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  #1  
Old 08-05-2018, 08:57 AM
eldudderino eldudderino is offline
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Jeep J20 stock height

Hi, could anyone tell me what the stock measurement is from the front axle to the fender on a J20? This would tell me lift height correct? It has 35s on it and they do not rub. No cutting has been done. Also the rear has a spring over axle set up not sure if thats stock. The rear springs are like flat but they have a good 6in spacer between the axle and the spring. I assume they are stock springs just spaced. Any thoughts?
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  #2  
Old 08-05-2018, 09:07 AM
joe joe is offline
 
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The factory TSM will have stock dimensions measured at various point. Overall height, height at drivers sill plate, cargo deck height. That's with stock wheels and tires.
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Old 08-05-2018, 09:18 AM
eldudderino eldudderino is offline
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where do I find that at? I have search for stock dimensions and height a lot I cannot seem to find anything.
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  #4  
Old 08-05-2018, 09:44 AM
77Deepj20 77Deepj20 is offline
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Is the front still spring under?

I was able to fit 35's with a spring over conversion on the front with a dana60. It was about a 6" lift from stock
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  #5  
Old 08-05-2018, 09:48 AM
joe joe is offline
 
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May vary by year but usually in Chapter A "General Information". In there you'll find a chart "General Dimensions".
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  #6  
Old 08-05-2018, 10:38 AM
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Cecil14 Cecil14 is offline
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Quote:
Originally Posted by eldudderino
where do I find that at? I have search for stock dimensions and height a lot I cannot seem to find anything.

There's a sticky at the top of the "tech" section with links to the TSMs.


aa
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  #7  
Old 08-05-2018, 12:23 PM
eldudderino eldudderino is offline
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The front is still spring under. Can someone just give me a link to the TSMs. What are TSMs anyway?
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  #8  
Old 08-05-2018, 02:14 PM
eldudderino eldudderino is offline
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I found what you are talking about but I do not see in any of the manuals on that site the measurement I think I need. To tell suspension lift you take the height of the center line of the axle to the fender and subtract that by the stock measurement correct? Or is there another way?
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  #9  
Old 08-06-2018, 10:47 AM
joe joe is offline
 
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If the factory didn't measure the locations you want, just use the locations and measurements the factory used. Measure yours...compare. Don't forget to allow for the tire dia differences cause the factory measured using "stock" tires.
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  #10  
Old 08-06-2018, 01:17 PM
eldudderino eldudderino is offline
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Quote:
Originally Posted by joe
If the factory didn't measure the locations you want, just use the locations and measurements the factory used. Measure yours...compare. Don't forget to allow for the tire dia differences cause the factory measured using "stock" tires.

So I measured and I assume its a 6in. The factory measures 12in from floor to bottom of the front part of the frame. Mine measures 24in, but I have 35in tires. The stock tires are about 28 inch so thats +7in. So then if you subtract 7inches from 24 and get 17 then 17-12 you get 5inch. I assume its a 6in I could be wrong but the ground may not be level or what ever. Is my math correct? Does that make sense? Also in the rear its spring over axle...is that stock? They put a pretty high spacer in looks like 6+inch I have not measured yet. Do you think the stock springs are in the back still? They are flat I am trying to figure out what springs to get for the rear end.
Thank you!
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  #11  
Old 08-06-2018, 02:16 PM
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Cecil14 Cecil14 is offline
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Stock front (after '74 or so) is spring under, this was done to accommodate moving the spring hangers from the side of the frame to under the frame. Stock rear has always been (to my knowledge) spring over.

When taking your tires into account, remember the difference is only half. You are only gaining half of the total tire diameter in height between the ground and the axle. I would encourage you to measure your tires to be 100% sure what size they are. A "35" is rarely truly 35" tall. A good, true, way to measure for this purpose is from the center of the hub to the ground. That's going to be the most accurate measurement you can really take. Then you'll just have to assume that the same measurement on a stock vehicle was 14". Does the TSM specify which tires were on the vehicle for those measurements? I know 31s were a pretty common option on the J-trucks.


aa
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  #12  
Old 08-06-2018, 03:17 PM
eldudderino eldudderino is offline
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Quote:
Originally Posted by Cecil14
Stock front (after '74 or so) is spring under, this was done to accommodate moving the spring hangers from the side of the frame to under the frame. Stock rear has always been (to my knowledge) spring over.

