Brake booster, and e-brake question/issues

manoa matt · Post by **manoa matt** » Tue Aug 07, 2007 10:53 pm

This question is directed towards anyone that has replaced their origional brake booster with an IAP booster. Or if you rebuilt your rear calipers.

The last stage of my restoration was going to be my brake system. The car did not move much in the 9 month restoration. I got it going good for my wedding a few weeks ago, but didn't have the time to do the brakes untill after the wedding. Everything went off without a hitch, except me.

So it was a Tuesday, and I was planning my brake system overhaul that weekend. On the way home a gasket or diaphram in the booster blew out. I figure it was because the fluid was old, the calipers and master hadn't moved much in 9 months, its 30 yrs. old, etc..etc.. And all of that put too much stress on the booster.

As soon as I got home I ordered a new booster from IAP and had it shipped out. When it arrived, immediately I could notice differences between the new and old booster. (1.) The mounting studs on the rear were longer and not threaded all the way down. Simple fix with some nylon 3/8" spacer bushings, and an auxillary neoprene gasket. (2.) The vacume check valve was plastic instead of metal and when I sucked/blow through them I noticed the new plastic valve gave less resistance =more vacume assist. (3.) The push rod protrusion specks were different. Fiat Factory Service manual says almost 1mm more protrusion than the IAP tech bulliten. I adjusted the push rod protrusion to a value that satisfied both specification references.

IAP tech support assured me that the boosters were the same.

I rebuilt all the calipers, replaced all flexible brake lines, installed new booster and new master cylinder, new pads all around, new rotors on the front, and existing front rotors went on the rear. I put in new dot 3/4 heavy duty brake fluid, and bleed, bleed, bleed.

The pedal feels firm when the car is off, with the car running the pedal feels a bit soft. I test drove a few times making shure not to brake to hard so i did not mess up the bedding in of the new pads. As the pedal is pushed down, not much braking power is experienced in the first 1/2 of pedal travel. Once the pedal travels 1/2 way down the brakes start to bite and the car will stop. It's not a gradual increase in braking power like before I overhauled the system. I know this is not normal opperation.

I recently read in a current issue of a classic sports car mag (which was reviewing 10 affordable classic sports cars) that they felt the 124 spider had too much vacume assist. Could this be from the new valve?

I am thinking that either their is still some air in the system, or the new check valve allows too much vac assist, or the push rod protrusion is not enough.

Also I can't get the E-brake to grab. It worked great before the overhaul. When I rebuilt the calipers I made shure to keep the compression washers in their correct orientation. However, I have 4 different Fiat repair manuals and they all differ with regards to the orientation of the mark on the rear caliper piston. Some say it should be opposite the bleeder screw, some say it is on the same side. I can get fluid to come out with it oriented both ways, it shoud only bleed with it oriented the right way. Right now it is oriented on the same side as the bleeder screw.

With the rear axel supported on jack stands I adjusted the e-brake to grab after 2-3 clicks. With the e-brake on 2-3 clicks i can't turn the rear wheels, while supported. If I let the car back down and put the e-brake on 4-5 clicks the car will still roll backwards, but it jerks a little as it rolls. (I park on an incline, so e-brake is important)

Do I need to waight till the brake pads are fully bedded in untill the e-brake will fully grab and hold?

I plan on bleeding more tonight and maybe switch air check valves to see what effect it will have.

I know its a long post, but you guys know, thats how I roll.
Any help is greatly appreciated.

Matt

P.S. I plan on posting a long exhaust system question tomorrow.

mdrburchette · Post by **mdrburchette** » Wed Aug 08, 2007 6:56 am

I'm confused. I thought to bed in pads, you braked hard a few times. When it grabs, can you tell if it's the front or rear?

mbouse · Post by **mbouse** » Wed Aug 08, 2007 8:25 am

while i wait for the loong exhaustive question tomorrow, you may want to separate the mechanical brake system from the hydraulic brake system.

i believe you are looking at two separate issues here.

your hand brake (emergency brake) is adjustable at the Y where the cable splits for the two wheels. Crank those adjusting nuts in to get better grip with the hand brake.

since it is so simple to swap the check valve in/out; is it safe to assume that you threw in the old unit for a test, and it had no effect on your symptoms?

So Cal Mark · Post by **So Cal Mark** » Wed Aug 08, 2007 10:18 am

the check valve merely holds vacuum in the booster after the engine is shut off, so that you have a couple of assisted brake applications in an emergency situation. Sounds like you've still got some air in the system. The e-brake was never a very good system in the Spider, everything has to be perfect for it to work marginally.

Not sure how much you paid for a new booster from IAP, but you can get your old one rebuilt for $75-$100

mbouse · Post by **mbouse** » Wed Aug 08, 2007 1:08 pm

Or, i could sell you the one off the '74 parts car that worked just fine when parked in june of this year.....

manoa matt · Post by **manoa matt** » Wed Aug 08, 2007 3:23 pm

Thanks for the prompt responses and the offers, to answer everyones questions.

Bedding in: ALL my manuals, and everything I've read about replacing brake pads say not to brake hard for the first 100 miles or so. I know it grabs in the front, To test the back I held the pedal down with a stick while the rear axle was on stands. I could not move the wheels.

