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5/2/17 7:26pm - Original Message: 'Now I have solid brake pedal but not good stopping power?????'
rlu1968
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 222
Brakes were spongy, and did not stop quickly nor could I  lock down the brakes in an emergency stop. (See my previous post on 68 brakes).
 The shop that specializes in high HP vehicles and  Hot Rods,  have got the brakes solid and not spongy as before. But the car won't stop quickly. No locking down the brakes. It comes to a stop but not quickly.
 The mechanic has gone through all the calipers, new rubber brake lines, the pads, master cylinder good. Everything concerning the brakes have  been gone through.
 I think he now is a little lost at what to do. He has worked on many corvettes and even went back and drove a 68 he had worked on in the past. He said it stopped like it should. 
Now he has mentioned putting a gauge on the brake line to see how much pressure it is putting out to the calipers. I guess it has a certain pressure number to get the brakes to lock down. Shocked
If this does not work then he wants to install a booster for the master cylinder. Which I think from 1972 on they all had the boosters. 
My Cam is taking up most of the vacuum so he will need to put a electric motor of sorts to keep the vacuum up enough.
Any other ideasUnhappy 




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5/2/17 8:16pm - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
johnu
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Eagan, MN - USA

Vette(s):
1981 Corvette Two-Tone Claret color, 4 spd, C7 Vert

Joined: 5/23/2007
Posts: 507
My first thought is a master cylinder, weak booster or vacuum loss....power brakes correct?

|UPDATED|5/2/2017 6:16:25 PM (AZT)|/UPDATED|


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5/2/17 9:19pm - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19458
It's possible it has the wrong master cylinder on it. Non-power brakes take a different master....it sounds like your car is non-power brakes, correct? I would verify it has the correct master on it before going thru the hassle of installing power brakes, but....power brakes are nice, so it might be the best solution all around, unless you want to keep it original. 

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5/2/17 10:08pm - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
rlu1968
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 222
non power brakes, no booster. 
 Changed out master cylinders probably 7-8 times since 1989.  All the shops tell you first that the problem is the Master Cylinder.  Not the case here. 
I don't know much about the booster, but if it works then I need the stopping power.
I only have about 5lb of vacuum pressure left with my cam, just didn't know how much a vacuum pump to increase the booster vacuum and what kind of noise this might make.


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5/3/17 12:15am - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.

Joined: 7/9/2003
Posts: 399
Might try a vacuum reservoir with a check valve in it assuming that the 5" of vacuum is just at idle.

Power brakes were still optional in '73.


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1973 L-82 4 spd

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5/3/17 4:45pm - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
rlu1968
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 222
This has always been a non power, non booster car.
  However all the master cylinders over the years have come from Auto zone, Napa or O'reillys. Wonder what vendors they got them from?
But now, no sponge, just brakes that won't stop fast, lock up or otherwise. 
I guess we will try the booster, it will still look original in the car. 
 Then go with  another master cylinder to go with the booster. An an extra vacuum source. 
I don't use the rebuilt stuff. Unless it is a" have to case" being it is a 1968! 
This just looks like one of those "BUBA" repairs. Where as you keep throwing new parts at it Confused and  trying to figure out what is wrong. 


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5/4/17 5:48pm - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
indy99
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Newport, MI - USA

Vette(s):
1980 L-48 still in the middle of a frame-off.

Joined: 6/9/2005
Posts: 926
Are the brake pads and rotors in good shape?   Glazed pads will have an effect as well as glazed rotors.   Had this happen on my AMC quite some time ago.

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5/4/17 6:56pm - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
rlu1968
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 222
Went all through the calipers and the pads and removed any glaze buildup. All is in great shape. 

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5/6/17 1:48am - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
stingrayjim jr Lifetime Member
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SHELBYVILLE, TN - USA

Vette(s):
1976 L48 auto

1978 L82 4speed

1994 LT1 6speed

Joined: 7/5/2002
Posts: 3937
If by chance you have power steering, you might be able to set up a hydro-boost, rather than go the vacuum booster route....  just a thought, otherwise you might need to look into a larger bore master cylinder... 

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StingrayJim
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Stingray's '76                             StingrayJr's '78                           Lil Red '94

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5/6/17 3:22am - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
Grahamred70
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, - United Kingdom

Vette(s):
1970 convertible in red 350

Joined: 10/6/2015
Posts: 82
A larger bore master cylinder will make the brakes worse! you need the multiplication of a small master and greater area of caliper pistons to make the pressure applied at the calipers higher, that's why the brake pedal moves a lot further than the caliper piston, simple hydraulics.
A power assisted master cylinder has a larger piston than a non assisted because it has the vacuum to add to the force of your foot, could it be that someone has fitted a power assisted master cylinder by mistake in the past and then subsequently just replaced like for like? The poster did say that the master cylinder has been replaced several times which in itself is unusual, I just replaced the one in my 70 as it was starting to leak but I think the one that came out was original.
My brakes are non assisted and my car stops very well, just needs a bit more of a push than a modern with servo.
Are all the flex hoses in good order as they can collapse internally and reduce pressure to the caliper, a good time to upgrade to braided PTFE hoses if your in any doubt.
Graham
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5/7/17 12:29am - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
stingrayjim jr Lifetime Member
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SHELBYVILLE, TN - USA

Vette(s):
1976 L48 auto

1978 L82 4speed

1994 LT1 6speed

Joined: 7/5/2002
Posts: 3937
ok, that makes sense to me, having a smaller bore master cylinder creates more pressure. Sorry  i didnt think that one through.....i'm in the typical "bigger is better" zone.....

and  i do agree about the braided flex lines, they did firm up my pedal


|UPDATED|5/6/2017 10:29:05 PM (AZT)|/UPDATED|


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StingrayJim
NCM Lifetime Member #1936

Stingray's '76                             StingrayJr's '78                           Lil Red '94

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5/7/17 1:09pm - Reply: 'Re: Now I have solid brake pedal but not good stopping power?????'
Grahamred70
Former Member
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, - United Kingdom

Vette(s):
1970 convertible in red 350

Joined: 10/6/2015
Posts: 82
No problem, its a trap that many people fall into, a case of less is more!
Regards
Graham
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