brake advice needed

H

heroszeros

Active Member
Messages
67
Reaction score
4
Location
san diego,ca
Hey I've run into a mystery with the rear brakes on my 71 2800 and hoping that somebody has some experience with similar situations.. forgive the long description, but i want to describe the problem all the way.

-rear left drum is binding sometimes, causing drum to smell, and brake pedal feel is inconsistent. (i am suspecting worn return springs, and maybe air in the system)
-first i tried adjusting the shoes and they where fine for the first few stops, but the rear left binds again after a few applications
-I tried to bleed the system second, starting with the rears surprisingly very little fluid comming out (2-3 inches in the tube, then nothing) pumping the brake pedal makes very little difference also), front brakes bleed just fine
-new fluid, and again very little fluid moving in the rear
-install new shoes and return springs, adjust brakes and the rear left is binding again.
-i then removed the wheel, drum, and check everything and readjusted.. now the rear right brake is stuck. adjusted again but no difference.
-there doesn't seem to be any leaks in the system, pedal pressure is spongy but constant, and the system doesn't seem to be eating fluid through the breather.

is this master cylinder sounding? pressure regulator/accumulator?

any advice would be greatly appreciated before i start ordering random brake parts..
 
John:

How old are your rear flex lines? Those things can fail by swelling internally, so that they act as a one-way valve, allowing pressure to expand the brake cylinders, but now allowing it to run back to the MC when the pedal is released.
 
Brakes

Zeros,

Several things based on your description:

1. If you can't bleed much out one side it's likely the master cylinder. The dual master has two internal cylinders which can shut off one part of fluid to save the other. ( front works, no fluid rear) Usually it's the spring or the cylinder sticks. To test to see if you can move it, crack the union on the one side that's working while someone gently pushes the pedal. Sometimes you could get lucky, the stuck side moves, and opens the other side. Newer cars have this bleeding procedure with a small switch that activates the warning light if one side is non operating. (E9s only comes on if the fluid drops) If your getting fluid there, then there is a center hose before the pressure regulator that may have collapsed internally. ( Less likely but possible.)

2. Left rear then right- mmm. Fix number 1. But be careful of drum brake adjustments- a little loose is better. As brakes are used, a lot of heat builds up and then clearances go to zero. In race cars, that used drums, you would actually run them so loose that they barely worked at full extension. But as soon as you got moving the pedal would come back full pedal- heat caused the brake shoes/ drums to expand. A little loose is good. I don't recall if the manual addresses drums much. But usually when adjusting you adjust till it starts to drag then back off two to three flats. If I were racing- 10-14 clicks/ flats.... scary.

3. Mainly one side- bad cylinder; sticking. Springs nor air would cause what you describe.

4. As a suggestion- if you find yourself doing cylinders-- replace the rubber hoses. They're still cheap and you'll know for sure what you have. If they look original; they should have been changed long ago.

Hope this helps.
 
You have the classic symptoms, as Jay pointed out, of a rear brake hose that is plugged or collapsed which does not allow the fluid to return to the master, hence the sticking brake shoes. Replace hoses and re-bleed.
 
Thanks for your advice gents, I have quite a list a of things to check out, but hopefully I can sort this problem out-

btw- i checked the flex lines externally and they all seem fine. If they are collapsed/not functioning, do they do so without external signs of failure?
 
You can not tell from external apearance. Undo flex hose from caliper and see if anything comes out. These absolutely need periodic replacement and are cheap. HTH.
 
Replace the two rear flex hoses, if you can get the metal braided teflon lines for 2800 rears do it, they are very secure and you may never need replace them again.

Just replace both wheel cylinders ... on 2800's the stock wheel cylinders were 22mm diameter ... some people have used wheel cylinders from '02's (16mm, and 18mm for Tii's) but am not sure I want to go on record as saying they'll work...too many lawyers in the hobby now-a-days. Flush all the fluids from your brake system before doing these.

One other thing that Carl told me about years ago, the rear proportioning valves (which maintains a proper pressure balance between the two and also front to rear) on these cars go south far more frequently than on the 3.0's ... stock ones for the 2800's are often unavailable, and if thats the case at the dealers call CNPR in La Jolla or you can get a modded or aftermarket one that is adjustable.

