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By Talkwrench - 14 Years Ago
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I have the "old Irish Dave" power booster and dual circuit corvette master cylinder in for a while now. Its been great but right from the word go Ive had a fair bit of travel in the pedal before it takes up, works ok though. The other week I decided to adjust the pedal so it was a bit lower to the floor by putting a bigger rubber stopper and adjusting the rod to suit it , wasn't a big change 1/2". I know that I didnt have a lot of freeplay but I thought it would be fine because of the amount that it takes to take up with the booster working. Brakes worked great. However when I pulled into my garage I noticed the brake lights still on ..Bugger! the brakes had "energized" and where partially on. I adjusted the pedal back to roughly where it was the next day and left it for a week or so. Jumped in and the pedal was going waaaay down ! I had a look at the fluid and the level is the same , fluid is cloudy ? I cant see any leaks from wheels cylinders etc even when I pulled the master cylinder away from the booster no evidence of fluid in there... Brakes are all adjusted fine.. SO whats the deal??? Does anyone know what year the master cyl is that is used and what bore size, where would I find another one with the 4 way outlets ? Thanks guys..
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By PWH42 - 14 Years Ago
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If the M/C Dave sent you is the same as the one I got from him,it's a 77 Corvette.
If you still have the original pedal as it was.there is quite a bit of travel.I've had mine for several years and have gotten accustomed to the long pedal travel.
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By Talkwrench - 14 Years Ago
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Ok good to know its just not me with the long travel. Any Idea of the bore size? just seems to be many types that look like it . If I do need to order one I'll make sure its the right one so its a direct replacement. Maybe rockauto would have them?? usually gets to this side of the world quick.
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By oldave57 - 14 Years Ago
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I have had the Old Irish Dave setup on my 57 Fairlane for a couple of years now and for the first year, I had similar "symptoms" of long pedal travel, nearly bottoming out before it took hold although it had good stopping power. What I discovered was that the pedal was not returning fully "up" and that apparently did not allow the master cylinder piston to return to its full back position, causing the problems. I think it is related to having both the master cylinder and the vacuum booster having to fully retract and the original brake pedal spring wasn't quite strong enough to fully pull the whole assembly back to the correct starting position. You can test this by pulling back on the pedal with your foot to see if there is a little bit of travel left after the pedal is returned by the spring. If there is a bit of travel left, then the master cylinder piston is likely not returning fully and therefore not getting a full charge of fluid for the stroke action when brake is applied. You might made it somewhat worse by adding a stop (although you adjusted the rod to compensate). In any case, if the brake light was staying activated, there is a good chance that the piston was not being fully retracted. On my system, I added a small booster spring to the pedal return spring and it works so much better with the pedal fully retracting. The pedal now travels a much shorter distance and the pedal is much more firm, just giving a better performance all around. Your problems might be different, but sound so similar to my experience that I thought it might be worth your checking. Regards, Dave
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By Grizzly - 14 Years Ago
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Guy's, I installed an old irish dave master/booster with my upgrade. I had some trouble getting the adjustment so that there was as little play as possible. The biggest issue that I found with the setup is the clevis & pin setup that attaches to the Brake lever. The lever works on about an 8:1 ratio so a 1/8" play in the link means 1" at the pedal. I replaced the clevis & pin with a rose joint. This required a small spacer 3mm between the lever and the rose joint. The bolt needs to be tight so that the only movement is rotational in the rose joint. Small amounts of adjustment (1/4 of a turn) are needed to find the correct adjustment of the rod. I agree there could be better spring return pressure but the rose joint has hardly any friction compared to the clevis & pin. This has improved the return of the peddal. I use all braided lines and have about an 1" 1 1/2" freeplay. cheers Warren
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By Talkwrench - 14 Years Ago
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Seems to be a common issue with bit of travel before it starts to bite, Im sure Mark drilled another hole in the pedal, more for lining up if I remember..? Mine seemed to be fine, but perhaps drilling one slightly lower might help this problem if you can do it. Well my problem is not this so much anymore as mine is just about touching the floor and with not much braking effect. I just have to assume my master cylinder has sh*t itself and look to fixing it, not much more it can be...Unless anyone else has an idea.. Anyone know the bore size?
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By Grizzly - 14 Years Ago
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Talkwrench, If your brakes were partially applied it's possible that you boiled your fluid and have air (gas) in your system. Try bleeding the whole system with fresh fluid and you should get your pedal back. 1" bore cheers Warren
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By Talkwrench - 14 Years Ago
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I'll give it a go. There was no funny smells and the car was no different to drive. Hope the linings are ok ?? I recon that the brakes where not on for long. I think it might have been from the few roundabouts only 2 k's or so from home, I was braking harder than I normally would nothing serious..
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By Grizzly - 14 Years Ago
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Talk, If you had damaged the seals in your master it would have leaked and/or lost fluid. Bleeding is a lot less expensive and a lot less trouble than a new master. Good luck with it. Cheers Warren
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By Talkwrench - 14 Years Ago
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Last night I had a look at the front brakes to start, all looked fine...Fluid def' cloudy tho'. Quick repack of the wheel bearings while at it , they looked like they may of had some heat at some stage. Bleed the front with the help of my 13 y/o daughter much to her disgust.. Daaaadd nooo do I have tooo! So I'll get to the back ones tonight all going well. See what happens..
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By Talkwrench - 14 Years Ago
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Checked the back all good, bled, but the pedal still seems a bit soft and travelling a fair bit ...Hope is fading [with the pedal  ] see what happens tomorrow if I can go for a drive..
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