I'm Thinking Bout Good Vibrations

[55 Fargo]

Hi all, now today I realized how messed up my pinion angle is on my diff, as how it correlates to the engine and trans.

It is bad, like 9-10 degrees going north, and the engine and trans your stock 3-4 degrees going south, as it should be.

Now I missed this obvious area, for quite some time, not sure why it eluded me, but it did.....LOL

Have a look, going to get new spring perches and fix this up quick.

I am also about 75% sure I will be swapping in my LA 318/904 combo, I have almost all I need, and a very good friend and I will do the job, he has done many, and is a great fabricator and welder....

I have most of everything for the swap, still need a few things, but could go ahead anytime and get it done.

I really love flathead 6s, but mine is a bit tired, and do not think I could afford a rebuild and the speed parts I would like to get the Ponies some more juice......

[William Davey]

As long as your swapping the motor/trans you'll need a new drive shaft, so maybe install a new differential (limited slip, maybe 3:55 ratio) and get the pinion angle right on the new one?

[55 Fargo]

As long as your swapping the motor/trans you'll need a new drive shaft, so maybe install a new differential (limited slip, maybe 3:55 ratio) and get the pinion angle right on the new one?

What on earth for, got a 8 1/4 diff now with 3.23 gears, reason why pinion angle is so far out to begin with. I did not do the swap, whoever did, did not remedy this.

Any modern 70-80s driveshaft will bolt right up, and will for the 904 trans, will have to shorten the driveshaft and have it balanced.

The trans angle is 4 degrees negative to the back, the diff/pinion angle is 9 degrees positive to the front, not very good at all......LOL

Edited October 20, 2015 by Fargos-Go-Far

[Dave72dt]

if you're going to swap in the 318, wait on the diff until you find the angle the engine ends up at after the install.  Otherwise, you're matching the engine to the diff angle and there's less maneuvering room in the engine compartment there than is under the bed.

[55 Fargo]

if you're going to swap in the 318, wait on the diff until you find the angle the engine ends up at after the install.  Otherwise, you're matching the engine to the diff angle and there's less maneuvering room in the engine compartment there than is under the bed.

Yes I was also thinking that, but wouldn't the 318 and 904 be angled down 3-4 degrees, at least that's what I will shoot for. This diff is currently pointing up 9 degrees ouch.

But most likely will wait and do all at same time...

[NiftyFifty]

Have you pulled the cover and inspected that diff? Do you know it's history at all? Might consider a different one if your going to the work to cut the perches and weld new ones off. If you went jeep/Dakota it wouldnt change the driveshaft ends, but of course you'll still need to shorten and balance....both of which I recommend having a shop doing with a lathe...they can weld it on the lathe so they know it's perfect vs. a buddy welding on a table etc.

Just remember when you do weld on new perches that under load your diff will tilt down...likely why yours hasn't caused you too many issues, under load it's at just at the limit of what will work.

[55 Fargo]

Have you pulled the cover and inspected that diff? Do you know it's history at all? Might consider a different one if your going to the work to cut the perches and weld new ones off. If you went jeep/Dakota it wouldnt change the driveshaft ends, but of course you'll still need to shorten and balance....both of which I recommend having a shop doing with a lathe...they can weld it on the lathe so they know it's perfect vs. a buddy welding on a table etc.

Just remember when you do weld on new perches that under load your diff will tilt down...likely why yours hasn't caused you too many issues, under load it's at just at the limit of what will work.

Did you not see the other posts, 1980s Mopar 8 1/4 diff 3.23 gears, been using for years, nothing wrong with it, has the correct yolks for what I need. I DON"T NEED ANOTHER DIFF......LOL

[Dave72dt]

It probably will be down at 3-4 but you don't know for sure until it's in..  You can get to 3 or 4 but sometimes you have to move a lot of metal to do it.  Crossmembers and firewall at the back and steering in front are physical limits you'll have to work within when leveling it out so you may end up with 4-5.  It's a lot easier to turn the diff than finding/making that extra inch of clearance  up front.

[Plymouthy Adams]

Fargos-Go-Far, on 20 Oct 2015 - 11:40 PM, said:

Yes I was also thinking that, but wouldn't the 318 and 904 be angled down 3-4 degrees, at least that's what I will shoot for. This diff is currently pointing up 9 degrees ouch.

But most likely will wait and do all at same time...

Fred..the big picture is that and is what Dave is saying..your drive line is phased as per the install of the components in relationship to each other...set your engine..it will be the item that will  define the angle of the output shaft of the tranny and the very item you will match in phasing of the rear axle input...your have a range of X angles that work best with the engine and you will want to stay as close to this as possible, many can recommend but do a read so you can get a good feel for what is going on and try to set it accordingly.  In setting the eng/tran, rear gear, angle of the driveshaft is next item of concern as it also has to be in X degrees to not only work the u-joint properly, but to be able to run at X RPM of the shaft, again, another chart you may wish to consult when making the upgrade get this angle to great and your safe operating prop shaft speed will be cut...failure to adhere to all these would still put you at risk of vibration and premature failure of u-joint.

