Rear springs

[Doobie]

Just wondering if anyone knows how many leafs are in a stock set of springs , not positive but I think the previous owner of my 620 may have added a helper leaf 

[datzenmike]

They started very stiff in '73 and then lightened around '77 and up. There was an optional 'camper' spring which was basically the same as the original '73-'76.

 

I have a 73 FSM and it says 5 leaves of various lengths and thicknesses. My '78 FSM says only 3.

 

 What are your plans? lowering?

[Doobie]

Yes planning on lowering it , my truck just seems to sit a little high  

[datzenmike]

Use lowering blocks and longer U bolts. Never remove a leaf to lower. The last thing you want is to be closer to the pavement and the springs are softer and travel farther on bumps. If anything you want them even stiffer to prevent bottoming out.

 

These are 3" but you can get less... https://www.amazon.ca/Belltech-6100-Lowering-Block-Kit/dp/B000CIMEPE/ref=asc_df_B000CIMEPE/?tag=googleshopc0c-20&linkCode=df0&hvadid=292992180896&hvpos=&hvnetw=g&hvrand=15257457437751320046&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9001614&hvtargid=pla-521790039529&psc=1

 

[Doobie]

I have three inch blocks and u bolts , I’m asking because I think the previous owner might have added a leaf to raise the rear to fit the massive tires he had on it

[datzenmike]

5 or 3 is my guess so if you have 6 or 4 then maybe one added.

[620slodat]

I have a 1973 Datsun 620 available to me to look at, which I did. I know for a fact that it hasn't had anything changed on the rear suspension since my dad bought it brand new in 1973. It has 5 leaves total. The top three are standard thickness, the fourth is an overload leaf about 1/2": thick and about 3/4 length (or slightly less) of the first leaf, and leaf #5 is back to standard thickness and about 1/4 the length of the top leaf.

 

Don

[Doobie]

Thank you!!

[datzenmike]

12 hours ago, 620slodat said:

I have a 1973 Datsun 620 available to me to look at, which I did. I know for a fact that it hasn't had anything changed on the rear suspension since my dad bought it brand new in 1973. It has 5 leaves total. The top three are standard thickness, the fourth is an overload leaf about 1/2": thick and about 3/4 length (or slightly less) of the first leaf, and leaf #5 is back to standard thickness and about 1/4 the length of the top leaf.

 

Don

 

620slowdat: The spring rate is progressive becoming stiffer and the spring is compressed. The '73 5 leaf spring rate was 145 to 560 pounds/inch. The later springs that were 3 leaves were 106 to 308 lb./in. A lot softer.

[620slodat]

DM, just out of curiosity, do you know the rear spring rate for a 1982 720? I had a 1982 720 diesel frame given to me by wayno, and I am curious to know what it might have. I don't have an OEM book for it. Also, I looked on-line and haven't found it yet. I will continue looking though unless you have that information. 

 

Don

[datzenmike]

I only have the '84 FSM.

 

The US standard spring is 109-310 lb/in. The optional spring, which is the same as the 4x4 spring and is the standard spring for Canada is 138-442 lb./in. and the optional Canadian spring is the same as the US standard. The Cab/Chassis spring is 166-649 lb./in.

[620slodat]

Thank you DM! You may not have the 1982 FSM, but 1984 is pretty close. Close enough for me to be able to know that the spring rate should be a lot less than the 1973 spring. The average 1984 spring rate is 210 lbs (310-109, divide by 2+109=209.5). The average 1973 spring rate is 352.5 lbs (same formula as used previously). Over 140 lbs difference between the two makes for a big difference.

 

Don 

[datzenmike]

Not sure if that's a good ruler.

 

At rest it takes 210 pounds to compress one inch but as it's being compressed the rate is also going up as more leaves come under compression.