Changing rear end angle.

[wayno]

So all the pieces are ready to go - engine in - transmission in - drive shaft bolted up - now trying to everything lined up - so from my reading I see that the tail of the transmission should be between 5 and 6 degrees and the pumpkin in the rear 5 to 6 degrees up - so can I just in between where the two meet in the rear to get the front of the pumpkin to turn down into the acceptable range and if so - should I put a couple of thick washers in between to act as a shim - how much variation can I really get this method... a half of a degree? Any thoughts greatly appreciated....

[DURG]

I would make tapered shims but why so much angle? I have always shot for around 3 degrees tranny down? You have consistent research showing 5-6 degrees?

[LEEVON]

I don't have a link handy, but since these are the same trailing arms that NASCAR uses, there are some vendors that sell shim inexpensive shim kits. 5-6 degrees down is fine, like Durg said 3 degrees is pretty common also. Keep in mind the rear end will rise on accelleration from about 1-3 degrees. So you should aim for 3 up instead of all 5-6.

[padresag]

engine-rear axle should be in the 3 1/2 degree range, that is usually where the relationship between your carb and crankshaft surface
ron

[DURG]

Right - MOST Chevy intakes will set your carb level with the engine down 3 to 3.5 degrees at the rear.

[wayno]

In doing some more research it looks like you are all correct calling for 3" down on transmission - at 5" ride height measured at the frame by the rear cab mount- I thought I had read somewhere that the pumpkin in the rear should be on a matching angle - should that be pointing 3" down as well... (I thought it was 3" up - but then my drive shaft won't pass through the trailing arms cross member - so I can't be right there) I am extremely outside my comfort zone here.... so much so that I just read article after article on pinion angle that I've stopped making any progress on my build. Any help greatly appreciated.

[geezer#99]

The centreline of the motor and the centreline of the rearend should be parellel.
If tranny is down 3* then pinion should be up 3*.
You need to set your pinion angle with the suspension loaded. Tires on, sitting on a flat surface.
There's a good chart in this thread.
http://67-72chevytrucks.com/vboard/s...d.php?t=569350

[DURG]

Also, if you are running a 5" frame height, you may need a 2 piece shaft. More pictures of your crossmembers?

[wayno]

It's a porterbuilt rear cross member - running a tko 500 transmission (if this thing ever turns a wheel) - but I did discuss with them that I was running a one piece drive-shaft.

[wayno]

These file limits are killing me

[wayno]

so the thought process was to set the frame level at 5" inches - get the angle of the transmission to 3 degrees - drill and bolt in the transmission member... put the drive shaft in place and set the pumpkin up the same 3" - but I'm definitely not going to clear this thing with this one piece if that's the case

[DURG]

Originally Posted by wayno

It's a porterbuilt rear cross member - running a tko 500 transmission (if this thing ever turns a wheel) - but I did discuss with them that I was running a one piece drive-shaft.

What is the angle in this picture of the TKO ? Looks steep.

[wayno]

It's super steep - maybe 10-12 degrees in the picture - the transmission cross member is just laying in the bottom of the frame rails - the thought process was to hook up the drive shaft - crank up the rear of the transmission to 3 degrees and then bolt drill and bolt that and then get the rear pumpkin into the right position - but I was leaving it sort of in the breeze until I was sure I could get the angles I needed.

[DURG]

Put it this way I have a Porterbuilt touring setup with coilovers with a 6" rear ride height. When I am on the stops in the rear at about a 3" frame height, my one piece 3-1/2" od shaft just BARELY clears the cab. I had to modify my mid crossmember heavily for clearance but I have a four link so no big deal. Check my build thread for some pictures just for reference if you are interested.

[DURG]

You need to:

1. Set your frame at desired ride height. I would put at least a half inch if not an inch of rake front to rear

2. Install motor at the correct angle. Say 3 to 3-1/2 degrees down at rear.

3. Set pinion angle at opposite EQUAL angle as tranny. Yoke up the 3 to 3-1/2 degrees.

3. See if a one piece driveshaft will work for you through ALL the suspension travel you plan on using. Are you going to lay frame? You need adequate clearance with shaft here too!

4. Determine if the cross member you want to use will work with the one piece shaft.

[geezer#99]

You're going about it bassackwards!
With your motor in the frame sitting on the front suspension with wheels/tires installed, set your carb level and then install your tranny mount. Leave the rearend alone until you have the rest of the weight on the truck. Then set your pinion angle and install your driveshaft. At that point in time you'll know whether you need a one or two piece driveshaft to clear your truck arm mount. Otherwise you're spending a lot of time mocking up what you might need to change later.
JMHO