1972 Suburban 4X4 3/4 Ton K20 "The Beast"

[nsiti]

I thought I'd report back with the little progress that's been made over the past few months.

The camshaft came back from Howards and was re-installed. This time it was a perfect fit. They never confirmed what the problem was. I suspect they had sent me the wrong grind initially. This made it so we could continue with the top end of the motor, see attached photos. Any suggestions as to what color to paint the engine block when it's assembled? The truck will be painted Dark Olive Metallic, with a white roof and upper rear barn doors (including rear pillars).

One interesting thing to note about the Dart Sportsman block is the peculiar design of the dipstick hole, which does not allow much clearance. This necessitated some grinding of the freeze plug boss on the block as well as the dipstick tube base so that the Milodon 22005 stainless braided could fit.

In addition, we finally got the rear wood bed seated and placed on new bushings.

Now to finalize the bodywork in preparation for painting this summer.

Cheers,
Nick

[Richard]

I would suggest that you address the rear suspension before going on the road. The rear shackle flip hanger needs to move forward so the shackle is pointing down. The way it is now it will most likely invert and lock the spring against the frame not allowing any movement. Real bad ride and a recipe for disaster. Have to be careful when going to a compression type shackle. Proper placement is needed to avoid inversion. The spring cannot compress as you have it now. Probably why you think it sits high.

[nsiti]

Originally Posted by Richard

I would suggest that you address the rear suspension before going on the road. The rear shackle flip hanger needs to move forward so the shackle is pointing down. The way it is now it will most likely invert and lock the spring against the frame not allowing any movement. Real bad ride and a recipe for disaster. Have to be careful when going to a compression type shackle. Proper placement is needed to avoid inversion. The spring cannot compress as you have it now. Probably why you think it sits high.

Richard, thank you

We are also concerned about the shackle flip angle, so I reached out to Offroad Design, where the kit was purchased from. Kyle over there responded as follows:

Regarding the weight sitting on the springs, there is a body but it more or less is a bare shell at the moment. It makes sense that your shackles are sitting at a forward angle, our springs are much more reactive to weight than a standard lift kit springs and a set of springs for a Suburban are built heavier to start with to compensate for the addition body weight. Once the truck is full assembled the springs will flatten out and correct the shackle angle.

Nevertheless, this remains a concern for us and we agree this needs to be addressed before hitting the road. I really appreciate your comment and wonder what you think of ORD's response? What angle would you consider safe, and do you have suggestions for us to consider in case their theory is not correct?

Regards,
Nick

[Richard]

Originally Posted by nsiti

Richard, thank you

We are also concerned about the shackle flip angle, so I reached out to Offroad Design, where the kit was purchased from. Kyle over there responded as follows:

Regarding the weight sitting on the springs, there is a body but it more or less is a bare shell at the moment. It makes sense that your shackles are sitting at a forward angle, our springs are much more reactive to weight than a standard lift kit springs and a set of springs for a Suburban are built heavier to start with to compensate for the addition body weight. Once the truck is full assembled the springs will flatten out and correct the shackle angle.

Nevertheless, this remains a concern for us and we agree this needs to be addressed before hitting the road. I really appreciate your comment and wonder what you think of ORD's response? What angle would you consider safe, and do you have suggestions for us to consider in case their theory is not correct?

Regards,
Nick

Would bet if you hit the shackle up with a hammer (dead blow if you have one) with the truck weight on spring it will swing up to the frame. If you hit it down it might swing back. As it sits the spring is bound up and in use the shackle will want to swing the wrong way. The shackle needs to be in path of rear swing at full droop to prevent inversion. Hope that makes sense.

[nsiti]

Originally Posted by Richard

Would bet if you hit the shackle up with a hammer (dead blow if you have one) with the truck weight on spring it will swing up to the frame. If you hit it down it might swing back. As it sits the spring is bound up and in use the shackle will want to swing the wrong way. The shackle needs to be in path of rear swing at full droop to prevent inversion. Hope that makes sense.

Richard, thanks, my interpretation is that we need to make sure the shackle swings towards the rear. We'll definitely address this when more weight is placed on the rear. The springs and shackles will definitely need some persuasion from a dead blow hammer (and hopefully that's all)!

[Richard]

Unfortunately the hanger needs to be moved or the spring de-arched to make it longer at rest. If just hitting the shackle to move it with a load on it. As soon as unloaded such as going over a bump the spring will pull shackle back as it is now and next bump will invert it to the frame. With a compression shackle as you have the shackle must be in the rear path with the spring unloaded. Make sense? Just trying to help you understand how it will work.

[nsiti]

Originally Posted by Richard

Unfortunately the hanger needs to be moved or the spring de-arched to make it longer at rest. If just hitting the shackle to move it with a load on it. As soon as unloaded such as going over a bump the spring will pull shackle back as it is now and next bump will invert it to the frame. With a compression shackle as you have the shackle must be in the rear path with the spring unloaded. Make sense? Just trying to help you understand how it will work.

Hi, yes, ORD says the spring will de-arch with some movement and some weight on it. I'll report back on the actual outcome!

[Richard]

I came across this by accident and thought it may help https://67-72chevytrucks.com/vboard/...1&postcount=71 About the max angle you can get away with on a compression shackle. Notice there is zero weight on the spring.

[nsiti]

Hi all, I hope you had a wonderful Thanksgiving.

I'm back to report that the build continues. It's painfully slow progress but we are very close to the paint stage. Hopefully it's all downhill after that (famous last words!).

