Hydraboost and master cylinder question

[CapSS92]

Hi all,
I have a hydraboost setup on my 65 Chevelle with C5 fronts, LS1 rears, and a 1" MC. They work fine most of the time but whenever I have to do a hard stop they lock up pretty bad. If I don't have my seatbelt on I come awfully close to kissing the windshield. I did some research and it looks like some people use a 1 1/8" to make them a little less sensitive. I wanted to use a modern day MC and I found that 88-98 3/4 ton Chevy trucks use a 1 1/8" bore MC. But when I went to the salvage yard every single truck that had a hydroboost setup used a 1 1/4" bore setup. This was in all 3/4 and 1 ton trucks whether it was a truck or a suburban. I know that the brake setup is different in the trucks than what I am using but I am looking for anyone with real world experiences. Has anyone used a 1 1/8 or 1 1/4 in their hydroboost setup and if so what kind of difference did it make? I am going to buy a new 1 1/8" to try out but if a 1 1/4" works better I'd rather have to only change it out once. Any suggestions would be greatly appreciated. Thanks.

Alex

[Hydratech®]

Here is a link to a previous discussion where we had found a late model 1 1/8" bore plastic / aluminum GM MC that you may consider:

https://www.pro-touring.com/showthread.php?76737-Need-a-new-MC-which-is-best&p=769162&highlight=#post769162

Do please make sure to note that the ports on this MC are REAR PORT = FRONT BRAKES / FRONT PORT = REAR BRAKES (lots of guys get this backwards and have all kinds of troubles as a result).

The difference between a 1" bore and a 1 1/8" bore MC can be considerable, roughly 20 % firmer pedal effort.

There are additional factors that also come into play, especially how new the brakes are at the wheels and the type of brake pad compounds:

http://www.lateral-g.net/forums/showthread.php4?t=29580

In many cases, swapping out brake pads from high friction ratings to standard pads with less friction ratings can make all the difference in the world. Also, many replacement PS pumps are flowing WAY too much pressure and volume, which can lead to brake response being somewhat overactive (in PS driven hydraulic brake assist systems). Bringing the PS pump output back down to a stock level can make a considerable difference.

[CapSS92]

Thanks this is perfect. I appreciate the answer. I was using a 283 with a GM truck PS pump but now I'm switched to an LT1 with a stock pump. I'll see how it works before I swap it all out. Thanks again.

Alex

[Chev67]

What about a 7/8" bore master cylinder?