Soft Pedal, suspect rear drums

[DaveR]

Checked a few things tonight.

Front pads were from a new loaded set of calipers. (installed before my ownership) Things look good, and the pads are basically right on the discs and not backing off. I don't seem to have an issue with the shims as far as I can tell.  Runout of the front rotors is .003 to .004".  More than I'd normally want, but in spec to the FSM that states max of .0059". I do not get vibration under braking and the braking surface looks good so I'm not inclined to replace them right now. They will soon be the only non new component in the braking system with the exception of some of the proportioning valves.

Rear drums have a run out of .020 to .025". Maybe even .030".  So quite a bit back there. I think I'll replace those as they are right around the max allowable diameter anyway. It makes adjusting them quite hard without a uniform surface to set them to. Shoes look decent enough with lots of material left, but for the low cost of them I may get new just to check it off the list.

The only two things really remaining are to replace those drums/shoes and readjust, and to smack the front calipers and bleed them a bit more. After that I will really be at a loss.... or i've just been creating a problem that doesn't exist.

 

[DaveR]

Also I read about a trick where I can clamp off the flexible lines at the front corners and check pedal feel in that situation. Maybe I'll do that and see if anything changes. Would be a good indicator if there is one or more corners that are causing issues.

[grannyknot]

10 hours ago, DaveR said:

Also I read about a trick where I can clamp off the flexible lines at the front corners and check pedal feel in that situation. Maybe I'll do that and see if anything changes. Would be a good indicator if there is one or more corners that are causing issues.

That made me start thinking about the condition on the flex hoses, are you sure they are all in good condition? An interesting test would be to clamp all four hoses right up next to the hard lines and see how the pedal feels then clamp them on the other end of the flex line so you can feel how the flex line affects the pedal feel.

[DaveR]

I mentioned the hose clamping trick to a guy at work and he STRONGLY recommended not to do that.  Thinking back I had the front two corners vice griped for about a week when I was doing my strut install. The flexible lines were newly purchased by me at the time, but I may replace them again in case I did any damage. Totally not necessary but for $5 a corner and with brakes, I will just do it. It does give me the opportunity to clamp them down again for testing though, which I will probably do... although I don't know what it will tell me really. I suppose it could isolate the MC entirely which might be useful given what I write below...

I am starting to suspect my master cylinder may be the culprit, and let me explain why I don't 100% trust it...

The master cylinder is a new 7/8" Sanyco brand. The guys who sold me the car were getting it drive-able out of 30 years of storage and they replaced the MC and the front calipers/pads.  What they didn't realize is that this swapped the circuits on my 71, and they were trying to bleed the front circuit that was connected to the rears since they didn't reroute the hardlines or something to that effect.  Compounding this issue is that the rear cylinders were leaking and spewing fluid out whenever you braked, and if my memory serves me one of the reservoirs had no fluid in it, or it drained out rapidly.... 

So yea, there could have easily been a time when there was no fluid at all in one side of the MC and the brakes were attempting to be bled a lot or lightly driven. I have no idea what this could do to the seals, but its bringing it back into the equation as a possible culprit. Especially since its right at the start of the pedal travel.

[grannyknot]

1 hour ago, DaveR said:

 Compounding this issue is that the rear cylinders were leaking and spewing fluid out whenever you braked, and if my memory serves me one of the reservoirs had no fluid in it, or it drained out rapidly.... 

If this is the case the brake failure sensor plunger thingy might be pushed over to one side and will need to be re-set.  I wouldn't use vise grips to clamp those lines, maybe just some C clamps with a couple thin pieces of wood or plastic to protect the rubber, there are also dedicated hose clamp pliers.

[Zed Head]

You can isolate corners by sticking a piece of rubber under the fitting at the end of a line, as a plug.  Something like a BB might work also.  You can also isolate at the MC to see if the problem is in the front or back.

The material inside the lines might not be as flexible as the exterior.  Clamping the lines will damage a thermoplastic, like Teflon.  You definitely don't want to clamp a stainless steel line.

[DaveR]

anyone ever seen a new brake drum with a groove cut out of it on the outside? Can't tell if its for balancing (if so its a big groove) or just an defect during production.

I would guess balancing, but I'm not super keen on the size of the cutout. Seems like quite a bit. Plus how can it need that much material removed to balance, and the other one needed nothing at all? A bit disconcerting. 

Edited May 18, 2017 by DaveR

[87mj]

I have a '71 and was having trouble bleeding mine out.  What would appear to be a successful bleed always resulted in poor braking performance.  I was sure I didn't allow air into the lines but I suspect I was wrong.  The thing that helped me was install speed bleeders.