Brake Problems

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motob
Posts: 41
Joined: Sun Sep 05, 2004 10:56 pm

Post by motob » Tue Sep 19, 2006 2:33 am

The unit incorporated into the front brake circuit is not a valve, nor is it a safety braker. It is a proportioning cylinder. It is designed to increase the pressure to the front brakes.

It is very simple, has only two parts: a piston and a return spring. The way it works is that brake fluid pressure from the power brake booster is applied to the backside of the piston. This moves the piston forward. The front side of the piston has the same outer diameter as the rear, but the center of the front of the piston extends through a seal to the outside of the unit. so the effective area of the front side of the piston is the outer circle minus the inner circle (diameter of the part that sticks out from the unit).

Let's say that there is 100 psi coming from the brake booster and the back side of the piston is 1 square inch, now there is 100 pound of force pushing on the piston. Let's say that the front side of the piston is 1/2 a square inch (due to the center missing from the doughnut). 100 pounds of force divided by 1/2" creates 200PSI coming out of the unit.

The unit can cause the front brakes to stick on. If the piston sticks, then the front brakes will stay on. Also if the unit is improperly assembled, then the front brakes will stick on. There is a flat spot on the top of the piston, it must line up with the compensation ports on the housing, if it doesn't then then pressure in the unit cannot be released when the brakes are released.

The hardest thing about rebuilding the unit is finding seals that will work.
Otherwise it is about the simplest part on the whole car.

Later cars used a proportioning valve in the rear circuit to limit pressure to the rear brakes, rather than boosting pressure to the front.

Brian

william
Posts: 515
Joined: Tue Jul 08, 2003 9:39 pm
Location: Rochester, Indiana

Post by william » Tue Sep 19, 2006 9:43 am

Thanks a lot Guys,

Lots of information here.

Last night I removed the master cylinder....The fluid looked dirty and smelled awful. There was crud around the cylinder and the rubber boot that covers the shaft was torn.

Next step will be to remove right rear caliper and look at it and see if it needs attention. If it does I'll pull all calipers. Matter of fact, I'll probably end up taking all the calipers off and go through the whole system (rebuild/clean) as Jim R. Suggested.

I'm also wondering about the Hvac because of the heavy pedal. The pedal almost acts like it does not want to return after being pressed. I looked for the return spring and I'm pretty sure its there ( next to the master cylinder). It does return just not like I think it should.

Any Ideas on what brake fluid to use? I think Tom told me castrol LMA, Not sure what dot this is?

I also need the replacement rubber boot for the master cylinder. any suggestions?

If calipers need reselved Any thoughts where to send?

What a great group of guys we have here!!!!!!

Thanks again for all the replies.
William
1979 Avanti s/n Rqb-3016
1962 GTE s/n 3447
1960 Alfa Romeo Giulietta Spider 1495*09775

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treue
Posts: 140
Joined: Mon Sep 16, 2002 8:49 am
Location: Oklahoma

Post by treue » Tue Sep 19, 2006 11:32 am

Guys,

I had an 83 VW Rabbit for 9 years. After the better portion of that period, and at over 100,000 miles, I had the right front caliper lock up. After sitting for a while, it would self-correct, but lock again, down the road. I took it to the dealer and he replaced the entire right front caliper at no small expense. That caliper would still lock up. Something told me to bleed all the brakes, replacing all the brake fluid. This corrected the problem. I don’t know what would have caused the lock up-moisture?, dirt? I think most manufacturers recommend fluid replacement every other year. It does go bad.

Tom
Tom Treue
67 330GT 2+2, No. 9129 (former owner)

t walgamuth
Posts: 151
Joined: Sat Oct 07, 2006 4:29 pm
Location: lafayette indiana

Post by t walgamuth » Sun Oct 08, 2006 12:56 am

yes, that proportioning valve works the same with the same ratio then as the one in my pf coupe.


thanks for the link.

tom w
tom walgamuth
pf coupe #1421

eve23
Posts: 56
Joined: Mon Jun 14, 2004 1:15 pm

Post by eve23 » Mon Oct 09, 2006 3:43 pm

im having the same problem on my lambo boosters.....
it seems the rear one is the culprit......it was rebuilt about 5yrs ago .....
after sitting and whatever maybe moisture got in.....

also the oil is very black so that could mean a vaccum leak......

