Deto. alloy GT5 brake set problems

A few questions: did the conversion include a new master cylinder? Because adding bigger calipers will take more volume of fluid to pressurize the bigger pistons. Running a too-small master can give symptoms like this, as can a leaky vacuum booster diaphragm. And which pads are you running? Some pads are really hard, and thus last a long time on the street, but take a little more effort on the pedal to stop you, especially if they're cold. There are stickier pads available. Finally, is it possible the pads are simply glazed? This is the cheapest thing to fix, since all thats required is to take the pads out and lightly sand them, then replace them and go drive the car. If stopping is improved, good. Maybe a fast trip thru the mountains will bed them in better.

Yeah, the master cyl/booster was with the kit, and I assume correctly sized. The reciept says the pads are "GN73" and that "GN83" pads are available for more aggressive usage. What differences could I expect between the two? And if that's the trouble, is it normal to feel a difference in pedal firmness between the first and second push? They brake much more satisfactorily after being pumped twice.???

You have steel Briaded lines on them right ?
This will also help to firm up the pedal if you don't.

Coz, No, when they installed the brakes, they didn't upgrade the lines (!?!), does that make sense? Is it possible there's that much bulge in them as to reduce the caliper travel so? And aren't braided lines more or less a given if you're going to drive these things? Thanks for your help. Paul

Youn new system probably generates higher line pressures, so the stock rubber lines are swelling a little more under use. I would arbirarily change them all to a good set of braided stainless or braided-Kevlar lines regardless of whether I had new brakes or not. Old rubber lines on any car are a hazard IMHO. Such replacement lines are cheap (relatively) and simply eliminate another potential weak spot from your system.

This problem has occured to me before. It is the same problem that I had when I built a cobra kit car. You need to research on using a residual valve inline. This will keep the line from bleeding back buy keeping a couple of pounds pressure on the brakes.

Thanks everybody. A further update: The brakes are apparently made by Sierra, out of Carson City, NV. They sat on a shelf for 5 yrs. or so, so the master cyl might have problems from disuse. It's being checked now for problems and/or improper sizing. I'll also check into a 'residual valve' Dave, thanks. Paul

You would think it would be a given to also change the lines to steel braided when upgrading the barkes. For the 60 to 80 dollars for all the lines, it's worth the money and the time.
Let us know how it turns out. Good luck.

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Originally posted by Paul Underwood:
Coz, No, when they installed the brakes, they didn't upgrade the lines (!?!), does that make sense? Is it possible there's that much bulge in them as to reduce the caliper travel so? And aren't braided lines more or less a given if you're going to drive these things? Thanks for your help. Paul

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[This message has been edited by Coz (edited 05-07-2001).]