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DatsuNissanLove

short shocks for front

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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.

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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.

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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.  

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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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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.  

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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.

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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.  

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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.

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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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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.

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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.  

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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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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.

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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.

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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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Adding weight shifts vehicle height.  Its always been part of the argument.  Unless you run a rigid/fixed suspension???  Racers add ballast. Truckers add payload.  It all has to be accounted for.  

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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.

Good point. How did we get off subject anyway?

 

Find shocks that fit and that don't bottom or top out. If you like the ride, then your job is done.

 

Someone mentioned bumpstops. You can cut a hair off them so you're not constantly riding on them. But don't get rid of them.

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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.

It took time to make this truck what it is and still be able to drive it empty comfortably, although it is much nicer with the trailer connected, empty I do have to slow down going over big speed bumps.

I thought we were talking about adding weight and how it effected the front end weight of the truck now, and my point was that it depended on the truck, I used my work truck as an example to show that adding weight on my flatbed was not lifting the front of the truck, my truck drops evenly when weight is added evenly on the bed, start at the bottom and work my way up, I don't load it that way, I plan ahead so that it is evenly distributed when finished.

My flatbed is also as low as I could build it and still clear the rear tires, any higher and it would act differently especially on freeway curves depending on how the curves were built.

I thought for a while about posting to this actual subject, in the end I could not keep quiet about the statement that any weight added to the box would lift the front end/take weight off the front end, it depends on the truck/vehicle and where the weight is put.

The only issue I have is when I put these kind of heavy weights on my truck, my rear coil over shocks have no effect, you cannot even tell there is a shock back there, there is zero dampening, that is why I mentioned crappy roads.

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I was trying to bring the discussion back to the OP's original question of what were the right length of shock for a lowered truck.

 

Seems like we've been arguing about something he didn't even ask.

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I was trying to bring the discussion back to the OP's original question of what were the right length of shock for a lowered truck.

 

Seems like we've been arguing about something he didn't even ask.

 

I jumped in after it started, but I will now put my 2 cents worth in on the front shocks for a lowered 620 that has disc brakes.

What I did was cut the lower shock mount out of the lower control arm, it's a bitch to do, then I bought a high quality set of 66-70 front Datsun Roadster shocks which are stud/stud, I mounted the lower shock stud in the sway bar connection hole, I drilled a hole for the sway bar connection in between the shock and ball joint and mounted it there, the Roadster shock is very short when compressed, I would then trim the bump stop to just before the shock bottomed out.

You will also have to flip the upper control arms from a 720 and put the right side on the left side and the left side on the right otherwise the upper ball joints will bind.

I went farther and made my lower control arms into drop arms, but the same thing can be achieved using late 720 drop spindles.

Another issue that will always rear its ugly head will be that you will start bottoming out the tension rod on the pittman arm/steering arm, this was a very big issue for me as I was really low, I was also always hitting the front tension rod mounts on the ground, everywhere I went they were hitting the ground or curbs, I finally had to relocate them to the rear and cut off the mounts on the front, I have had no issues since.

I have no advice for lowering a kingpin truck other than I found the 521 front shock to be the shortest shock of that type, but it appears that others have found shorter shocks recently.

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What I did was cut the lower shock mount out of the lower control arm, it's a bitch to do...

 

You will also have to flip the upper control arms from a 720 and put the right side on the left side and the left side on the right otherwise the upper ball joints will bind.

I have no advice for lowering a kingpin truck other than I found the 521 front shock to be the shortest shock of that type, but it appears that others have found shorter shocks recently.

That's the right way to do it. Get the longest shock you think will fit and cut the brackets and make new ones.

 

Does swapping the upper control arms from side to side affect the caster?

 

Sometime in the recent past, there was a discussion about short shocks and someone gave part numbers.

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Has anyone even measured the stock shock to see if it even bottoms out at full suspension travel??? Just can't see a car maker having shocks that bottom out before the suspension does.

 

If riding on bump stops or cut bump stops the shock isn't doing any compressing when hitting, say, a speed bump. Only the air in the tire will and maybe some of the rubber bump stop, and it isn't damped at all. The stored energy will rebound undampened, throwing the vehicle upward harshly. On the other side of the bump the tire will extend down to follow the road surface and the shock will dampen this extension and then dampen the compression as the body weight comes down on it. This is why extreme lowered vehicles have a shitty harsh ride quality.  Best bet is to run as low a tire pressure as you can safely get away with or find a way to extend the suspension travel so the shock can actually do something. 

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Good point.

 

I think you need to cut the bumpstops to get it as low as these guys like them, in which case, the shocks do bottom out.

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Does swapping the upper control arms from side to side affect the caster?

 

 

 

If you don't flip them upside down it does, but we are talking about on a lowered disc brake frame in this circumstance, the offset of the arm needs to be forward on a disc brake frame and that is what I am talking about here.

Here is a upper control arm(UCA) in stock configuration lowered as far as it will go.

DSCN0616.jpg

Here it is flipped on the other side.

DSCN0612.jpg

See how close the tension rod is to the idler arm.

DSCN0614.jpg

Here is the steering arm.

DSCN0610.jpg

Doing all this using 620/720 parts on a 521 frame is the same but very different, way more is involved.

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