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Old 07-02-2020, 11:17 AM   #1
RyanAK
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1978 K10 Suburban Suspension Assessment

Hey, guys. I have a more detailed thread of what I'm trying to do up in the squarebody forum, but thought I'd ask some simple questions here too.

Here's the thread with all the details: http://67-72chevytrucks.com/vboard/s...d.php?t=808476



Basically I'm a little concerned about the front springs and my rears sag a bit with a full (40 gal) tank of gas. Looking to go back to stock or "stock plus" but could use some eyes on my current suspension. Rides nice enough as it is... but I think it's time to freshen it up.

Front: Gaps between leafs (I can get a finger between them...) and the front axle isn't centered beneath the body. Negative arch, but still pretty good distance to the bump stops. There are marks on the main leaf from the stops though... Bushings need replaced. Tired shocks. Something to worry about?







These are the best photos I could get showing the off-center axle:








Rear: pretty flat with anything more than 1/2 tank of gas that gives a noticeable sag. 'Chevy Lean'. Broken leaf pack clamp. Bushings shot. Tired shocks. No broken leafs though.







Thoughts on what I've got and what should be done? Appreciate the help.
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Old 07-02-2020, 12:54 PM   #2
Keith Seymore
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Re: 1978 K10 Suburban Suspension Assessment

Regarding the "off center axle": I would suspect the axle is centered in the chassis but the front end sheet metal is not square.

If the body gets set on the chassis crooked during assembly then the hood goes shooting off in that direction. The front fenders get pushed out of square to maintain the hood to fender gap.

That manifests itself as a difference in the relationship between the front tire and the fender lip or, because the bumper is attached directly to the frame, a differing gap between the inside edge of the bumper and the fender surface from LH to RH.

I'm not seeing that in the photos but it is worth checking and is the more common failure mode, especially with regular cab pickups as a result of the shorter cab length.

K
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Old 07-02-2020, 12:59 PM   #3
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Re: 1978 K10 Suburban Suspension Assessment

Some things you can do to tighten the front end up:

a) Install the optional three leaf front spring pack

b) Run as much caster as you can generate (ie, 10-12 degrees if you can get it).

c) Tighten the steering gear up: 20 in lbs over center torque and 8-10 in lbs preload. The procedure for doing this properly is in the Unit Repair Manual.

K
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Old 07-02-2020, 01:01 PM   #4
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Re: 1978 K10 Suburban Suspension Assessment

For Chevy lean: I usually just put a spacer (often just a piece from another leaf) on the low side to bring that side up to square.

K
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Old 07-02-2020, 01:41 PM   #5
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Re: 1978 K10 Suburban Suspension Assessment

Quote:
Originally Posted by Keith Seymore View Post
Regarding the "off center axle": I would suspect the axle is centered in the chassis but the front end sheet metal is not square.

K
This may be the case. I'm trying to find good places to measure. There's some variation between the bumper and each fender sheetmetal, but not enough to account for the amount the passenger-side tire projects from the wheel well. I'm not overly concerned if it's just cosmetic... it is an old truck after all. But with the front springs as they are I was concerned something got torqued or bent to throw the axle off. I do have a mild vibration at certain speeds that I haven't been able to isolate.
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Old 07-02-2020, 01:44 PM   #6
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Re: 1978 K10 Suburban Suspension Assessment

Quote:
Originally Posted by Keith Seymore View Post
Some things you can do to tighten the front end up:

a) Install the optional three leaf front spring pack

b) Run as much caster as you can generate (ie, 10-12 degrees if you can get it).

c) Tighten the steering gear up: 20 in lbs over center torque and 8-10 in lbs preload. The procedure for doing this properly is in the Unit Repair Manual.

K
Thanks, Keith. The front end seems to dive fine. It does want to drive downhill on crowned roads. Other than that it is pretty smooth and steering is tight. It's the visual inspection of the springs that gave me pause.

Is the gap in the leafs something to worry about?

Does the three-leaf pack have a higher (stiffer) spring rate?

What will adding caster do? I'm not overly familiar with alignment fine-tuning.
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Last edited by RyanAK; 07-02-2020 at 01:51 PM.
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Old 07-02-2020, 01:50 PM   #7
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Re: 1978 K10 Suburban Suspension Assessment

Quote:
Originally Posted by Keith Seymore View Post
For Chevy lean: I usually just put a spacer (often just a piece from another leaf) on the low side to bring that side up to square.

K
I was thinking the Chevy Lean in the rear might be caused by the wonky springs in the front and was going to wait until I had the front addressed (with whatever approach...) to see the effect on the rear.

My other thought (other than needing to replace bushings so potentially would just stuff new springs in...) would be to use something like Hellwig auxiliary load leveling springs to eliminate the sag and, by setting the pretension, dialing out the lean.

My current rears are 5 + 1 overload. I have a line on a set of 4+1 rear springs that I think were on 80-87 K10 Suburbans. Are these equivalent leaf packs?

