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VERY soft brake pedal after wheel hub swap

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50
43
Exp. Type
HPDE
Exp. Level
Under 3 Years
South Carolina
My car is a 2009 GT 3V, currently daily driven but I hope not much longer. About a year ago I installed Brembo 6-pot calipers, 15" Gyrodisc rotors, titanium shields and GLOC street pads. (The front brakes are also ducted, but I don't think that has anything to do with my current issue.) As usual I completed that swap successfully only with the help of patient old heads on this forum, especially @OPMustang Tim, so thanks much again. Last night I finally finished swapping the front wheel hubs--see separate thread for my travails. Long story short: left front of, on, and reassembled in an hour or two. Right front issues required removing the spindle, so the caliper hung from the spring for a week. No fluid leaks, reservoir is still full. I followed the steps in the FSM for removal/installation , including torquing everything to spec. When I drove it last night, I had 3"-4" of pedal travel before the brakes would grab. A tap or two before hard braking would reduce travel some, but not much. Once the brakes grab I can stand the car on its nose. Clutch pedal is fine (other than having 82K miles). I understand the increased piston area creates some extra travel, but this is much more than before installing the new hubs. Brake fluid has less than 4K street miles, and I will bleed all four corners this weekend. I hope the bleed will restore my pedal. Otherwise, any insight why I have this issue? Is there something else I need to do?
 
2,190
1,048
Bay Area
I did the upgrade on my Boss. I had the same issue after i bled my brakes. I had to do another full bleed and they seem to work good now. I still need to get used to that initial soft pedal since im used to GT350 brakes, but everyone that has tried it out says its normal for the set-up.
 

Mad Hatter

Gotta go Faster
5,206
4,191
Santiago, Chile
I found the good old fashioned brake bleed with two people was much better then the typical Motive pressure pump. As far as the soft pedal, using a very aggressive brake pad like a Pagid RST 2 or 3 or a GLOC R16 or 18, left the pedal feel ideal for me.

With the right pads, the setup can give really great results, Half way through a 20min sprint race, my Boss could out brake most of the GT4 Caymans we ran against.
 
My car is a 2009 GT 3V, currently daily driven but I hope not much longer. About a year ago I installed Brembo 6-pot calipers, 15" Gyrodisc rotors, titanium shields and GLOC street pads. (The front brakes are also ducted, but I don't think that has anything to do with my current issue.) As usual I completed that swap successfully only with the help of patient old heads on this forum, especially @OPMustang Tim, so thanks much again. Last night I finally finished swapping the front wheel hubs--see separate thread for my travails. Long story short: left front of, on, and reassembled in an hour or two. Right front issues required removing the spindle, so the caliper hung from the spring for a week. No fluid leaks, reservoir is still full. I followed the steps in the FSM for removal/installation , including torquing everything to spec. When I drove it last night, I had 3"-4" of pedal travel before the brakes would grab. A tap or two before hard braking would reduce travel some, but not much. Once the brakes grab I can stand the car on its nose. Clutch pedal is fine (other than having 82K miles). I understand the increased piston area creates some extra travel, but this is much more than before installing the new hubs. Brake fluid has less than 4K street miles, and I will bleed all four corners this weekend. I hope the bleed will restore my pedal. Otherwise, any insight why I have this issue? Is there something else I need to do?
Is it possible you entrapped some air or maybe damaged a brake hose? Make sure one isn't twisted and you didnt knock the fittings at the caliper loose. Bleed the rear while cycling the parking brake. Make sure the pads are floating freely in the calipers.
 
There was no brake in the fluid system and the pedal is worse. That's weird. I wonder if there was some air in the line from last years conversion down around the ABS block that made its way up to that one caliper when it was hanging. It might have been just high enough. When I did the 6 pot upgrade even with a full fluid flush I had to do an abs bleed with forscan then another full flush to get my pedal to a reasonable feel.
 
