78 HP axle inner axle length ?

DEEPWOODS · Nov 14, 2019

I see there is 2 different length inner right side and 2 different length inner left side axles listed for 78 HP axles is it because of the different carrier for high or low gears? I don’t have the original axles and don’t know what length to order. Right side 33.91 inner and 34.750 inner Left side 18.630 inner and 18.91 inner need help figuring this out .Also I am going to be using An ARB ,Thanks Keith

Broncobowsher · Nov 14, 2019

Lets figure this out...
4.11 gears in regular, or in thick cut (they don't actually exist but for demo this works).
Looking at this from the front, the ring gear is on the left side (if the rotation in my head is correct).
The pinion will be the same diameter, The difference is the thick cut gears move the carrier further left. So the 3.54 ratio will be the shorter passenger side and the 4.11 ratio will be the longer passenger side. Now go back and check your numbers.

You show nearly an inch difference between the right side axles, that doesn't sound right. There is less than an inch difference in regular to thick cut gears.
The left side axles are about a quarter inch difference, that sounds correct compared to how different a thick cut gear is.

At this point I don't really trust the numbers in your options.

garberz · Nov 14, 2019

The differences in those lengths, is the difference between the F150 HP44 and the F250 HP44.

Mark

DEEPWOODS · Nov 14, 2019

Thanks Mark will it matter on the left side if I used the shorter F250 18.63 axle it looks like it would be about 1/4” shorter on spline engagement? I have a used left side F250 axle Thanks Keith

garberz · Nov 14, 2019

DEEPWOODS said:
Thanks Mark will it matter on the left side if I used the shorter F250 18.63 axle it looks like it would be about 1/4” shorter on spline engagement? I have a used left side F250 axle Thanks Keith

I’m thinking that it won’t matter being a 1/4” less spline engagement. Ther’re lots of people running narrowed HP’s, using EB short side axles that are 5/8” too short. Most don’t even know, and they haven’t had any issues yet.

Mark

nvrstuk · Nov 14, 2019

I don't think the engagement would be much of an issue...however, the centerline of the kingpin should align with the center of the ujoint. At least I was told that it is beyond "extremely important" by 2 different axle manufacturers (actually one- the other said very important).

If the spindle/knuckle assbly turns in a different plane than the axle/ujoint, you won't be able to turn the strg wheel. One tech said he didn't care if you weighed 300+ lbs and could press your car, you wouldn't be able to turn the strg wheel. They were both stressing the importance of obtaining accurate inner and outer axles lengths... I'm sure there is a point of no-return on this measurement-whether it's 3/8" or 3/4" I have no idea...

That's all I know...

nvrstuk · Nov 15, 2019

Keith- If I haven't hauled my stock HP D60 axles to the scrap bin yet, I'll measure them this am.

thesnake · Nov 15, 2019

Mark, Thank You for posting the diagram, it will help my faltering memory!

JD

DEEPWOODS · Nov 15, 2019

I think the outer stub axle with the c-clip will keep the u joint at the proper location and the inner axle will be just about 1/4” less engaged in the ARB. There is also different stub axle lengths I think for the longer f 250 spindle .

nvrstuk · Nov 15, 2019

Agreed...if only the inner axle is the wrong length. However, if the outer axle length is off then the "C" clip would be holding the ujoint in the wrong location...

Broncobowsher · Nov 15, 2019

The inner axle can be off by a little bit. Don't let it bottom out. But a little short isn't that big of a deal. The axle floats around. If you ever installed an axle there is a lot of play until you install the spindle. The spindle and outer stub hold the U-joint in place. The U-joint is what locates inner axle on the outside.

You still need fairly decent lengths, there is a sealing surface that has to be in the correct location. But exact length isn't that critical. Otherwise all these backyard cut and turn axles, narrowed full width using a chop saw, or just look at the original build quality, none of this stuff would ever have worked. How many early broncos are running around with a GM short side axle in place to get the big U-joint? And those are the wrong length.

But we are not talking an inch off either.

Do you still have the BOM on the axle housing? Pull that number and look it up (or post it here and someone will look it up) and that will tell what it was built with.

nvrstuk · Nov 15, 2019

That's why I mentioned I didn't know where the "limit" was... I've also cut axle ends off as an "upgrade" and never had any issues but obviously there is a limit as to how far off you can be.

We also ran almost all of those cut off axle ends w/o the C clips and yes, the axle moved back and forth a lot...and it worked.

Just wanted to post up that two different axle manufacturers stressed that alignment was important... so get it as close as ya can.

DEEPWOODS · Nov 16, 2019

The outer stub axles have 2 C clip groves on the after market stub axles is this so they will work on f150 and F250 or why 2 Grooves ?

Broncobowsher · Nov 16, 2019

2 grooves will let them work with both Ford and GM brakes.

DEEPWOODS · Nov 17, 2019

Thanks Guys for all the help and info. Thanks Keith

78 HP axle inner axle length ?

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