GMT 800 Brake Conversion > Silverado HD 2500

[Big T]

Update: Son had a Milwaukee 1/2" right angle drill, so I'm going that route for the lower holes. Could never find a separate 1/2" drill chuck with 3/8" hex adapter. It will take a bit longer to do the holes as I will not be able to generate the force that I could with the drill press, but you can only apply so much with the reams anyway. They don't chew out a lot of metal quickly.

I will try to get this job done on my Friday off.

 

[ak diesel driver]

use the drill press to push on the angle drill

 

[Big T]

use the drill press to push on the angle drill

Still face the obstruction issue with the upper portion of the knuckle.

 

[ak diesel driver]

If the holes line up all you need is a shaft in the drill press. It doesn't need to turn on just use it for pushing on the back of the angle drill. Probably a 2 man job then.

 

[Big T]

So I went to ream the lower ball joints. I bolted the knuckle to the table on the drill press and used the angle drill. First hole reamed rather quickly, like less than 10 minutes. Second one was also going quickly, but I got a bit over zealous with the pressure and the ream bit bound and shattered. So I need to order another as I still have that hole plus another set of knuckles to ream. I did ream the tie rod holes on the second set of knuckles. The first set is using the tie rod adaptor bolt to the stock GMT 800 tie rod end, so do not need to be reamed. The tie rod holes took about 15 to 20 minutes.

Pics show the lower ball joint and the amount exposed below the knuckle and the clearance to the CV axle joint. I measured these clearances on the existing vehicle. I will note that on the GMT 800 knuckle the arm with the hole for the lower ball joint is 1 1/4" thick, whereas the GMT 400 is 1 1/2" thick. So you need to watch the depth closely to get the clearance to the CV axle hub, but still retain thread under the knuckle.

 

[Big T]

And this job is nearing completion. Also replaced the bushings on the lower control arms.

 

[Will L.]

Yeah, progress! Idk if it's good or bad that hours of work easily gets compressed in a sentence starting with "also". I just know it feels good to have it behind you instead of infront of you.

 

[Big T]

Yeah, progress! Idk if it's good or bad that hours of work easily gets compressed in a sentence starting with "also". I just know it feels good to have it behind you instead of infront of you.

Behind me is the axle project for my son's. Need to pick that up from my welder. We'll do his front brakes first.

 

[Big T]

Alright got it fully back together and went for a test drive around the block. It needs to be aligned as the tops of the tires are cocked out. I also guessed on the tie rods based on the old ones.

As for the the brakes, WOW! Now this is what this truck always needed. Even better, the pedal height is higher and harder than before and significantly so. All those speculating it would be worse and that you'd need the GMT 800 master cylinder and hydro boost, they're wrong.

 

[Big T]

I took the truck in Accurate Alignment in Orange and I like them. We went through the work I did. Before even test driving it, they said I need a new steering box based on the slop in the steering wheel. They said they would do an alignment, but they'd never get the toe right with the slop in the existing box. I had previously pulled the box and did a tightening procedure, but the slop came back within 20K miles. It's what happens with a vehicle this heavy. A new box was on my to do list, so it has now jumped to the top of the list. I will get a Redhead blue printed reman steering box. Accurate Alignment likes the Redhead steering box as well as the brand new Delcos.

As for the brakes, WOW! Dramatic improvement. There discussion here that the dual piston calipers would result in lower pedal height due to the volume of fluid being pushed is IMO speculation. I can tell you unequivocally that the pedal height is much higher and significantly harder. Now all my girl needs is a tighter box.

 

[FellowTraveler]

Most GMT400 bad brake feel I've witnessed is after larger diameter tires are installed and only the VSSB is calibrated for speedo and the most important calibration is ignored the "ABS." Tire size brake calibration for GM C/K Truck under 15000 GVW and 03-04 under 8600 with no VSES.

At times a bad P/S pump can cause bad brake feel too in a hydro-boost system additional p/s coolers are required for towing and adding a hydro operated winch like I have.

The newer steering boxes for Dodge Ram w/6 bolts on top cap can be retrofitted to the GMT 400 platform too.

 

[Big T]

I have BFG ATs 265 on stock Alcoa wheels. They will be replaced shortly with Cooper AT3s. The ABS is still not working with the new bearing hubs, though harness plugs right in.

I just talked to Redhead and since this is not a primary driver, I'm just going to pull the steering box and send it to them. Before doing so, I took it over to my son Colby so he could test drive it. His reaction was "Holy Shit. These are the brakes it always needed." He's next. I've already done all the bushings, upper and lower, and ball joints, so his job will be just swapping out the knuckles that I have already prepped and reamed. I warned him that he'll need a new steering box.

