Calling all Mathmaticans

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mopar head

mopar head

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I`m gonna narrow a 8-3/4, and purchess the fixture. but before I slice&dice, Hopefully someone could lookover my crude drawing and see If you come up with the same measurements. To make it more confuseing I`m altering the offset from its 2.625 to 1.5" to line up to my existing tunnel, 52 Wayfarer. I will also have 2 different length axles. Yet to be figured. thanks

8-34.jpg
 
Your drawing is too busy. The tires you have drawn is irrelivant if you already know the total length of what your looking for. I see your offset on the pinion. No issue. It's a matter of simple subtraction. Start at the original width and go down from there. If you decrease the housing width, on either side, simply decrease the axle length to correspond accordingly. If you take out 4" on the right on the housing you will also decrease the axle by that much also. Same with the other side. By the way, Pie are round....
Small Block
 
It looks to me like you are taking out the correct amount from each end of the housing to get your 50 1/2", but your numbers to get the pinion offset is not right. Looks like you are taking out 2.25" instead of the 1.5" that you need. This is considering that you housing is the same length on each end. Correct?
 
You sure about the pinion offset. My understanding is the offset is ~1 3/16-1 5/16" to the pass side on mopars.

If you took the measurements from pinion centerline and subtracted the lengths to each flange, you end up with double the actual offset.

You need to move it further to the pass side? If you need the pinion offset 1.5" to the pass side...

I come up with a measurement from pinion centerline to flange of:
23.75" for pass side
26.75" for drivers side
50.5" Total

I would not try to figure out how much to remove from each side. Get the ends cut off close to the welds, true them up if re-using, then use a pinion centerline gauge and get the housing marked where it needs to be be cut and the total length if the housing is long enough. Then double and triple check your measurements.
 
If you are shooting for a 1 1/2" offset then you need to take out 4 7/8" from the drivers side and 3 3/4" from the passenger side. Double check these numbers and see.
 
Small Block said:
Your drawing is too busy. The tires you have drawn is irrelivant if you already know the total length of what your looking for. I see your offset on the pinion. No issue. It's a matter of simple subtraction. Start at the original width and go down from there. If you decrease the housing width, on either side, simply decrease the axle length to correspond accordingly. If you take out 4" on the right on the housing you will also decrease the axle by that much also. Same with the other side. By the way, Pie are round....
Small Block
Click to expand...
Just helps me visualize,lol, Pie? Please read last post

Badart said:
It looks to me like you are taking out the correct amount from each end of the housing to get your 50 1/2", but your numbers to get the pinion offset is not right. Looks like you are taking out 2.25" instead of the 1.5" that you need. This is considering that you housing is the same length on each end. Correct?
Click to expand...
The houseing is centered, and the pinion is offset 2-5/8". so I would like to pull the pinion center to 1-1/2" makeing up the difference in the tube sections cut out.please read last post

crackedback said:
You sure about the pinion offset. My understanding is the offset is ~1 3/16-1 5/16" to the pass side on mopars.

If you took the measurements from pinion centerline and subtracted the lengths to each flange, you end up with double the actual offset.

You need to move it further to the pass side? If you need the pinion offset 1.5" to the pass side...

I come up with a measurement from pinion centerline to flange of:
23.75" for pass side
26.75" for drivers side
50.5" Total

I would not try to figure out how much to remove from each side. Get the ends cut off close to the welds, true them up if re-using, then use a pinion centerline gauge and get the housing marked where it needs to be be cut and the total length if the housing is long enough. Then double and triple check your measurements.
Click to expand...
As stated above, the houseing is centered and the pinion is 2-5/8 offset to the passenger side, so was the engine.. I thought all the older mopars were off set about this much, My cuda is also, to clear the steering box. I measured the center of the tunnel on the 52 and it`s only offset 1.5" toward pass. side. please read below

Badart said:
If you are shooting for a 1 1/2" offset then you need to take out 4 7/8" from the drivers side and 3 3/4" from the passenger side. Double check these numbers and see.
Click to expand...
here`s my thinking, Rear needs narrowed 8-5/8" overall. Half of that is 4-5/16" each side. subtract the difference of 2-5/8 and 1-1/2" = 1-1/8". Add that to the left section to be removed and subtract from right side section to be removed to come up with my 1-1/2" offset. Cutting it in these locations keeps the perches equadistant from each end, moves the pinion center over to what I need and chassis can be built to suit the perch centers. Am I makeing any sense? Please bare with me and recalculate to this info just stated. I know the pros use the gauges, but its seems math can solve the measurements for the pieces to be removed. Instead of cutting off perches, possibly warping tubes, buying new/welding possibly warping tubes. Cutting off the ends and trying to salvage them without messing them up, if so then buying new. I figured this would be the most cost effective way of doing it. As I`m jobless and spending/= not good:-D
 
I am a seventh grade math teacher (fractions are my specialty). If I understand the goal, then this is my thought:
It all relates to the center line! If the factory offset from center is 2 5/8 and you want it to be 1 1/2, then the offset needs to move 1 1/8 to the left (per your drawing). Then if you want to take out 8 5/8, that would be 3 3/4 on the right side and 4 7/8 on the right (3 3/4 + 1 1/8 ). Shorten each axle accordingly. Your numbers will work. However, using your numbers will yield axles that will have 2 1/4 inches difference in size. My numbers will yield axles that are only 1 1/8 inches difference in size. Everyone chime in on this difference in axle sizes, and whether it makes a difference. Seems to me, they should be as close to the same size as possible. Any cuts done inside of the perches will leave the perches equidistant from the ends of the axles.

