LS1 front brakes on G body spindle

81cutlass

Royal Smart Person
Feb 16, 2009
1,149
896
113
Western MN
#11
Bout damn time someone has a nice neat up to date thread on this old subject, thanks for posting it. Some of those old S-10 forums threads are an absolute dragged out mess.
I got a set of calipers & lines years ago, drilled some brackets with extra lightening holes in them{ to look cool also}, and never got around to the project. I think I can both cut and turn down the stock rotor/ hub in place or on another spindle with a good 4 1/2" grinder & years of skill using them. Installing studs before turning down hub was an option some did to help prevent cracking I may consider.

Don't remember noticing having to modify G-body steel line before. So you just cut off factory flared end and did newer style flare with flare tool, leaving g-body connector in place behind flare?? Line flaring is one of my weaker skill areas and I need to either buy or rent a tool. Maybe Oreilly's, Autozone or Advance Auto may have a worth while tool to rent or buy? Don't feel like spending $200 plus on some of the professional models.

Now, one change I'm planning on making when I do finally get around to mine::: larger rotors. I have 18's so I could get either stock or aftermarket 14" z-06 vette rotors for not too much more money from Rock Auto.. Not sure if the in & out disc to rotor mount spacing is any different, but I think all I'd have to do is move caliper bracket holes out an inch. OR, 1/2" for some 13" c-5/6 rotors.
A sidenote of interest here, A friend recently told me our local Oreilly's store would now price match rock auto.
Yes, I used a tube cutter to cut off the G body double flare and used a lisle bubble flare tool to reflare the line 1/4" back from where the stock double flare was. I have heard the lisle or rigid tool is good. Harbor fright and other cheap ones aren't forged of good enough material and bend which is where most problems lie. Getting good bubble flares is hard and I struggled for years but finally found out how. I suggest getting some old GM line (the new stuff just seems softer) and giving it a shot before you do it on the car. I found tightening the clamp really tightly (finding one with good hard knurling is important too so the line doesn't push in when you tighten the form tool) and deburring the inside of the line really well before flaring helps a lot. Also, getting the height of the tube extending out of the clamp is critical.

81cutlass: I don't mean to bother but on the brackets does it have to be 5/16" I found a piece of 1/4 will that work with maybe a washer with it?
I used 3/8. 5/16 would work with a washer I am sure but my local menards had 3/8. 3/8 is such an easy size to find and then you don't have to worry about washers. I'm sure it would work with the right washers but why bother when 3/8 is a common stock size. 1/4 is too thin in my opinion, there is a lot of force in the system.
 

Griffin84ss

Greasemonkey
Apr 14, 2017
146
80
28
Georgetown, ky
#12
Yes, I used a tube cutter to cut off the G body double flare and used a lisle bubble flare tool to reflare the line 1/4" back from where the stock double flare was. I have heard the lisle or rigid tool is good. Harbor fright and other cheap ones aren't forged of good enough material and bend which is where most problems lie. Getting good bubble flares is hard and I struggled for years but finally found out how. I suggest getting some old GM line (the new stuff just seems softer) and giving it a shot before you do it on the car. I found tightening the clamp really tightly (finding one with good hard knurling is important too so the line doesn't push in when you tighten the form tool) and deburring the inside of the line really well before flaring helps a lot. Also, getting the height of the tube extending out of the clamp is critical.



I used 3/8. 5/16 would work with a washer I am sure but my local menards had 3/8. 3/8 is such an easy size to find and then you don't have to worry about washers. I'm sure it would work with the right washers but why bother when 3/8 is a common stock size. 1/4 is too thin in my opinion, there is a lot of force in the system.
Thanks for your help with this I will look around for some 3/8 size stock I'm sure I can find a piece. Thanks again
 

MC96

Greasemonkey
Dec 7, 2015
212
77
28
#13
I used 3/8. 5/16 would work with a washer I am sure but my local menards had 3/8. 3/8 is such an easy size to find and then you don't have to worry about washers. I'm sure it would work with the right washers but why bother when 3/8 is a common stock size. 1/4 is too thin in my opinion, there is a lot of force in the system.


