Caliper Surprise

[DixieWASP]

Today I removed both front calipers from my 1989 Silverado RCSB to rebuild them. The left front brake was not working properly so I figured a rebuild and new brake hoses were needed. I discovered the driver’s side caliper had too much damage from rust to be rebuilt. I didn’t take the other caliper apart after I saw the poor condition of the driver’s side. The brake fluid is the same color as tea; I don't think it has ever been flushed and new brake fluid added.

This afternoon I took both calipers to O’Reilly’s Auto Parts to get rebuilt calipers and pads. The O’Reilly employee discovered the caliper pistons were different sizes. Evidently, a previous owner replaced the passenger’s side caliper with a “heavy duty” caliper by mistake. I purchased two calipers with the larger piston and hope to install them along with the new pads, brake fluid flush, and performance brake hoses tomorrow.

Here are a couple of photos of the rusty caliper.

 

[DixieWASP]

Another photo.

 

[GrimsterGMC]

When you buy a vehicle that's had work done on it by a previous owner, like most of our trucks due to their age, it can be quite concerning to find just this sort of mistake. You would never know about it if you didn't pull it apart. Sometimes it can be downright scary to know what faults you were driving around with.

 

[DixieWASP]

When you buy a vehicle that's had work done on it by a previous owner, like most of our trucks due to their age, it can be quite concerning to find just this sort of mistake. You would never know about it if you didn't pull it apart. Sometimes it can be downright scary to know what faults you were driving around with.

You are correct!

 

[Erik the Awful]

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[any4xx]

I’m surprised that it wasn’t pulling to one side while braking with mismatched calipers.

 

[DixieWASP]

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That is a good one.

 

[DixieWASP]

I’m surprised that it wasn’t pulling to one side while braking with mismatched calipers.

That is exactly what my auto mechanics’ instructor said when he found out about the different size calipers.

 

[Schurkey]

Let me guess: Your truck had the weakass JN3 brakes, pancake brake booster, and small master cylinder.

Now you've upgraded the calipers to the JN5 spec, but you haven't installed the JN5 master cylinder or booster, or the thicker rotors. The bigger caliper pistons need more fluid, you need the bigger master cylinder to supply it...and the bigger booster to maintain power assist. Thicker rotors (and the hubs to match) would be nice but not essential. Apparently, there's enough piston still in the caliper when the pads are worn-out.

The JN3 master has a 1" main bore, and a 32 or 36mm Quick Take-Up bore. The JN5 master has a 1 1/8 main bore, and 40mm QTU bore.

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The booster is similarly huge compared to the "pancake" booster.

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I got all my brake parts from the Treasure Yard, from an extended-cab truck that would have come with JN5 or JB5 brakes.

 

[DixieWASP]

Let me guess: Your truck had the weakass JN3 brakes, pancake brake booster, and small master cylinder.

Now you've upgraded the calipers to the JN5 spec, but you haven't installed the JN5 master cylinder or booster, or the thicker rotors. The bigger caliper pistons need more fluid, you need the bigger master cylinder to supply it...and the bigger booster to maintain power assist. Thicker rotors (and the hubs to match) would be nice but not essential. Apparently, there's enough piston still in the caliper when the pads are worn-out.

The JN3 master has a 1" main bore, and a 32 or 36mm Quick Take-Up bore. The JN5 master has a 1 1/8 main bore, and 40mm QTU bore.

You must be registered for see images attach

The booster is similarly huge compared to the "pancake" booster.

You must be registered for see images attach

I got all my brake parts from the Treasure Yard, from an extended-cab truck that would have come with JN5 or JB5 brakes.

Thank you for telling me about the upgraded brake parts. I appreciate you sharing this with me.