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Old 01-13-2018, 07:02 PM   #1
Thebrownturd
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Need new brake boster

I have a blown diaphragm in my brake booster that was sucking vacuum from the engine causing me to fail smog twice. I finally got the truck to pass by plugging the line.

The real question I have is to go with the 11'' or 8'' brake booster. right now there is an 8'' on the truck. The truck is a 70 K20 4x4 with drums all around, and I am pretty sure the 11'' is what would have come in the truck. By visual inspection it looks like the 11'' may hit the shifter (for auto tranny) rod coming out of the column, but there may be plenty of room.

I can get an 8'' with master, like the one in the truck now at NAPA or I can get an 11'' tuff stuff booster and master for about $60 more at Summit Racing a block away from NAPA.

Is there any one that has used either one and what will make appropriate for a heavy drum brake equipped truck?
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Old 01-13-2018, 09:43 PM   #2
Bigdav160
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Re: Need new brake boster

Theoretically 4 wheel drums doesn't need power assist. But a K20 is a fairly heavy vehicle so I can understand that it could use some help.

With vacuum assist, more power, is all about the diameter and the number of diaphragms. Larger is more powerful.

Hydraulic power assist if even more powerful.

That's why I put hydraboost on my K20 Suburban
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Old 01-13-2018, 10:02 PM   #3
Steeveedee
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Re: Need new brake boster

Measure carefully. There is a reason that the 8" booster is on there. My '70 3/4T truck, Custom Camper and all, came with the 8" booster, and stopped just fine when everything was new. I put disc brakes on it for the extra margin and wet braking safety, but still with an 8" booster.
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Old 01-13-2018, 10:22 PM   #4
Thebrownturd
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Re: Need new brake boster

Thanks guys. Steeveedee I agree they the 8" works well. There is no problem getting the brakes locked up. I would like to convert the front to disk but time and money will determine that. I am considering the 8" so I know it will fit. What brad and where did you get them if you don't mind me asking?

With the 8" I believe there is dual diaphragms. Were you able to keep the setup other than a disk/drum proportioning valve which I am assuming you would would have had to put on.

Bigdave I've been on some steeeeep hills in the mountains around the ranch and do a little towing so extra braking won't hurt other than I will need to feather the peadal a little more. I've locked up even with leaky blown out boosters and seals
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Old 01-13-2018, 10:32 PM   #5
Steeveedee
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Re: Need new brake boster

Just pick up the new booster at a local parts store. You might have to get a master with it. Some suppliers will only sell them as a combined unit. I got mine from POL, but it was broken, so you can avoid that if you go local. I bought the whole conversion kit, but if I ever did it again, I'd go with Scarebird or something that didn't cost so much.
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