Appreciate the input. Thank you!
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Old 07-03-2020, 11:49 AM   #8
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Re: 1978 K10 Suburban Suspension Assessment

I'd either replace all the springs with 3/4 ton stuff with an add-a-leaf in the rear or if there is a local spring shop that can rebuild them to your specs then go that way. Get some fresh shocks on the beast, then go after the steering. I'm on my third Suburban. Not going to be stupid with this one and sell it. Just doing the factory springs will lift that thing about 3''. And good grief....fix the exhaust leaks on that thing before you asphyxiate yourself
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Old 07-03-2020, 12:12 PM   #9
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Re: 1978 K10 Suburban Suspension Assessment

Ha. I’m actually under the truck right now tearing the exhaust out. New manifold-back pipes and mufflers laid out in the grass.

Appreciate the thoughts. It’s a good plan.
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Old 07-06-2020, 12:23 PM   #10
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Re: 1978 K10 Suburban Suspension Assessment

So while underneath the truck doing the exhaust, I noticed just how tweaked the front shackles are. They're both bent to the passenger side and I assume this is contributing to the front axle not being centered beneath the body. Guess we'll be replacing shackles when we do springs. Amazing how nicely the truck rides and steers with the old shocks, worn out bushings, gaps in the leafs, and tweaked shackles!





New exhaust. More quiet, less sleepy.

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Old 07-06-2020, 08:45 PM   #11
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Re: 1978 K10 Suburban Suspension Assessment

Quote:
Originally Posted by RyanAK View Post
... Amazing how nicely the truck rides and steers with the old shocks, worn out bushings, gaps in the leafs, and tweaked shackles!
Further proof into the 21st Century of the old(ancient) saying - A Chevy will run (or run badly) longer than most others will run.
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Old 07-07-2020, 01:58 AM   #12
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Re: 1978 K10 Suburban Suspension Assessment

One of the biggest mistakes people make when fixing these older leaf sprung trucks is to install new heavy duty springs and stiff gas shocks. Ride worse than when new.
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Old 07-07-2020, 11:41 AM   #13
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Re: 1978 K10 Suburban Suspension Assessment

Completely agree, SilverMiner.

Richard, I’d love to hear how you’d approach this. Just trying to gather as many strategies as I can before I commit to a plan of action.
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Old 07-07-2020, 06:04 PM   #14
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Re: 1978 K10 Suburban Suspension Assessment

Quote:
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One of the biggest mistakes people make when fixing these older leaf sprung trucks is to install new heavy duty springs and stiff gas shocks. Ride worse than when new.
It is after all..........A Suburban and a Truck. Driving my suburban with the old suspension was soft and squishy. Now it drives firm and controlling, not harsh, but there is more control especially around corners and stuff. You don't have to wait for the vehicle to catch up to the steering wheel where you want to put the vehicle. You want soft and pillow like, buy a full size car with coils
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Old 07-08-2020, 01:53 AM   #15
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Re: 1978 K10 Suburban Suspension Assessment

Probably should not have made that blanket statement. See a lot of posts with people stating the ride is not acceptable on lifted, lowered and stock trucks. Agree that the old solid axle trucks will not ride like a car even with the extent I am going with my project. I had no load capacity built into my rear leaf packs as I will drive unloaded 95% of the time. My strategy for going stock height on a semi DD would be stock spring rate for front and rear replacement leaf packs. Softer if going with a progressive custom pack. If you are going to haul extra weight at times consider a helper bag setup. Universal setups are not costly. The bags can actually improve dampening when unloaded running at 10-15 psi. Unless you will be driving the vehicle hard and need the performance use a hydraulic shock not a stiff gas shock.
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Old 07-08-2020, 08:45 AM   #16
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Re: 1978 K10 Suburban Suspension Assessment

Thanks for chiming in, Richard. Your build looks great. I'm not looking for a car-like ride... I actually enjoy the ride of a solid-axle truck. But don't want my teeth rattled either. The Suburban gets used as a DD... family hauler and truck stuff. Just brought a heavy load of lumber home with it. Squatted pretty good. Made the front end light and a little squirrely...

Looks like there were quite a few options for Suburban front springs as far as spring rate and number of leafs. A couple steps between 1/2 ton and full 3/4 so should be able to choose something appropriate there. Anyone have a source for stock shackles?

Rear springs... I just want to bring it back to stock height or a bit higher and be able to control the squat when loaded. They'll get swapped because the bushings are shot and I'll be pulling the leafs for that, so might as well get new/fresh leaf packs to put in to bring the back up where it should be.

I've thought about helper bags but think I'd go with a progressive helper spring... it's there all the time, doesn't need to be aired up or down, and only comes into play when there's enough weight to engage the helpers. Sorta set and forget. Doesn't seem like it's as popular a strategy as bags and I haven't been able to find much about them on the forum. Wish I could get some thoughts on these.

