Thread: More brakes

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46 chevy truck 468 small cam. MII front S10 rear both disc.. The brakes were installed in 05 by the original owner. It got the power master pedal assembly form RB's who is not in business anymore. I did find the receipt and the part number is 1R-949. Could not find anything on line to tell me what this is. So I don't know where I am starting from. If some one has an old catalog that would be great. There is a Wildwood adjustable valve between the mc and rear brakes. The front pads, rotors, and calipers I have just replaced. The rears I have left alone. I have vacuum bled and old school bled the fronts and rears. I cant seem to get any peddle. I have about 3 inches of travel. I don't get any brakes until the bottom and they are not good. How much travel is at the booster. Is there an inch/two? Could be I am not getting the correct travel. I am trying to understand what should be happening.

Originally Posted by sfort

46 chevy truck 468 small cam. MII front S10 rear both disc.. The brakes were installed in 05 by the original owner. It got the power master pedal assembly form RB's who is not in business anymore. I did find the receipt and the part number is 1R-949. Could not find anything on line to tell me what this is. So I don't know where I am starting from. If some one has an old catalog that would be great. There is a Wildwood adjustable valve between the mc and rear brakes. The front pads, rotors, and calipers I have just replaced. The rears I have left alone. I have vacuum bled and old school bled the fronts and rears. I cant seem to get any peddle. I have about 3 inches of travel. I don't get any brakes until the bottom and they are not good. How much travel is at the booster. Is there an inch/two? Could be I am not getting the correct travel. I am trying to understand what should be happening.

Has it had brakes since you got it? Or have you replaced master cyl,or booster? I bought a new master cylinder and had this problem. Upon further checking I discovered it was not quite the same. Replacement cyl had hole for the push rod from the power booster to go into, and was aprox 1" deeper than original. I had a longer rod so just swapped them out. Problem solved. If you changed m. cyl or booster, or it never had good brakes I would check this first. Power booster has enough spring pressure you cant really tell when it contacts the piston in the master cyl by pedal feel. Unlike straight mechanical linkage to standard master cylinder, you can feel the slop. Hope this helps. Drove me crazy for half a day, before I figured it out.

Opps One more thing. there should be almost no clearence between the push rod from booster into master cylinder. If yours is adjustable make sure it just barely touches bottom of bore in piston of master cylinder, but does not push piston in when master cylinder is bolted to booster.

It had brakes when I got it but they were poor. Just a little better than now. All I have done is the replacement of pads, rotors, and calipers on the front. It did sit a while with the hoses disconnected while I rebuilt the front end. I am assuming I will have to replace the booster and mc. Maybe just the mc. It was painted and than brake fluid poured on it which bubbled and rusted. Looks bad. The inner lip of the mc has a lot of rust on the sealing surface. There may be some trash in the mc. If I replace the mc how do I know what to replace it with.

If you could post a couple of pics of the master cyl, I'm sure these guys can give you some sugestions. Any numbers on these parts might be of use as well.

is the master cylinder on the fire wall or under the floor board

The booster/mc is under the floor. I have been crawling around under it today but have not found any numbers. Looks like a std. gm mc but I will have to remove to get the specs.. It needs replacing just to make sure i catch a problem before it happens. It looks pretty bad. I am thinking the previous owner put it on and lived with the problem. I will take a picture tomorrow.

I have a 2006 catalog . Your part number shows as "Universal power brake booster/master cylinder and pedal assembly" The description reads: "This unit includes a universal bracket that is made of heavy steel and welds to the frame at your desired location. For cars with automatic trans only." There is no mention of bore diameter. Another master cyl in the same section with almost the same description says it has a 1" bore, so it might be that. Hope this is helpful.

I took it off see picture. From other posts I had read that the small contact point of the booster is supposed to be flush with the housing but not touching the mc. It appeared mine was 1/4" recessed.

Had problems attaching a picture.

The reason I asked where the master cyl. was mounted was because, even tho you vac. bleed it that may not be enough to get all the air out of the line. I use a power bleeder. you use air pressure to push brake fuild threw the brake lines at a high pressure and it forces the air out. I had a a race car that was mounted under the floor board and my roadster now is mounted the same way and had to bleed both of them the same way to obtain good pedal.

I found a mc today. Bench bled it and put it on. Vacuum bled the rears. Found an issue with almost nothing but air coming out of the drivers side. The passenger and fronts bled great. Got to be a problem at the wheel. That said I still have no peddle. What is the failure mode of the power booster. Right now I am going to the flood and not returning. There are two springs look like carburetor springs on the peddle for return. Got a match! Just kidding. I am committed!

Check for leaks or bad wheel cyl on drivers side. If you keep getting air, and only on that wheel, the problem is there check all lines all the way to t on rearend and check that wheel cyl. If you got air in the lines, even only one wheel you will never get decent pedal. Hope this helps.

I am going to put the rear on stands tomorrow and see what I can find. I am surprised I have not seen any leaks.

Easy check to do is crimp the flexible line at all four corners. If pedal is hard the MC is fine. Start removing the crimp one at a time and check the pedal. If still hard continue till you find the wheel that is bad. I have corvette calipers and they have gone bad from sitting. Never had a leak either but this trick found the problem quickly.