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Does anyone have any braking questions.

 
Old 05-04-2019, 04:39 PM
  #1801  
steel_3d
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Where the caliper is placed on the knuckle is completely irrelevant from the point of view of physical force vectors, since the caliper and knuckle are essentially one unit, and the knuckle and rotor spin on the same axis with a single degree of freedom (rotation). When the brakes are applied, there is an equal and opposite torque (angular moment, rotational force) applied to the rotor+wheel, and also to the knuckle+control arms+chassis. Because there is only one degree of freedom, and the caliper is one unit with the knuckle, it's completely irrelevant WHERE the caliper is on the knuckle. The knuckle will experience exactly the same twisting force around the same axis (there's only one axis - the center of the wheel bearing, and the same amount of braking force from the friction of the pads). Again, the knuckle and caliper are one unit, so the force is the same no matter where on the knuckle the caliper is. If there were moore degrees of freedom it would be different, but since there's only one degree of freedom - rotation, angular position doesn't matter. (Radius, for example, does matter, but angular position does not).

Where the caliper is placed is simply a packaging question.

It doesn't even matter from a center of gravity point of view, because the caliper is sprung mass, so doesn't affect the balance of your chassis. There's a miniscule effect of pulling on the wheel under lateral acceleration (turning). If the caliper is toward the rear, centrifugal force on it will try to turn the wheel more into the corner. If it's toward the front, it will try to turn out of the corner. If it's on top, it will try to add positive camber on the outside, and negative camber on the inside wheel, which is the opposite of what you want. But it's such a small amount of weight compared to the thousands of pounds of car working against the wheel, it's completely irrelevant.

In short, it's simply a question of packaging.

Now, if you're talking about inboard calipers, that completely changes the game because it removes all the torque from the knuckle+control arms (removes the effect on dynamic alignment on rubber bushings), and transfers the brake torque directly to the chassis. But here, too, the caliper is one unit with the chassis, and there is only one degree of freedom around the axle, so angular position of the caliper doesn't matter. Lower down is better here, though, because it lowers the center of gravity of the chassis.

Last edited by steel_3d; 05-04-2019 at 04:47 PM.
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Old 05-06-2019, 10:08 AM
  #1802  
Bruce Powelson
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I haven't been able to get a firm pedal in a 1968 Corvette with Wilwood brakes. Tried gravity bleed, Speedybleed, pumping pedal. Had rear calipers turned vertical, new master cylinder, hits capitals with rubber hammer, and still brake pedal almost goes to the floor.
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Old 05-08-2019, 10:10 AM
  #1803  
mr.beachcomber
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Does the red "brake" light illuminate when you press the brake pedal while the engine is running? If so that would indicate a loss pressure during braking. Since you replaced the master cylinder, I would suspect air in the M/C. Your stock M/C has two bleeders - one for the front and rear reservoirs. Try bleeding both reservoirs to see if that helps or eliminates the problem.

Do you have manual braking or power braking on your '68? If you have manual braking, did you accidentally install a power braking M/C. With a larger bore, that alone will cause a soggy brake pedal.

The stock rear calipers have two bleeders, not just one. Try re-bleeding the rear calipers to see if that helps.

Finally, do a visual inspection of your rubber brake lines connected to the calipers, Sometimes an old rubber line will balloon when braking is applied due to old age and deterioration.

Hope this helps!
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Old 05-08-2019, 11:34 AM
  #1804  
Bruce Powelson
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Brake light does not illuminate when driving. Bench bled master and it is for the manual brakes that are on the car. Bled all calipers multiple times both inside and outside bleeders. Even bled rears while holding them vertical as some say that is a problem. I can't see any air bubbles coming out. Original calipers didn't have this problem. They lines to the calipers are new stainless ones that came with the Wilwoods. It only happened after installing Wilwood calipers. New master was installed at the same time and I tried two different ones just in case that was the problem. I even tried extending the rod from the brake pedal a little bit. Wilwood hasn't been much help. They say must have air in the lines, but I've gone through two quarts of fluid.
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Old 05-08-2019, 11:44 AM
  #1805  
tommyc6z06
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about 10yrs ago (different car), I had recurring problems with Wilwoods...i struggled endlessly to get a firm pedal. It ended up with a catastrophic brake failure where a kinda-firm pedal just went to the floor. It turned out that a bunch of calipers were 'porous'.

