K10/K20 frame

[Jalopy_J]

I was at a salvage yard last weekend and almost nabbed the rear springs off a 76 K20. My truck has the HD front spring (3 leaf) option, but not the HD rear leaf option, and the front sits noticeably taller than the rear (that HD front spring also rides like garbage). My dad said he remembers the truck being nose high like that since the day it was new. I figured the 8 leaf spring on the K20 might raise the rear a little over the 6 leaf on mine, but I'm guessing that 8 leaf is 56in instead of a 52in. I've read on at least a dozen threads on this forum that K10 and K20 frames are identical, and that the frame already has holes drilled to move the rear spring mount back 4 inches for a 56in spring. My truck sure doesn't have those second set of holes in the frame. I would have to drill 8 holes in the frame if I want a 56in spring. I'm curious to hear what others' thoughts are, but it seems there's some incorrect information floating around about the frames.

 

[75gmck25]

My '75 GMC is an 8200 GVW camper special, and it still uses 52" springs. I believe they are 7 leaf, and this is the highest GVW available in '75 for a 3/4 ton.

Be prepared for a fairly rough ride, especially if you use the 10 ply rated tires that go along with those springs. It begins to ride better once you get about 1000 lbs in the bed. However, it also handles weight extremely well. I accidently overloaded it when getting rid of some old brick, and it handled a lot more weight than the GVW listed.

Bruce

 

[bucket]

Even with higher capacity, longer springs can improve the ride quality. My '88 Burb came with 5 or 6 leaf 52's (can't remember which) and I installed a set of 8-leaf 56's from an '83 C30 and the ride was actually better than stock. And no more saggy butt when towing.

 

[QBuff02]

1/2 and 3/4 ton trucks use a 52" rear spring and 1 ton trucks use 56" rear springs. If I remember there were a select few of the heavy duty sub-one tons that used a 56" rear spring but very limited. So you should have no problem swapping out the springs direct.

 

[bucket]

1/2 and 3/4 ton trucks use a 52" rear spring and 1 ton trucks use 56" rear springs. If I remember there were a select few of the heavy duty sub-one tons that used a 56" rear spring but very limited. So you should have no problem swapping out the springs direct.

Many 3/4 tons used 56" springs.

 

[QBuff02]

Many 3/4 tons used 56" springs.

I've only seen one 3/4 ton with 56" rear springs. Is it a year split thing? Because I would say 85% of my square work/experience is north of the 80 model year. I have seen some frames with the extra holes already in them though but a lot of frames don't and I hear people say that they all should.. I do know they tell you to measure spring lengths when ordering lift kits, but apparently they're a little more spread than I figured them to be @bucket

 

[Craig 85]

I've had (2) 3/4 ton trucks and Suburban with 454's. All had the 56" springs.

 

[bucket]

I've only seen one 3/4 ton with 56" rear springs. Is it a year split thing? Because I would say 85% of my square work/experience is north of the 80 model year. I have seen some frames with the extra holes already in them though but a lot of frames don't and I hear people say that they all should.. I do know they tell you to measure spring lengths when ordering lift kits, but apparently they're a little more spread than I figured them to be @bucket

I've seen a lot with 56's. Worked in a garage, worked a junkyard and spent a lot of time in other junkyards. I've owned 4 different 3/4 ton Burbs with 56's. Two of those were 2wd big blocks, the other two were 4x4 small blocks. A '78, a couple 86's and a '90. They were very common in 3/4 tons, and even used in 1/2 tons too.

 

[Jalopy_J]

The main question though was does anyone here have holes in the frame to mount the bracket for BOTH 52 and 56 springs? I've seen a dozen threads here that say K10 and K20 frames are the exactly same. I think this is probably wrong, at least it was in 76. No K10 had 56in springs, and my K10 frame does not have provisions for that. Maybe that's the only difference in a K10 and K20 frame, maybe there are other changes as well (strength, geomemtry, etc, idk), but I was surprised to see the lack of holes given the amount of threads I've read stating that otherwise.

 

[yevgenievich]

The manuals stated thickness difference on k10 vs k20. If there is no holes, likely there is some indication on the frame where the mounts would go. My 3/4 burb has the 56" springs.

 

[bucket]

The main question though was does anyone here have holes in the frame to mount the bracket for BOTH 52 and 56 springs? I've seen a dozen threads here that say K10 and K20 frames are the exactly same. I think this is probably wrong, at least it was in 76. No K10 had 56in springs, and my K10 frame does not have provisions for that. Maybe that's the only difference in a K10 and K20 frame, maybe there are other changes as well (strength, geomemtry, etc, idk), but I was surprised to see the lack of holes given the amount of threads I've read stating that otherwise.

Yes, all three of my K-Burbs have had the holes in the frame for both spring lengths. I'm pretty sure many trucks did too, but I don't currently have one so I won't guarantee it.

 

[Jalopy_J]

The manuals stated thickness difference on k10 vs k20. If there is no holes, likely there is some indication on the frame where the mounts would go.

So it sounds like K10 and K20 frames are actually a lot different then. (And what "manuals" stated this, btw? I'd be interested to read it.) A lot of bad info floating around then it seems. An no, there is no "indication on the frame" of where the mount would go. I'd just have to measure 4" back from the current holes.

 

[Jalopy_J]

I'm pretty sure many trucks did too, but I don't currently have one so I won't guarantee it.

K20's would have because those came with 52 or 56 depending on options. I was just surprised reading here that K10s had both as well because they were the same frame, when (at least in 76) they weren't.

 

[86 SCOTTSDALE]

My 86 K10 has holes for both.

 

[Rusty Nail]

I don't buy a 10 frame is the same as a 20.
That sounds ridiculous.