The Stupid Axle Questions Thread

[Schurkey]

it seems to me its easier to rebuild what i got

Maybe.

Easiest/best is to find a "light duty" GMT400 2500 as a donor. Needs to be a 4WD to donate to a 4WD, or a 2WD to donate to a 2WD, since the width is different. Match the gear ratio.

arent GM 14 bolts 8lug?

"14-bolt" 9.5" semi-float axle can be 6 or 8 lug, depending on how the vehicle it's in is optioned. The "light-duty 2500" axle is 6-lug, in the K2500 version it's a wonderful drop-in for a K1500. Needs only a conversion U-joint and four U-bolts plus the U-bolt plates from the donor axle.

C1500s need more, since they start out as 5-lugs. The 6-lug axle requires special 5-lug axle shafts, or the 6-lug wheels from the donor vehicle.

The "14-bolt" 10.5" full-float axle is 8-lug.

 

[DerekTheGreat]

I'm looking to pick up a six lug, 14 bolt SF axle for the '89 K1500 in my signature. Question is, will I need to upgrade the front brakes to match?

The drums on those are huge by comparison to what's there now with my 10 bolt. (factory) I've read about plenty who did the swap, haven't read anything about braking issues after the swap. They've talked about what an upgrade the bigger brakes are, but the wannabe engineer within me says those big ole brakes will upset the braking balance and make stopping unpredictable in the slippery stuff.

 

[Schurkey]

I changed to the 6-lug, 14-bolt semi-float axle in my '88 years before I upgraded the front brakes.

Upgrading the rears from the crappy 254mm (10") leading-trailing shoe drums to the 11.x Duo-Servo drums made more difference than upgrading the front brakes from the thin-rotor/small-piston JN3 set-up, to the thicker rotor/bigger piston/bigger master cylinder/bigger booster JN5/6 system.

YES, if you have JN3 brakes, I recommend that you upgrade the rotors, calipers, master and booster...but you'll be "ok" with just the rears until you can collect the parts for the front, master, and booster. I got all the heavier-duty parts from the Treasure Yard, although eventually I put a "new" master cylinder on.

OR you have an extended-cab truck with JN5 brakes, and you've already got the better front brakes, master and booster.

 

[InsanePyro1990]

Replacing the hardline that goes from the module on the driver's side over to the passenger front caliper. What's the nut size for the module?

'99 K1500 Suburban

 

[DerekTheGreat]

I changed to the 6-lug, 14-bolt semi-float axle in my '88 years before I upgraded the front brakes.

Upgrading the rears from the crappy 254mm (10") leading-trailing shoe drums to the 11.x Duo-Servo drums made more difference than upgrading the front brakes from the thin-rotor/small-piston JN3 set-up, to the thicker rotor/bigger piston/bigger master cylinder/bigger booster JN5/6 system.

YES, if you have JN3 brakes, I recommend that you upgrade the rotors, calipers, master and booster...but you'll be "ok" with just the rears until you can collect the parts for the front, master, and booster. I got all the heavier-duty parts from the Treasure Yard, although eventually I put a "new" master cylinder on.

OR you have an extended-cab truck with JN5 brakes, and you've already got the better front brakes, master and booster.

Thank you for the response.

That "difference" is what has me a bit concerned. However, I think I'll pull the trigger on the axle, have it installed and report back with my experience.

I believe I've got JN5 brakes- it doesn't have the "pancake" booster. My truck is a 4x4 regular cab, short box.

 

[Schurkey]

I think I'll pull the trigger on the axle, have it installed and report back with my experience.

Wise.

Maybe install it yourself--you'd need a conversion U-joint, four U-bolts, the U-bolt plates used on the donor axle, and a cover gasket and gear lube so you can inspect and replace the lube in the axle assembly. Maybe axle seals and brake parts. A torque wrench capable of 150-ish ft/lbs is recommended for the U-bolt nuts and the lug nuts.

You've verified that the donor gear ratio is the same?

