Dual rear shocks?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cobinder · 11-12-2007, 12:04 PM

I'm thinking I want to put dual rear shocks on the rear of my 80 K20 chassis.
I'm running 39" Michelin run flat military tires that weight over 100 pounds each. So I think dual shocks is not too outta line

Why did they run one shock in front and one in back? I'd like to just run two each side in the rear. Anyone have a good way of doing this? kits?

thanks for any input.

LONGHAIR · 11-12-2007, 01:18 PM

There is really no point in it, other than looks. If that is what you are after, go for it, but there is no performance gain. Off-road racers use them to dissipate heat. They use multiple shocks that are softer than the single unit that they would be replacing. They have very long travel and are raced over long distances. This builds a lot of heat in the oil. By using multiple shocks, each handling less of the load, the heat is spread over a greater area and more oil. They belong on long-travel suspensions.

Finding a shock that is soft enough to be used in pairs would be cost prohibitive in most cases, especilly since there is no need. Doubling up with "normal" shocks just stiffens the suspension you already have. Your 3/4 ton truck probably is plenty stiff now

68K20 x Drill · 11-12-2007, 05:57 PM

Rancho adjustables set to soft should be alright doubled up on a heavy truck.
The front and back shock came out in 69 or so to reduce axle wrap.

**special-K** · 11-12-2007, 06:01 PM

The only place dual shocks serve a purpose is up front under all the engine weight.Your weight is unsprung,not sitting on the axles/springs.Can you use powder balance in runflats?

cobinder · 11-12-2007, 08:04 PM

This begs the question, does a shock dampen the wheel as it travels up or the weight of the chassis as it moves down?

If it is the wheel (pro active) as it moves up then the weight tire and wheel assembly would have an affect on the damping of the shock.

If it is the chassis (re active) then a single damper sized for the weight of that corner of the chassis should be enough.

Off-road race trucks take great pains to get their suspension,wheels and chassis as light as possible which helps reduce the amount of damping force it takes to offer the best ride for them. Because they have such long amounts of travel which results in high piston speed they produce lots of heat. They run several dampers with light resistance to reduce the heat.

In my case I have very heavy wheel weight hence my concern

Powder balance is the only way to go on the big Michelins

**special-K** · 11-12-2007, 10:39 PM

Answer:Both.Your thinking isn`t off.But,the lack of weight on the rear axle (sprung weight) is why you`ll add to the harshness and have no give in your suspension.I think better shocks are your answer.The Rancho 9000RSXs are 9-position adjustable.They are expensive,but so are two shocks in place of one,then theres what it takes to mount the 2 extra shocks.

OLDCHEV4X4 · 11-14-2007, 07:56 AM

I run the Bilstein 5150 reservoir shocks on my obstacle course Blazer. They have 2 different style valving. One for dual setups and one for single setups. And a bunch of different travels.
Since i am trying to go as fast as i can thru the woods, I run 2 shocks per wheel.
Any size Bilstein 5150 is $99....darn good pricing for a reservoir shock. And i havent had any problems or broke one yet.

vtblazer · 11-15-2007, 06:26 AM

I changed from 1/2 ton springs to 3/4 ton springs on the rear of a 2wd truck one time and found it mandatory to change out the brand new 1/2 ton shocks due to the fact they couldn't control the higher rebound rate produced by the heavier spring pressure.
Installed a shock rated for the purpose and the problem was solved.

Not really a direct comparison to your issue but IMO, it's all about the valving of the shock your running.

11-12-2007, 12:04 PM	#1
cobinder Everything is work in progress Join Date: Apr 2006 Location: Denver Colorado Posts: 326	Dual rear shocks?? I'm thinking I want to put dual rear shocks on the rear of my 80 K20 chassis. I'm running 39" Michelin run flat military tires that weight over 100 pounds each. So I think dual shocks is not too outta line Why did they run one shock in front and one in back? I'd like to just run two each side in the rear. Anyone have a good way of doing this? kits? thanks for any input. __________________ Good luck with your truck! How much?! It's just an old truck part!! 49 International on a 80 GMC 3/4ton 4x4 chassis 48 International KB-5 2 ton dump bed 04 Honda CRF "500" 09 Honda CRF450 fuel injected rocket 03 Suzuki hayabusa carbonfiber wheeled monster. 02 Ford diesel stretch van (toy hauler) 01 38' Monaco diesel pusher motorhome