In the meantime, I'm still dealing with the rear leaf spring issue where the ride angle is improper and too high (see posts 79 and 83 for photos). I continue to be in conversation with ORD as to how to best proceed. Based on our analysis and thoughtful comments by Richard and others on this board we have pushed back against the theory that the rear springs will settle. Unfortunately, the rear leaf springs were improperly designed.

Originally, I ordered a full suspension set, with 5" lift including rear shackle flip, from ORD and it seems they miscalculated in the design of the rear leaf springs (the front are fine).

When I placed the order I was not asked for the weight of the vehicle, which is stock, except for the 40 gallon fuel tank. Now I am being asked for the weight and thought I would get some advice from you as to how to respond. Any assistance would be appreciated. I've also posted this in the 4x4 section.

Once this is settled, I trust I will have more time to post lots of progress photos in the coming weeks.

Thanks,
Nick

[LockDoc]

-
It might be hard to figure with a 40 gallon tank. There will be a lot of weight difference full and empty (or almost empty). Approximately 330#. I suppose you would use half of that for a static weight.

Here is the information for the '72 3/4 ton 4x4 Suburban posted by member "Vectorit" back in 2013.

3/4-Ton Commercial 4x4 - Model C/Series 20 - 127-in. w.b

Here is a link to the full thread for anyone that might need it...

https://67-72chevytrucks.com/vboard/...d.php?t=575238
.

[nsiti]

Originally Posted by LockDoc

-
It might be hard to figure with a 40 gallon tank. There will be a lot of weight difference full and empty (or almost empty). Approximately 330#. I suppose you would use half of that for a static weight.

Here is the information for the '72 3/4 ton 4x4 Suburban posted by member "Vectorit" back in 2013.

Here is a link to the full thread for anyone that might need it...

https://67-72chevytrucks.com/vboard/...d.php?t=575238
.

Hi, thanks for sharing.

I've given some thought as to how to account for the weight of a larger gas tank. It's heavier than stock (maybe 50 lbs?), plus 20 gallons additional max capacity (124 lbs), so that's about 175 lbs extra weight when full. That's the equivalent of an average person's weight. These heavy duty springs probably wouldn't sag much with an extra 175 lbs of weight, but something to consider in the design.

I also looked at the full range of vehicle weights in the link you provided and compared them to the figures you posted, which raises some concern as to accuracy for the 1972 3/4 ton 4x4. Notice that the weight difference of the doors (4,141 lbs) vs gate (4,585) figures you posted is 444 lbs, while in all other instances the differences are near zero. Any idea why that might be? I would guess it's a typo.

To cross reference, I looked at the official Chevy Suburban 1972 spec sheet and read that the curb weight is 4,857 for the 8-cylinder K20 variant (with a fairly even 2,374 lb / 2,483 lb front / rear split).

All this analysis made me think, what are we trying to measure when designing for the weight load capacity of rear leaf springs? They are not going to support the entire rear weight of the truck, but rather the frame and body weight, excluding the axle, wheels and tires, right?

Any additional feedback would be appreciated.

Regards,
Nick

[LockDoc]

Originally Posted by nsiti

Hi, thanks for sharing.

I've given some thought as to how to account for the weight of a larger gas tank. It's heavier than stock (maybe 50 lbs?), plus 20 gallons additional max capacity (124 lbs), so that's about 175 lbs extra weight when full. That's the equivalent of an average person's weight. These heavy duty springs probably wouldn't sag much with an extra 175 lbs of weight, but something to consider in the design.

I also looked at the full range of vehicle weights in the link you provided and compared them to the figures you posted, which raises some concern as to accuracy for the 1972 3/4 ton 4x4. Notice that the weight difference of the doors (4,141 lbs) vs gate (4,585) figures you posted is 444 lbs, while in all other instances the differences are near zero. Any idea why that might be? I would guess it's a typo.

To cross reference, I looked at the official Chevy Suburban 1972 spec sheet and read that the curb weight is 4,857 for the 8-cylinder K20 variant (with a fairly even 2,374 lb / 2,483 lb front / rear split).

All this analysis made me think, what are we trying to measure when designing for the weight load capacity of rear leaf springs? They are not going to support the entire rear weight of the truck, but rather the frame and body weight, excluding the axle, wheels and tires, right?

Any additional feedback would be appreciated.

Regards,
Nick

I didn't read the whole chart but yes, that weight difference is suspicious. Like you suggested it may just be a typo.

I can't offer much else because the '69 Suburban I built didn't need any adjustments and my '67 Panel Truck already had drop springs under it when I bought it.

[HO455]

Q10I'll add that my 2wd, 1/2 ton, SBC, Burban weights 4780 with my 200 lbs and about 1/2 tank of gas and no second row seat installed.

It's great to see you're making progress! Keep up the good work!

[nsiti]

I was informed by ORD that they will provide a spring to hold 1050# at a 6 to 6.5” loaded arch measured from the spring perch up. I'm not sure what to make of this and have call into them but the owner is away for the week, so I thought I would ask for some feedback from all of you. Thanks!

[LockDoc]

Originally Posted by nsiti

I was informed by ORD that they will provide a spring to hold 1050# at a 6 to 6.5” loaded arch measured from the spring perch up. I'm not sure what to make of this and have call into them but the owner is away for the week, so I thought I would ask for some feedback from all of you. Thanks!

I hope someone else can give some insight on that. I am lost on that one....