Brake issues......

OK. so when I changed the front suspension on my truck this spring, I put Lincoln MK VII rotors, calipers & pads on it, because they're a little bigger than the Mustang rotors & they're 11". Plus, they came with the 5 on 4-1/2 lug pattern. Anyway, for some reason, I can't get good pressure on the brake pedal. I pressure bled them with an air bleeder (3 times) & then we (my son & I) bled them the old fashioned way, and we're not getting ANY air from the system. If you pump the pedal 4-5 times they get nice and solid, and if you hold the pressure on the pedal, it won't bleed off. But, if you let off the pedal for even 5 seconds, and press the pedal again, it goes right to the floor. Yeterday, I took the master cylinder apart, cleaned it out, the seals looked great, & put it back together, filled & bled it on the bench, and put it back on. Went throught the whole bleeding thing again to make sure there's no air anywhere, and still no brakes. I'm not mad, just puzzled. Besides, the former gets ya nowhere, but furthering your frustration. The master cylinder is and Aerospace unit that I got from my brother for a Foxbody manual brake conversion. I ran it last year with no issues. All I changed was the rotors, calipers, & pads, and 2 brake lines because they got kinked when doing the frontend swap. Somebody smarter than me on this stuff please jump in, or give me a call (406 431 3265) so I can get my brakes working. There's a race next weekend, and I'd be kinda happy if I made it.


Thanks fellas.


Doug...

Rear brakes out of adjustment?? Calipers on upside down??

Doug i was thinking about it all night and seen that you change the front lines are they the same type? If they are not you mite be getting the flaring/growing and the need to pump it. Just a thought im no brake export.

Like nos-stang says, be sure he rear brake shoes are adjusted, otherwise they'll take a large volume of fluid before the system is pressurized. If that doesn't help, I'd guess that your master cylinder is too small for the new larger calipers.....Not enough volume per pump stroke. It's possible you may need a larger master cylinder. JMO. Could you use the one from the Lincoln?

I doubt it is the master cylinder but it may be. I run 6 calipers (2 front and 4 rear) and don't have any volume problems and we send a lot of fluid to the rear with the proportioning valve.

Do you have a residual pressure valve in your system?

Whatbumper, Is your master cylinder similar to Doug's?

doug what is the bore on your master? what rear brakes do you have? A lot of masters have one end with a longer stroke which should go to the wheels that require the greater volume. On a street car with front discs and rear drums that will usually be the front but on a custom or race vehicle you need to look at the combo.

dkp

maverick wrote:Whatbumper, Is your master cylinder similar to Doug's?

should be the same one.

whatbumper wrote:I doubt it is the master cylinder but it may be. I run 6 calipers (2 front and 4 rear) and don't have any volume problems and we send a lot of fluid to the rear with the proportioning valve.

Do you have a residual pressure valve in your system?

I still have the factory proportioning valve mounted on the frame. You can see it under the steering shaft in the 1st pic below. I have an adjustable one from Wilwood, but haven't gotten put on yet.

bosshoss wrote:doug what is the bore on your master? what rear brakes do you have? A lot of masters have one end with a longer stroke which should go to the wheels that require the greater volume. On a street car with front discs and rear drums that will usually be the front but on a custom or race vehicle you need to look at the combo.

dkp

I'm not sure what the bore size is, but you can see it in the pics. I believe when I had it apart, the seals were about an inch diameter, maybe a touch more/less.





Doug...

ThndrChkn wrote:

whatbumper wrote:I doubt it is the master cylinder but it may be. I run 6 calipers (2 front and 4 rear) and don't have any volume problems and we send a lot of fluid to the rear with the proportioning valve.

Do you have a residual pressure valve in your system?

I still have the factory proportioning valve mounted on the frame. You can see it under the steering shaft in the 1st pic below. I have an adjustable one from Wilwood, but haven't gotten put on yet.

bosshoss wrote:doug what is the bore on your master? what rear brakes do you have? A lot of masters have one end with a longer stroke which should go to the wheels that require the greater volume. On a street car with front discs and rear drums that will usually be the front but on a custom or race vehicle you need to look at the combo.

dkp

I'm not sure what the bore size is, but you can see it in the pics. I believe when I had it apart, the seals were about an inch diameter, maybe a touch more/less.





Doug...

Might want to check these out to see if they will help...
http://www.speedwaymotors.com/Wilwood-Drum-Brake-Residual-Valve-Red-10-PSI,18908.html
http://www.speedwaymotors.com/Wilwood-Disc-Brake-Residual-Valve-Blue-2-PSI,1377.html

Doug,
No brake expert either, but it was explained to me as...........

1" bore, factory disc and drum combo
1 1/16" bore aftermarket disc and drum combo
1 1/8" bore aftermarket front and rear disc brakes

Now that being said maybe your lincoln stuff is of large capacity like and needs the larger bore ?????? Is the lincoln calipers 4 piston or 2 piston deals or single piston ???

Travis

longroofracer wrote:
Might want to check these out to see if they will help...
http://www.speedwaymotors.com/Wilwood-Drum-Brake-Residual-Valve-Red-10-PSI,18908.html
http://www.speedwaymotors.com/Wilwood-Disc-Brake-Residual-Valve-Blue-2-PSI,1377.html

Those valves are for master cylinders that are mounted lower than the calipers - like street-rod setups or chassis cars. Doug is using the stock high-mount.