I switched to AP and never looked back
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Old 05-09-2019, 09:51 AM
  #1806  
Todd TCE
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Originally Posted by Bruce Powelson View Post
Brake light does not illuminate when driving. Bench bled master and it is for the manual brakes that are on the car. Bled all calipers multiple times both inside and outside bleeders. Even bled rears while holding them vertical as some say that is a problem. I can't see any air bubbles coming out. Original calipers didn't have this problem. They lines to the calipers are new stainless ones that came with the Wilwoods. It only happened after installing Wilwood calipers. New master was installed at the same time and I tried two different ones just in case that was the problem. I even tried extending the rod from the brake pedal a little bit. Wilwood hasn't been much help. They say must have air in the lines, but I've gone through two quarts of fluid.


"Replaced all the calipers, hoses and master cylinder" ie. everything. "Didn't have the problem before, now I do".

Pretty certain that's not a brand issue so much as an installation or application problem.

Some pics or specific part numbers you would like to share? What kit number? Which calipers? MC part number?


****************************** Additional info***********************

Having picked up on another thread here: you are not attempting to "bleed the lower bleed screws" correct? There is no such thing, many calipers have top and bottom only to allow a universal fit. Lower fittings are NEVER used for any bleeding procedures. This is stated in page 4 of the PDF on all Wilwood factory kits.

Last edited by Todd TCE; 05-09-2019 at 11:56 AM.
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Old 05-09-2019, 06:23 PM
  #1807  
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Originally Posted by Bruce Powelson View Post
Brake light does not illuminate when driving. Bench bled master and it is for the manual brakes that are on the car. Bled all calipers multiple times both inside and outside bleeders. Even bled rears while holding them vertical as some say that is a problem. I can't see any air bubbles coming out. Original calipers didn't have this problem. They lines to the calipers are new stainless ones that came with the Wilwoods. It only happened after installing Wilwood calipers. New master was installed at the same time and I tried two different ones just in case that was the problem. I even tried extending the rod from the brake pedal a little bit. Wilwood hasn't been much help. They say must have air in the lines, but I've gone through two quarts of fluid.
Bleeding that much fluid would have flushed any air through the lines. Somehow air may have stuck in the ABS unit. I'm pretty sure at that point you need a Tech II to bleed the ABS.
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Old 05-09-2019, 07:02 PM
  #1808  
Bruce Powelson
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It is a 1968 and doesn't have ABS.
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Old 05-09-2019, 07:29 PM
  #1809  
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I never installed stainless lines because people have posted here about them leaking. Try putting the factory lines back on, bleed and test to eliminate the lines. If it isn't the lines, then put the old calipers back on, bleed and re-test. As an aside, if you have speed-bleeders, those have been known to leak too.
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Old 05-09-2019, 07:46 PM
  #1810  
Bill Dearborn
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Originally Posted by Bruce Powelson View Post
It is a 1968 and doesn't have ABS.
Are these direct stock caliper replacement brake kits the ones you installed?
Front Brake Kit Part No.: 140-10789
Rear Brake Kit Part No.: 140-10790

How have you been bleeding the brakes? With a pressure or vacuum bleeder or having another person pumping the brakes? If you have another person helping you may need to make sure they aren't releasing the brake pedal while you are tightening the bleeder screw. I have seen that screw up more than once when the person doing the pumping doesn't understand why they are doing the pumping.

