replacing brake system

simplemind7 · 10-07-2004

the brakes on my gt are so bad they're beyond repair and i was thinking that it might be easier, and cheaper to take the brake system off of some other car. maybe one with a better braking system, 4 wheel disk would be nice, and put it on a gt. if any of you have tried or heard about something like this give me a little advise, maybe suggest a donor car? thanks

kwilford · 10-08-2004

Brendan,

There are lots of suggestions in this forum heading on both how to repair the Opel's brakes, and how to upgrade them. Have a look around.

In a sound-bite, the stock GT brakes were "sufficient" for the time, but a bit lacking by today's standards. That said, if you do a reasonable re-build job (new pads and shoes, re-surfaced or new rotors and drums, rebuilt or new calipers and wheel cylinders, NEW BRAKE FLEX HOSES (VERY important!), and rebuilt or new master cylinder (and a properly functioning booster and check valve), they are fine for the weight and horsepower of a stock GT. Not BMW/Lexus braking, but just fine.

As for upgrades, the most common is to at least install the bigger front rotors from a '75 Opel Manta or Ascona, which gives QUITE a bit better braking. The next step up would be the vented rotors and matching calipers from the '77 to '81 BMW 320i. But in truth, the only advantage of the vented rotors is to reduce rotor temperature after REPEATED panic stops (reduces brake "fade", which is caused by gassing of the overheated pads and glazing of the pads).

The advantage of rear wheel disc's has been discussed ad nauseum on this and other boards. There are pretty good instructions around to use Isuzu Impulse rear disc's on the GT rear end. Those who have spent a lot of money and time to do this will tell you it was worth it. I would be surprised if they didn't (who wants to admit that they spent all that time and money for no benefit, other than the "cool" effect? And rear disc's ARE cool!). But those that know (including RallyBob, who you will find is the mother lode of smarts on this site) will tell you that a well set up and properly functioning front disc/rear drum system is PLENTY adequate for the 2000 pounds (900 kg) that a GT weighs, especially for a street car.

As for lifting a brake system from a donor car, unless you have the initials R.L. (RallyBob's real name is Robert Legere), I wouldn't suggest it. There are issues as to system balance, mechanical strength (and even as a Professional Mechanical Engineer, I would hesitate to calculate all the required stresses), and just plain do-ability. And before you ask, no, I don't think that ABS is required on a GT. Just go back to the first paragraph, and do a good job of rebuilding your brakes as they are.

OK, off my soap box...

soybean · 10-08-2004

You might want to do what I did this summer when I upgraded mine. I got a rebuilt Mc from one of the places that have been reviewed on this board. Get new front and rear brake pads. Turn the drums, buy some brembo rotors for the front, also reviewd on the board. Vintage Imports on E bay sells nos rear pistons for the drums at times.If it's needed Get a rebuild kit from OGTS for the front calipers, do them. At the same time get the 3 flex hoses that Keith recommended. When all the lines are disconnected from MC open the bleed ports on all wheels, blow them out with air a couple of times. Disconnect the flex hoses, blow all the lines out again. Rebuild, bleed, as per FSM or some of the threads discussed here and you're good to go. It made a world of difference to mine. HTH, Jarrell

10-07-2004	#1 (permalink)
simplemind7 Opel GT? Who makes that? Join Date: Oct 2004 Location: Ayr, Ontario, Canada Posts: 632	Unanswered: replacing brake system the brakes on my gt are so bad they're beyond repair and i was thinking that it might be easier, and cheaper to take the brake system off of some other car. maybe one with a better braking system, 4 wheel disk would be nice, and put it on a gt. if any of you have tried or heard about something like this give me a little advise, maybe suggest a donor car? thanks __________________ Brendan: 72 Manta Rallye 69 GT 72 GT - parts car

10-08-2004	#2 (permalink)
kwilford Über OpelGT.com Moderator Join Date: Mar 2002 Location: Calgary, Alberta, Canada Posts: 4,087 Real Name: Keith Wilford Provided Answers: 4	Brendan, There are lots of suggestions in this forum heading on both how to repair the Opel's brakes, and how to upgrade them. Have a look around. In a sound-bite, the stock GT brakes were "sufficient" for the time, but a bit lacking by today's standards. That said, if you do a reasonable re-build job (new pads and shoes, re-surfaced or new rotors and drums, rebuilt or new calipers and wheel cylinders, NEW BRAKE FLEX HOSES (VERY important!), and rebuilt or new master cylinder (and a properly functioning booster and check valve), they are fine for the weight and horsepower of a stock GT. Not BMW/Lexus braking, but just fine. As for upgrades, the most common is to at least install the bigger front rotors from a '75 Opel Manta or Ascona, which gives QUITE a bit better braking. The next step up would be the vented rotors and matching calipers from the '77 to '81 BMW 320i. But in truth, the only advantage of the vented rotors is to reduce rotor temperature after REPEATED panic stops (reduces brake "fade", which is caused by gassing of the overheated pads and glazing of the pads). The advantage of rear wheel disc's has been discussed ad nauseum on this and other boards. There are pretty good instructions around to use Isuzu Impulse rear disc's on the GT rear end. Those who have spent a lot of money and time to do this will tell you it was worth it. I would be surprised if they didn't (who wants to admit that they spent all that time and money for no benefit, other than the "cool" effect? And rear disc's ARE cool!). But those that know (including RallyBob, who you will find is the mother lode of smarts on this site) will tell you that a well set up and properly functioning front disc/rear drum system is PLENTY adequate for the 2000 pounds (900 kg) that a GT weighs, especially for a street car. As for lifting a brake system from a donor car, unless you have the initials R.L. (RallyBob's real name is Robert Legere), I wouldn't suggest it. There are issues as to system balance, mechanical strength (and even as a Professional Mechanical Engineer, I would hesitate to calculate all the required stresses), and just plain do-ability. And before you ask, no, I don't think that ABS is required on a GT. Just go back to the first paragraph, and do a good job of rebuilding your brakes as they are. OK, off my soap box... __________________ Keith Wilford working on my '71 GT and '75 SportWagon Last edited by kwilford; 10-08-2004 at 12:34 AM.

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10-08-2004	#3 (permalink)
soybean Moderator Join Date: Nov 2002 Location: Reidsville N.C. Posts: 2,160	You might want to do what I did this summer when I upgraded mine. I got a rebuilt Mc from one of the places that have been reviewed on this board. Get new front and rear brake pads. Turn the drums, buy some brembo rotors for the front, also reviewd on the board. Vintage Imports on E bay sells nos rear pistons for the drums at times.If it's needed Get a rebuild kit from OGTS for the front calipers, do them. At the same time get the 3 flex hoses that Keith recommended. When all the lines are disconnected from MC open the bleed ports on all wheels, blow them out with air a couple of times. Disconnect the flex hoses, blow all the lines out again. Rebuild, bleed, as per FSM or some of the threads discussed here and you're good to go. It made a world of difference to mine. HTH, Jarrell

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