68-70 rear leafs harder or softer?

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ppeters914
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68-70 rear leafs harder or softer?

Post by ppeters914 » Tue May 15, 2018 8:28 pm

Came across this from 2004 while searching for something else:
spl310 wrote:
Wed Dec 08, 2004 9:30 pm

For the record, the early spring part number is 55020-10500 (that is for 1600s through engine R-40000 - or prior to the 67.5 model) while the other part number of 55020-25500 is for the later 1600s (67.5 and later) and all 2000s.

I have not driven a roadster with the comp springs, so I cannot comment on it. I can tell you that the later roadsters do have a little better ride than the earlier since the -25500 spring is softer than the -10500 spring. With some good shocks, I would say it is the way to go. A lot of racers reported that the comp springs were too stiff even for some tracks, and they modified them by removing some leaves. The Bob Sharp manual talks about it too. Your mileage may vary though...
According to The Datsun Roadster Book, Part 1, page 174:
The spring rate of the assembled 1968-70 leaf spring is about 140 lbs. per inch (25 kg/cm), which means that the spring will bend 1 inch (2.54 cm) if you apply a 140 pound (63.6 kg) load to it. The spring rate for the 1966-67 cars was about 87 lbs. per inch (15.6 kg/cm) while the competition leaf springs were a bone-jarring 207 lbs. per inch (31 kg/cm).
I'm curious how the later ('68'-'70) leafs could be softer than the early ('66-'67) if the later ones require more weight to deflect an inch. Or is this a misprint in the book (I have the two volume edition published in 2007)? Experts?

Thanks.
Pete
-------------------------------------
'67 1600 - frame off in progress
'66 1600 - parts car or future engine swap
'66 WPL411
A couple of Porsches, a pickup, and a motorcycle

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theunz
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Re: 68-70 rear leafs harder or softer?

Post by theunz » Tue May 15, 2018 10:14 pm

Might just be a misprint where they left the 1 off and should of read 187. Just a guess on my part, but 87 lbs. per inch is significantly less than 140.
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Re: 68-70 rear leafs harder or softer?

Post by Gregs672000 » Wed May 16, 2018 11:52 am

While this may be somewhat apples to oranges, my flex forms are something like 230lbs, and were to more or less mimic the (worn out) comps I had. The reality is that it was the shocks that made the biggest (incredibly better) ride change. I've run the gas adjusts, revalved Koni and now the Bilsteins. The flex forms were a definite improvement over the sagging comps (no surprise there) and had a nicer ride despite their 230lb rating, but it all came together with the Bs.
Greg Burrows
'67 2000 #588
Tacoma, WA

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ppeters914
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Re: 68-70 rear leafs harder or softer?

Post by ppeters914 » Wed May 16, 2018 1:44 pm

Gregs672000 wrote:
Wed May 16, 2018 11:52 am
While this may be somewhat apples to oranges, my flex forms are something like 230lbs, and were to more or less mimic the (worn out) comps I had. The reality is that it was the shocks that made the biggest (incredibly better) ride change. I've run the gas adjusts, revalved Koni and now the Bilsteins. The flex forms were a definite improvement over the sagging comps (no surprise there) and had a nicer ride despite their 230lb rating, but it all came together with the Bs.
Were the leafs worn out when we did the Mt Shasta run in 2007? If yes, that would explain a lot. :mrgreen:

I may go for the Flex-Form composite depending how the stock leafs work. As for Bilsteins, I thought those were unobtainium eons ago, or did you buy them eons ago?
Pete
-------------------------------------
'67 1600 - frame off in progress
'66 1600 - parts car or future engine swap
'66 WPL411
A couple of Porsches, a pickup, and a motorcycle

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Re: 68-70 rear leafs harder or softer?

Post by SLOroadster » Wed May 16, 2018 2:15 pm

The Bob Sharp comp prep manual states to find the early 65-67 springs rather than running the later 68-70 or Comp rear springs. It states that the 68-70 springs were softer than the early ones, and the comp springs don't work. My Volvo springs from Lou M were a revolution in the way the car handled, and its comfort. Same Koni dampers still set full hard. The ride is firm, but not harsh. The old comp springs were harsh.

Will
Sorry, I find modern engine swaps revolting. Keep your G, R, or U series in your Roadster!

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Re: 68-70 rear leafs harder or softer?

