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Discussion Starter #1 (Edited by Moderator)
I'm looking for some input on how the brake pedal should feel and the braking action of the GT. Although I have had my GT for over 35 years, I have only recently, after about 16 years in storage, started to drive it once again. In the 16 years of not driving it, I have gone through just about all of it to repair and upgrade engine and systems, including the brakes. I have completely replaced all major components, to include calipers, pads, shoes, drums, pistons, vacuum boosters, master cylinder and vacuum check valve. I then flushed all the lines and filled the system with DOT 5 fluid and bled the system.

So here's my issues/question... When the car is not running, the brake pedal is tight with little play (maybe 1/2 or so"), which it should be. When I pump the pedal I get no additional build up of pressure indicating the system is bled well. Now, with slight pressure on the peddle and I start the engine, I can feel the draw down on the peddle from the vacuum booster. This draw down is about an additional 1 to 2 inches of pedal play. This is also as it should be. My issue is that when you drive the car, this extra draw down from the vacuum booster equates to very little breaking actions in the car. It's as if I went from a tight break pedal to having 2 to 3 inches of slop in the breaks. I can pump the brakes and it really doesn't change the braking action in the first 3" of the peal. Park and shut the car off and the pedal is tight again..

Is this how the brakes should feel and work ? Not sure what the vacuum booster is for since after that 2 to 3" of easy pedal, the brakes feel as if they are none assisted brakes.

Any input appreciated..


Thad

Thad
 

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How dependable is the vacuum hose and Check valve for the booster? They used to be braided steel, now the aftermarket hoses can be guilty of collapsing. Did you replace the 3 (2 front 1 rear) rubber hoses, they tend to swell over time as well. That would weaken your performance too.
 

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Just Some Dude in Jersey
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That's very odd. With my engine running, my brakes engage very well at 1" of pressure and stop so well you'll fly through the windshield. I have the fully maxed out set up: '78 vented rotor BMW 320i calipers, Honda booster and MC, VW rear disc brakes, new hoses and stuff. But even with that same set up and just the drum rear brakes on my previous GT, I had the same 1" of travel before wheel lock up.

As previously suggested, look into your rear brake adjustment. I would suggest totally loosening up the rear brakes, so that only the front brakes are engaging and then do your tests. You may still have bubbles in the front brakes, but you've adjusted the rear brakes so tightly that they lock up before the front ones compress their bubbles.

:veryhappy
 

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Discussion Starter #5
How dependable is the vacuum hose and Check valve for the booster? They used to be braided steel, now the aftermarket hoses can be guilty of collapsing. Did you replace the 3 (2 front 1 rear) rubber hoses, they tend to swell over time as well. That would weaken your performance too.

Thanks,,, I do have new hoses,,, but, I did not replace the front two break lines,,, However, they were not corroded on the outside and appeared to have good flow when I bled them. Maybe there is some blockage on the inside of these two lines that is hard to detect..

Thadman
 

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Discussion Starter #7
That's very odd. With my engine running, my brakes engage very well at 1" of pressure and stop so well you'll fly through the windshield. I have the fully maxed out set up: '78 vented rotor BMW 320i calipers, Honda booster and MC, VW rear disc brakes, new hoses and stuff. But even with that same set up and just the drum rear brakes on my previous GT, I had the same 1" of travel before wheel lock up.

As previously suggested, look into your rear brake adjustment. I would suggest totally loosening up the rear brakes, so that only the front brakes are engaging and then do your tests. You may still have bubbles in the front brakes, but you've adjusted the rear brakes so tightly that they lock up before the front ones compress their bubbles.

:veryhappy
Thanks,,, you may have something here. I think what you are saying is that the fluid maybe going tight in the master cylinder for the rear breaks before enough piston action/pressure can be generated for the front system to fully bleed.... I'll have to look into to this..

Thadman
 

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I'm looking for some input on how the brake pedal should feel and the braking action of the GT. Although I have had my GT for over 35 years, I have only recently, after about 16 years in storage, started to drive it once again. In the 16 years of not driving it, I have gone through just about all of it to repair and upgrade engine and systems, including the brakes. I have completely replaced all major components, to include calipers, pads, shoes, drums, pistons, vacuum boosters, master cylinder and vacuum check valve. I then flushed all the lines and filled the system with DOT 5 fluid and bled the system.

So here's my issues/question... When the car is not running, the brake pedal is tight with little play (maybe 1/2 or so"), which it should be. When I pump the pedal I get no additional build up of pressure indicating the system is bled well. Now, with slight pressure on the peddle and I start the engine, I can feel the draw down on the peddle from the vacuum booster. This draw down is about an additional 1 to 2 inches of pedal play. This is also as it should be. My issue is that when you drive the car, this extra draw down from the vacuum booster equates to very little breaking actions in the car. It's as if I went from a tight break pedal to having 2 to 3 inches of slop in the breaks. I can pump the brakes and it really doesn't change the braking action in the first 3" of the peal. Park and shut the car off and the pedal is tight again..

Is this how the brakes should feel and work ? Not sure what the vacuum booster is for since after that 2 to 3" of easy pedal, the brakes feel as if they are none assisted brakes.

Any input appreciated..


Thad

Thad
I'm thinking that you may have the brake mechanism rod adjusted wrong. There is only so much travel on the brake booster. If you are using all of that to take the slack out of the brake system, you may not be getting help from the booster. Adjust the rod so that there is only a small amount of brake travel before brakes are engaged.
 

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I had the same issue, and the advice to check the rear brake adjustment is spot-on -- I found the right-rear brakes to be a bit loose this afternoon, and the pedal travel and braking action improved considerably. The most recent piece of advice is something that also makes sense and I will look into it tomorrow -- understand that when I received the car almost three years ago, I completely disassembled and rebuilt the suspension and brake systems. And while I kept the brake rod adjustment where it had been when I removed everything, the fact is that replacement of the master cylinder and brake booster may have required further adjustments to the rod. Above advices much appreciated on my part.
 