 

for the time being...you can easily correct a few degrees at the pinion by purchasing and installing corrective wedges designed for this purpose.

[55 Fargo]

Fred..the big picture is that and is what Dave is saying..your drive line is phased as per the install of the components in relationship to each other...set your engine..it will be the item that will  define the angle of the output shaft of the tranny and the very item you will match in phasing of the rear axle input...your have a range of X angles that work best with the engine and you will want to stay as close to this as possible, many can recommend but do a read so you can get a good feel for what is going on and try to set it accordingly.  In setting the eng/tran, rear gear, angle of the driveshaft is next item of concern as it also has to be in X degrees to not only work the u-joint properly, but to be able to run at X RPM of the shaft, again, another chart you may wish to consult when making the upgrade get this angle to great and your safe operating prop shaft speed will be cut...failure to adhere to all these would still put you at risk of vibration and premature failure of u-joint.

 

for the time being...you can easily correct a few degrees at the pinion by purchasing and installing corrective wedges designed for this purpose.

Tim y I am fully well aware of an engine swap changing things up, but have you ever installed and engine and trans 9-10 degrees down to the rear?

I should think not, with the 318 carb at or very near level, what do you think the 904 trans angle to be, I am betting 3-4 degrees down,not 9-10 degrees down, correct?

It may make more sense to shim current spring perches to adjust pinion angle for now, but thinking I would mount and engine and trans 9-10 degrees negative is not going to happen

On the flathead, carb is level, engine is going down 4 degrees from front to back, that is what most factory spec would be wouldn't it.

I would be a whole lot safer on pinion angle set to 4 degrees postiive on the diff, and setting 318/904 to that, betcha carb will be level on that.....

Edited October 21, 2015 by Fargos-Go-Far

[Plymouthy Adams]

no Fred..I install my engines correctly as I approach the build in correct manner..

[55 Fargo]

no Fred..I install my engines correctly as I approach the build in correct manner..

Exactly my point, you know that when the carb base is level, the engine and trans will most likely be 3-4 degrees negative.

In my case running my truck with current pinion angle at 9-10 degrees north is not a good thing, so will adjust correctly, to avoid abnormal wear and problems..... BTW how is your coupe coming along, getting near road ready yet?

Edited October 21, 2015 by Fargos-Go-Far

[Plymouthy Adams]

Fred..going to try to shoot some top coat paint soon..only thing holding me back..lots of family matters of the aging relatives has taken me from my shop past couple years...but at the moment it seems to be calming down for me.  Past couple weeks I have been able to paint the underside of the panels and trunk in ecosheen and I just sprayed the last of the brackets and pieces that are going black..Had another small project I wanted in a certain color so while mixing paint I shot some items going the same for the 41 Dodge as this was original purpose of the paint.  I repaired the step treads on three of four small stepladder I use to place a walk board for shooting the roof of tall cars..yeah, height challenged to a degree...it is progressing a bit at a time.  tons of stuff to do here...and I never set a time schedule...these cars make me happy when I get to play with them...not necessary to have them completed for me to have fun, and well, with all the cars I have here...never a dull moment.

[NiftyFifty]

Hey...I'm just saying, don't go to the effort until you check everything....I did an engine and trans on a 89 Chev I owned and thought the rear diff was great, so it was the least of my worries...no noise no nothing...then About 2 weeks later the pin fell out and dropped the spiders and broke through the back of the cover. And honestly, the yoke means nothing...there are conversion joints for just about every combo, it's what I used to use the original DS when I changed my rear diff....so that would never force me to use "what I've got"

Your pinion angle is wrong, no doubt you have to fix it and shims are likely fine, but will increase your height a bit I imagine.

[55 Fargo]

UPDATE:

 

Okay got creative yesterday and made a drawing of a 6 degree shim, then mad a shim out of 1/4 flat stock.

I had a lot of truble with 1 u-bolt nut, and I installed them only 3 years ago. Once the job was done, witha lot of time and cursing, decided to go for a test drive. Well guess what, engine would not start, not sure if me newly installed electronic ignition failed or what, installed points dizzy, still no luck, and killed battery.

Let battery charge over night, re indexed dizzy, again no luck, then changed cap wire arrangement one over, it fired right up. The electronic ignition ran fantastic, not sure what happened...

I then installed, and the pinion angle in the diff, now matched engine and trans.

I drove the truck seems better, but the driveshaft was custom made, so it seems out of balance too, never ending... some pics, please excuse dusty/rusty underside, ain't no sense making her purdy for my gravel road, thinking of spraying the whole underside in chainsaw bar oil.

[Dave72dt]

What do you suppose that black gooey tar like coating often found on frames, diff, trans etc and cussed at when it has to be scraped and chiseled off later is made from .  Sticky oil and road dust!    You may want to reconsider the bar oil.

Edited October 27, 2015 by Dave72dt

[Jeff Balazs]

PB Blaster has an aerosol product called Corrosion Stop that might work well. I have been using it on my leaf springs. It is a penetrating oil that develops a pliable film over time. A lot of folks use it on boat trailers that are exposed to saltwater. Works pretty well.

 

Jeff