Leaf springs.

[Datsun620longbed]

Hi, I have a 1977 datsun 620 longbed. I need new leaf springs and was wondering if anyone could point me in the right direction. Also I want stock ride height in the back and just out of curiosity, how much work would it be to swap over to coils all around?

[datzenmike]

What's wrong with the old ones? Slightly sagged? Take them to a spring shop and have them arched back into shape. If you stretch a string between the two rounded ends with the rubber bushings in them and measure down to the top of the spring pack, it should be 6.34 inches. Have the shop bend them back to this measurement..

 

 

Coil springs???

Leaf springs support and hold the axle from moving forward and back and also from side to side, a coil spring does none of this, just compresses up and down. You would have to add flexible upper and lower links forward to prevent the axle moving and rotating from the torque. You would need a horizontal panhard bar to prevent sideways motion and somewhere to mount the coil springs on the axle and to the frame. All this would have to be carefully engineered so that nothing binds as the suspension moves.

[ishnish]

If someone is trying to modify their rear suspension (assuming they have a leag spring setup) for track racing, what would be their options? I'm really trying to find out what I can do for my rear suspension on a 78 b210 (sorry for the thread jack). I've looked but can't find much info on the subject. Apparently leaf springs are better for racing vs IRS. If so, how can they be modified for better cornering, handling, etc..?

[datzenmike]

 

If someone is trying to modify their rear suspension (assuming they have a leag spring setup) for track racing, what would be their options? I'm really trying to find out what I can do for my rear suspension on a 78 b210 (sorry for the thread jack). I've looked but can't find much info on the subject. Apparently leaf springs are better for racing vs IRS. If so, how can they be modified for better cornering, handling, etc..?

Generally lowering the vehicle ride height lowers the vehicle center of gravity making it more stable and less 'tippy'. There may be rules to limit lowering so be aware of this. You can have the leaf springs de-arched to lower or add lowering blocks.  Lowering comes with risks that must be addressed.

 

For one, the car is now obviously lower to the pavement and with extreme speeds and cornering will force extreme suspension movements and bottoming is a real risk. Stiffening of the spring rate is a good control for this and also adds stability. The front must also be stiffened and front and rear rates interplay and be in harmony with each other. In very general terms stiffening the rears excessively more than the fronts will cause a neutrally handling vehicle to suddenly develop oversteer. Everything affects everything else.

 

For another, lowering can cause the drive shaft to vibrate because the U joint angles have been altered. The rear axle can be shimmed to correct this. A good tool is a drive shaft level to check results.

 

To stiffen a rear leaf spring pack, additional leaves can be added or the complete spring replaced. They need not necessarily be the same leaves. The leaves could be thicker to be stiffer.

 

A rear sway bar can be installed to reduce body tipping in corners. A sway bar reduces, or fights, the body being lower or higher on one side or the other. Again an excessively stiff rear bar compared to a front sway bar can cause a neutrally handling car to suddenly develop oversteer.

 

Tires and shock absorbers are part of the suspension too. Just remember everything has to work with everything else and affects everything else. Differences in front to rear tire pressure, worn or stiff shocks, lower or raising the ride height, wider or taller tires, front camber and toe, empty vs. full gas tank, spoiler down force.... minor changes to the front suspension can have dire effects to the rear handling. Balance... is everything.

[ishnish]

Datzenmike, that is some awesome info, thank you! So, in essence, lowering blocks or de-arching are ways of lowering for lower center of gravity, adding more leaves or replacing with different (thicker) leaves all together for stiffness, sway bar for reducing body tipping in corners, and of course tires and shocks.

 

Some more questions:

What would be the better option in lowering between lowering blocks or de-arching?

What would be better between adding leaves as oppsosed to replacing them with thicker ones all together?

[datzenmike]

Don't forget that changes to the rear have profound effects on the front and all handling in general. Some of these effects are very negative so be aware.

 

Lowering blocks are the easiest/cheapest to do. May not be allowed on a track? Does not compress the shock absorber length.

 

De-arching means removing the spring and dismantling them so more work/expense. Shock absorber is more compressed.

 

 

In both cases you may want to dismantle the spring to remove a leaf and replace with a flatter/thicker stiffer one.  I had an extra set of rear leaf springs for my 710 so I picked a fairly flat pair and trimmed them for length and added one each side between the 2nd and 3rd leaf. I also used a set of lowering blocks. Ride is lower and firmer.

 

I left the main leaf in the car and undid the spring pack and let the leaves drop out. Added a leaf and used two pair of vice-grips to compress them back to get the bolt pin back in... with good results.

 

 

I'll try PB later and post some pictures.

[ishnish]

Yes definitely haven't forgotten about the overall balance between front and back which is why I'm also asking questions on another thread which I see that you've replied to.

 

Okay so even if I do lowering block, I should add another leaf anyway and a thicker one at that for a stiffer ride. Now since I'm removing and replacing with a slightly thicker spring, it shouldn't be enough of a difference to compress the shocka significant amount right?

 

I've never worked on suspension before so I'm nervous but excited to approach this.

 

Pictures would be awesome! Thank you

[datzenmike]

An additional leaf is only about 1/4". Lowering buy de-arching will definitely compress the shock by the amount dropped. The axle will hit the bump stops well before the shock bottoms out else why would they have them? Lowering by blocks have no effect on shocks.

[ishnish]

Any sites you recommend on buying these extra leaves?

[datzenmike]

I just pulled them from a wrecking yard. On my 620 I got a set of Ford F-150 rear springs and added them under my main leaf. Raised and increased the load carrying. You can split the spring packs apart and just select one that will do the job. I agree a bit of guess work.

[datzenmike]

PB is cooperating again...

 

 

Stock spring was 5 leaves now 6. The very bottom one was very short, about half the size of this bottom one I got somewhere. The next one up was likely a 3rd spring up with ends trimmed off to shorten it.  With 2" lowering blocks.

 

 

 

[ishnish]

So I can just get any leaf sprig, trim them down if needed, and stick them right in and I'm good to go? Thank you for the picture! I'm not sure how many leaves the 78 b210 2dr sedan comes with stock but I have 3. I'm also not sure what shocks they come with stock but I feel like mine is aftermarket because its red

[datzenmike]

Well a flatter thicker one would lower and stiffen the rate. You want firmness but less arch which will raise the height,

[ishnish]

I thought less arch would lower the height?.. isn't that why it's termed "de-arching"? Any addition to leaves would stiffen I assume. Are you saying if I add a leaf and dont flatten it (or de-arch), it won't stiffen the rate?

[ishnish]

Sorry, I just scrolled back up and I guess de-arching means to remove a spring. S what I meant was, I can just remove a leaf, add in a thicker one that's flatter and that should lower my car. I assumed arching it would raise the height.

[ishnish]

I see you added a spring though so I figure adding a fourth spring to my car without removing my stocks ones whether it's thicker than my stock or not should still stiffen my car because any addition of springs should stiffen my ride, correct,?