Hand brake adjustment at "y", Place rear axle on jack stands then pull hand brake 5-6 times to take up slack. Then adjust nuts so that calipers lock the wheels when brake is pulled up 2-3 notches. Hand brake works when axle is supported on stands (like it would be supported if on ground)
When car is on ground hand brake will grab slightly but not enough friction to hold car on an incline. I think pads need to bed in before maximum friction is attained.

Did not know that about the check valve, I thought the valve would regulate how mutch assist/vacuum. Intestering to know. The first time I bleed the brakes I used a pressure bleeder connected to the master cylinder reservoir. Bleed untill all showed clean clear fluid and no air bubbles. Then when the new wife came home she pumped the pedal as i opened and closed the bleeder screws. No air bubbles that time. Reservoir was always full durring bleeding.

I could have gotten a rebuilt kit for $15, but I figured I would get a new booster for piece of mind, and rebuild the old one and sell it later. I don't want to install a 32 year old booster to have it blow out in a few months. Too mutch work to get it in and out.

Never got a chance to bleed again last night, a water main broke up the street and I would have needed to take a shower before bed. Also it was raining alot, didn't want to do brake system test drives down a steep wet hill.

Now my own question:

If that valve holds vacuum even after the car is shut off then why is my pedal firm with the car off and soft when the car is on?

Matt

mbouse · Post by **mbouse** » Wed Aug 08, 2007 4:24 pm

manoa matt wrote:Then when the new wife came home she pumped the pedal as i opened and closed the bleeder screws.
Matt

when something doesn't work, always look for the NEW things you changed, first. process of elimination. work backwards from the last thing you did until you find the one that caused the problem.

New wife !! that has to be it.

manoa matt · Post by **manoa matt** » Wed Aug 08, 2007 4:47 pm

I have two great loves. I know my wife is jelous of all the time I spend with the car. Now that I'm married I've slowed down on time spent on the car. Now I think the car is jelous.

Funny story:

A few months ago I was trying to diagnose an ignition problem before I switched to electronic. I got the car started and running with points and took it for a drive by myself, the car worked great. Later a buddy came over and we took a drive no problems. Then my fiance, (at the time) came home and I offered her a joy ride. As we were comming home she suggested an alternate route, not soon after we turned off, the car died in the middle of the road and I couldn't restart it for 2 days. If we would have went my way the car would have died after I got it into my parking space.

racydave · Post by **racydave** » Wed Aug 08, 2007 6:22 pm

I agree with Denise on new pads, they wont seat untill you do some serious stopping. The important part is to let them cool off between attempts. Cleanliness of the rotors and pads is very important.Also a problem is the rear proportioner valve. Im not sure, but isnt it supposed to increase rear operation during a nose dive? Should the rear axle be unsuported? Mines still on stands, but I bypassed the valve because it was seized and causing problems. Alot of fellow Fiaters have eliminated theirs. Congrats on the new marriage.

manoa matt · Post by **manoa matt** » Wed Aug 08, 2007 6:38 pm

As I re read some previous posts about brake trouble I came across a comment made by so cal Mark.

"are you getting pressure when you bleed the rear calipers? If you're not getting much fluid, disconnect the link from the compensator to the axle. Push up and retain the link as high as it will go. That will allow full pressure to the rear brakes. If you don't do this, you'll never get the rear brakes bled."

I'll try this

Matt

mbouse · Post by **mbouse** » Wed Aug 08, 2007 6:41 pm

cars generally don't get mad....they get even. Watch out!

Congrats on the nuptials.

mdrburchette · Post by **mdrburchette** » Wed Aug 08, 2007 7:13 pm

I'm sure you had a load on the rear axle when bleeding the brakes, right? It does sound like there's still air in the system. Sometimes it's hard to get the master cylinder bled. A little trick Ron showed me was to have the reservoirs half full and the caps off when bleeding the brakes so you can see bubbles come up from the master cylinder. Make sure you slowly pump the brakes or you'll have brake fluid everywhere! Don't even ask how I know.

So Cal Mark · Post by **So Cal Mark** » Thu Aug 09, 2007 1:49 am

just supporting the rear axle doesn't open the compensator enough, you have to disconnect the link and keep it up as high as it will go.

The reason your pedal gets soft with the engine running is that you have power assist. You should be able to get power assist with the engine off at least on two applications of the brakes. If you have none with the engine off, either the booster is leaking or the check valve isn't holding vacuum

manoa matt · Post by **manoa matt** » Thu Aug 09, 2007 6:11 am

I disconnected the compensator link, supported it, and bled out a lot more fluid and a few bubbles from the rear calipers.

I checked the e-brake adjustment again and found a slight kink in the cable. You couldn't tell the kink was there until all the tension was taken off. The kink was off center from the adjustment yoke so it only activated one caliper while the other was still slack. The cable is still good so I'll just take it off and work the kink out.

I finished too late to test drive.

mbouse · Post by **mbouse** » Thu Aug 09, 2007 1:56 pm

i always end a tech session with a test drive, no matter how late. You see, my Spider is a daily driver six months a year. It's gotta work or i ain't done wrenching.

I am glad to hear you found that kink in that cable. my hand brake works quite well, and i use it a lot. it is a simple system, and oh so nice when it works correctly.

sounds like you are on the road to a successful project conclusion.