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Project Rear Disc Brakes

Big T

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Thread starter #83
Thanks. I've learned that keeping busy is the best thing I can do. I got back to work as soon as possible as I was behind from being out. I had take vacation for this week, but that has turned into truck work and today I'm replacing the lateral drain line from the kitchen at my mother's house (older sister and her son will stay there under a life trust). Lot of deferred maintenance on that home and I committed to my mother to help with the repairs. She left $200K in a trust specifically to rehab the home and it's going to need it. So I don't get much fun time this vacation, but wrenching and home repairs are a good diversion from the normal work I do. It keeps my mind focused.
 

Big T

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Thread starter #84
I looked at the kits with the El Dorado Calipers and they were close to $500. I went and got a GMT 800 14 bolt FF axle from the pick a part bone yard during one of their 40% off Sales for $200. The GMT 800 axle is about 2” wider so you have to cut off the spring perches and weld new ones in place. Also need to fab a weld new perches for he jounce snubbers. You’ll need to use the yoke from the GMT 400 axle. I have th GMT 800 all prepped to go on my son’s truck, but have not installed yet. Just too busy. This will be a winter project.

http://www.thetruckstop.us/forum/threads/project-rear-disc-brakes.45238/page-2

If you really want stopping power in your Suburban, I would first do the GMT-800 front brake conversion.
 

FellowTraveler

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#86
GM 14 ff differential in the Suburban is different than most others in that if the drum slides off a disk conversion is not just a bolt on conversion and IMO not wroth the time or effort to fabricate either.

The GM 14 bolt w/disks from a 3500 van is most common method to match up the front/rear track.
 

spdgofast

Active Member
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#87
From what I've read the van rear axle is the widest one wheel hub face to wheel hub face. The one I bought for my mud K5 blazer was out of a 2000 or so 3500 van with 4:10s and I think it was 72" WF TO WF (wheel face). I'm also pretty sure my Suburban has the original proportioning valve not the newer updated one mentioned earlier in this thread I believe.
 

spdgofast

Active Member
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#88
I tried to edit last post.....From what I've read the van rear axle is the widest one wheel hub face to wheel hub face. The one I bought for my mud K5 blazer was out of a 2000 or so 3500 van with 4:10s and I think it was 72" WF TO WF (wheel face). I'm also pretty sure my Suburban has the original proportioning valve not the newer updated one mentioned earlier in this thread I believe. And I do believe the front brakes are more of an issue than the rear in my truck anyway. I stood on my brake pedal with both of my size 13 feet pushing as hard as I could and I could feel the ABS go on and off and still pushed a VW Passats LR tailight up to the back window and I think it really should have stopped. No damage to my truck at all. Not sure if the ABS is reacting on and off fast enough, like to much time releasing pressure when it senses a tire skid, I always wondered if it was the 33 inch tires throwing of the calibration even with a new speed buffer to recalibrate the speedo due to the larger tires.
 

FellowTraveler

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#89
I tried to edit last post.....From what I've read the van rear axle is the widest one wheel hub face to wheel hub face. The one I bought for my mud K5 blazer was out of a 2000 or so 3500 van with 4:10s and I think it was 72" WF TO WF (wheel face). I'm also pretty sure my Suburban has the original proportioning valve not the newer updated one mentioned earlier in this thread I believe. And I do believe the front brakes are more of an issue than the rear in my truck anyway. I stood on my brake pedal with both of my size 13 feet pushing as hard as I could and I could feel the ABS go on and off and still pushed a VW Passats LR tailight up to the back window and I think it really should have stopped. No damage to my truck at all. Not sure if the ABS is reacting on and off fast enough, like to much time releasing pressure when it senses a tire skid, I always wondered if it was the 33 inch tires throwing of the calibration even with a new speed buffer to recalibrate the speedo due to the larger tires.
Your larger diameter tires do effect the ABS ability to stop the vehicle as designed and re-calibration of the VSSB does nothing for the ABS however there are tire diameter to brake tables on some GMT400 applications that allow a % change to ABS that change would be the same % difference between the original tire diameter and the newer tire diameter (loaded). Name in carcode is; Tire size brake calibration for GM C/K Truck under 15000 GVW and 03-04 under 8600 with no VSES

