318 and a904 swap into 51 b3b

[jerseycj8]

Question (or likely several) for the master builders on this forum..

 

Leveled the B3B frame, welded motor mounts and installed transmission cross member.  Motor/trans is about 2 inches offset to the passenger side.  When frame was level and motor/trans mounts installed, the engine intake was almost perfectly level.  Put the vehicle on the ground, on tires and now the engine intake reads 1-deg too high (i.e. trans needs to drop 1-deg) resulting in a transmission angle of 2.5 degrees down (when measured with a digital cube angle finder placed on the vertical face of the output shaft).  I can reduce the trans poly mount to 1/4" thick, and/or add 1/4" thick spacer to raise engine mount.

Q1 - Am I over thinking this?

 

My next step is to weld new spring perches onto a Chrysler 8.25 from Jeep Cherokee.  I have the axle centered on rear frame (same distance between springs on both sides) with the weight of the frame (no bed) on the axle.  The perches are not welded yet, and i need to set my rear pinion angle.  Using a floor jack, i plan on rotating the pinion up to correct angle.

Q2 - What is the correct angle for the pinion......assuming the response is entirely dependent upon what I need to do for Question 1.

 

 

 

 

[55 Fargo]

Mine is 3 down at trans output shaft and 3 up at diff yolk.

4 is fine too.

So far not 1 issue.

I had my donor driveshaft cut 2 inches to fit. It works great 

Your gonna love this combo. 

My old truck still like 60 mph, but getting there is 3 times faster than an old 6...lol

[jerseycj8]

Adding some pics to show what I tried to explain.  Again, these are taken with motor weight on frame and frame sitting on rear axle without bed.  Cab is sitting on frame.

[Dave72dt]

General theory is the crankshaft and pinion shaft run in parallel lines so a 2.5 down on the trans would mean a 2.5 up on the pinion.  U joints require some angle to work properly so with the offset engine and centered diff, there is some built in.  As far as the engine angle is concerned, bear in mind our roads are not flat.  We go up and down grades so the carb angle consistently changes and as you add the box and front sheet metal, that angle may change again.

 

Doing a search for pinion angle should bring up all kinds of info including diagrams of correct and incorrect settings.

[jerseycj8]

24 minutes ago, Dave72dt said:

General theory is the crankshaft and pinion shaft run in parallel lines so a 2.5 down on the trans would mean a 2.5 up on the pinion.  U joints require some angle to work properly so with the offset engine and centered diff, there is some built in.  As far as the engine angle is concerned, bear in mind our roads are not flat.  We go up and down grades so the carb angle consistently changes and as you add the box and front sheet metal, that angle may change again.

 

Doing a search for pinion angle should bring up all kinds of info including diagrams of correct and incorrect settings.

Ok, and all the reading I have been doing about this has made my head spin.  So, if I read your response correctly, don't fret and match my diff pinion angle (up) to how the motor/trans (down) is sitting now.  Then grab a beer.

[Los_Control]

I would grab the beer first, then do next step

[jerseycj8]

17 minutes ago, Los_Control said:

I would grab the beer first, then do next step

Didn't say it was my first beer.....

[DJ194950]

jerseycj8-

 

https://www.summitracing.com/parts/mor-65030

 

They do sell carb. spacers that are wedge shaped if you fell it is necessary. This is the first I saw just to give you an idea.

 

DJ

[jerseycj8]

1 hour ago, DJ194950 said:

jerseycj8-

 

https://www.summitracing.com/parts/mor-65030

 

They do sell carb. spacers that are wedge shaped if you fell it is necessary. This is the first I saw just to give you an idea.

 

DJ

Thanks for the heads up, never saw the wedge carb plate before.  I think I am good.  Others talked me off ledge and I welded up the spring perches today such that pinion angle was same, but opposite, the trans output angle.

[Radarsonwheels]

If the carb pad is close don’t worry about it.

 

Like was said above the pinion and transmission output want to be parallel but don’t have to be in line. 
 

The part that inspires debate (besides dummies that are measuring from the ground instead of from rear to crank/trans) is that when you put power to the tires the pinion tries to climb the ring gear. So the pinion tries to nose up as you get traction. That’s why mopar sells a pinion snubber and chevy guys use slapper bars- to limit spring wrap, axle windup, and keep the pinion parallel to the driveline under power. 
 

So some dragstrip cars might run the nose pretty far down on a leaf spring car so that when it winds up you get it where you want it. A couple or few degrees nose down is good for a street car with unspectacular torque and traction. More than that will have you feeling the vibrations on the highway any time you’re cruising and not applying power. 
 

I just added wedge shims to mine today to correct that very issue- it drives great around town but had highway vibes that I hope are gone now!

[Tooljunkie]

I downloaded the tremec app on my phone,fabbed my own perches for my 8-3/8 dodge truck rear end. 
its such a hassle for the app, basically a pass/fail. So i made driveline level, by jacking diff with perches in place,u bolts loose. 
pointed diff down 2 degrees if i recall and the app shows it as a pass. Box was off so i put some weight on frame to make up for it.