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to you LS swappers, trans mount and pinion angle question...

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75K5

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I just got my 75 up and running with the new powertrain: 2009 5.3L, 4L70E, and nP241 swapped in. I am getting some really bad vibrations around 70mph, I think the pinion angle to the rear differential is too steep.

I am curious, what did you use to mount the 4L60E to the cross member? I used the transmission mount that came off the 4L60E from a 2009 tahoe, but it's about 2" tall. What did everyone else use? something shorter would reduce drive shaft angle. I haven't changed the body lift since the original powertrain, but this drivetrain combo is about 6" longer with the advanced adapter, thereby increasing the angle from the transfer case to the differential.

Also, how easy is it to rotate the rear axle up?

thanks,
Brian
 
75K5 said:
I just got my 75 up and running with the new powertrain: 2009 5.3L, 4L70E, and nP241 swapped in. I am getting some really bad vibrations around 70mph, I think the pinion angle to the rear differential is too steep.

I am curious, what did you use to mount the 4L60E to the cross member? I used the transmission mount that came off the 4L60E from a 2009 tahoe, but it's about 2" tall. What did everyone else use? something shorter would reduce drive shaft angle. I haven't changed the body lift since the original powertrain, but this drivetrain combo is about 6" longer with the advanced adapter, thereby increasing the angle from the transfer case to the differential.

Also, how easy is it to rotate the rear axle up?

thanks,
Brian
Click to expand...

i'm not actually at this step of my drivetrain swap yet but i just ordered a "generic" poly trans mount from Summit. for my truck i'm building a custom crossmember/belly pan so i'll be setting the crankshaft angle where i want it. i hear LS engines are happy around 5* so i'll start there. of course ive got a lot more rear driveline to work with.

changing the pinion angle is as easy as loosening the u-bolts and adding in a shim. www.diy4x.com sells shims.
 
If you are talking about too short of a shaft, CV is the only way out AFAIK.

Both angles need to match (pinion and t-case output) but even when matched, they also need to be within the working range of the joint for decent life. Running different angles at either end will cause vibration.
 
here is what I am looking at.

As far as I can tell, there is about a 7.5 degree angle difference between the drive shaft and the rear axle.

I don't have much room to lower the transmission because the front driveshaft will crash into the cross member.

Also, for reference, I am attaching a pic of the engine mounts I am using. It raises the engine up a couple inches to give extra oil pan clearance and allowed me to use the stock 5.3L manifolds.

1.JPG

2.JPG

3.JPG

download.jpg

4.JPG
 
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I don't know of any way out other than CV.

Google operating angle u-joints, maybe throw spicer in the search box. I know there is a chart out there that tells you what the operating angles are of the various u-joints, and I think anymore than somewhere around 3* starts to significantly decrease lifespan of the joint. It doesn't take much before joint life is cut in half IIRC.

There is quite a bit of information out there. All I've ever read/seen/been told (by driveline shop) is that the angles need to be within a couple of degrees of matching, and if you can't match them, you need to run a CV. IIRC, running them harder by too much angle will also help to contribute to vibrations. If the goal is to eliminate vibrations, only one choice.

As you mention, dropping the trans/t-case will only work so much, and that isn't actually fixing the issue if you can't make the angles match and be within operating angle specs.
 
does anyone have a pic of a NP241 mounted to a 4L60E and the trans cross member installed? I am wondering if I have it rotated one bolt over by accident and maybe it shouldn't be hanging down that far?
 
You can lower the transfer case by putting spacers between the crossmember and the frame. I have them in mine. Rancho use to make a kit for this, not sure if they offer it any more but you can just make some a get some longer grade 8 bolts.
 
how much were you able to lower it? Can I see a pic of your setup?
 
normally the mounting pattern of the T-case is one way only, unless a clocking ring is used. You can't "accidentally" mount it wrong.

That driveshaft is pretty short. I would mess with axle angle some, wouldn't hurt and would be cheap. Grab some degree shims from a local auto parts store. Pepboy, Oreily, Autozone normally carry the aluminum ones. Worth a shot
 
75K5 said:
how much were you able to lower it? Can I see a pic of your setup?
Click to expand...

Probably only an inch. Basically use some square stock like 1"x2" between the frame and crossmember. The wider side will help spread the load across the frame.
 
I would think there is a pic in there, but if not I can take one for you.
The kit would lower it about two inches. It is 3 pieces of 1/4" steel. Mine is lower then that.You will need to watch the engine to firewall clearance, because you are also tilting the motor back when you do this.
How much lift do you have? I have 9" of lift. mine drive shaft my be long because I have a 205 with a bolt on yoke not a slip yoke.
 
I only have 4" of lift. that's why I think I must have something wrong, it shouldn't be this far out for just swapping the motor/trans/tcase.
 
Here's a pretty good article on u-joints/driveshafts: http://www.pirate4x4.com/tech/billavista/PR-shaft/index2.html

As numbered on the pages, page 6, also states how close the angles need to be http://www2.dana.com/pdf/J3311-1-DSSP.pdf

Do as you will with the info.

AFAIK all the GM t-cases from this era have a large amount of "drop" to them. My 205 hangs quite a bit lower than the frame, and since an NP208/241 skidplate fits over it, the distance they hang down is obviously pretty similar. Your pic shows the frame rail, my 205 hangs down about the same amount.
 
I would first get an angle finder or something to figure out what all your angle are that you are working with.
Did you put new u joints in that shift when you did your swap?
 
quick and dirty estimate is about 8 degrees. Only a 4" lift, so that seems off.

I think I know the problem. I am using the stock transmission crossmember from my 75, originally intended for a NP203. I have been looking at google images, and I think the newer crossmembers have a dip for the driveshaft. can anyone confirm this?

Here are some pics I found on the web of other crossmembers. Does anyone have one that looks like this? What year can I fetch one of these from?

241.jpg

DSC01406_Medium.JPG

$_57.JPG
 
I think this is what I need. This will give me the clearance I need for the front driveshaft. I just have to find one now!

6.jpg
 
You do need to find the correct crossmember for your adapter plate and transfer case first. I would then get a new rubber mount for it too. That might fix your vibration. I do remember having to still lower some transfer cases with only a 4" lift back in the 80's, when I use to build truck at a friends shop.
 
'85+ all used the "new" crossmember with one exception, the CUCV's, they kept the older flat ones.

Doublehump or singlehump is how I refer to the '85+ ones. Crapshoot on what got which crossmembe, never taken the time to try and deceipher if it was a year change deal, or something else.
 
I was using the wrong crossmember. I switched to a newer style and it solved my problems!

Brian
 
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