This stuff is fun, eh?
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Old 07-08-2020, 02:02 PM   #17
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Re: 1978 K10 Suburban Suspension Assessment

I'll post up some pics later on what I did with my recent burb. Before pics and where the suspension sits now on 1 ton axles. I got rid of both the 10 bolts, put a 14 bolt full float in the rear and a dana 60 in the front. Had the front 2 leaf springs rebuilt with a 3rd spring and the rear pack rebuilt and upped the pack 2 leafs and rearched to match the front.
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Old 07-08-2020, 09:11 PM   #18
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Re: 1978 K10 Suburban Suspension Assessment

Few Pics for ya
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Old 07-08-2020, 09:13 PM   #19
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Re: 1978 K10 Suburban Suspension Assessment

Afterwards
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Old 07-08-2020, 09:16 PM   #20
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Re: 1978 K10 Suburban Suspension Assessment

couple more
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Old 07-09-2020, 11:18 AM   #21
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Re: 1978 K10 Suburban Suspension Assessment

Really very well done! Thanks for sharing. You took that rig from 'huge station wagon' to 'capable truck'. I don't have any plans for major driveline changes unless something in the diffs would fail. Only possible thing would be converting the full-time NP203 to part time. I get about 10mpg at the moment.

Here's the wrinkle with all this... this is my daily driver and my slider is currently being used by a friend that got jammed up. So I don't have the luxury of having my truck laid up for days or weeks while I rebuild. So this will be a 'phased' approach. Which also let's my phase out my budget to buy everything I need. So right now I think it'll look something like this:

Spring rates and height TBD, but will be between stock 1/2 ton and 3/4 ton. I like the idea of going towards 3/4 rate and height.

Step 1 - Shocks. Front and rear. I've always had good luck with Bilstein 4600s. I can fit the install in in an evening or Saturday.

Step 2 - Rear springs. Buy new or grab pull-a-part leaf packs to have rebuilt/re-arched. New bushings, new U-bolts, new center pins. Have everything ready to go so I pull the old and slam in the new. I have 5+1 leafs now.

Step 3 - Front springs. Buy new or grab pull-a-part leaf packs to have rebuilt/re-arched. New bushings, new U-bolts, new center pins. NEW SHACKLES. Have everything ready to go so I pull the old and slam in the new. I have 2-leaf fronts.

Step 4 - fine tune height and level with ORD 1" zero-rates or spacers.

Step 4 - Steering and alignment.

A couple questions...

Bushings - rubber, poly, grease-able poly (ORD)?

Re-arch - is this a long-lasting solution? I have a line on pull-a-part springs for cheap that I could rebuild and have re-arched.

Any thoughts on a supplier for front shackles? I'm not seeing any stock ones around...

Really appreciate everyone's input. This should bring the old Burb back to it's former truck self.

R
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Old 07-09-2020, 11:39 AM   #22
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Re: 1978 K10 Suburban Suspension Assessment

Cannot see in the pics, but I replaced the front shackles with some I found made out of 3/8'' steel plate with a 5'' center to center. Won't be bending those-----I'll see if I can provide a link later. Also with the axle upgrades I get a lot better braking system. I have always found that the 1/2 ton baking system is less than stellar when towing anything more than a thousand pounds with a 7000 lb vehicle/truck. The 10 bolt rear axle in a Suburban was not a smart idea from GM. IMHO it was a huge mistake on such a large vehicle. The rear should at the minimum should have gotten the 14 bolt semi-float.
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Old 07-10-2020, 01:24 PM   #23
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Re: 1978 K10 Suburban Suspension Assessment

I have a Corporate 12-Bolt rear, 10-bolt front. I'd consider upgrading down the road if this becomes a serious tow vehicle. Right now it isn't in the budget... but I do agree with what you're saying. Towing the Airstream with our 04' Z71 Suburban once upon a time would have been hairy except for the very, very good trailer brakes and the way I had the brake controller dialed in. I wouldn't even consider a heavily loaded no-brake trailer with this rig.

3/8" plate shackles? Sheesh! Agree. Not bending those!

Anyone have thoughts on bushings and re-arching?

Appreciate all the input.
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Old 07-11-2020, 01:37 PM   #24
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Re: 1978 K10 Suburban Suspension Assessment

Quote:
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3/8" plate shackles? Sheesh! Agree. Not bending those!

Anyone have thoughts on bushings and re-arching?

Appreciate all the input.
Being in PA, there should be a few truck or leaf spring shops that can rebuild the fronts and add a leaf to them. I would re arch the rear and add a leaf to that also. Do the fronts first then have them do the rears to match


here ya go-- https://keystonespring.com/

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Old 07-14-2020, 09:39 AM   #25
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Re: 1978 K10 Suburban Suspension Assessment

Thanks for all the input. Much appreciated. I've been looking for a spring shop in the area... PA is a pretty large state and most shops seem to be near the metro areas. I think I have a plan. Now to implement it!

R
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