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#21 82m

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Posted 22 November 2017 - 06:06 PM

I just saw a shock at work yesterday, I didn't have time to measure it up unfortunately.. but im sure it was shorter than any other shock ive seen. it was from a little Isuzu truck. NKR66e

 

Isuzu part number 8972535920

KYB part number 444261

 

If someone has the resources to look up the dimensions that may be an option..



#22 datzenmike

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Posted 22 November 2017 - 06:57 PM

Cut a re-position the shock mount and run the shock designed for the 620 truck weight.The 620 is about 2,750 lbs plus 1,000 lb of payload. The shock would be designed for this and the spring rate used on the 620. I imagine the Isuzu is a lot lighter with lighter spring rate.


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#23 distributorguy

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Posted 05 December 2017 - 05:21 AM

Mike how does payload play into front shock rates?  And what makes you think the front corner weights of the Isuzu are less than the Datsun?  Does their cast iron engine weight less?  Maybe its the fenders or bumper that weight less?  I'd be more worried about the shock installation angle.  That can easily change the rate by 30%+.  



#24 datzenmike

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Posted 05 December 2017 - 05:53 AM

If you put weight in the back it also bears some on the fronts and you would definitely feel it when hitting the brakes.

 

Said I imagined. Assumed it was like a Samurai or something. He did say 'little'

 

 

Will NKR66e shocks work? Don't know, but I know they are not 620 shocks with the proper length, stroke and compression and rebound damping rates. As the OP is asking about them I assume he has checked that they are physically the same and will bolt in??????

 

Here's something else. Are the stock shocks really in danger of bottoming out? Surely car makers would design them so that at the most extreme of suspension travel they do not. Why have rubber bump stops then?

 

 

'78 620 shock

 

Stroke ....... 1.57"

Damping force @ 1 foot per second...

 

Expansion.................. 88-128 pounds

Compression................ 35-62 pounds


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#25 distributorguy

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Posted 05 December 2017 - 09:22 AM

Actually when you add weight to the rear, it shifts weight off the front.  Yes, under hard braking the fronts will gain more weight but that won't affect the spring rate, which is more important.  The shocks are there to absorb road abnormalities.  So I guess if you hit a bump with a  loaded bed in a lowered truck  while braking hard, it might matter?   You can however blow out a shock if it bottoms out or over extends to where its supporting suspension weight.  Hell, I blew out shocks every 2 years in my Ford just from the snow plow weight, but we're talking about a 3000+ lb front corner weight.  

 

I wish those compression and expansion numbers you list for the 620 shocks were opposite Mike.  Don't assume the manufacturer does what's best.  Sometimes they just use an existing design because its functional and saves design/manufacturing dollars.  Its always cheaper when the tooling is paid for.  I'm sure there's no way to improve the ride of a 620 because the designers got it perfect?  



#26 Stoffregen Motorsports

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Posted 05 December 2017 - 10:32 AM

I say mod the hell out of it. Make it better than the engineers ever imagined.

 

I just read an article in Hemmings about the Saab with the Ford sourced V4. Ford engineers told Saab that the engine was only good up to x amount of HP. Saab eventually doubled it using the same architecture.

 

I'm sure this has already been mentioned, but most shock MFG's have generic listings by length (extended and compressed). Buy some cheap shocks to make sure the length is right and then improve upon that as needed.



#27 Lockleaf

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Posted 05 December 2017 - 10:35 AM

If Saab Sonnets were RWD i would already own one of those goofy things. Only car i know of personally that actually ran a v4 engine.

Half Pint ('71 510 Goon) http://community.rat...agon/p?=1269361

 

Audrey ('69 Roadster 1600) http://community.rat...rey-the-ratster

 

Tiny Havok ('85 720 DIY built Crewcab 4x4) http://community.rat...ache/?p=1395455

 

720 Shenanigans http://community.rat...20-shenanigans/


#28 distributorguy

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Posted 05 December 2017 - 12:35 PM

We almost ran one at Bonneville instead of the 620.  Too light, no way it'll make 200+ hp without coming apart, and flimsy as hell. Aero was good, but it'd need to hit 180 to break a record in class.  Scary for the wheelbase.  Plus they have that goofy balance/jackshaft in the motor.  

 

As for shocks, the best way to increase shock rate is to straighten its compression to get more travel.  When I see guys using the same coil over shocks and changing the installation angle by 30% to make them fit, that's just a mess.  When you get to that level, figure out how to make them fit, THEN pick a shock and spring combo.  I'm all for modifying, just do some basic homework.  In the 620, almost any shock will do if it fits.  If you ARE using it as a truck, use gas charged in back.  



#29 datzenmike

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Posted 05 December 2017 - 08:19 PM

Actually when you add weight to the rear, it shifts weight off the front.  Yes, under hard braking the fronts will gain more weight but that won't affect the spring rate, which is more important.  The shocks are there to absorb road abnormalities.  So I guess if you hit a bump with a  loaded bed in a lowered truck  while braking hard, it might matter?   You can however blow out a shock if it bottoms out or over extends to where its supporting suspension weight.  Hell, I blew out shocks every 2 years in my Ford just from the snow plow weight, but we're talking about a 3000+ lb front corner weight.  

