Re: [Amc-list] t-tube broke.

["Swygert, Francis G MSgt 436 CES/CECM" <Francis.Swygert3@xxxxxxxxxxxx>]

Yes, I just went and looked for it! The two missing bolts explain a lot.
Every time you accelerated, the rear axle pushed forward and flexed
those bottom bolt ears (gap opened at the top). When you stopped, it
straightened back out. The constant flexing is definitely what broke the
ears. NOT the brakes. The brakes just moved the axle back. Oh yeah, when
the axle moved back the park brakes engaged -- the park brake cable
won't stretch! 

Changing to a larger wheel cylinder in the rear brakes will make matters
worse. Don't do that!! 

I was wrong on the MC size -- it needs to be BIGGER!! When I first
suggested a SMALLER MC, I thought you had the more common 38mm PBR
calipers. (1.5" -- 1.77 square inches x 2 = 3.54 s.i. total, a lot less
than the 5.3 s.i. of the stock Jeep calipers). 

I was just checking MPBrakes troubleshooting guide. This is why I asked
about pedal travel and hardness. I also included a method of checking
the MC itself from the site.

----------------- QUOTE -------------------------
Disc Front & Drum Rear: Manual Brakes with Soft Pedal

Master cylinder piston diameter too small.
If the diameter of your master cylinder piston is smaller than required
by wheel system volume requirements then you will experience a long
pedal travel. Determine what the original master cylinder bore diameter
was and replace the master if too small. Remember with an old vehicle
the master could have been incorrectly replaced by a previous owner.

A defective master cylinder.
If the bore in the master cylinder is pitted or the rubber seals have
decreased in size then some fluid will bypass the seals under pressure
giving a lower pressure to the wheels and a softer spongier brake pedal.

To test for this condition remove the brake lines from the master
cylinder and plug the outlets (obtain outlet plugs from a local auto
parts store). When you apply the brake pedal it should be high and firm.
If it is spongy or slowly goes down then either the bore of the master
cylinder is pitted or the rubber seals are bad.
--------------- UNQUOTE -------------------------

We've already determined that the piston area in the PBR (Mustang GT)
44.5mm piston calipers is greater than the area of the stock AMC 2.6"
calipers. So the PBR calipers have to have more volume, NOT MORE
PRESSURE. Instead of a 7/8" MC, you need to try a 1-1/8" MC. A stock 73
Matador w/power disc brakes MC will fit the bill just right! A 1-1/16"
bore MC (73 Matador w/manual disc brakes might be enough, but I'd try
the bigger one first. If the pedal is too hard or doesn't move enough,
then drop to the 1-1/16". There's no way around this -- you'll have to
try one then the other. 

There shouldn't be transmission oil coming out the back. If the
driveshaft yoke pulled back far enough to come out of the seal that's
where it came from. If it's not a continuous leak I wouldn't worry about
it. I know you just replaced that seal, but make sure it's not damaged
before you put it all back together. 

-----Original Message-----
From: d stohler [mailto:das24rules@xxxxxxxxx] 
Sent: Tuesday, February 27, 2007 1:04 PM
To: Swygert, Francis G MSgt 436 CES/CECM
Subject: RE: [Amc-list] t-tube broke.

my pedal goes all the way to the floor. i can feel
about half stroke when the rear brakes are
pressureized, but the pedal will still go to the
floor. i have installed a gm style combo valve. didnt
notice much difference. i have replaced almost all the
lines up front. the rear line was replaced a couple of
years ago before it sat for 3 1/2 years before i could
get home to get the car again. i think im going to
just find me a 15/16 bore master cylinder to swap on
and try. i was looking thru my tsm. my front wheel
cylinders are 1 1/8 bore. if i was to swap them out
(if i can) with the rear. is that only going to make
the problem worse? bigger area for more pressure in
the wheel cylinder correct? 

did you get my post of what i discovered happend to
cause it to break? feel pretty stupid about it. thanks
for the help. i am so busy lately i dont really have
time to be on and post but i cant stand when my
rambler is broke. 


 
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