Be sure to verify the brake shoes, axle seals, wheel cylinders, park-brake cables aren't seized, etc.

I believe I've got JN5 brakes- it doesn't have the "pancake" booster. My truck is a 4x4 regular cab, short box.

Surprised.

Regular-cab trucks usually got JN3 up to '91 or '92. Of course, the heavy-duty JN5 brakes could be supplied if the correct box on the order-form was checked.

Given the age of these trucks now, anything might have been swapped-in at some point. Would be worth checking the front rotor thickness, the caliper piston size, and the glove-box label for the brake code.

 

[DerekTheGreat]

Wise.

Maybe install it yourself--you'd need a conversion U-joint, four U-bolts, the U-bolt plates used on the donor axle, and a cover gasket and gear lube so you can inspect and replace the lube in the axle assembly. Maybe axle seals and brake parts. A torque wrench capable of 150-ish ft/lbs is recommended for the U-bolt nuts and the lug nuts.

You've verified that the donor gear ratio is the same?

Be sure to verify the brake shoes, axle seals, wheel cylinders, park-brake cables aren't seized, etc.


Surprised.

Regular-cab trucks usually got JN3 up to '91 or '92. Of course, the heavy-duty JN5 brakes could be supplied if the correct box on the order-form was checked.

Given the age of these trucks now, anything might have been swapped-in at some point. Would be worth checking the front rotor thickness, the caliper piston size, and the glove-box label for the brake code.

Ah, great information. Thank you, I was not thinking about the U-bolt plates from the donor axle. I was going to ask how to verify axle ratio with the cover off. Listing is from car-part.com and claims the axle is a G80 3.73, which is what I need, but it would be nice to verify that before I buy. Best I can tell is that it's just the axle, drum to drum with no extra parts, I'll call them once I verify the shop will swap it in. They've swapped one for me in the past, but that was about ten years ago. While I've swapped an axle before, I don't have the motivation to do this one.

I plan to go through the brakes on the axle once the shop has given it the "all clear" like they did with the axle I had 'em put in the Firebird.

I'll check the RPO code, not 100% certain it's JN5. I did replace everything up front when I first got the truck some five or six years and 60k miles ago. Pads are still in great shape, not sure about rotor thickness. I plan on replacing both the rotors and pads when the time comes, or upgrading the fronts to match the "new" rears if I feel it stops funny. At this point, I feel I've gotten my money's worth out of those front brakes. Rears too, actually..

 

[someotherguy]

Ah, great information. Thank you, I was not thinking about the U-bolt plates from the donor axle. I was going to ask how to verify axle ratio with the cover off. Listing is from car-part.com and claims the axle is a G80 3.73, which is what I need, but it would be nice to verify that before I buy. Best I can tell is that it's just the axle, drum to drum with no extra parts, I'll call them once I verify the shop will swap it in. They've swapped one for me in the past, but that was about ten years ago. While I've swapped an axle before, I don't have the motivation to do this one.

I plan to go through the brakes on the axle once the shop has given it the "all clear" like they did with the axle I had 'em put in the Firebird.

I'll check the RPO code, not 100% certain it's JN5. I did replace everything up front when I first got the truck some five or six years and 60k miles ago. Pads are still in great shape, not sure about rotor thickness. I plan on replacing both the rotors and pads when the time comes, or upgrading the fronts to match the "new" rears if I feel it stops funny. At this point, I feel I've gotten my money's worth out of those front brakes. Rears too, actually..

With the cover off it's super easy to ID the ratio. One could count the teeth on the ring and pinion, OR.. way easier, rotate the ring gear until you see the numbers stamped into the edge of it. In this example, 41 and 10 would be 41 ring gear teeth, 10 pinion gear teeth, divide 41 / 10 and you get 4.10, naturally.

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Richard

 

[DerekTheGreat]

Great information, thank you Richard!

 

[DerekTheGreat]

Alright, so I looked at my RPO sticker and I don't appear to have any "J" codes. Maybe someone can help me determine what I've got for front brakes?:

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