 

I wish those compression and expansion numbers you list for the 620 shocks were opposite Mike.  Don't assume the manufacturer does what's best.  Sometimes they just use an existing design because its functional and saves design/manufacturing dollars.  Its always cheaper when the tooling is paid for.  I'm sure there's no way to improve the ride of a 620 because the designers got it perfect?  

 

Rubbish.

 

If the load is completely centered/balanced over the rear axle there is no change to the front but no one does this accurately and besides, the load would have to be tied down to prevent forward shifting when braking. If loading a truck everyone starts behind the cab first and then it is loaded toward the back.  If you put the load behind the rear axle it would lift some small weight off the front, but no one with any sense would do this. On a short wheelbase truck (100") putting 100 pounds 10" behind the rear axle would only remove 10 pounds from the front. If it was 10" in front of the axle it would add 10 pounds to the front.

 

 

Think of a seesaw. An adult has to sit closer to the fulcrum in order to offset the weight of a child.

 

 

 

Absolutely you can improve the ride of anything. Best to know where you are so you can decide where you want to go.


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#30 distributorguy

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Posted 06 December 2017 - 09:24 AM

Mike, you're full of shit.  Speculating again?   I'm one of the only guys here who OWNS corner scales and balances cars after building them, including my race truck.  I know exactly how much weight comes off the front end of my truck when I add each 80 lb sheet in the rear.  When you lower the rear, the front lifts a bit and weight is shifted, and its not ounces.  If I recall, the last weight we added (centered in the bed) took 80 lbs off the nose.  

 

The fulcrum is the center of the truck, not the center of the rear axle.  



#31 wayno

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Posted 06 December 2017 - 10:34 AM

It really depends on what truck your talking about, and where the weight goes in the box, that will determine what it effects, there are a lot of variables.


 

 


#32 distributorguy

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Posted 06 December 2017 - 10:44 AM

Because the center of the truck varies from truck to truck?  Makes no sense.  Anytime you add weight in the rear, unless the ass end is jacked up really, really high, you will offset weight from the front.  The percentage of weight transferred has to do with the stance and prior weight distribution.  A relatively "level" truck will have the greatest change in front bias.  

 

When I set up the coil-over shocks in the rear of my Willys truck, I surprisingly had set it up to an even 25/25/25/25 weight distribution on the first try.  Merely raising the back 1/4" shifted 600 lbs off the back tires.  I put it right back where it was - 20 lbs difference between the heaviest and lightest corners.  Not bad for a 2400 lb truck.  



#33 wayno

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Posted 06 December 2017 - 07:38 PM

It really depends on the truck, let us look at my regular cab 521 work truck, it basically has the same wheel base as cab/chassis 720 which is a regular cab on a kingcab frame/chassis, if I put 1000 lbs on the truck I put quite a bit of it in front of the rear axle, what this does is put more weight on the front suspension compared to if I centered the weight over the rear axle, what I am doing is putting 1/3rd of the weight on the front and 2/3rds on the rear, I am not taking weight off the front, I putting less weight on the front and more weight on the rear, I do it this way as the rear suspension is way stronger that the front suspension, my truck squats evenly and drives just fine as long as I am on nice roads, it's not so nice on crappy roads.

Let us look at your Bonneville salt flats race truck, it is a regular cab/short box truck, if you had been lucky and gotten a regular cab long box truck with the longer chassis it would have been way easier to add weight in the box in front of the rear axle(better if added on the underside of the box) and have the truck squat more evenly as weight was added, again your not taking weight off the front, your just adding less weight to the front than you are adding to the rear.

Here are 2 wood loads I have carried on my truck, I have done this hundreds of times.

DSCN0393.jpg]

 

DSCN1312.jpg

I have been doing this too this truck for close to 20 years now, except for power steering issues because of where I mounted the power steering gear(frame damage), I have had no issues hauling these loads, when I tore my roof off and threw it in the back of my truck I rolled over the scales at 7200lbs, my 521 work truck weighs 3400lbs empty with me in it, it does take time to get these kinds of weights moving, it also takes time to stop these kinds of weights.

Here is a ton on the bed.

DSCN0873.jpg

And a ton in the trailer.

DSCN0876.jpg

This truck of mine is purpose built, but as I mentioned it basically has the same wheel base as the cab/chassis option with a regular cab.


 

 


#34 datzenmike

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Posted 06 December 2017 - 08:07 PM

Mike, you're full of shit.  Speculating again?   I'm one of the only guys here who OWNS corner scales and balances cars after building them, including my race truck.  I know exactly how much weight comes off the front end of my truck when I add each 80 lb sheet in the rear.  When you lower the rear, the front lifts a bit and weight is shifted, and its not ounces.  If I recall, the last weight we added (centered in the bed) took 80 lbs off the nose.  

 

The fulcrum is the center of the truck, not the center of the rear axle.  

 

 

It really depends on what truck your talking about, and where the weight goes in the box, that will determine what it effects, there are a lot of variables.

