The Stupid Axle Questions Thread

[Schurkey]

Hmm. From the looks of it, I've got the bigguns. The only difference is the rotor diameter?

No. JN3 vs. JN/JB5 or JN/JB6 front rotors are the same diameter. Different thickness--1" vs. 1.25".

Calipers are the same?

No. Smaller pistons in the JN3 calipers than in the JN/JB5 or 6 calipers.

I think measuring my rotors now would be a wash, there's 60k miles and six years of wear & tear on 'em now.

There's no way that you'd lose a quarter-inch of rotor thickness and not see ENORMOUS scoring. Measure 'em and see.

 

[DerekTheGreat]

I was hoping to avoid taking a tire off. Oh well. The calipers, is there a reliable way to differentiate between the smaller (JN3) and larger (JN/JB5 JB6) versions? Wondering if all I have to do is purchase new calipers, pads and rotors if I'd like to upgrade. Isn't the master cylinder different as well? Picking up the "new" axle today.

Thank you for the responses, I appreciate the advice.

 

[Schurkey]

The calipers, is there a reliable way to differentiate between the smaller (JN3) and larger (JN/JB5 JB6) versions?

Measure piston diameter. JN3 has the smallest piston of any GMT400 caliper.

Wondering if all I have to do is purchase new calipers, pads and rotors if I'd like to upgrade.

If you're going from JN3 rotors to JN5/6 rotors, you'll also need JN5/6 hubs. I just slapped the entire steering knuckles from the JN5 extended-cab onto my truck. The whole reason I was in there to begin with was that I needed a non-damaged steering knuckle.

Isn't the master cylinder different as well?

To convert JN3 to JN5/6 up front, you'd need the master AND booster.

Picking up the "new" axle today.

Excellent.

 

[DerekTheGreat]

Donor axle aquired:

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The donor truck was still in the yard and I was able to lay eyes on it and the RPO sticker: "GT4," "G80" and "JB6." Yay! Unfortunately, the entire front suspension was missing, so I wasn't able to look at the brakes. I also forgot to ask about the U-bolt pads. One is present, but looks extremely crusty.. Would any of you fine folks happen to have some usable pads and U-bolts I could buy?

Schurkey, I'd need new hubs eh? I replaced those hubs/bearings about 60k miles ago. Guess I could preemptively replace them again. Since my axle looks like it was at the bottom of the Atlantic for a decade, I'll have to have it sand blasted and all that while hoping it's not rotted through where the U-bolts & pads were. Looking like I'll end up having it gone through, installed and then wait for the coffers to build back up before upgrading the fronts, if deemed necessary.

 

[Schurkey]

"JB6."

Yay! Unfortunately, the entire front suspension was missing, so I wasn't able to look at the brakes.

Master cylinder and booster?

I also forgot to ask about the U-bolt pads. One is present, but looks extremely crusty.. Would any of you fine folks happen to have some usable pads and U-bolts I could buy?

Yeah, they look bad until they're cleaned-up. Grab the one that's available, look around for the other one.

Probably want to buy the U-bolts "new" with new nuts/washers.

Schurkey, I'd need new hubs eh? I replaced those hubs/bearings about 60k miles ago.

Or use the JN3 rotors with the upgraded calipers. You'd lose out on some rotor mass and perhaps cooling area; but at least you'd have the bigger pistons in the JB5/6 calipers.

Be REALLY careful with the sand-blasting. Grit inside the axle will do nobody any good.

 

[DerekTheGreat]

Strike two, I did not look under the hood or even think to. I'm not the brightest crayon in the box, sometimes I'm amazed at what I do actually accomplish..

I called & asked about the other pad. They said if it wasn't with the axle, it was most likely thrown in the scrap bin. It was a crummy drive even just the one way. Coming back through Dee-troit reminded me of why I hate driving through there. It's no wonder it's impossible to have a nice car out that way.. Would eBay be any help here? Not sure how to search for the specific pad or how to verify it's the right one. Hoping to drop the truck off with two pads on Monday. Being that the shop specifically does axles, hopefully they can figure out the U-bolts, maybe even the pad..

Heh, didn't even think about sand/grit getting in the axle.

The bigger calipers are a direct fit?? A caliper swap is easy enough and sounds like the ticket. Do they run the same pads?

 

[Schurkey]

The friction material and backing plate are the same. The spring clip on the two inner pads may be different--resulting in a different part number--to fit the larger caliper piston.

I bent the spring clips outward so they still have some grip on the bigger pistons.

 

[SNCTMPL]

These guys have u-bolt kits, you just need to figure out the length of the u-bolts. If that’s not what you’re looking for, I probably have a set of saddles, you would need u-bolts.

https://www.autoandtrucksprings.com/chevy-leaf-spring-upper-and-lower-saddle-ubolt-kit-9/16-x-10-1/2-uboltsfree-shipping-bt5-218ck/

 

[DerekTheGreat]

These guys have u-bolt kits, you just need to figure out the length of the u-bolts. If that’s not what you’re looking for, I probably have a set of saddles, you would need u-bolts.

https://www.autoandtrucksprings.com/chevy-leaf-spring-upper-and-lower-saddle-ubolt-kit-9/16-x-10-1/2-uboltsfree-shipping-bt5-218ck/

Dammit, had I opened this thread in time I could've saved ~$45! Really nice that ATS sells all you need as a kit. Thank you for the information, may it help someone else down the road.. I ended up buying all that stuff from LMC truck, hope it fits.

The friction material and backing plate are the same. The spring clip on the two inner pads may be different--resulting in a different part number--to fit the larger caliper piston.

I bent the spring clips outward so they still have some grip on the bigger pistons.

Word. If I end up replacing stuff up front, I'll take the measurement of the current caliper's pistons and compare against the part store's listing for JB6 calipers. Well, after confirming that I don't already have the bigger stuff.