Front Leaf Springs


IHC in the early to mid-fifties.

Golden Jubilee
Golden Jubilee

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Joined: Wed Sep 05, 2018 1:50 pm

Location: Northern New Mexico

Post Mon Sep 16, 2019 8:21 pm

Front Leaf Springs

I was crawling under my truck today looking at transfer case options when I noticed my front driveshaft slip joint is not half way on the splines in the static position. There are no splines showing and it is nearly against the yoke which tells me my front springs have sagged. Years ago when I lived in the north east there was a great spring shop there where you could drive in, tell them what you wanted and come back a few hours later and pick up your truck. No such thing exists here and the nearest spring shop is 150 miles away. It looks like I need a couple of inches of lift in the front and I was wondering what other options I might have to correct this problem. I could shorten the shaft and the truck would be fine but I'd really prefer the correct fix. My truck is a 3/4 ton 4x4 S model.
56 S120 4x4,

Golden Jubilee
Golden Jubilee

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Location: Canada's left Coast

Post Mon Sep 16, 2019 9:55 pm

Re: Front Leaf Springs

The height of the front of the truck pivots on the center-line of the rear axle.
Make sure the rear spring shackles are at the back of the springs. The rear spring should pivot on the spring perch at the front of the spring. A full spring compression should move the axle away from the transmission.
I would rather have tools I do not need than to need tools I do not have

Golden Jubilee
Golden Jubilee

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Joined: Wed Sep 05, 2018 1:50 pm

Location: Northern New Mexico

Post Tue Sep 17, 2019 2:55 am

Re: Front Leaf Springs

Just to make sure we are on the same page with this my truck's a 4x4 and I am talking about the front driveshaft that goes from the transfer case to the front axle differential. My front axle has the spring shackles at the front of the truck. My rear axle does have its spring shackles at the back.

My concern is with my front drive shaft. So when my front springs compress and the spring shackles are forward you are saying my drive shaft should get longer? If that is the case then my slip joint position on my front drive shaft is less of a concern but maybe not ideal?


Lastly would it not be best for my front driveshaft to have 50% of its slip joint splines showing and 50% within the shaft when the truck is static to allow for spring movement in either direction and if that is the case then re-arching the springs is not the fix and my shaft would need to be shortened by a few inches? In the 60 some years this truck has been around the front drive shaft may very well not be original and could be the wrong length. ??
56 S120 4x4,

Golden Jubilee
Golden Jubilee

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Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Tue Sep 17, 2019 8:27 am

Re: Front Leaf Springs

I am sorry. I missed the 4x4. I will have no further comment.
I would rather have tools I do not need than to need tools I do not have

Golden Jubilee
Golden Jubilee

Posts: 547

Joined: Wed Sep 05, 2018 1:50 pm

Location: Northern New Mexico

Post Tue Sep 17, 2019 8:41 am

Re: Front Leaf Springs

nikkinutshop wrote:I am sorry. I missed the 4x4. I will have no further comment.


No biggie, I was hoping you would have much more to say.
56 S120 4x4,

Golden Jubilee
Golden Jubilee

Posts: 7535

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Tue Sep 17, 2019 10:44 am

Re: Front Leaf Springs

Maybe I have exceeded my limit. I get the impression you know what you are doing.
I would rather have tools I do not need than to need tools I do not have
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Golden Jubilee
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Post Tue Sep 17, 2019 11:18 am

Re: Front Leaf Springs

Maybe a difference in terminology of what we're calling shackles, but the pivot for the springs should be at the front, with the shackles at the back of the front springs. In this diagram from MT-103, the front of the truck would be to the left.

Springs.jpg

Golden Jubilee
Golden Jubilee

Posts: 547

Joined: Wed Sep 05, 2018 1:50 pm

Location: Northern New Mexico

Post Tue Sep 17, 2019 2:36 pm

Re: Front Leaf Springs

nikkinutshop wrote: I get the impression you know what you are doing.


I fool people with that a lot, like the old saying goes "A little bit of knowledge is dangerous" I have many limitations when when it comes to auto mechanics.
56 S120 4x4,

Golden Jubilee
Golden Jubilee

Posts: 7535

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Tue Sep 17, 2019 3:43 pm

Re: Front Leaf Springs

If I cannot see 4X4, it is time for me to go to pasture.
I think you should have the springs rearched, or replaced. I installed a n air spring set under my R120. I used a Holland Neway height control air valve for control . Just talking here. It was expensive but it worked.
I would rather have tools I do not need than to need tools I do not have

Rookie
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Joined: Mon Dec 17, 2018 1:35 pm

Post Tue Sep 17, 2019 8:25 pm

Re: Front Leaf Springs

So you made me look at my S120 4x4. On mine, as the parts book shows, the pivot is at the front and shackles at the rear of the front springs. At rest the shackle is canted back a little. As a rough visual, the rear eye of the spring is about 3/4" behind the pivot of the frame mount. I also have what looks like very little distance for the front drive shaft to compress and no splines showing.

With that said, I don't think it is a problem. For one thing, after removing and replacing driveshafts, it becomes apparent there is much more travel than the amount of splines showing. They really will compress just about to the shoulders. I also laid on the creeper and studied the geometry and tried to visualize the amount of potential rearward movement of the axle. It is a relatively long front drive shaft and in stock configuration it is not at a very steep angle from horizontal. The other part of it is how much front axle travel can you reasonably expect. typically static load does not vary on the front as much as it does in the rear, unless you are posing a football team sitting on the front fenders. Dynamic load can occur from bumps or potholes, but if you are not 4wd racing it or doing jumps you will probably never see full vertical travel of the front axle.

In short, I think you are looking for a problem that doesn't exist. However if you have modified suspension or any kind of non-stock lift - which it doesn't appear you do from your pictures, ignore everything I just said.

If you are still concerned, I would be happy to compare some photos and/or dimensions with mine to see if they are similar or whose is the most worn.
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