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Project Rear Disc Brakes

Big T

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Thread starter #4
Judging from his pics, my guess is he's doing an axle swap. 01's have an internal drum style parking prake, and I see he got the cables with it for them.
Good eye there Ferm. I cut the parking brake cable ahead of a splice that was ahead of the "Y" where the cables split to both wheels. I'm hoping to splice the existing cable into this set-up. Otherwise, not sure the existing would match up with this set-up.

I measured the OD distance on the spring perches and they're 2" wider than our existing. So they'll have to be cut off and new ones welded in place. I'm told the perches for the rubber snubbers will similarly have to be moved. I'm also told that these axles have a 2" wider track than the GMT-400 models. Haven't taken a tape to that.

Total for everything was $300. I looked into disc brake conversion kits for our GMT-400 axles and they were $400 to $500 for everything. That got you single piston calipers from a 1980s Cadillac Eldorado, with or without parking brake.
 
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Big T

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Thread starter #8
Don't know if it is or not. Haven't worked on a new style yet to see if it is or not.
I went out to compare. Both have similar square, 4-bolt mounting plates. The drum brakes mount using bolts from the outboard side; the disc brakes mount using bolts from the inboard side. If those plates are the same size, it might be possible.
 

JayTheCPA

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#12
I'm also told that these axles have a 2" wider track than the GMT-400 models.
If that is truly the case and presuming you are going to use it versus just swapping the brake parts, then only need 1" spacers to equalize them out with the front and complete the project :) But if you keep the existing GMT400 axle, will need 2" spacers.
 

Big T

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Thread starter #14
If that is truly the case and presuming you are going to use it versus just swapping the brake parts, then only need 1" spacers to equalize them out with the front and complete the project :) But if you keep the existing GMT400 axle, will need 2" spacers.
Not quite sure I understand. Where would the spacers go and what would their function be?

I'm told that the existing track width in the front is already wider than the back.
 

Big T

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Thread starter #15
This thing is going to stop so quick when you are done you will be setting the airbags off!
I doubt it. These are very heavy vehicles. The front brakes should help with stopping, but we'll also get substantially longer life out of the brake pads.
 

Big T

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Thread starter #16
I did some quick measurements of the end mounting plates this AM and they're completely different. GMT 400 is a 4" x 4" square and smaller bolts. GMT 800 is a 5" x 4" rectangle and the bolts are substantially larger. Check the inside width between the plates and the GMT 800 is approximately 1.5" wider on that measurement. This is going to be an axle swap.
 

JayTheCPA

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#17
Where would the spacers go and what would their function be?
Seeing a it is looking like an axle swap, then the spacer is probably not worth it.

To answer the question though, the spacer attaches to the axle and the tire in turn attaches to the spacer.

Point of the 2" spacer (for just the rear axle (one 2" spacer on each side)) is to give the GMT400 truck the same stance in the front and rear. Having an equal stance makes a minor and noticeable difference in handling; especially when towing.

The spacers are not absolutely necessary, but do help.
 

Big T

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Thread starter #19
Seeing a it is looking like an axle swap, then the spacer is probably not worth it.

To answer the question though, the spacer attaches to the axle and the tire in turn attaches to the spacer.

Point of the 2" spacer (for just the rear axle (one 2" spacer on each side)) is to give the GMT400 truck the same stance in the front and rear. Having an equal stance makes a minor and noticeable difference in handling; especially when towing.

The spacers are not absolutely necessary, but do help.
I was told that on our vehicles the track was wider in the front. So with the wider track on this rear axle, you're saying that I would need spacers in the front to keep it consistent?
 

Big T

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Thread starter #20
This discussion of spacers has me lost. The GMT-800 axle has a track that appears to be 2.5" wider than my current GMT-400 axle. So I'm being told here to add spacers to the rear axles to keep it consistent? Adding more to more to make it consistent makes no sense.

Maybe we need to start at the beginning as far as front and rear track and its effect on handling? Is it a fact that the front track on our GMT-400s is wider than the rear track? If so, what is the purpose for that? Then what would happen with the proposed wider track of this GMT-800 axle?
 
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