'59 Drum Brakes - prim/secondary springs

[Steve G.]

Re: '59 Drum Brakes - prim/secondary springs

Very interesting stuff. I can tell you that in the field they probably very seldom went back on the correct shoe, like about a 50/50 chance. Pretty hard to tell when the colour is all gone, which is how they look after in service any length of time. Maybe why, in later years, where you had a different spring tension they moved the holes and made them a different length.

Steve

[Steve G.]

Re: '59 Drum Brakes - prim/secondary springs

Bob------



I'm getting into this a little late here but here's what I can offer:

Attached are photos of GM brake spring kit GM #3981995. This is a SERVICE spring kit applicable to 1953-62 Corvettes. It is supplied to SERVICE one wheel. The two long springs, the subject of your original question, APPEAR the same, except for color. They are both exactly the same length at 5.12" total length. They both have 20 coils. They both have exactly the same configuration of the extensions on either end of the coils. However, they are NOT the same. The red painted spring has a wire diameter of 0.100". The green-painted spring has a wire diameter of 0.107". That may seem like a small difference but it makes for a significant difference in the tension the springs exert.

I feel pretty confident that the difference in the painted colors of the springs is intended to denote the differences in the springs which, otherwise, is pretty visually subtle.

The GM #3981995 was discontinued without supercession in November, 1986.


[ATTACH=CONFIG]59321[/ATTACH][ATTACH=CONFIG]59322[/ATTACH][ATTACH=CONFIG]59323[/ATTACH]

Joe,

Where do you get this info? It truly is amazing. I'm sure there's some kind of paper trail for the supercession (sp?) of part numbers, but how do you find the specs on the items like this?

Did you have these springs in stock and pulled them off the shelf, photographed and measured them? You must have about a 3 acre warehouse in your backyard.

However you work your magic, it is amazing and incredibly helpful.

Steve

[Joe L.]

Re: '59 Drum Brakes - prim/secondary springs

Joe,

Where do you get this info? It truly is amazing. I'm sure there's some kind of paper trail for the supercession (sp?) of part numbers, but how do you find the specs on the items like this?

Did you have these springs in stock and pulled them off the shelf, photographed and measured them? You must have about a 3 acre warehouse in your backyard.

However you work your magic, it is amazing and incredibly helpful.



Steve

Steve------


As far as the information goes, I have many sources of information which the vast majority of folks don't have. I've also studied Corvette parts for well over forty years. So, I share.

As far as the parts, themselves, go, I have over 23,000 NOS Corvette parts in my collection. So, I can usually lay my hands on a part in question for further study, if necessary. Now, let me be clear: very often I have the part in question but I don't always go out and dig it out. It all depends upon how my back feels, how many tote bins I have to go through to find it, and how heavy the tote bins are for that, particular, GM parts group.

In the case of these brake springs, I was able to find them pretty quickly.

[Steve G.]

Re: '59 Drum Brakes - prim/secondary springs

Steve------


As far as the information goes, I have many sources of information which the vast majority of folks don't have. I've also studied Corvette parts for well over forty years. So, I share.

As far as the parts, themselves, go, I have over 23,000 NOS Corvette parts in my collection. So, I can usually lay my hands on a part in question for further study, if necessary. Now, let me be clear: very often I have the part in question but I don't always go out and dig it out. It all depends upon how my back feels, how many tote bins I have to go through to find it, and how heavy the tote bins are for that, particular, GM parts group.

In the case of these brake springs, I was able to find them pretty quickly.

Joe,
I probably should search the site before asking this, but have you shared your story with this organization?

A collection of 23,000 NOS parts and 40 years of research and study goes beyond extraordinary. Not only should your story be told, you should have an apprentice working with you to ensure this information is never lost.

Am I correct in assuming your parts collection is just that, a collection, and is not for sale?

Steve

[Robert C.]

Re: '59 Drum Brakes - prim/secondary springs

Thanks Joe (and everyone !.....as always)........very interesting.

I always know if anyone knows the right answers, it's NCRS folks !

[Joe L.]

Re: '59 Drum Brakes - prim/secondary springs

Joe,
I probably should search the site before asking this, but have you shared your story with this organization?