I know the math works, but I may not understand the goal.
p.s. I think the tires drawn are relevant to you because you are looking at the whole idea of the rear axle's new location.
 
How did you arrive at the 2 5/8 offset. Just asking. I believe you got it from the way I described above.

You must have a one-off third member because I just measured the offset on three I have and they are all 1-5/16", which when doubled is coincidentally, 2 5/8". There are casting lines on the topside, at both the third member center and the pinion center lines.

The axle tubes on 8.75's are equi-length.

What were your measurements for the centerline on the wayfarer? Rocker to tunnel on each side.

My guess.

If you really need 1.5" offset. From the centerline of the housing you need it to be 3/16 longer to the drivers side. So add 3/16 to 25.25 for the drivers side and subtract 3/16 from 25.25 for your pass side. That should put the pinion at the desired 1.5" offset to pass side.

I've shortened more than my share of Dana's and 8.75's, the 2 5/8" offset assumption is a common issue and that's the difference number you want to come up with when measuring flange to pinion centerline for each tube.
 
If crackedback offset info is correct ( and I have no clue there, he seems to know), you need to cut 4 7/32 from the right and 4 13/32 from the left to move the centerline over 3/16 (which is the 1 5/16 - 1 1/2 on the offsets, before and after) and still narrow it 8 5/8.
I would then STAMP each axle end with L-left and R-right as there is only 3/16 difference in size, and that could result in a mishap if put in on the wrong side.
 
mopar head, stop by the house and I'll show you some tools to make this a little easier. If you get it all worked out I'll give you a hand with the cutting and welding.
 
crackedback said:
How did you arrive at the 2 5/8 offset. Just asking. I believe you got it from the way I described above.

You must have a one-off third member because I just measured the offset on three I have and they are all 1-5/16", which when doubled is coincidentally, 2 5/8". There are casting lines on the topside, at both the third member center and the pinion center lines.

The axle tubes on 8.75's are equi-length.

What were your measurements for the centerline on the wayfarer? Rocker to tunnel on each side.

My guess.

If you really need 1.5" offset. From the centerline of the housing you need it to be 3/16 longer to the drivers side. So add 3/16 to 25.25 for the drivers side and subtract 3/16 from 25.25 for your pass side. That should put the pinion at the desired 1.5" offset to pass side.

I've shortened more than my share of Dana's and 8.75's, the 2 5/8" offset assumption is a common issue and that's the difference number you want to come up with when measuring flange to pinion centerline for each tube.
Click to expand...
Hey Cracked, I layed a straight edge off the edge of each housing flange and measured to the center of pinion, subtracted these 2 measurements and got 2-5/8. I put the carrier back in and rechecked and come up with 2-3/8 difference. Maybe the housing sprung this difference, being the carrier was setting in loose. So where am I screwing up here, not dividing by 2? As you pointed out 2-5/8 divided by 2= 1-5/16. this is where my confusion begins. And prodart I just noticed your post as I`m typeing this. I`ll be over! stay home lol
 
mopar head said:
Hey Cracked, I layed a straight edge off the edge of each housing flange and measured to the center of pinion, subtracted these 2 measurements and got 2-5/8. I put the carrier back in and rechecked and come up with 2-3/8 difference. Maybe the housing sprung this difference, being the carrier was setting in loose. So where am I screwing up here, not dividing by 2? As you pointed out 2-5/8 divided by 2= 1-5/16. this is where my confusion begins. And prodart I just noticed your post as I`m typeing this. I`ll be over! stay home lol
Click to expand...

Yes, you need to divide the difference in lengths by 2.

If you have something that is 50" long, 25" at center and you offset to one side by 1", you end up with a 26" and 24" length, 2" difference. However, the offset is really only 1/2 of that, 1". It gets lots of people. If you measured your tunnel the same way, please double check it before cutting the rear.

The tolerances when these cars where built are fairly large. That 1/4" difference wouldn't surprise me one bit! Best thing, check the rear for straightness, and make your rear up where you need the pinion to lie.

Prodart sounds like he's willing to help and that never hurts either.

Good luck.
 
Finally got it figured:cheers: and I feel pretty stupid,:scratch: but smart enough not to cut anything yet. When I`m in doubt I like to lay it out full scale. took a board and layed it out, then took a piece of material, did same. NOTE to self and anyone trying a narrow job. TAKE the pinion offset out of the equasion!! The tunnel was offset 1.5" eyeballed, probably more like 1-5/16"- same as pinion offset. So the cut pieces are 4-5/16" each side, pinion is offset as is the tunnel. Axles will be reduced the same length. My mistake was not divideing by 2 and takeing pinion offset into the equasion. thinking I needed to work off the pinion center, when I should have been working off housing center, or overall center, jeesh.. I will rethink my location of cuts, a weldjoint would be stronger towards the end instead of out towards the center of houseing tube, and just buy new perches. Thanks so much Crackedback and the rest of you that responded, sorry for the goofy math problem8)
 
Moparhead.
Re-think cutting the tubes like you have marked on your drawing.
It can not be done this way. You MUST cut at the base of the
flanges,(bearing housings) then re-weld them back on.
This re-welding needs to be done with a gig, or use the straight
edge like you did the check the length, front to back, top to bottom, and every 45 degrees.
The tubes have tappers from the pig to the axle ends. Also the tube is NOT
a true circle, it's pretty crude.
I have had one done for me and then did the last one my self.
GoDartGo
 
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