There really is no reason to not replace all your brake components, particularly the hydraulics...and you've done a lot of the r&r already. In new proper order your brakes will be nicer than you ever imagined they could be, and is the frustration you're having now worth the false economy and likely compromise of safety?
 
very good points, you are right and the more i think about it, the more it is making sense and i am going to replace/rebuild the whole system. i don't have a long history with the car, and for all i know many of the parts could be 40 years old! it's not a wise idea to just chase fixes every few months when a whole new system would give me more piece of mind.

BTW, if you guys have drums in the rear of your coupes, the guys at Mesa say that parts are getting harder to come by, so if you need to change parts soon, i would get them before the supply dries up-
 
Thanks all for your advice.. It's been a few weeks and here's the ditch i dug for myself so far:

new stainless flex lines all around, rebuilt the front calipers, and rear cylinders, new hard lines all around, new pads/shoes/drums..

okay so all of this, and somehow the brakes still feel wierd. i have a power bleeder and bled the system with new dot4 fluid, and am planning on re bleeding again soon just in case (i've managed to go through 4-32oz bottles of fluid in the process). My problem is that the pedal has alot of travel, and then the brakes feel like a rock. this happens when the engine is off or on (although when running there is more resistance). i measured, and the pedal travel when running is about 40mm until there is significant resistance.

i read some other threads and have tried pumping the pedal when off, and after 4 pumps the pedal is hard, and there is little movement, starting the car then lets me press the pedal in further.

has anybody had similar symptoms? is this normal? any advice would be very appreciated-
 
Last edited:
same problem

My 70 2800CS showed same symptoms,plus front caliper... fix was replacing rear pistons and front calipers with new parts, new master cylinder,new stainless flex hose and repacked bearings as well
 
Rock brakes

HZ,

The change to SS lines will result in a harder feel to the pedal. That said, my pedal on a 4 wheel caliper system depresses to about an 1".

Since drum brakes aren't discussed much let's try. In thier day, shoes were "arched" to drums. What this means is that the shoes were sanded/ machined to a slightly different arc of about 1mm less than the drum whereby the most area of contact would occur, less tendency to squeal, the leading edge ( the shoe on the direction of rotation) took the most of the action. New shoes require a breakin of perhaps 100- 500 miles to fully seat in without glazing; so take it a little easy at first and the shoes will act better.

Suggestion- recheck your rear adjuster cams to make sure you have equally adjusted the shoe contact and free wheeling. You will probably need to recheck in a couple hundered miles when the brake shoes set or bed in.

Suggestion- pedal brake actuating rod- try to acertain the amount of free play between the pedal action and the master cylinder. If you remove the interior cover you can check by visually looking at the brake light swith which normally is about 1/4"-3/8" exsposed. If more than this, adjustment needs to take place. Sometimes you can feel the pedal action and the start of the master cylinder piston movement.

Also, seems like a lot fluid has been bled- might try manual bleeding since you can generate a lot of pressure that the power bleeder can't and sometimes results in getting the last bits of air out.:)


For those that are going to do the drums/ shoes- a Porsche technical bulletin recommends that the lining be relieved with two cuts per shoe just as the new pads/ shoes are by using two hacksaw blades on an angle not quite through the material and a slight bevel to the 1/2 edge of the material as a precaution against squeal.
 
Last edited:
Master Cyl bleeding

hans3 said:
I had to bench bleed my master cylinder to obtain proper pedal feel.
Click to expand...

I've just refreshed my whole hydraulic system; new hard & flexi lines, rebuilt calipers front & rear, rebuilt brake master and stripped 2x remote servos (RHD) plus new clutch master and slave cyls. Phew.

According to my E3 service manual, bleeding should be servos, then rears and finally fronts (outer top, inner, outer bottom nipples in that order).

Problem is, after bleeding through 2 litres of new fluid with a pressure bleeder at 15-20 psi, I still have virtually no pedal feel unless I "pump" the brakes. Fluid is flowing freely out of each nipple with no signs of any more air. Clutch works fine.

Anyone got any ideas ? I'm guessing I still have trapped air pockets somewhere hence perhaps reverting to old-fashioned manual pumping ? I'm intrigued by the posts on bleeding the master cyl. Would I do that by loostening the hard lines from the master cyl ?

Finally, I'm assuming I should do all this without engine running as servo pressure won't necessarilly help ?

As ever, any advice from thise who've been thru similar would be great !

Thanks, Rich
 
You must log in or register to reply here.
Back
Top