 

[FellowTraveler]

I have BFA ATs 265 on stock Alcoa wheels. ABS is still not working with the new bearing hubs, though harness plugs right in.

I just talked to Redhead and since this is not a primary driver, I'm just going to pull the steering box and send it to them. Before doing so, I took it over to my son Colby so he could test drive it. His reaction was "Holy Shit. These are the brakes it always needed." He's next. I've already done all the bushings, upper and lower, and ball joints, so his job will be just swapping out the knuckles that I have already prepped and reamed. I warned him that he'll need a new steering box.

So you made are completely different animal with that brake conversion "that's great" I have to read this toic again...

 

[Big T]

So you made are completely different animal with that brake conversion "that's great" I have to read this toic again...

It's not cheap. With new top drawer stuff, the parts came in at $1,100, not counting the steering box. Then there's the effort to harvest the knuckles, reaming them, etc. I threw in the bushings on the lower control arm, but I think I'll be redoing the uppers as they're cracked and the driver's side has a little slop in the back one. With all the labor, this would easily be a $3K to $4K job at a shop. No one would spend that on a truck this age. That said, at 212K miles, I'm at half life on this diesel and I like it, so my treat to me.

 

[Will L.]

Your not in a rustbucket, so it isnt like you'll loose the frame or body. New brake system, suspension and steering, lots of life in the engine, shoot- your just ensuring the next decade or two.

 

[Big T]

Your not in a rustbucket, so it isnt like you'll loose the frame or body. New brake system, suspension and steering, lots of life in the engine, shoot- your just ensuring the next decade or two.

So true. Original cost of the Suburban was $6750 back in 2010 and 62K miles ago. Compared to a new 3/4 ton diesel truck at $65K, this is a bargain. Hell that $65K truck would depreciate the amount of my original cost in just the first year. I like it this way.

 

[THEFERMANATOR]

Most GMT400 bad brake feel I've witnessed is after larger diameter tires are installed and only the VSSB is calibrated for speedo and the most important calibration is ignored the "ABS." Tire size brake calibration for GM C/K Truck under 15000 GVW and 03-04 under 8600 with no VSES.

At times a bad P/S pump can cause bad brake feel too in a hydro-boost system additional p/s coolers are required for towing and adding a hydro operated winch like I have.

The newer steering boxes for Dodge Ram w/6 bolts on top cap can be retrofitted to the GMT 400 platform too.

You're the ONLY one I have ever heard say anything about calibrating the ABS. The ABS is completely out of the equation until it detects wheel slippage, then the isolation valves are opened, and it can function. When the isolation valves are closed, then the KELSEY HAYES system does nothing except allow the proportioning valve to work. If it does anything, it's news to me as I actually went to school on these systems, and at DODGE we had the capability to go into the programming of them somewhat, and there was nothing in there along those lines.

 

[Big T]

You're the ONLY one I have ever heard say anything about calibrating the ABS. The ABS is completely out of the equation until it detects wheel slippage, then the isolation valves are opened, and it can function. When the isolation valves are closed, then the KELSEY HAYES system does nothing except allow the proportioning valve to work. If it does anything, it's news to me as I actually went to school on these systems, and at DODGE we had the capability to go into the programming of them somewhat, and there was nothing in there along those lines.

The ABS light has been on basically throughout ownership of this vehicle. When I pulled codes it showed fault in the RF sensor, but I'm now on 3 different bearing and 5 different sensors and the same result. I've basically given up on ABS. That said, these GMT 800 brakes are the shit.

 

[FellowTraveler]

You're the ONLY one I have ever heard say anything about calibrating the ABS. The ABS is completely out of the equation until it detects wheel slippage, then the isolation valves are opened, and it can function. When the isolation valves are closed, then the KELSEY HAYES system does nothing except allow the proportioning valve to work. If it does anything, it's news to me as I actually went to school on these systems, and at DODGE we had the capability to go into the programming of them somewhat, and there was nothing in there along those lines.

Again, Ferm thanks for the heads up, however I had a braking issue related to the ABS calibration after I installed big tires re-calibrated the ABS & no problem. I'm not an expert by any means but the re-calibration worked for me and some other people I know after going to larger diameter tires.

So, what's your take on why such a calibration table exists?

 

[FellowTraveler]

The ABS light has been on basically throughout ownership of this vehicle. When I pulled codes it showed fault in the RF sensor, but I'm now on 3 different bearing and 5 different sensors and the same result. I've basically given up on ABS. That said, these GMT 800 brakes are the shit.

Ever test the RF wiring for a break, or?