Spongy brakes........see;
 

spdgofast

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#90
I'll have to look into the ABS calibration, my 94 Burb has a different module than the one on the video. FYI I snagged a 14 bolt 4:10 ratio full floater rear from a 04 GM 2500 yesterday, It measures 68.5" wide which is what the front measurement is on my Suburban. The drum brake rear measures 65.5", so it should make my wheels line up perfectly instead of the rears being set in 1.5' on each side. I was at a U pull today and saw a 2wd 04 front caliper and now I see why the GMT 800 brakes work so much better, the caliper is like twice the size as the one on my GMT400. I also stumbled across a 2000 3500 dually 6.5 that someone obviously wanted the IP, they were nice enough to unbolt the no EGR manifold and dual therm housing and left them laying for me to just pick up and carry to the counter along with the IP gear. It looks like they busted the aluminum IP mount housing with a hammer, I guess they couldn't loosen the IP bolts. Are the later model lower control arms any better than the previous model stamped ones? They look like they may not be as strong, I don't have a problem with rust on my stamped ones.
 
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Big T

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Thread starter #91
I'll have to look into the ABS calibration, my 94 Burb has a different module than the one on the video. FYI I snagged a 14 bolt 4:10 ratio full floater rear from a 04 GM 2500 yesterday, It measures 68.5" wide which is what the front measurement is on my Suburban. The drum brake rear measures 65.5", so it should make my wheels line up perfectly instead of the rears being set in 1.5' on each side. I was at a U pull today and saw a 2wd 04 front caliper and now I see why the GMT 800 brakes work so much better, the caliper is like twice the size as the one on my GMT400. I also stumbled across a 2000 3500 dually 6.5 that someone obviously wanted the IP, they were nice enough to unbolt the no EGR manifold and dual therm housing and left them laying for me to just pick up and carry to the counter along with the IP gear. It looks like they busted the aluminum IP mount housing with a hammer, I guess they couldn't loosen the IP bolts. Are the later model lower control arms any better than the previous model stamped ones? They look like they may not be as strong, I don't have a problem with rust on my stamped ones.
The later model lower control arms are forged and superior to the stamped and welded steel ones. They afford a steering radius that is approximately 4' less than can be achieved with the stamped steel LCAs. That alone makes them better. The forged construction is stronger and less vulnerable to rot from rust.

Unfortunately, I have yet to install the GMT 800 14 bolt 4:10 full floater on my son's Suburban. Too many things on my plate and my son was having issues with lift pump, but it was solved with a new OPS. I am also slated for a second surgery on my right foot to address issues not addressed by my first surgeon. That will have me out of commission about 8 weeks, starting from just before Thanksgiving.
 

THEFERMANATOR

FRANKENBURBAN
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Staff #92
Your larger diameter tires do effect the ABS ability to stop the vehicle as designed and re-calibration of the VSSB does nothing for the ABS however there are tire diameter to brake tables on some GMT400 applications that allow a % change to ABS that change would be the same % difference between the original tire diameter and the newer tire diameter (loaded). Name in carcode is; Tire size brake calibration for GM C/K Truck under 15000 GVW and 03-04 under 8600 with no VSES

Spongy brakes........see;
I would NEVER reccomend what this guy shows in this video. What he is pressing is NOT an air bleed, it's the shuttle valve in the proportioning valve. When he depresses it like that, he is forcing it past MAX travel and forcing fluid out where it was NEVER meant to come out. If you have the ABS bidirectional tool, you can do this the right way WITHOUT destroying the seals inside a NLA proportioning valve.

And FYI, the gmt-800 trucks do NOT use the corporate 14 bolt full float like ours. They are very similiar, but they are a completely different axle. So keep this in mind when you order parts to be certain to order parts for the correct year axle. Many have adapted the gmt-800 rear discs to the earlier axles. If you have a 3500 srw or SUBURBAN, you have the over the hub design just like the gmt-800 uses. So you can weld on a new plate to the axle to retain the disc backing plate, and bolt disc brakes onto them. I discovered this AFTER I had just replaced EVERYTHING in my drum brakes.
 