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Just Some Dude in Jersey
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Isn't proper brake rod adjustment set to neutral, so that there is no dead play in the pedal and the spring on the pedal is just barely or not at all pulling/pushing at the brake booster diaphragm?

:thinking:
 

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Can Opeler
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I hate how my brakes feel with the big Opel gt source booster. If I take the booster hose off and plug it the brakes feel great. There is no play in the pedal and I like how firm it is. Hook up that big booster and the pedal is way too soft. I can still lock up the wheels but it just feels like crap. I’ve bled the brakes several times in the last 3 years and it’s never helped. It might be worth checking into the rear brake adjustment like someone else suggested, but I don’t think my rears are engaging too early. My entire braking system is brand new. I do miss the old booster though.

Maybe it feels so light of a pedal because I have several springs on the throttle and my daily driver has a very firm clutch and brake.


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Just Some Dude in Jersey
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I agree that the Honda booster/mc combo has an unusually light pedal feel........compared to my 30 years of driving the crappy stock GT brakes. But as compared to my other recent non-Opel vehicles(Ford Escape, Pontiac Solstice, Jeep Cherokees) the pedal feels about the same as them, maybe a tad lighter. It took a few months getting used to the new feel and learning not to stomp on the brakes. I suppose that if I had a 4sp with those dreadful stiff clutch pedals, I would notice a HUGE disparity between the required brake pedal pressure and the clutch pedal pressure. Like Kyler, though, I have an SSD set up and the light gas pedal feel that I boosted with an additional spring, so, since I have an automatic, I now have a light feeling brake AND gas pedal, but no stiff clutch pedal. So, I've learned to be a bit more restrained in my pedal pressures on my relatively new set up.
 

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Can Opeler
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I used to think my clutch was stiff, but my truck is much much much stiffer. I can hardly feel the Opel clutch anymore lol. My throttle is bit stiffer than your top Gordo. I have 3 springs on mine. The fix for my brake may be making another spring return mount for it?

You said this booster is from a Honda? Which one?


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I've heard of numerous instances where guys sold their 4sp GT's because they had aged knees or medical conditions. I know of several guys who converted to autos for the same reason.
I'm a guy with bad knees who is replacing the automatic with a getrag. I'd rather have fun and bear the pain.
 

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Discussion Starter #17
I'm thinking that you may have the brake mechanism rod adjusted wrong. There is only so much travel on the brake booster. If you are using all of that to take the slack out of the brake system, you may not be getting help from the booster. Adjust the rod so that there is only a small amount of brake travel before brakes are engaged.
Thanks,, I'll look into this rod adjustment a bit more this winter. What I did now however, was, I disconnected the vacuum hose to the booster and went for a drive. Without the booster, although the pedal was stiffer, it took considerable effort to stop the car, and it felt as if only the back breaks were locking up. I then jacked all four wheels off the ground reconnected the booster and started the car. I had my wife slowly apply the breaks checking both back and front to see which set locked up first. I found with no load on the breaks the fronts did engage first and it took considerable more pressure to engage the back breaks..... I thought this may mean I have a little air in the front circuit, that under heavy breaking action cannot put good pressure on the front system allowing for the back to do most of the work. So, I re-blead the front circuit, both master cylinder and lines ( got a very small bubble out of the master) and re adjusted the rear breaks, which were set looser than they should. The breaking action al around, however, I still feel that most of the break pedal travel under booster assist is wasted, it is much better.

Thanks for all the suggestions.

Thadman
 

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Opeler
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where are these adjusters??
If you remove the rear brake drums, you can see that there are pins that the shoes rest on, against the tension from the bottom spring. These pins act as stops to keep the shoes close to the drum, which reduces the travel required of the pistons in the wheel cylinder. The pins are eccentric, so that when you turn them from the back side of the brake backing plate, they move the shoes in or out.

The adjustment procedure is done with the brakes assembled and wheels on the car. You lift the wheel and while turning the wheel forwards, turn the front adjuster downwards until you feel a light drag. Then do the same on the rear adjuster except while turning the wheel backwards. In other words, you always turn the adjuster downwards while turning the wheel in the same direction as the wrench. It's helpful to have an offset box wrench to do this because the adjusters are recessed. This procedure has to be done every so often as the shoes wear.

Bill
 

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If you remove the rear brake drums, you can see that there are pins that the shoes rest on, against the tension from the bottom spring. These pins act as stops to keep the shoes close to the drum, which reduces the travel required of the pistons in the wheel cylinder. The pins are eccentric, so that when you turn them from the back side of the brake backing plate, they move the shoes in or out.

The adjustment procedure is done with the brakes assembled and wheels on the car. You lift the wheel and while turning the wheel forwards, turn the front adjuster downwards until you feel a light drag. Then do the same on the rear adjuster except while turning the wheel backwards. In other words, you always turn the adjuster downwards while turning the wheel in the same direction as the wrench. It's helpful to have an offset box wrench to do this because the adjusters are recessed. This procedure has to be done every so often as the shoes wear.

Bill
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I had replaced the flex lines a few years back and went through all of the brakes with new hardlines in the front, and all has been well for all the time driving it since. Saturday morning, driving to get my car inspected, all felt fine until I slowed to turn into the inspection station driveway. Soft pedal and very little braking action unless pumped. As luck would have it, the station was actually closed "for employee vacation". Very carefully drove home, the whole time brakes feeling soft and not normal. Figuring I will be finding a burst line when I get home and the reservoir low...but no. Reservoir is fine and brake connections are dry. What should I be checking next?
 
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