When taking your tires into account, remember the difference is only half. You are only gaining half of the total tire diameter in height between the ground and the axle. I would encourage you to measure your tires to be 100% sure what size they are. A "35" is rarely truly 35" tall. A good, true, way to measure for this purpose is from the center of the hub to the ground. That's going to be the most accurate measurement you can really take. Then you'll just have to assume that the same measurement on a stock vehicle was 14". Does the TSM specify which tires were on the vehicle for those measurements? I know 31s were a pretty common option on the J-trucks.


aa

It does say the size and it converts to a 28.3in or something mine are 33inches tall on the vehicle.
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  #13  
Old 08-06-2018, 03:48 PM
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tgreese tgreese is offline
 
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This may be too straightforward, but if it's lifted, and you have blocks in the rear, isn't the height of the lift equal to the height of the blocks? The blocks are used on the rear because it's spring-over (so it's possible), and because it's cheaper than new springs. The front is spring under, requiring new springs. You'd expect the front and rear to match.
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  #14  
Old 08-06-2018, 04:04 PM
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Cecil14 Cecil14 is offline
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Quote:
Originally Posted by tgreese
This may be too straightforward, but if it's lifted, and you have blocks in the rear, isn't the height of the lift equal to the height of the blocks? The blocks are used on the rear because it's spring-over (so it's possible), and because it's cheaper than new springs. The front is spring under, requiring new springs. You'd expect the front and rear to match.

I have seen cases of people using a combination of springs and blocks, ie: 2" blocks and 4" springs. The less lifted springs tend to flex a little bit better, and are usually cheaper. Not my personal preference, but then neither are large lifts.

I would say the block is probably a decent place to start, and you're obviously getting at least that much lift in the rear. If it's sitting level, then the front springs are likely at least matching that lift block.


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  #15  
Old 08-07-2018, 05:53 AM
eldudderino eldudderino is offline
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Quote:
Originally Posted by Cecil14
I have seen cases of people using a combination of springs and blocks, ie: 2" blocks and 4" springs. The less lifted springs tend to flex a little bit better, and are usually cheaper. Not my personal preference, but then neither are large lifts.

I would say the block is probably a decent place to start, and you're obviously getting at least that much lift in the rear. If it's sitting level, then the front springs are likely at least matching that lift block.


aa

So the rear block is exactly 6 inches from the bottom of the leaf to the top of the axle. I can post a pic to show you what I am talking about, but both leafs in the back are flat...like more then flat they are bending the other way slightly. Even being spaced this should not be happening correct?
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  #16  
Old 08-07-2018, 08:09 AM
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Cecil14 Cecil14 is offline
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They sound like stock rear leafs. Extreme wear like that is not uncommon, the stock leafs on these are usually ~40 years old. They were usually built for ride quality as well, and not longevity, so long term wear wasn't really considered.

If it were me, I would ditch that block. I'm not a fan of blocks in general, but a block that tall is just asking for trouble. Do you need a lift? How much do you actually want? A new high quality kit might be a good option for you.


aa
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  #17  
Old 08-07-2018, 09:35 AM
eldudderino eldudderino is offline
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Quote:
Originally Posted by Cecil14
They sound like stock rear leafs. Extreme wear like that is not uncommon, the stock leafs on these are usually ~40 years old. They were usually built for ride quality as well, and not longevity, so long term wear wasn't really considered.

