darklordftt

I'm currently in the process of pricing out new rear end\suspension parts for my '81 (trailing arms, strut rods, etc...). The car still has the stock monoleaf in it, and there doesn't appear to be anything wrong with it. Should I replace it anyways, or re-use it? I'm all for re-using it so I don't have to deal with the different spring rates of the replacement monoleaf spring, and risk the chance of having to use the 10" mounting bolt to correct a "jacked-up" ride height.

From what I have read on this forum, the monoleaf shouldn't lose any of its spring rate over time. However, the car also used to be an automatic, and is now a 5 speed manual, and the manual 4 speed '81 vettes originally came with the steel 9-leaf spring. Does anyone know why the manual vettes for '81 still used the steel spring? I know the monoleaf was used on the automatics to save weight, but are they as strong or stronger? Should I put a steel spring in it now that the car has a manual transmission in it? I'm converting the rest of the rear end parts to use the larger u-joints that the '81 manual vettes came with (I recently blew a halfshaft u-joint... thus the rear end\suspension upgrade), but I'm not sure on the spring.

morleyz

No help from me...but thanks for posting this question...I was going to ask almost the exact same thing today. Only difference is I'm not switching to manual.

Rebelrob

Mine is an auto and has the mono composite spring. I am happy I have it. Number one, its lighter, and its not prone to rust and squeaking like the steel springs. Plus I have read also that they should keep their spring rate unlike the steel springs.
VB&P told me that the stock mono composite spring on our cars are rated probably at 290 lbs. If I upgrade, I am going with the 330 lb spring which is a litte more stiffer but not to harsh from everything I have read. Sort of middle of the road.
Not sure if a new spring will jack the rearend up or not. Thats where you would have to buy some new longer bolts to adjust the height.
Be curious to see what your broken u joint looks like. Post a pic if ya can.

Thx
R

darklordftt

What I think happened is the u-joint retainer on the wheel flange broke or the screws holding it where stripped out of the flange because they are gone. The halfshaft then spun around and sheered off 2 of the u-joint bearings when it struck the shock, and the top of the trailing arm. The top of the trailing arm has been 1/2 broken off from the main frame of the arm.
pic 1
pic 2
pic 3

So all of the rubber is shot, and If 'm going to replace 1 side of the rear end, the other side is going to get upgraded to. I'm just unsure about the spring.

Rebelrob

Dang... I bet that made a helluva noise........
either you got some muscle under the hood or just bad luck....
Did it leave ya stranded?

darklordftt

I have the stock motor(190hp lol) + 28yrs of sludge
and I replaced the automatic with a 5 speed manual
sidepipes and 235/60/16 tires

I launched it at a street light against my friend's\neighbor's c5, with our wives in the car. It squealed the tires for a second, and then it sounded like the rear end exploded. We then waited like 20 minutes for a flatbed to take it back to the house.

vettehardt

I believe you could get the monoleaf with either the manual or auto tranny. It was used on the gymkana suspension option. I have a monoleaf from VBP on the back of my 73 and my 76. I dont' know the ratings on them though, but the rear ends are not jacked up. I do know the 73's is very stiff. It is an autocross car so the stiffer the better. I don't believe dad used any longer bolts when he put it on.

OURSHARK

My 81 vette was an auto and I changed it to a five speed. I still have the original mono spring and everything is fine. I wouldn't put a steel spring in your car.

alswagg

my 81 had a monoleaf and was an original 4 speed. the mono leaf was starting to show some stress cracks so I replaced with a new 340 rate from Muskegan Brake. Very easy to replace. At the same time I also replaced all u joints and rear shocks. I use KYB g2 ?? shocks. Rides great no significant rear height.

markids77

If we assume the T/A is the "flog" ride and the 'Vette the "cruise" ride, keep the steel spring... you'll not notice any difference. Spend the price of the spring somewhere else (a cozy room with a view?) and enjoy the ride. If you intend to drive the 'Vette hard, a monoleaf makes sense, but probably not with GR-2 rear shocks. Forum consensus appears to require a more aggressive shock with a monoleaf. Then there's balancing front and rear action... a whole other post awaits if you are so inclined!

Rebelrob

VB&P makes a specific rear KYB GR2 shock for the mono composite spring. Which I have. Its a nice smooth soft ride, much better than the OEM but not as stiff as you hear from the KYB whites or Billsteins. Its all in the preference and how you plan to drive the car.

darklordftt

Well, the engine is going to remain stock for another year or so. Then a 350 - 400HP upgrade is going to happen.

I'm going to keep the mono spring in the car... but since I'm replacing everything else in the back of the car, and since there will be an engine upgrade in the future I'm thinking maybe I should put a "NEW" monospring in (thats what I really wanted to know... is the stock 28yr old spring still good to use). I have to look at the back side of the current spring to see if the halfshaft hit it and caused a fracture or not.

if the stock spring has a 296lb spring rate (or something), why is the 330lb the one everyone seems to go with and not the 315lb which is closer to the stock setting? I keep reading that one is to bouncy or the other is to stiff.

Thanks for all the feedback guys

Rebelrob

Well if I do upgrade mine I am going with the 330 from VB&P. IN their catalog, and probably the web site they have a break down of all the different spring rates and you can decide on your application that best suits you. I would leave the one you have in their for now, pending it not damaged. As I have read, they should not lose their strenght. If your looking for some slalom/road racing driving down the line, then you should probably upgrade. Or maybe if you plan to street race/drag race it. I stiffer spring might cause it to no squat as hard from high rev launches.
I do plan to upgrade my engine this fall to a much higher HP. So I guess I will see how it performs and go from their.
Oh , I think the 330 is just the middle of the road, stiffer than stock but not as stiff or extreme as the 360 and beyond. My stock is a little bouncy right now, thats with new shocks also.
Good luck with your rearend rebuild.

darklordftt

You make a good point about having the new shocks and how they make the ride more bouncy... I think you just sold me on getting a new 330 monoleaf.

7T1vette

The spring you have is a 315# TRW unit. If it has no damage on the edges of the spring and it shows no sign of delamination, it's as functional as a new one. Why spend the money?

jb78L-82

I have a VBP 360 monospring in my 78 L-82 4 Speed that I installed in 1986 (and still have)with Bilstein Sports and prior to that KYB Gas A Just (way bouncy) and before the Sports, Bilstein HD's. Never would go back to a steel spring and the 360 with the Bilstein Heavy duties rode real smooth but I wanted a stiffer ride so switched to sports. Definitely go with the mono spring, match it to your front springs and shocks, and enjoy the ride!

larryg3

Last winter i changed my stock '81 suspension monospring for the VBP street and slalom wow what a difference.l it is like the car is on rails. worth every penny. rear spring 330 front 550 with bilestien