FellowTraveler

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#93
I would NEVER reccomend what this guy shows in this video. What he is pressing is NOT an air bleed, it's the shuttle valve in the proportioning valve. When he depresses it like that, he is forcing it past MAX travel and forcing fluid out where it was NEVER meant to come out. If you have the ABS bidirectional tool, you can do this the right way WITHOUT destroying the seals inside a NLA proportioning valve.

And FYI, the gmt-800 trucks do NOT use the corporate 14 bolt full float like ours. They are very similiar, but they are a completely different axle. So keep this in mind when you order parts to be certain to order parts for the correct year axle. Many have adapted the gmt-800 rear discs to the earlier axles. If you have a 3500 srw or SUBURBAN, you have the over the hub design just like the gmt-800 uses. So you can weld on a new plate to the axle to retain the disc backing plate, and bolt disc brakes onto them. I discovered this AFTER I had just replaced EVERYTHING in my drum brakes.
Thanks for the 'correction' on both topics........."in the name of safety perhaps deleting the video is in order too."
 

spdgofast

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#94
Well guys, I've found all of the GMT 800 front brake parts for $300.00 and a set of 2000 3500 GMT 400 forged lower control arms for $200.00 which seems reasonable. I have come across a little hickup in my brake project, check out pics. My Burb has a 4 inch trailmaster lift kit with aftermarket upper control arms and spacers between the knuckles and the upper CA. So I need to get both a GMT 400 along with a gmt 800 knuckle in my hand along with this spacer to see if I can go any further or what I can do to make it work. Anyone have any pics of the tops of these two knuckles side by side? Any ideas? I really don't want to start tearing my front end apart right now since I am really trying to concentrate on my fuel system right now. I know this thread was originally for rear end stuff so if I go much deeper maybe I should start my own thread?
 

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Big T

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Thread starter #95
So you have a spacer welded onto the top of the GMT 400 knuckle that then connect to the ball joint of the upper control arm?

During my GMT 800 conversion journey, I first pulled the knuckles from a 3/4 ton GMT 800 van and they were significantly taller than the truck versions. Had side-by-side photos of the knuckles in a thread her. I'll try to find.

See pics post #20 in the following thread:

https://www.thetruckstop.us/forum/threads/gmt-800-brake-conversion-silverado-hd-2500.45047/
 

spdgofast

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#96
The spacer is a cast piece that is bolted to the top of the knuckle with a big bolt going where the ball joint was before the lift was installed. It also looks like it has like a 4 bolt plate also attaching it to the knuckle. So it would have to fit correctly on the top of another knuckle to work. I saw you pics, I didn't realize that the GMT 800 knuckles were that much taller, I would think that would be an issue but you already did you fronts right? I just noticed you said the one GMT 800 knuckle in the pic is from a van? Sorry I thoroughly read the post and see that the van ones were taller and the truck ones were basically the same as the gmt 400 of 13 inch tall.
 
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spdgofast

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#97
Now that I think about it I need to double check with the lift kit manufacturer to see it I can even install the forged LCAs, the way the lift is set up is there is a subframe that lowers the differential, axles and LCAs 4 inches, then they use different upper CAs with a 4 inch spacer between the knuckle and the upper CA. Since the differential was lowered 4 inch I was able to install the P400 without modifying the oil pan.
 

Jaryd

Love my 6.5
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#98
Now that I think about it I need to double check with the lift kit manufacturer to see it I can even install the forged LCAs, the way the lift is set up is there is a subframe that lowers the differential, axles and LCAs 4 inches, then they use different upper CAs with a 4 inch spacer between the knuckle and the upper CA. Since the differential was lowered 4 inch I was able to install the P400 without modifying the oil pan.
The kits for these trucks come different ways depending on which lower control arms you have. There is a guy on one of the Facebook sites who found this out after ordering his lift kit. I’ll try to find it again.
 

spdgofast

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Thanks, I was just looking around to see if any other lift kit companies did their 4 inch lifts with stock control arms upper and lower, lowering just the lower CAs therefore having a 4 inch longer knuckle I could use without the spacer I have now. I doubt any of them will sell me parts if I tell them what I'm trying to do. The sad part is my truck rides perfect much better than a Excursion and all the front end components are new, bushings, bearings, ball joints, rotors, calipers etc. thus the reason I've spent so much time and $ upgrading it. It just doesn't stop well and I'm trying to make it faster. LOL
 
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