Speedway Motors wrote:•The two pound valve is used in disc brake applications where the master cylinder is mounted below the horizontal plane of the calipers and fluid drain back occurs from gravity and vibration, thereby causing excessive caliper piston retraction and a longer brake pedal stroke. The minimal two pound residual pressure prevents fluid from flowing back without causing the brakes to drag.

TravisRice wrote:Doug,
No brake expert either, but it was explained to me as...........

1" bore, factory disc and drum combo
1 1/16" bore aftermarket disc and drum combo
1 1/8" bore aftermarket front and rear disc brakes

Now that being said maybe your lincoln stuff is of large capacity like and needs the larger bore ?????? Is the lincoln calipers 4 piston or 2 piston deals or single piston ???

Travis

Travis, with all the combinations possible with brake m/c, calipers, drums, the entire system needs to be taken into account, kinda like carburetor sizing. I can't really quote sizes on the truck stuff, but I know for sure there were multiple m/c & caliper bore sizes in the Mustang stuff over the years. The Mk VII stuff Doug has I'm pretty sure are 73mm calipers.

So, with those variables, I'll throw in another vote for evaluating the m/c volume (bore size), and also verifying the rear brake adjustment.

Hope this helps

I think you just still have air in the lines. IMO the only differance the master cylinder bore dia would make is stopping power. It's just a case of simple hydralics! (if all the air is out you should still have a stiff pedal)

You shouldn't need residual valves because your master cylinder is above the brake calipers.

Have you checked the rubber hose in the rear for expansion?
Did you bench bleed the master cylinder?
Start the bleeding process on the passanger side rear / driver side rear / passanger front / driver front?
What is the fluid level doing in the master cylinder as you pump the brakes?

The calipers are a single piston design. The guys @ Aerospace said this master cylinder is good for anything from stock front disc/rear drum combos, to 4 wheel disc setups. I'm thinking I just have to keep bleeding them until I get all the air out. My buddy up here said he had the same problems with his car. He just kept bleeding them until he finally got all the air out. I'll mess with it some more, and see if it comes around.


Thanks guys.







Doug...

ThndrChkn wrote:The calipers are a single piston design. The guys @ Aerospace said this master cylinder is good for anything from stock front disc/rear drum combos, to 4 wheel disc setups. I'm thinking I just have to keep bleeding them until I get all the air out. My buddy up here said he had the same problems with his car. He just kept bleeding them until he finally got all the air out. I'll mess with it some more, and see if it comes around.


Thanks guys.







Doug...

I have had a truck get an air bubble in the rear lines and give me fits trying to get it out. Plus, it's not as easy doing it on a manual brake truck (old fassion way) I'm not 100% on the air stuff.

Then there has been times where I have forgot to keep an eye on the fluid level and let it suck air and have to start all over again!

Doug on the m/c if it was working the old truck rotors it should work the linc. m/c ford trucks have some big piston in the cal and I don't think it the m/c like said I think it is some air left in the lines some where or the rear brake out of adjustment when doing a burn out the rear brakes take a beating

jones wrote:

ThndrChkn wrote:The calipers are a single piston design. The guys @ Aerospace said this master cylinder is good for anything from stock front disc/rear drum combos, to 4 wheel disc setups. I'm thinking I just have to keep bleeding them until I get all the air out. My buddy up here said he had the same problems with his car. He just kept bleeding them until he finally got all the air out. I'll mess with it some more, and see if it comes around.


Thanks guys.







Doug...

I have had a truck get an air bubble in the rear lines and give me fits trying to get it out. Plus, it's not as easy doing it on a manual brake truck (old fassion way) I'm not 100% on the air stuff.

Then there has been times where I have forgot to keep an eye on the fluid level and let it suck air and have to start all over again!

Well, I got about 95% of it out. Now, when I push the pedal on the initial push, it only goes about 2/3 of the way to the floor. After that, it's solid as a rock. I'm sure it's all in the rears too, 'cause the more I mess with them, the better it gets. I'll mess with it some more tomorrow and see how they are after they sit over night.




Doug...

Doug, If you have a persistant problem with getting all the air out, get one of those deals that pulls the air UP out of the system. Conventional bleeding is trying to push the air DOWN, making the process a bit like shoveling shit uphill.....it naturally wants to go the other way.

maverick wrote:Doug, If you have a persistant problem with getting all the air out, get one of those deals that pulls the air UP out of the system. Conventional bleeding is trying to push the air DOWN, making the process a bit like shoveling shit uphill.....it naturally wants to go the other way.

Doug,
Maverick's suggestion is very good and kind of goes along with the suggestion that we discussed on the phone yesterday about "backwards bleeding". The process of forcing clean, bubble-free fluid in though the bleeder screw and letting it push the air back up into the master cylinder and out the compensating ports works like a dream. A large syringe or turkey baster and a little piece of rubber hose for connection works great. Just be sure and keep the turkey baster in the shop as a tool after this use.

Putting it back in the kitchen will rank right up there with pre-heating parts to weld in Momma's oven. ( please don't ask how I know,,,)
Good luck.
Keith

Saw this on Gears Sunday. Might help.
http://www.brakebleeder.com/powerblock.html
Lonnie