....but if the mc is ok on the GTE then it mus be a booster problem.......

eddie

william
Posts: 515
Joined: Tue Jul 08, 2003 9:39 pm
Location: Rochester, Indiana

Post by william » Mon Oct 09, 2006 8:46 pm

Ok, everything is back together I bled the brakes three times, and I'm still having some problems.

The problem now is that my brake pedal goes to the floor, and after a few pumps, the pedal is back to the top with a heavy feel. As I drive (slowly, of course) I lose brakes, I mean I still have brakes, but the pedal goes to the floor, then with a few pumps, the pedal is back up top. I also notice a slight drag on the rear brakes. So what do think MC shaft not returning all the way and after a few pumps it does? or Hvac ?

When I had the MC off, I noticed it was brass sleeved. I honed it out carefully and noticed a small flat spot.

I'm trying to rule out the Hvac.

I removed the MC tonight and will send it off for rebuild. Any thoughts on where I should send it?

White Post? I know Yale mentioned Karps. Any other shops recommended?

White Post is $225.
Karps is around $180.

Thanks as always
William
1979 Avanti s/n Rqb-3016
1962 GTE s/n 3447
1960 Alfa Romeo Giulietta Spider 1495*09775

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330GT
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Post by 330GT » Mon Oct 09, 2006 9:07 pm

When my master cylinder went, a slow push would go to the floor. A sharp push would work properly. I think that the worn rubber bellows would allow fluid by when slowly (or lightly) depressed. A sharp push would flare it out and make a good seal.

I had mine rebuilt by White Post.
Regards, Kerry
http://www.330gt.com 330 GT Registry
http://www.parrotbyte.com/kbc/ferrari 250 PF Coupe 1643GT, 330 GT 2+2 8755GT, 308 GTS 23605

motob
Posts: 41
Joined: Sun Sep 05, 2004 10:56 pm

Post by motob » Tue Oct 10, 2006 1:13 am

We had so many problems with White Post that we stopped using them.

I discovered Sierra Specialty http://www.brakecylinder.com/index.htm and have had nothing but good experiences with them, excellent quality workmanship at a cheap price. If you call on on the phone, you are talking to the guy that is doing the work. He cares about what he does and goes out of his way to help you. I wish there were more companies like this.

Brian

william
Posts: 515
Joined: Tue Jul 08, 2003 9:39 pm
Location: Rochester, Indiana

Post by william » Tue Oct 10, 2006 8:21 am

Thanks Kerry,

How long ago did you use White Post? I have heard alot of negative stuff lately.

Brian,

I linked to Sierra it appears they just resleeve. I would like to have new seals and a new rubber boot.

thanks
William
1979 Avanti s/n Rqb-3016
1962 GTE s/n 3447
1960 Alfa Romeo Giulietta Spider 1495*09775

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330GT
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Location: Seattle, WA
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Post by 330GT » Tue Oct 10, 2006 9:23 am

william wrote:Thanks Kerry,

How long ago did you use White Post? I have heard alot of negative stuff lately.

...thanks
I had my MC rebuilt 2 years ago. I also had my front brake calipers redone by them about a year before that. No problems with either since.

I thought I had a problem with a sticking front caliper. White Post rebuilt it under their warranty with no question. They did say that it probably was a collapsed brake line and that's what it turned out to be.

They also turned around my MC in about 6 hours. I over-nighted it on Monday and had it back and in the car by noon Wednesday.
Regards, Kerry
http://www.330gt.com 330 GT Registry
http://www.parrotbyte.com/kbc/ferrari 250 PF Coupe 1643GT, 330 GT 2+2 8755GT, 308 GTS 23605

william
Posts: 515
Joined: Tue Jul 08, 2003 9:39 pm
Location: Rochester, Indiana

Post by william » Tue Oct 10, 2006 11:59 am

Thanks Kerry,

I live in Indiana so VA a little closer then CA. as far as shipping time is concerned. It sounds like White Post has a fast turn around. I'll make a choice and go for it.
William
1979 Avanti s/n Rqb-3016
1962 GTE s/n 3447
1960 Alfa Romeo Giulietta Spider 1495*09775

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