Brake booster

[BDD]

I was having the brakes done on my '72 GT today so I could actually drive it. My mechanic thinks that I need a new brake booster and master cylinder. He says that there is vacuum but he hasn't actually measured it and that he has found no vacuum leaks. He also said that he doesn't think that the booster is leaking. rebuilt master cylinders are available but if it is truly not working I may need to find a brake booster that works. I am also having him put on new rubber brake hoses. I also have a new seal for between the master cylinder and booster and a seal for the vacuum hose connect to the booster. Maybe they would help. I know that the rubber where one line goes into the top of the m.c. is dried and cracked. He thinks that the booster diaphram might be broken. I asked if there was brake fluid in the booster. He didn't think so. He also said that he didn't think that the booster was leaking. Sounds contradictory

Any info. on where I could get a brake booster or get one overhauled? I do see an address on this site for a place in California that should be able to rebuild one. Any other sources?

Also, what would be a definitive test that would tell if the booster is at fault and not the master cylinder?

Right now I don't really have hydraulic brakes and one caliper drags. The existing rubber hoses are not flexible and are no doubt complete garbage. That's why I'm having them replaced. That could be the problem with the caliper dragging....if they were bad enough (acting like a check valve in both directions) could they also make it seem that the booster wasn't working?

Also: does anyone ever switch over to a modern brake booster and master cylinder system that will work with the standard GT brake hardware, frame, mounting position, etc. and also have readily replaceable parts in the future?

[wrench459]

Whats the brake pedal doing?
Oh for sure the 72 has a hydraulic braking system.
New hoses are a great start all three of them.
The pistons in the calipers love to freeze up and there a pita to rebuild if you can find the parts.
Its really a power assist booster.

[Gordy]

To check the booster operation push on the brake pedal with the engine off and while maintaining the same even pressure start the engine up. If the booster and lines are working as they should you will feel the brake pedal depress further as the vacuum assist kicks in.

[BDD]

I was quoting the mechanic about "no hydraulic brakes". The pedal action is actually quite stiff. The pedal will go down so far and stop. It's gone down a bit more with the engine running but only so far. I probably haven't started the car with my foot on the brake pedal though to see exactly what happens. The car will stop (and of course that can only be by some degree of hydraulic action) but you do have to apply a lot of pressure. I suppose this could mean the booster is not working...or there isn't enough vacuum pressure for it to work well (he says it's there but he didn't measure it yet...may have thought the pressure was o.k.) or maybe the rubber lines are so blocked they resist hydraulic pressure going in either direction.

I don't see any visible leaking at the booster, m.c, steel brake lines or rubber lines. The hydraulic fluid in the reservoir is clear and clean, it doesn't seem to leak out but then again I don't really drive the car yet till the brakes work well.

[sawdust]

If you can find an empty parking lot, try running in tight lefthand circles.
If there is brake fluid in the booster, the centrifical force will push the liquid to the vacuum hose and get sucked into the engine. It will look like you blew a head gasket with all the white smoke coming out the exhaust.

no.

[wrench459]

one thread to look into http://www.opelgt.com/forums/group-5...3-opel-gt.html
The GT brakes arent the best in the first place.

[BDD]

This is a neat idea (a cheap, easy 4 disc brake conversion method using Isuzu parts) and thanks for refrring me to it. It would be good approach for later but right now I just want to get my brakes working with minimal changes and cost at the moment. I think that going to a modern booster, master cylinder to work with the otherwise stock Opel brakes would be a good thing. Everyone will face bad and non repairable brake boosters in the future.

[West Coast GT]

I really like that idea of driving in a tight left circle to check for a bad seal between MC on booster. Cool.

As far as the brakes are concerned, you need a starting point from which to assess which parts are functioning, and which are not. Since the pistons are locked, tear them down and reassemble them. It's got to be done regardless of the MC & booster units' condition.

Yes, replace those three hoses. (I'd even replace the booster hose & check valve as they're 36 years old - how much longer were you planning on them working?)

Evaluate the master cylinder at this point. Can you bleed the brakes? Does it lock your wheels? Test it, gingerly, out in a parking lot or side street. If it feels pretty good, then move on to the booster.

Do the tight left circle to see if brake fluid gets sucked up through the vacuum line into the engine. If not, but you're not getting boost, check your adjustment per the factory manual.

Master cylinders can be hard to find. It took me six months to locate one, and then I had to rebuild it. Last time I checked, Opel GT Source had some in stock (April). If you're going to get one anyway, don't dottle - just order it now. If you think it's good, and you can live with it as-is (that takes on a new meaning), then defer this expense until its really necessary.

[BDD]

Wrench459:

What does the pedal action I described above indicate any particular thing to you?

Thanks,

[BDD]

I already replaced the brake booster hose.
The mechanic says that he thinks the check valve is working correctly, I asked him.

My original plan (and instruction to them this morning) was to replace the 3 rubber brake hoses and they have to bleed the system to do that. This would tell them if the calipers are o.k. If not they can rebuild them or replace them. Several sites claim to have them. They were also supposed to check the brake system in general and see what else needs work. They are going to do some work on the rear brakes too.

Rock Auto claims that they have rebuilt master cylinders that ship in 2 days. I was assuming that I'd replace that.

I asked OGTS last month about a master cylinder. They told me they had just sold their last one a day or so before. Rebuilding kits should be readily available.