11-12-2007, 01:18 PM	#2
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: Dual rear shocks?? There is really no point in it, other than looks. If that is what you are after, go for it, but there is no performance gain. Off-road racers use them to dissipate heat. They use multiple shocks that are softer than the single unit that they would be replacing. They have very long travel and are raced over long distances. This builds a lot of heat in the oil. By using multiple shocks, each handling less of the load, the heat is spread over a greater area and more oil. They belong on long-travel suspensions. Finding a shock that is soft enough to be used in pairs would be cost prohibitive in most cases, especilly since there is no need. Doubling up with "normal" shocks just stiffens the suspension you already have. Your 3/4 ton truck probably is plenty stiff now

11-12-2007, 05:57 PM	#3
68K20 x Drill Registered User Join Date: Apr 2007 Location: Freedom CA Posts: 488	Re: Dual rear shocks?? Rancho adjustables set to soft should be alright doubled up on a heavy truck. The front and back shock came out in 69 or so to reduce axle wrap. __________________ 68 Chevrolet k20 Longbed 350 SM465/205, Dana 44, 14bolt, Power steering, Power Disk Brakes, 35" BFGs. 84 Chevrolet Suburban K20 6.2 Banks turbo TH400/NP208 Now with G80 68 GMC C20 Parts? Truck And a few cars

11-12-2007, 06:01 PM	#4
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Dual rear shocks?? The only place dual shocks serve a purpose is up front under all the engine weight.Your weight is unsprung,not sitting on the axles/springs.Can you use powder balance in runflats? __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

11-12-2007, 08:04 PM	#5
cobinder Everything is work in progress Join Date: Apr 2006 Location: Denver Colorado Posts: 326	Re: Dual rear shocks?? This begs the question, does a shock dampen the wheel as it travels up or the weight of the chassis as it moves down? If it is the wheel (pro active) as it moves up then the weight tire and wheel assembly would have an affect on the damping of the shock. If it is the chassis (re active) then a single damper sized for the weight of that corner of the chassis should be enough. Off-road race trucks take great pains to get their suspension,wheels and chassis as light as possible which helps reduce the amount of damping force it takes to offer the best ride for them. Because they have such long amounts of travel which results in high piston speed they produce lots of heat. They run several dampers with light resistance to reduce the heat. In my case I have very heavy wheel weight hence my concern Powder balance is the only way to go on the big Michelins __________________ Good luck with your truck! How much?! It's just an old truck part!! 49 International on a 80 GMC 3/4ton 4x4 chassis 48 International KB-5 2 ton dump bed 04 Honda CRF "500" 09 Honda CRF450 fuel injected rocket 03 Suzuki hayabusa carbonfiber wheeled monster. 02 Ford diesel stretch van (toy hauler) 01 38' Monaco diesel pusher motorhome

11-12-2007, 10:39 PM	#6
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Dual rear shocks?? Answer:Both.Your thinking isn`t off.But,the lack of weight on the rear axle (sprung weight) is why you`ll add to the harshness and have no give in your suspension.I think better shocks are your answer.The Rancho 9000RSXs are 9-position adjustable.They are expensive,but so are two shocks in place of one,then theres what it takes to mount the 2 extra shocks. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

11-14-2007, 07:56 AM	#7
OLDCHEV4X4 Registered User Join Date: Apr 2000 Location: Chester County PA, USA Posts: 1,228	Re: Dual rear shocks?? I run the Bilstein 5150 reservoir shocks on my obstacle course Blazer. They have 2 different style valving. One for dual setups and one for single setups. And a bunch of different travels. Since i am trying to go as fast as i can thru the woods, I run 2 shocks per wheel. Any size Bilstein 5150 is $99....darn good pricing for a reservoir shock. And i havent had any problems or broke one yet. __________________ 72 k/10 short wideside 72 k/5 Blazer 72 K/5 Blazer - obstacle course racer 72 custom/10 8' bed 70 K/5 Blazer 67 C-30 GMC Flat bed 86 GMC K2500 Plow Truck 85 GMC K3500 84 M1008 85 M1008 77 G30 Motor Home 72 Sears 12hp Tractor Glenmoore, Pennsylvania

11-15-2007, 06:26 AM	#8
vtblazer Registered User Join Date: Oct 2003 Location: Central Vermont Posts: 8,537	Re: Dual rear shocks?? I changed from 1/2 ton springs to 3/4 ton springs on the rear of a 2wd truck one time and found it mandatory to change out the brand new 1/2 ton shocks due to the fact they couldn't control the higher rebound rate produced by the heavier spring pressure. Installed a shock rated for the purpose and the problem was solved. Not really a direct comparison to your issue but IMO, it's all about the valving of the shock your running.



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