50
43
Exp. Type
HPDE
Exp. Level
Under 3 Years
South Carolina
There was no brake in the fluid system and the pedal is worse. That's weird. I wonder if there was some air in the line from last years conversion down around the ABS block that made its way up to that one caliper when it was hanging. It might have been just high enough. When I did the 6 pot upgrade even with a full fluid flush I had to do an abs bleed with forscan then another full flush to get my pedal to a reasonable feel.
I did the ABS Forscan bleed and two bleeds with Motive Products after adding the big brakes. The pedal has been soft-ish, but about what everyone who has done the upgrade describes. My post was because it got much worse after replacing the hubs, even though the fluid system wasn't opened. I will follow Tim's lead and recheck that I twisted no lines, and try the ABS bleed (first need to find a Windows notebook). Thanks again to everyone who responded.
 
1,070
1,065
Exp. Type
HPDE
Exp. Level
5-10 Years
Lenoir City TN
I did the ABS Forscan bleed and two bleeds with Motive Products after adding the big brakes. The pedal has been soft-ish, but about what everyone who has done the upgrade describes. My post was because it got much worse after replacing the hubs, even though the fluid system wasn't opened. I will follow Tim's lead and recheck that I twisted no lines, and try the ABS bleed (first need to find a Windows notebook). Thanks again to everyone who responded.
The Autel Maxicheck diagnostic tablets have the abs bleed function without using Forscan. It is easier to use if you have access to one.
 
If it is air in the system, pumping the pedal will bring the pedal up higher.

Silly question, but the new hubs are tight, correct? Any play there will knock the pads back and make the pedal shiznit. Though it usually comes back on the second pump.

Also, the car was sitting for a bit? Make sure the rear calipers are moving smoothly and free. THe rears are actually more responsible for the top part of the pedal feel than the fronts.

DaveW
 
50
43
Exp. Type
HPDE
Exp. Level
Under 3 Years
South Carolina
Thanks for the replies. Bled Saturday-nary a bubble from the rears, but small streams of tiny bubbles from both fronts. Pedal now feels like it did before my hub adventure. DaveW: Not a silly question. Hub nuts (both sides) torqued out at 221 lb-ft with a full inch of play left on the spindle. Kept grinding away until I could feel no movement nor slip the thinnest leaf of my plug gap gauge between spindle and hub. Rear calipers seem fine, but I will take a closer look next weekend. Eric EF1: Haven't dropped the $400-500 on the Autel; ordered a $80 refurbished Dell laptop and will use that with Forscan. Byronj: Will do the ABS bleed once the "new" laptop arrives, then re-bleed each wheel. My back is hurting after this weekend's effort-I don't know how blacksheep1 has handled tires all these years.
 
6,289
8,021
FWIW, when I did the clutch on my 07 Gt500, it took about 2 days to finally get the clutch to work after the install. It all seemed fine, but after it set for a few hours it would have a tough time engaging first gear. It went away after more bleeding.
 
1,070
1,065
Exp. Type
HPDE
Exp. Level
5-10 Years
Lenoir City TN
Thanks for the replies. Bled Saturday-nary a bubble from the rears, but small streams of tiny bubbles from both fronts. Pedal now feels like it did before my hub adventure. DaveW: Not a silly question. Hub nuts (both sides) torqued out at 221 lb-ft with a full inch of play left on the spindle. Kept grinding away until I could feel no movement nor slip the thinnest leaf of my plug gap gauge between spindle and hub. Rear calipers seem fine, but I will take a closer look next weekend. Eric EF1: Haven't dropped the $400-500 on the Autel; ordered a $80 refurbished Dell laptop and will use that with Forscan. Byronj: Will do the ABS bleed once the "new" laptop arrives, then re-bleed each wheel. My back is hurting after this weekend's effort-I don't know how blacksheep1 has handled tires all these years.
I am fortunate enough to have a good friend with an Autel Maxicheck MX808 that he rarely uses. It pretty much lives in my garage and he borrows it back once in awhile.
 

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