I have a new seal to go between the master cylinder and booster. I'd have them install it if the booster is good and the one to stay with.

There's an adjustment for the booster in the factory manual? Is that by adjusting a threaded rod? I provided a '73 manual to the mechanic for his use in case he needed it.

[yellaopelgt]

keep it simple BDD......start out with the basics first. Your mechanic should realize that this "Opel" isnt a complicated machine. Change out the brake hoses ASAP....THEY ARE JUNK(THIS I CAN ALMOST GUARENTEE YOU) then bleed that ol'gal out.....sounds to me as if you may have air in the lines. Systematically, go through the rest of the system.If the booster is bad, you will know. Wheel cylinders freeze up and detieriorate, calipers will do the same after time of non-use as well. Dont let the mechanic jump to conclusions right off the bat and try to get you to replace expensive and hard to find parts when he hasnt done the basics.
HTH
Joe

[BDD]

I don't see anything yet about using a Honda brake booster but there are some interesting comments about using a 1990's Honda master cylinder on stock and 4 disc brake set ups. You use a different master cylinder for each. They both use the original brake booster. It is supposedly an easy change (just the master cylinder swap) and gives better braking.

I wonder if there are possible problems with this like too much hydraulic pressure, some detail differences between the hardware, etc? Have other poeple tried this with success?

The site's tech center parts intherchange page doesn't seem to be working right now.

As of yet I don't see any options for different boosters. I'll search later today.

[ungermm]

Originally Posted by yellaopelgt keep it simple BDD......start out with the basics first. Dont let the mechanic jump to conclusions right off the bat and try to get you to replace expensive and hard to find parts when he hasnt done the basics. HTH Joe

That would be my advise also. The mechanic makes a lot more money if you replace everything he thinks might be a problem. Start with the brake lines. I have seen them swell up so much that you can't see the inner channel and can't blow air through them.
Jerry

[BDD]

Well, that's what I'm doing and what I asked them to do when I took the car over. I'll have to stress again though that they have to replace the rubber brake lines first and bleed the brakes since now they're trying to push a new M.C. and a new booster.

The existing hoses are not even flexible any more.

I wonder...if I am forced to replace the master cylinder now because they can show that it doesn't work....should I opt to go for the Honda one?

[GTJIM]

Originally Posted by BDD ...should I opt to go for the Honda one?

The Honda one is for use with 4 wheel discs - not the front disc/rear drum of the standard GT - if it is standard best use standard parts.

There are Companies that re-sleeve the original cylinders with a stainless steel sleeve and restore them to better than new - both Master cylinders and Wheel cylinders. Discussed somewhere on here previously.

[blancojp]

Originally Posted by GTJIM The Honda one is for use with 4 wheel discs - not the front disc/rear drum of the standard GT - if it is standard best use standard parts.

There are two types of Honda master cylinder:
1) The ABS unit is best for 4-wheel disk brakes.
2) The non-ABS will work just fine on the standard Opel brake system.

On Stealth I used a 9" Suzuki Esteem booster and on the "Animal", I used a 7" booster from a Geo Metro coupled to the brake shaft. You can also install it on the firewall removing the standard eye soar cover.

If you do install it on the firewall, you can use the following combos:
1) Geo metro brake booster and master cylinder.
2) Geo metro brake booster and Honda Civic master cylinder.
3) Suzuki Esteem brake booster and master cylinder.

I have tried all of the above with very good results.

I made a kit for any of the above combos and also I have several Opel master cylinders and brake boosters in stock.

[Gigsworth]

i am interested in your retrofit kit, email me with details.

travisev@yahoo.com

[BDD]

Are there and replacement booster/ master cylinder combinations that work with stock brakes and which fit in the stock location under the hood and nose of the car? This would require the least bit of modification.

When mounting on the firewall what kind of modifications are required to the pedal, linkage, etc?

[opelspyder]

I think you guys are forgetting the stock ones are avaialbe from GT Source. Though not cheap, they came across several "NEW" ATE ones. I ordered one, a while back and didn't open it for a month or so, got to looking and it was brand new!!!! I thought I was getting just a rebuilt one -which they have as well) I ended up ordering a second one for my Kadett and a new Master Cylinder for that car. Rock Auto states on the master cylinder, you have to send in your core for rebuild now. Also GTSource may have one rebuilt with the stainless steel sleeve installed. If you need a booster, they run about 280.00. Not cheap, but you can't get them anywhere else really, so the cost doesn't seem too bad. They only had a limited supply on the new ones what they told, and if you wanted one, I would not hesitate
Keith

[gt crazy]

What i wouldve done instead of wasting money to put the car in shop is just go buy a new brake booster and master cyclinder i think its about 250 bucks for rebuilt parts from OGTS. And its quite simple to install them im 16 and did it. Thats what i wouldve done instead of wasting all that money on a mechanic

[blancojp]

Originally Posted by BDD Are there and replacement booster/ master cylinder combinations that work with stock brakes and which fit in the stock location under the hood and nose of the car? This would require the least bit of modification. When mounting on the firewall what kind of modifications are required to the pedal, linkage, etc?

You can also use a BMW E-30 type brake booster, it is slightly larger but it bolts right up to the existing location. The stock master cylinder bolts right up as well and gives a bit more boost than the stock unit.

[krewzer]

JP,
are you talking about using the BMW e30 booster with the Opel m/c, or both parts from the BMW?