Based on the installation instructions for those two kits you are limited to the stainless hoses provided by Wilwood. With all of the fluid you have run through the system it seems you should have removed all of the air as long as you didn't do anything with the lower bleed screws. As Todd and the instructions say don't touch those. I suspect you could have the wrong master cylinder. It is not unknown for parts houses to provide the wrong part under the correct part number.

​​​​​​​Bill
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Old 05-10-2019, 09:26 AM
  #1811  
Todd TCE
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Bill mentions a point I was waiting to hear back on: the master cylinder. "What" master cylinder?

I'm leaning towards the calipers in question being those of the kit above. But we don't know that either.

Thus the reason for exact information on things: kit or part numbers, and or measurements. As in a 1.0" bore mc for example. If the part numbers and sizes check out then my money remains on a bleeding issue.
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Old 05-10-2019, 09:52 AM
  #1812  
Bruce Powelson
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Wilwood D8-4 part no. 950-140-10790 for fronts and 950-140-10789 for rears. I tried two different 1 inch master cylinders, both Chinese reproductions. Used a Speedybleed pressure bleeder and also a friend holding down the pedal. Only bled using upper bleeders.
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Old 05-11-2019, 07:09 PM
  #1813  
mr.beachcomber
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Originally Posted by Bruce Powelson View Post
Wilwood D8-4 part no. 950-140-10790 for fronts and 950-140-10789 for rears. I tried two different 1 inch master cylinders, both Chinese reproductions. Used a Speedybleed pressure bleeder and also a friend holding down the pedal. Only bled using upper bleeders.
According to the info on Wilwood's website, the 140-10790 kit is for the rear calipers and the 140-10789 kit is for the front. I have no experience with these brakes so I'm hoping that the swap of the kits numbers was just a human error and that kits cannot be installed on the wrong ends of a 65-82 Vette.
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Old 05-11-2019, 07:32 PM
  #1814  
Bill Dearborn
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"Wilwood D8-4 part no. 950-140-10790 for fronts and 950-140-10789 for rears", are you sure you installed them that way or just finger fumbled the numbers while typing your response?

If you actually did install them with the 10789 caliper in the rear that could be the problem. The 10789 caliper has a 5.56 sq in piston area while the 10790 caliper has a 3.00 sq in piston area. Not sure what the fluid volume difference would be when pushing the brake pedal but I suspect the brake lines for the rear have a proportioning valve that limits the pressure to the rear calipers.

I haven't worked on a C3 brake system in over 35 years so I don't can't remember whether the front and rear calipers can be swapped.

After digging through Wilwood's engineering drawings for the D8-4 calipers it doesn't look like the front and rear can be swapped. The mounting center for the front calipers is 7 inches Vs 5.16 inches for the rear mounting center. Plus the front calipers don't have mounting ears while the rears do.
Bill

Last edited by Bill Dearborn; 05-11-2019 at 07:53 PM.
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Old 05-14-2019, 12:29 PM
  #1815  
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Default Wilwood master vs power

I have 68 and I just purchased wilwood rotors pads and calipers for. I'm questioning upgrading to a power brake or just a wilwood master cylinder. Have you had any experience with what would be better? My assumption is obviously going to power brakes would be a better stopping verse the non.
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Old 05-14-2019, 12:51 PM
  #1816  
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Default Wilwood master vs power

I have 68 and I just purchased wilwood rotors pads and calipers for. I'm questioning upgrading to a power brake or just a wilwood master cylinder. Have you had any experience with what would be better? My assumption is obviously going to power brakes would be a better stopping verse the non.
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Old 05-14-2019, 02:11 PM
  #1817  
Todd TCE
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Correct, no way you can reverse the calipers. The mounting is way different.


I tried two different 1 inch master cylinders, both Chinese reproductions.

Aside form the obvious question on quality, I find that spec to be too small. I'll go on record as say I 'believe' the bore is 1.125" and thus the smaller size is going to generate a very soft and long pedal. Was the car fit with the 1.0 bore and D8 calipers prior? 5.56 + 3.0 is a lot of area for a 1" bore.
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