Reading through all the posts here, there's two themes:
(1) My fiberglass spring broke,
(2) My fiberglass spring has never broke.

Duhhh. There's really no message here as to why a fiberglass spring broke or didn't break. Accepting that some fiberglass springs have broken....does anyone know....WHY?

It seems accepted without controversy that fiberglass springs have broken, it seems someone should help out and say why. What are the reasons? What can you do to help prevent a fiberglass spring from breaking? It seems to me that when people report, on this forum, parts breaking there's a lot of posts as to why. Not here. Strange.

 

I was thinking of getting one after a few other fixes..Id rather find out now than later..thanks for the heads up..

 

GM wouldn't have gone to them if they weren't superior and safe.

 

My original factory GM steel spring DID crack a leaf before it was 10 years old.

I have had the TRW/AO Smith fiberglass spring in there for more years than that and it still works like new, rides at the same height too.

I would buy a fiberglass spring again if I ever needed to replace one.

FWIW.

-Mark.

 

Guldstrand claims they wont sell a fiberglas spring, because even a stone chip can cause the glass to fragment. He also said the other common cause is over torqueing the 4 mounting bolts. Thirdly, you have alot of heat, which can have an effect.

 

Now we have a first input as to why fiberglass springs might fail. Come on...don't be shy... why do you think fiberglass springs can fail?

I think that if all they have to do is their up and down spring thing they'll be OK. I think if there's a transverse motion (back and forth at the differential support bracket) or a twisting motion imparted at the trailing arms, they will snap/fracture.

There's a lot of technical expertise on this forum. Any other explanations as to why fiberglass springs can fail ??

 

Ok, the following is my educated opinion & I dont want to offend my seemingly sensitive Forum Brothers, but the first generation of "AFTERMARKET" fiberglass leafs were manufactured with glass fibers in an epoxy matrix. Some even tried multi directional fibers, hoping this would aid in stregth. Being that these springs in thier application are put to the test of stress. Any impact, or disturbance of these inherently stressed fibers can alter thier integrity. You will notice that VB&P now offers a "new & improved" generation of fiberglass leafs. This technology uses “S” glass for the load bearing tension and compression surfaces and selectively placed reinforcement fibers for the core, designed to resist de-lamination and shear and provide additional strength against twisting forces.This is more than likely result of necessity. We have all seen & heard pro's & cons of these leafs, with a rather large failure rating. Now, now, guys, I know there are people that had these for a long time & are happy. But just as many if not more have had probs. The OEM fiberglass springs also have had failures in fragmanting. Technolgy and manufacturing process' are improving, but for now the first gens are unpredictable. Ok, lets have it. I know someone is going to rip me a new one...

 

I don't think GM has had very many people need new fiberglas springs. The major benefits of fiberglas springs are that they're 40+ lbs. lighter AND aren't as prone to fatigue. For the few that break, for odd reasons, more have gone almost 25 years and work like new.

As stated, GM wouldn't still be using composite leaf springs if they weren't reliable.

 

I've never heard of a TRW/AO Smith replacement composite spring breaking or delaminating. I have had a VB spring break on me and heard of several others.

The cross section of these two springs is quite different - the TRW/AOS spreads from a rectangular section at the center mounting point to a wider, flatter section at the end/ bolt point. The VB spring has a constant rectangular section.

If the theory about failure due to twisting or torsional forces is true, the TRW/AOS design would resist this force more effectively than the VB design. This may explain no failures with TRW/AOS.

I think C4, C5 and C6 composite springs are shaped similarly to the C3 TRW/AOS replacement spring.

I think Guldstrand is right about mechanical damage ( impact, rock chips, debris impact, etc.) being the starting point of failure for composite springs. The failure I experienced with a VB spring started with an impact chip due to being driven on a gravel road. C3 rear and VB front transverse composite springs are more exposed than GM's design for C4, C5, C6 springs and hence will be more subject to mechanical damage.

Lesson: don't drive your C3 with composite spring off paved roads......

 

Mine too.

 

Because they sat in the back of the class and slept most of the time.

 

andy, any word on the spring, are they going to replace it, I'll be back in dfw on friday. Have you started taking the spring off and sending it back ,, seeya
butch

 

Thats why I asked if it was installed correctly, a side load or a hit on something can cause the dammage and subsequent failure.

 

I had heard somewhere about the rock-chips hitting the FG spring and causing problems, so I wrapped the whole spring with double-thickness HD 3M electrical tape (I read that somewhere else, also). For the heat issue, I wrapped my exhaust pipes under the diff with ThermoTec heatwrap, same as shown in "theandies" pics. however, I also noticed that when using the 9/16" bolts spring attaching bolts, that the bolts were awfully close to the spring, and it took quite a bit of juggling to get the spring positioned "just-so" so that when I was tightening up the bolts, it didn't rub against the spring too much. I have the Muskegon Brake diff cover, but I don't think that makes a difference.

Anyways, with all these "paranoia neurosis" concerns, I still use the FG spring, and had them on both of my C3's. from VBP. I'm pleased sofar, had my first one for about 15 years now.

Incidentally, I also bought a VBP Smart Strut setup a while back, and the bolt holes on mine are ferociously oversize, I'd guess 1/8" oversize. for that reason, I didn't use it.

 

I have the TRW composite rear spring and it seams to be good but I run side pipes. BTW I often check it for rust.