Brake Booster Adjustment

jakepressley · **Posted:** Sun Jun 14, 2009 11:33 am

1987 fox mustang, stock brake components...

I need more brake petal... I changed the master cylinder out and noticed that there is an adjustment on the shaft coming out of the brake booster. Would I spin the adjustment in or out to gain more brake petal? Or should my new master cylinder remedy this problem?

thanks
jake

Dustin Fredrickson · **Posted:** Sun Jun 14, 2009 8:33 pm

Paging Art McDonald....

Arthur McDonald · **Joined:** Fri Aug 29, 2003 1:54 am **Posts:** 2052

I'm not sure I'm the guy you want to ask for advice about brakes.

I'm pretty sure you turn it counterclockwise to extend the pushrod shaft.
According to my 1990 shop manual, the range of adjustment for a Bendix type booster is small. It says the pushrod length (extending from the face of the booster) should be between 0.98" and 0.995" (or 24.9mm and 25.27mm). The book describes a "MAX-MIN" gauge - looks like a 3" square block, with half inch holes or grooves in opposite sides, one 0.98" deep (min) and the other 0.995" deep. Pull the MC away and press this against the front of the booster (5 lbs force needed to seat the pushrod in the booster) to see if you're in range.

A mechanic who shall remain nameless (since I might one day need his services for other work) offered to make this adjustment for me to remedy the low pedal problem that resulted after I had replaced the original booster/master set. The pedal WAS very high and firm, but when I got home (25 miles @ 70 mph later), the brakes were pretty much on fire. Lesson - extend the pushrod too far, and the brakes drag.

If you haven't installed the MC yet, and you don't have anything to measure the current pushrod length, I suggest you go ahead with bench-bleeding the MC, install it and see what you have. If, after you have bled everything and the pedal is firm, you find that the pedal is lower than you like, you might consider pulling away the MC and adjusting the pushrod a little bit at a time.

jakepressley · **Posted:** Mon Jun 15, 2009 9:10 am

Thanks Art

I'm in the process of replacing the MC, and will test by extending a few threads at a time.

trial and error

I've got nothing but time, as I'm mothballed the car until November or December...

thanks again
jake

Kevin Harvey · **Posted:** Mon Jun 15, 2009 2:50 pm

Mothballed? Are you not driving until the baby is a year old?

jakepressley · **Posted:** Tue Jun 16, 2009 5:56 pm

it doesn't 100% have to do with the new kid... Its the $$ hits at work that have caused me to step back a bit... I'm ok with it though as my focus has changed a bit. I noticed this the last time I was at the track in March, I spent more time on the work phone and checking in with home than I'd like too when I'm at the track.

The good news is that I'VE GOT A JOB and the car is pretty much built, well for now anyway.. I've been able to sort out a laundry list of "issues" that only a 23 year old stang would have... Its on jack stands tucked away until Bev can give back the 11%

I'll be back soon enough

:wink:

Kevin Harvey · **Posted:** Tue Jun 16, 2009 7:32 pm

Good attitude, Jake.

Let me know if you need anything.

Mark Barnes · **Posted:** Thu Jun 18, 2009 10:08 am

Jake, I have done a few M/C on the Fox Mustangs. You are looking for some clearance between the M/C and the pushrod so they brakes do not drag. The little special tool will help with that. You can also use one of those fancy calipers to measure the rod and the hole in the M/C to set the gap. Trail and error will also work. Most I have replace are close enough that you don't have to make much of a change.

jakepressley · **Posted:** Thu Jun 18, 2009 8:20 pm

I'm inclined to leave it alone for now... The more I think about the boosters its function, the more I believe its a MC problem, or a line problem...

My fear is that I'll end up building pressure at the caliper, as it won't return the fluid to the MC... resulting in the brakes dragging...

Mark... on your fox is there a rubber section of brake line to allow the rear end to flex?

DickRasmussen · **Posted:** Fri Jun 19, 2009 8:36 pm

Jake,
In my experience with a stock brake 88 5.0 the key to pedal height was correct wheel bearing adjustment, gently bedded new pads with no taper, well bled lines, and properly adjusted rear brakes. If you only street and autocross the pedal feel will stay OK (considering the car :lol:

). Any track use will result in loooooong pedal very quickly even after they cool down. A lot of the pedal height can be attributed to the rear brake adjustment as I recall. I don't have my shop manual . . . it went with the car to Don Forrester in 1996 when I got the 97 GT.

Arthur McDonald · **Joined:** Fri Aug 29, 2003 1:54 am **Posts:** 2052

I found that bleeding the brakes after every track session was the norm for my '90 Mustang. The biggest bubbles were hiding in the rear wheel cylinders. Even then, after 4 laps so, the pedal started to drop.

Jake, have you ever looked into swapping in the 4 wheel disk system, rear end and front LCAs/spindles from a 94-95 Mustang GT? That's basically what a '93 Cobra R had. Don't recall if you have 4 or 5 lug wheels - if 4 lug, then you would need to hit Craigslist for 5 lug wheels.

I assume you're read through this website. It's old, but so is your car.

http://mjbobbitt.home.comcast.net/~mjbo ... /4lug.html

While you're chewing on that, go here and check out the 2010 Mustang drifting action in Japan:
http://www.fordvehicles.com/the2010mustang/?id=/

jakepressley · **Posted:** Mon Jun 22, 2009 9:15 am

Its time....

I posted a wtb buy add last week and happened to run across a guy upgrading his current setup... We got to talking and it turns out that he is very interested in what THSCC does in terms of AX and track.

I'm meeting him this afternoon at the house, as he wants to see the car.. and might co drive in an auto cross this fall, if his car isn't together.

I going to end up with a SSBC rear 4 lug disc kit (uses brackets and stock 93 cobra four lug rear discs... also the same as 88 turbo t-bird, all for half the shelf price..... I had to break the piggy bank

In march the only complaint my instructor had was that i was using my tranny to slow the car comming into 1 and a the top of rollercoaster... a very expensive way to slow the car..

It's going to be nice not to have to rebuild the rear brakes after every other session... I wonder what i'll do with that time>> :lol:

THSCC Forums

Brake Booster Adjustment

Who is online