 

Wayno gets it. Why can't you? I already explained that over the axle has no effect and behind the axle will lift an equal amount off the front proportional to the distance forward. Saying adding weight to the back removes weight from the front is the stupidest thing ever said here. Total BUBBISH!  If you got weight off the front then you had to have put weight behind the rear axle. Simple as that.

 

Each axle is a fulcrum. Add weight forward of the rear axle cannot help but add (some) weight to the front one.


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#35 wayno

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Posted 06 December 2017 - 08:32 PM

I agree with a lot of what he is saying Mike, if I centered that ton of material I had on my flatbed it would make the front of my truck slightly lighter, but I didn't do that, I put about 3/4s of the load in front of the axle, the back 1/4 is centered over the axle, the trailer was loaded just about center, maybe slightly forward, but it had quite a bit of tongue weight.

They really don't make our Datsun trucks to actually haul any real weight, there is more box behind the axle than in front of it on most trucks, them double cabs are a joke when it comes to hauling weight as all of it is either centered or behind the axle, same with the 510 wagon, all of the weight behind the axle when loaded, the trucks are not really meant to haul what they are rated for, they will drive weird when really loaded up, but they will do infrequent loads and keep the owner happy, but I would not daily drive it that way.

At one point my work truck looked like this, it was light in the front 24/7, it drove alright, but if the trailer was loaded I could lift the front wheels off the ground.

wayne_s_planes_things_015.jpg  

It really depends on the truck, long bed trucks with regular cabs can haul more weight and drive close to the same to a point as long as most if not all the weight is centered in front of the axle, hard to do in a regular cab/short box, one would have to be hauling lead to get any real significant weight forward of the axle in one of them trucks.


 

 


#36 distributorguy

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Posted 07 December 2017 - 05:32 AM

Wayne, if you look at your heavily loaded trucks, you can see that the added weight is added close to the center of the truck.  Weight added to the center of the truck (centered between its contact patches with the ground) is neutral.  It makes no change in handling.  That's why you're able to load 3500 lbs on such a small truck and still drive it safely. If all that weight were centered on the rear axle, the weight balance of the truck would be something like 40/60 or even 30/70 and the tail would be wagging the dog.  800 lbs added behind the cab of a short box truck shifts the center of mass the same as 200 lbs added just inside the tailgate, mostly by how it lowers the ride height.  

 

Mike, sorry but you're guessing wrong.  A truck isn't 2 fulcrums.  Its no different than a race car.  Your center of mass is your center of mass, regardless of where the axles are located.  Until you apply an outside force such as wind or hp, neither of which play into a 620 under normal use, the location of the rear axle only help determine where that center point is.  The axle is NOT a fulcrum until it becomes the center of mass - like on the "wheelie" race cars/trucks of the 60's.  The fulcrum is an invisible point at the mathematically determined center of mass.    On my race truck, I have the center of mass and the center of pressure both marked on the frame for reference.  Both critical for safety when going over 100 mph on a slick surface.  Yes, you can make larger changes more quickly by choosing WHERE you add weight, but any weight added behind the center of mass can reduce front corner weights by decompressing the front springs.  Just because your fulcrum isn't touching the ground doesn't mean its not a fulcrum.  



#37 datzenmike

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Posted 07 December 2017 - 05:59 AM

Not 'guessing' and definitely NOT seeing it. If I gas up, the front bears some of that weight. If I climb in the cab, the rears bear some of this weight also.

 

Think of wayno's trailer. Two of them, both are axle fulcrum points. Now load so they are absolutely level with zero tongue weight and weld the tongues together. Any weight added toward the front of one trailer's axle will tip it's tongue down pushing down on the other tongue. Just saying... adding weight to the rear lifts weight off the front is irrational.


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#38 Stoffregen Motorsports

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Posted 07 December 2017 - 07:26 AM

Because the center of the truck varies from truck to truck?  Makes no sense.  Anytime you add weight in the rear, unless the ass end is jacked up really, really high, you will offset weight from the front.  The percentage of weight transferred has to do with the stance and prior weight distribution.  A relatively "level" truck will have the greatest change in front bias.  

 

When I set up the coil-over shocks in the rear of my Willys truck, I surprisingly had set it up to an even 25/25/25/25 weight distribution on the first try.  Merely raising the back 1/4" shifted 600 lbs off the back tires.  I put it right back where it was - 20 lbs difference between the heaviest and lightest corners.  Not bad for a 2400 lb truck.  

Yeah, it's called weight jacking. Ever see Days of Thunder? Add weight by adding height.



#39 Stoffregen Motorsports

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Posted 07 December 2017 - 07:28 AM


DSCN0393.jpg]

 

DSCN1312.jpg

 

This is an extreme example and not completely relevant to the shock argument. I agree with what you are saying, Wayno, but a load like this throws all baseline suspension characteristics out the window.



#40 datzenmike

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Posted 07 December 2017 - 07:47 AM

Well if Robert Duval says so....   :lol:

 

 

Well you can't change the parameters of the argument now.  It was on weight being added.... not changing vehicle height.


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