If it were me, I would ditch that block. I'm not a fan of blocks in general, but a block that tall is just asking for trouble. Do you need a lift? How much do you actually want? A new high quality kit might be a good option for you.


aa

I think it needs a lift. I want to keep the 35s. I am thinking about a 4inch spring and a 2 inch spacer in the back. From what I have read the ride quality of 6in is awful and the thing already makes you almost pee blood hahaha. Who makes springs for these? I am having a hard time finding rear leafs.
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  #18  
Old 08-07-2018, 10:42 AM
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Cecil14 Cecil14 is offline
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You should be able to get 35s under a J-truck pretty easily with a good 4" lift. What year is your truck? There were some changes around the '74-'76 time frame. The biggest problem you're likely to encounter when looking for a lift is keeping the payload capacity of a J-20. I've never seen lift springs for the heavier trucks, just J-10s. They're the same physical dimensions, so you can bolt a long bed J-10 spring on your J-20.

If you want to maintain your J-20 carrying/towing capacity, you'll have to have custom springs made. Alcan is one extremely highly rated spring maker, but they're not cheap. I had a quote done for some pretty basic replacement springs from them and was at about $1250 for all four corners.

To the 6" springs...yes, those are going to be horrible. To make a lift spring, they have to make the spring physically longer, but still fit between the same two mounting points. This gives the spring its "lift." When you arch the spring that much more, though, it doesn't flex nearly as well. That is partially due to the static arch being that much higher, as well as being limited by shackle length.

Personally, I think 4" is probably the biggest leaf spring lift I would ever go with. If I wanted more than that, I'd be looking at a link/coil conversion or airbags.

Give us a few more details about your truck, and what your intended goals are, and we can start throwing out better options for you.


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  #19  
Old 08-07-2018, 01:08 PM
eldudderino eldudderino is offline
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Talking

Quote:
Originally Posted by Cecil14
You should be able to get 35s under a J-truck pretty easily with a good 4" lift. What year is your truck? There were some changes around the '74-'76 time frame. The biggest problem you're likely to encounter when looking for a lift is keeping the payload capacity of a J-20. I've never seen lift springs for the heavier trucks, just J-10s. They're the same physical dimensions, so you can bolt a long bed J-10 spring on your J-20.

If you want to maintain your J-20 carrying/towing capacity, you'll have to have custom springs made. Alcan is one extremely highly rated spring maker, but they're not cheap. I had a quote done for some pretty basic replacement springs from them and was at about $1250 for all four corners.

To the 6" springs...yes, those are going to be horrible. To make a lift spring, they have to make the spring physically longer, but still fit between the same two mounting points. This gives the spring its "lift." When you arch the spring that much more, though, it doesn't flex nearly as well. That is partially due to the static arch being that much higher, as well as being limited by shackle length.

Personally, I think 4" is probably the biggest leaf spring lift I would ever go with. If I wanted more than that, I'd be looking at a link/coil conversion or airbags.

Give us a few more details about your truck, and what your intended goals are, and we can start throwing out better options for you.


aa

Well I bought it a little over a month ago. It is a 1984 J20 with a flat bed. The main reason I would like to keep the 35s is because well they are there and the look of the big rubber in the wheel well. The ground clearance is also cool even though maybe not needed. I bought it because it was a good price and my family and I are jeep junkies so it is just a fun truck. Also I drive a 2dr JK so I wanted something that I could use to hall and tow things. (Like a 1963 CJ6 i have been thinking about) It has 3.90s in the rear ends just checked a couple days ago. The 360 was rebuilt 30k miles ago with an edelbrock performance package. It has a MSD distributor and ummm its reliable. The springs are not exactly the most important thing I am just making a list of things for later down the road. First thing first is to paint the under side before winter because illinois is brutal. No rust holes in frame the only holes are the cab corners..not bad. It has been a really cool truck thats for sure.
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  #20  
Old 08-08-2018, 05:59 AM
threepiece threepiece is offline
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Quote:
Originally Posted by Cecil14
Stock front (after '74 or so) is spring under, this was done to accommodate moving the spring hangers from the side of the frame to under the frame.




aa
To expand on this: I believe the front spring relocatin was done to accommodate the introduction of the Dana 44 open knuckle axle in 1974. With the springs placed outboard of the frame they would certainly interfere with the tires because the open knuckle offered more turning angle (less turning radius). With the springs in a lower position under the frame they had little choice but to move the axle on top to keep from too much lift.
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