Post by Gregs672000 » Thu May 17, 2018 11:31 pm

ppeters914 wrote:
Wed May 16, 2018 1:44 pm
Gregs672000 wrote:
Wed May 16, 2018 11:52 am
While this may be somewhat apples to oranges, my flex forms are something like 230lbs, and were to more or less mimic the (worn out) comps I had. The reality is that it was the shocks that made the biggest (incredibly better) ride change. I've run the gas adjusts, revalved Koni and now the Bilsteins. The flex forms were a definite improvement over the sagging comps (no surprise there) and had a nicer ride despite their 230lb rating, but it all came together with the Bs.
Were the leafs worn out when we did the Mt Shasta run in 2007? If yes, that would explain a lot. :mrgreen:

I may go for the Flex-Form composite depending how the stock leafs work. As for Bilsteins, I thought those were unobtainium eons ago, or did you buy them eons ago?
Yes, the sagging comps were on her then! The Bs are the new ones from JT68, custom made for our cars as well as for the flex form springs. Transformational.
Greg Burrows
'67 2000 #588
Tacoma, WA

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Re: 68-70 rear leafs harder or softer?

Post by JT68 » Fri May 18, 2018 8:42 am

All, I MEASURED early springs at 180 and 185 lbs/inch. Super close to 187.

The late springs I MEASURED were 160 lbs/inch.

These were "non-sagged" original springs and the part numbers were even still visible on some of them. Not much of a mystery, the late springs are definitely a bit softer. 20 pounds is no big deal but this is consistent with Bob Sharp info. Either style works perfectly with the custom Bilsteins.

I have never met anyone who liked the Nissan comp rear springs on the street- no one.
JT
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Re: 68-70 rear leafs harder or softer?

Post by 2mAn » Fri May 18, 2018 11:58 am

How can I tell if my springs are sagging?
Simon
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-1988 BMW 325i. The daily driver
-1968 SRL 01228 with Nissan Comp kit.

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Re: 68-70 rear leafs harder or softer?

Post by sfdaugherty » Fri May 18, 2018 1:08 pm

How can I tell if my springs are sagging?
When you drive, all you see is sky :D

Seriously . . . its an excellent question. If they're really bad, it would obvious that the back end is sitting MUCH lower than the front (if not lowered in the front) and it bottoms out frequently.

I'm sure Alvin has photos :lol:

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Re: 68-70 rear leafs harder or softer?

Post by JT68 » Fri May 18, 2018 1:23 pm

Usually it will be just one side as the tell-tale, so the car will be sitting lopsided when viewed from the rear.

If they both happened to settle equally, ( that would be rare in my experience but certainly possible), or if a PO had tried to partially correct it,
the car might just be sitting low in the rear compared to other roadsters.

Lots of time there isn't much tire showing up top since it is up high in the well.

Another tell would be i the rear spring is dead flat, not arched down toward the pavement, or certainly if one is curved upwards toward the frame.

We could do a poll to measure a particular height consistently on unmodified cars and average them, but we would have to pick a measurement unaffected by wheel/tire height and exclude anything except totally stock vehicles- probably grouped by year--Something like topofbanjohousing- to- underside of frame. Obviously the car has to be sitting with normal weight on all 4 wheels.

Badly settled springs are typically fairly obvious.
JT
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Re: 68-70 rear leafs harder or softer?

Post by pebbles » Fri May 18, 2018 10:51 pm

2mAn wrote:
Fri May 18, 2018 11:58 am
How can I tell if my springs are sagging?
We would have commented on your pics lol.
If the bumpstop is not denting the frame, they are likely still doing their job. Check the frame above the bumpstop.
David




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Re: 68-70 rear leafs harder or softer?

Post by 2mAn » Fri May 18, 2018 10:59 pm

pebbles wrote:
Fri May 18, 2018 10:51 pm

We would have commented on your pics lol.
If the bumpstop is not denting the frame, they are likely still doing their job. Check the frame above the bumpstop.
:lol: I appreciate that!
Simon
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-1988 BMW 325i. The daily driver
-1968 SRL 01228 with Nissan Comp kit.

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Re: 68-70 rear leafs harder or softer?

Post by pebbles » Sat May 26, 2018 7:08 pm

Swapped out the early? rear re-arched springs, and installed the late rear springs from the 69SRL/SR20 3.7 diff.
Drives so much better.
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Re: 68-70 rear leafs harder or softer?

Post by ppeters914 » Sat May 26, 2018 7:55 pm

WHOA!!!!!!!! When did you get a 67.5 2000????
Pete
-------------------------------------
'67 1600 - frame off in progress
'66 1600 - parts car or future engine swap
'66 WPL411
A couple of Porsches, a pickup, and a motorcycle

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Re: 68-70 rear leafs harder or softer?

Post by pebbles » Sat May 26, 2018 8:55 pm

ppeters914 wrote:
Sat May 26, 2018 7:55 pm
WHOA!!!!!!!! When did you get a 67.5 2000????
67. Not mine. Just “tuning” for a friend.....
David




"When we were standing next to the motor while on the dyno, and the motor hit VVL, eyes went watery.."