Big master cylinder
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Que? Habla ingles? You've got Rockwells under a Chevy and you're putting F550 calipers and MC on it...what's Chevy in this equation specific to the brakes. The brake pedal? Booster?DriveTime said:
F450/F500/5500 MC's were a straight 15/16" MC bore between 88-96 according to an ACDelco catalog I happen to have laying around. It sounds like if you've got F550 parts, that they're going to be newer than that. I personally think that you would be better off with a quick take-up MC that has a stepped bore. The large bore should solve your volume issue and the small bore will make sure that you can generate sufficient line pressure to make the calipers work...without both feet on the pedal and both hands pulling on the steering wheel. Plus, a Chevy QT MC could bolt right up depending on your booster. Chevy has made a variety of QT's over the years for everything from S-trucks to full sizes...
Post whatever details you have and I might be able to get you some more specific info.
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a good one is a hydroboost/master setup from a M series (Astro/Safari) van. 1" bore MC if I remember correctly. Hydroboost just ROCKs also, way better than 4 wheel steering. You might need it with the rockwells. The proffitts cruisers guys all run rockwells with toy driveline disks that stop very well. Might be worth a shot IMO if your braking is not very good.
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I've been using pinion brakes for a while, and they are what I'm trying to avoid. My question was if an F550 MC would bolt up to my Chevy booster. I don't have access to one of these, and don't have any pics or measurements to go off of, so I don't know if the bolt pattern of the MC matches the booster. And if it doesn't, what MC does match that will work with these calipers.dieselcruiserhead said:
A quick take-up master cylinder works exactly like a fast pump floor jack. The first stage moves a lot of fluid volume but only at very low pressure, so it doesn't have a lot of force. Once there is resistance in the system (i.e. when the pads hit the rotor and/or the shoes hit the drum), the fluid stops "flowing" and begins pressurizing to give you the force, and that's where the smaller secondary bore comes into play. It's so dirt simple I wish I'd thought of it.
It gives you the flexibility to move a relatively large amount of fluid volume with minimal pedal travle and still generate the pressure you need to make the brakes work without excessive pedal force or monster boosters. Keep in mind that those calipers (and the pads for the calipers) are designed to function optimally at a certain pressure. Unless you know what the F550 MC bore is, we're shooting in the dark. Also, correct me if I'm wrong, but you're planning on running front F550 calipers on all four corners, are you not?
I have to assume that you have the stock vacuum booster on your '81 Chevy since you haven't said otherwise. Since I'm fairly certain that the hole spacing and pilot register on the F550 MC is not going to line up, here are a few ACDelco part numbers for QT MC's of that era.
85-95 G35, Vacuum Brake System
31.75mm & 40.0mm ACDelco#18M348
85-94 G25, Vacuum Brake System
28.6mm & 40mm ACDelco#18M316
I have no idea if they'll bolt up to your booster, so you're on your own there. I'd think you'll have better luck Chevy to Chevy but I've been wrong before.
It gives you the flexibility to move a relatively large amount of fluid volume with minimal pedal travle and still generate the pressure you need to make the brakes work without excessive pedal force or monster boosters. Keep in mind that those calipers (and the pads for the calipers) are designed to function optimally at a certain pressure. Unless you know what the F550 MC bore is, we're shooting in the dark. Also, correct me if I'm wrong, but you're planning on running front F550 calipers on all four corners, are you not?
I have to assume that you have the stock vacuum booster on your '81 Chevy since you haven't said otherwise. Since I'm fairly certain that the hole spacing and pilot register on the F550 MC is not going to line up, here are a few ACDelco part numbers for QT MC's of that era.
85-95 G35, Vacuum Brake System
31.75mm & 40.0mm ACDelco#18M348
85-94 G25, Vacuum Brake System
28.6mm & 40mm ACDelco#18M316
I have no idea if they'll bolt up to your booster, so you're on your own there. I'd think you'll have better luck Chevy to Chevy but I've been wrong before.
Apogee, do you know if all vehicles are now using these quick take up mc? It seems to make good sense, so if not all vehicles are using them, I guess I am wondering why not?
Also are you sure the -96 F450 (I think they were known as the F-Superduty) used a 15/16 m/c. That seems mighty small for those big vehicles. I would have guessed something like 1 5/16?
Also are you sure the -96 F450 (I think they were known as the F-Superduty) used a 15/16 m/c. That seems mighty small for those big vehicles. I would have guessed something like 1 5/16?
Sorry, lost track of this thread...'96 F450 used a ACDelco #18M484 which looks to be 15/16" bore by my sources. That doesn't necessarily mean that it's gospel though, and it does seem a little small. Something to keep in mind though is that I don't know what the stroke is, so a small bore is capable of generating a higher pressure, while the volume issue can be adjusted up to a point with stroke as opposed to bore. That really comes down to the power booster and pedal ratio.jgarden1 said:
Not all vehicles use the QT MC's at this point, but they are becoming increasingly common for primarily one reason...gas mileage. Calipers designed to work with QT MC's have a slightly different piston seal design that acts to pull the caliper piston(s) back further so that the pads don't drag on the rotor, thus improving fuel efficiency by reducing drag. Even though the piston pull-back is very slight, it's enough to mandate a QT MC so that the pedal remains high and firm.
QT MC's work fine with all calipers, however calipers designed for QT MC's may have excessive pedal travel when used with non-QT MC's.
I hope that all makes sense. I'd cruise down to your local autoparts store and see what exact MC came with the F550 that your calipers came from, as that will be the best starting point to figure out what's going to work with your application.
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