The steel part of this is only 3/16"s and they work fine, although I would want the peace of mind of something a little thicker if I was building from scratch
 

roger1

Greasemonkey
Aug 23, 2010
183
129
43
San Angelo, TX
#14
A friend of mine advised me to use 4130 steel for the brackets.
Is that something you thought about?
Sounds like 3/8" is the way to go from your experience. Glad you posted about that. I would have used 5/16" otherwise.
 

roger1

Greasemonkey
Aug 23, 2010
183
129
43
San Angelo, TX
#15

jlcustomz

Master Mechanic
Nov 22, 2011
467
66
28
#16

81cutlass

Royal Smart Person
Feb 16, 2009
1,149
896
113
Western MN
#18
Was just looking up an older thread where stock g-body rubber lines were used with the f-body banjo bolts. Guess that's why I don't remember hearing about hard brake line modification.
https://gbodyforum.com/threads/ls-1-12-disc-brake-conversion-for-g-body.25333/
I looked into using the stock G body hose but it had to turn 90 degrees and ended up with a a funny kink that got worse in turns which i wasn't comfortable with. Difference between mounting the bolt going in from the top/bottom or from the side is what it boiled down to.

A friend of mine advised me to use 4130 steel for the brackets.
Is that something you thought about?
Sounds like 3/8" is the way to go from your experience. Glad you posted about that. I would have used 5/16" otherwise.
Not saying 4100 series isn't a good idea, but it's way overkill. If you want the closer dimensional control and not mill scale get some cold rolled 1018 or something. 4100 series can be heat treated where a low carbon steel like 1018 can't, but you aren't doing any heat treatment/case hardening.

I am almost certain looking at it a36/1018 is more than strong enough. The weak points will be the bolts.

If you really want confirmation give me a few days and I can do the math to prove it to you. The cast spindle or the bolts will fail long before even the lowest grade steel 3/8x2 flat bar will fail.
 

Clone TIE Pilot

Royal Smart Person
Aug 14, 2011
1,756
154
63
Galaxy far far away
#19
I have seen this type of brake upgrade before and sadly I have heard of one downside. The stock hub is designed to be reinforced by the integral rotor, so cutting it off really weakens the stock hub casting due to the grain structure of the cast iron. This is why cracks are common with a hub with a cut off rotor. There are aftermarket rotorless hubs that are designed for such use but they are not cheap. Aonther issue is I think LS1 brakes require a 16 inch and larger rim. Stock 15 inch rims won't clear them which can be a problem for some of us.
 

roger1

Greasemonkey
Aug 23, 2010
183
129
43
San Angelo, TX
#20
I have seen this type of brake upgrade before and sadly I have heard of one downside. The stock hub is designed to be reinforced by the integral rotor, so cutting it off really weakens the stock hub casting due to the grain structure of the cast iron. This is why cracks are common with a hub with a cut off rotor. There are aftermarket rotorless hubs that are designed for such use but they are not cheap. Aonther issue is I think LS1 brakes require a 16 inch and larger rim. Stock 15 inch rims won't clear them which can be a problem for some of us.
I can't see that would be a problem at all as long as the lug nuts were torqued correctly and the inside surface of the wheels aren't warped. And if spacers were used, they need to be of high quality machining to make sure they are in perfect uniformity.
I suspect if you saw or heard about any instances of failure, the lugs were loose or cheap spacers were used. Possibly both.

Custom made hubs are going to have the same diameter and not significantly different in thickness at the wheel mating surface.
Plus the hub gains back the strength of the whole structure when the rotor and wheel are all clamped together. The clamping force applied by the stretch of the lugs that are torqued down make the forces applied go to the entire bolted together unit, not just the hub. The unit could conceivable be even stronger than stock since the thickness of the rotor is now added to the total thickness of the single bolted together unit.
 

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