think an inch shim would work. I don't think you'd have anything to lose my loosening up the K-member bolts, letting it drop an inch and see how things shape up. I'd also loosen up the sway bar mounts, steering column bolts, and radiator hoses to allow it to freely drop and then check everything out. Make sure there is an inch of room at your power steering hoses and radiator shroud.
If it all looks good, build and slide in some shims.

Trade offs will be having to untension the T-bars to get back to normal ride height, you'll need a re-alignment, and if you drop the t-bars you'll have less ground clearance to the K and oil pan.

[Kern Dog]

I would never shim the K member. The shanks of the k member bolts are tapered to "center" the K member to the frame rails. Any shim used would likely result in the K member sitting out of square. Imagine what THAT does to alignment of the front wheels, the steering shaft, exhaust, everything....

[RallyeMike]

Assuming the stock K-member bolt is long enough for the desired shim thickness, the taper (which is really a shoulder) still does it's job engaging the k-member. To develop the full strength of a bolt, all you need is full thread engagement with the welded nut in the frame. Since the bolts are typically made longer than needed, there is room to back out the bolt and add shims without any concern for upsetting the centering of the k-member.

If you did need to replace the k-member bolts with something longer for a really big shim, you probably wont be able to find bolts with the correct shoulder. Measure carefully, mark it, and put the k back where it came out. I don't think this is a big deal. Your'e going to need to realign everything anyway. There is undoubtedly more nonconformity in the standard body/frame measurements off the factory floor in the 60's than the dimension of the k-member bolt shoulder which might be what, 1/16th inch?

Or not. Whatever.   

[RECHRGD]

I was able to get the car on the road today.  It did pretty much the same as it did while on the lift.  Smooth at all speeds except for the small vibration between 70 & 80.  I think I can get it completely smooth by getting the pig down another degree or so to match the tailpiece angle.  But for now I'm good.  I can now jump on it and light up the tires with no more drama, if fact, it feels like it's putting a few more hp on the ground with the pig down angle.  Maybe just my imagination, but there does seem to be a seat of the pants difference........

[RallyeMike]

Cool    When the car doesnt rattle and shake, its so much more fun!

[Just 6T9 CHGR]

So how exactly did you change the angle of the rear?

[RECHRGD]

Previously I had 4* shims in the axle perches to give me the pig up angle.  I reversed the shims and went to 2.5* ones to get the pig down angle that I have now.....

[Just 6T9 CHGR]

Cool!  Good to hear you got it sorted out

[firefighter3931]

Good job Bob !  


Ron

[MSRacing89]

Previously I had 4* shims in the axle perches to give me the pig up angle.  I reversed the shims and went to 2.5* ones to get the pig down angle that I have now.....

We run custom billitt 6.5º shims!  The car is very low so thus the extreme numbers.  We also off set the holes to center the rear end in the car.  Anyway, all the fun stuff you need to go fast....around corners that is.

All this being said we are still going Carbon Fiber drive shaft.  No matter what we seem to do with the angles this GV unit still wants to wiggle at revs.  Its not angle related, we believe its the length of the shaft and the harmonics from the unit.

[RECHRGD]

Had the car out today and ran into a guy that seemed really up on driveline problems.  We were talking about getting rid of the last of my vibrations between 70&80.  He said with the side to side offset of the trans yoke in relation to the pinion yoke on BB Mopars, vibrations are pretty much a given once the driveshaft is shortened to the extent needed for the GV installation.  He said I could try every up and down pinion angle possible and would never get rid of it.  He said the best way to address it was to have a "Cardan" double u-joint at the tailpiece yoke to take the offset / shortened DS problem out of the picture.  Has anyone ever worked with or know anything about Cardan u-joints?  I'm still going to try a little more down angle before going this route, but it made perfect sense to me.......

[Just 6T9 CHGR]

Sadly I tried some 2.5º shims in my rear to get the nose down from the 4.5º that I measured..... unfortunately my cyclic vibration is still there between 62 ish & 72 ish

had a thread going over at Moparts....

http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=8145447&an=0&page=0&gonew=1#UNREAD