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Old 04-17-2019, 07:53 PM
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Question Master Cylinder Bore Difference

Hi All
I bought a master cylinder kit (Booster/ master ) from speedway for my 41 coupe. I have a disc/drum set up from a 1980 camaro . From what I am seeing the GM master is 1.125" bore and the speedway is 1" . Because my motor produces low vacuum I am running a CVR vacuum pump. I have a hard pedal and good stopping power but not great. I don't think the booster (7") is the issue because pump only comes on after pedal has been pushed for a few seconds. If I pump the pedal 6 times with pump off and then turn pump on pedal drops about 1/4" . Could the master cylinder bore be to small or is the off shore master junk. Had rotors turned and new pads no difference. Calipers look to be new.



Thanks in advance for help
Joe

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Old 04-17-2019, 08:17 PM
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After reading the post on proportioning valve , could my lines be on backward ? I have a 1/4" from the rear of the master to the rear brake inlet on the proportioning block and from the front of the master to the front brake inlet of the proportioning block a 3/16" line going to the front brakes . I hooked it up just as it was from previous owner, master was bad I just replaced.


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Joe
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Old 04-20-2019, 11:40 PM
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A 7" booster does not give you much boost, there is just not enough area on the diaphram. Now if you use a 7" dual diaphram you double the boost, and in most cases the booster is all you have to change.

A 1" bore master cylinder will make more pressure for the same foot force than a 1 1/8" bore master cylinder, but has a bit more travel doing it.
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Old 04-29-2019, 06:56 PM
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Question

Thank you enjenjo for your help. I ordered a 8" dual booster from speedway, made a lot of difference. Now the pedal goes to the floor very easily , I have about 1/4 of the pedal travel before I feel pressure on the pedal. Can I adjust that out with the clevis from the pedal to the booster ?
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Old 04-30-2019, 04:57 AM
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Quote:
Originally Posted by tools View Post
Thank you enjenjo for your help. I ordered a 8" dual booster from speedway, made a lot of difference. Now the pedal goes to the floor very easily , I have about 1/4 of the pedal travel before I feel pressure on the pedal. Can I adjust that out with the clevis from the pedal to the booster ?
The pedal adjustment should mainly adjust pedal height, not the pressure engagement point.
Since you changed the booster, make sure to booster pushrod is adjusted correctly.
https://www.jegs.com/installationins...631010-116.pdf
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Old 04-30-2019, 06:55 AM
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Quote:
Originally Posted by tools View Post
Thank you enjenjo for your help. I ordered a 8" dual booster from speedway, made a lot of difference. Now the pedal goes to the floor very easily , I have about 1/4 of the pedal travel before I feel pressure on the pedal. Can I adjust that out with the clevis from the pedal to the booster ?

NO! Unless it already has too much play in it. Bob pointed you in the right direction but I thought I'd emphasize how important it is not to make the push rod too tight. It needs a bit of play. I think they should have given you a larger master cylinder to cut down on that travel. But yes maybe your rod is out of adjustment, easy to check.
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Old 04-30-2019, 10:10 AM
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Thank you bob and Tony very good advise. I have read the info on the link you sent from Jegs. I will work on that this weekend .


Joe
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