A collection of 23,000 NOS parts and 40 years of research and study goes beyond extraordinary. Not only should your story be told, you should have an apprentice working with you to ensure this information is never lost.

Am I correct in assuming your parts collection is just that, a collection, and is not for sale?

Steve

Steve------


Some folks in the organization pretty much know my story. I don't think there's wide-spread knowledge of it but quite a few folks know.

My parts inventory is a true collection. In my entire life I have sold a total of ONE part and I deeply regret selling it. I acquire more parts all the time (although not at the rate I once did). In fact, this week I added quite a few. In addition to the NOS parts I have quite a few used parts. Most of these I've obtained for research purposes and I don't really have them well cataloged. In general, I don't like used parts very much.

[Edward M.]

Re: '59 Drum Brakes - prim/secondary springs

Another car?

If the distance from the hole in the shoe to the pin is the same, so should the spring. No shoe requires greater return tension than the other. Brakes with self adjusters use different lengths because they attach into the adjuster linkages etc. But all take about the same amount of force to install them. One hand and a fairly easy pull with the tool I pictured.
Steve

OK, I'm coming in late to this discussion, but I was always under the impression that the secondary spring should be stronger than the primary spring. It's designed that way so the primary shoe moves first and the secondary shoe doesn't move until the primary shoe makes contact with the drum.

Here's why. If both springs are the same tension and both shoes move out at the same time, the shoe set will rotate slightly when making contact with the drum until the secondary shoe hits the anchor pin. That would result in a clunk each time the brakes are applied.

That works backwards when braking in reverse though. Brakes DO clunk when applied in reverse as the shoe set rotates slightly and the primary shoe hits the anchor pin.

I recall getting this explanation from a guy in Florida that seemed to know his stuff. Made perfectly good sense to me.

[Steve G.]

Re: '59 Drum Brakes - prim/secondary springs

OK, I'm coming in late to this discussion, but I was always under the impression that the secondary spring should be stronger than the primary spring. It's designed that way so the primary shoe moves first and the secondary shoe doesn't move until the primary shoe makes contact with the drum.

Here's why. If both springs are the same tension and both shoes move out at the same time, the shoe set will rotate slightly when making contact with the drum until the secondary shoe hits the anchor pin. That would result in a clunk each time the brakes are applied.

That works backwards when braking in reverse though. Brakes DO clunk when applied in reverse as the shoe set rotates slightly and the primary shoe hits the anchor pin.

I recall getting this explanation from a guy in Florida that seemed to know his stuff. Made perfectly good sense to me.

Yes, makes perfect sense to me now too. I now know that I likely placed some springs wrong back in the day. When they were in service for any length of time there was not paint left. So you looked at the length and matched them to the holes. Without paint on them .007" in wire thickness isn't that easy to differentiate the springs.

I think what compounded this mistake is that most of the cars where you found different spring strengths by design, they made them different lengths so that you were less likely to mix them up in service.

All that said, I guess one of the reason it never came to light previously was we didn't have comebacks as a result. If you happened to get them wrong, as long as you were wrong on the other side as we well you likely wouldn't know until the next brake job and found the front shoe worn more than the back.
I suspect if you mixed them up on one side only you might experience a slight tug when the primary shoe on one side hit the drum first on one side and the secondary hit first on the other side. Once applied, total spring tension is the same and hyd pressure is the same. Don't remember hearing that, but I came in one the tail end of brakes without self adjusters.

Steve

[Steve G.]

Re: '59 Drum Brakes - prim/secondary springs

I suspect if you mixed them up on one side only you might experience a slight tug when the primary shoe on one side hit the drum first on one side and the secondary hit first on the other side. Once applied, total spring tension is the same and hyd pressure is the same.
Steve

In thinking about this further, now I'm thinking this may not be correct. I over simplified. The total spring pressure and the total hyd pressure are the same side to side (right frt to left frt for example), but the frt shoe has less friction surface than the rear. On the other hand, the principle of the self energizing brakes also has to be take into account. The primary shoe with the lighter spring will apply more shoe pressure to the drum, which in turn wants it to rotate more with the drum and apply more force to the rear shoe. The rear shoe with the lighter spring is already having more force applied, and the front shoe is offering less of a self energizing effect.

Not as simple as I thought. I'd be interested to know if anyone has some first hand driveability experience with the springs mixed up