wcsinx

You can mismatch rods on either side of the booster. There's a short and long pedal side rod version of the booster. C3's use the long. The reason I did not think this was your problem is because it's really freaking obvious when you do this because your pedal rests way too low (should be about even with the clutch), your brake lights will stay on, and if you try to yank the pedal up you'll feel a *pop* as the pushrod unseats from to booster bladder. I personally went through this, and even with this situation I could lock up my wheels without bottoming out the pedal.

Now on the MC side, there are shallow and deep well pistons which use short and long pushrods respectively. The reason I did not think this was your problem is again because it's really freaking obvious. If you have a shallow well piston, the booster rod should be roughly flush with the lip of the booster port. If you have a deep well piston, it'll stick out by about an inch. I really think you would've noticed upon assembly a mismatch here. Furthermore, 1" is a BIG difference in the stroke of that piston, and I have serious doubts that you would ever be able to lock the brakes with that setup. But hey, pop that MC off and verify. It'll make Golden happy. You don't even have to crack the hardlines off.

They are not. There's some thread at the end of the pedal side rod, but it's very little and I do not believe it's meant to be used for adjustment. The rod should be seated in the pedal arm.

wcsinx

Well there's definitive proof right there that it must be a problem with the pushrods!

No, I said that was the most likely culprit.

They are known to leak introducing air into the system, and many people have difficulty purging this air.

I guess you also missed the part about how the behavior of brakes changed. He can now lock up all 4 wheels which is something he could not do before changing out that valve.

pauldana

i have the shallow hole or dimple in the M/C.... wih the willwood it comes with a ~1" long center plug so it can be used with both. if you were to remove the plug so as to work of the PB with the longer rid, there would be o, none, no brakes at all...and this is the larger M/C bore, 1 1/8" i think....

thx... p:-)

wcsinx

correct (bolded)

Golden, read this post carefully for the love of god.

pauldana

on the current PB, the "PIN" can be removed, i remember it being ~2" in length and as stated earlier, the M/C does has the divot..

wish i could adjust that rod/pin

pauldana

1. i will pull it later this week and pop some pics with a ruler or???

my brake peddle is up, all the way up... but that could be due to the spring return... again, the first ~1" of peddle travel feels as if i am ONLY pushing against a return spring, then after that it starts to work


2. Yes i have seen exactly what you are talking about... no adjustment there worth talking about...


Note: yesterday i had my son push on the brake peddle very slowly, and as he did, with the M/C removed, the rod coming from the PB also moved. IE, as soon as the peddle is moved, the rod between the M/C and the P/B moves.... i guess the question now is, is the rod in contact with the M/C before movement, or is there space there before contact? if so how much?

but why did it do the "pop" and bad brakes in the panic stop 20 years ago? no rod change then?????


this is way harder than it should be!!!!

wcsinx

It sounds like you already checked this, yes? You know that you have a deep well piston with a spacer mated to a shallow well booster, right? So I don't know what else there is to check unless you have the completely wrong booster or MC for your car.

In my experience, that return spring isn't nearly strong enough to unseat the pushrod from the booster. I maintain that you would know if this was your problem.

wcsinx

Then you have proved correctly that the pedal rod is not your problem.

Again ... shallow v/s deep well piston, it's a yes/no thing. There's no adjustment there. The only way I could see that being an issue is if you have the totally wrong MC or booster. If you're feeling ambitious, you might actually get out a caliper and measure all the resting lengths/depths. You will have to remove the MC though. There should just be a nuthair of play between the pushrod and MC piston.

Well despite Golden's naysaying, the *pop* is indicative of that valve moving around. The reason that valve moves is because of a pressure imbalance most often caused by air in the system which is most often caused by a leak be it in the valve itself, the MC or the calipers. Even having repaired the leak, you may still be dealing with air.

pauldana

just got this pm...
Check your pedal travel with the engine off. Pump the pedal 3 times to purge the vacuum from the booster. The shop manual spec. for pedal travel is 1.8 inches with 80 lbs. of force applied to the center of the pedal.


So i went out a measured just a sec ago... drove it to work today as it is going back into pant for 3 days for some touch up work,,,,

i have ~2.2" of peddle travel...

Golden

I don't care what you attempt with back tracking and distractions, you said it was the valve and it wasn't

wcsinx

And I don't care what sort of misinterpretations you care to make about my posts. At every step of way, I maintained it was the most likely culprit. Nothing more nothing less ... anything else was your own fabrication, Golden.

Furthermore, nothing Paul has posted rules it out! If anything, it was confirmed. By his own account, 1. it was gunked up (I know you don't think that matters, but as usual you have the diagnostic ability of a decapitated rat) 2. he went from being able to only lock up the rears to locking up all 4 .. HMMMM valve imbalance maybe!??!

But as usual, you're only going to read the parts you like and ignore the rest e.g. how he eliminated your pushrod theory (actually he did this a long time ago). I know how you operate, Golden.

427V8

Wow this thread moves fast, I'm getting confused...

having your son push the pedal with his foot isn't good enough. You need to get in the car with your head in the foot well, grab the push rod with two fingers of one hand and wiggle the pedal with two fingers of the other hand. close your eyes and feel the force luke.

you should be able to feel just a slight movement before the push rod contacts the booster seat.

And like someone above said, there are two places to check. I'd be surprised in fact if the Wilwood booster hole was the exact same depth as the stock MC hole. That one is harder to check since you can feel it nor can you reach the pedal and the MC at the same time.

And of course, listen the old man Gene, is the booster good?

wcsinx

The difference between the short and long pedal rods is huge. It works out to ~2" of pedal travel IIRC.

pauldana

thx... when I get her out this weekend again, I will pop the MC and do some feeling and measuring...
Does everyone agree that if the peddle will not pump up, that there is no air in the system?

as far as the booster, its days are limited, HB will be in a couple of weeks....


thx

so, that would rule our the wrong size rod.....???



still wish i had a physical picture or mechanical breakdown drawing of what is inside the PB... may answer some questions..

wcsinx

No

Based on your description, yes, I would think so. I have personally seen what happens when you put the short pedal rod booster in a C3. Trust me, it's obvious.

pauldana

well then.... once the PB is replaced with the HB there will be nothing left in the system that is not BRAND NEW, except the hard lines...

air.... where does it hide?......


hope the end is near....

noonie

It’s not a question of long rod vs short rod. You are using mismatched parts and the rod has to fit what you have, not the oem stuff. You may have to make your own rod so it fits precisely. A few thou of preload won’t hurt but play will drop your pedal.






I hope you realize that the hydroboost doesn’t come with a “magic” rod, you will have a rod issue with the HB too, have to have one that fits your combo or an adjustable.


Just one question, when wheels are jacked up, can you feel resistance from the brake pads while spinning? You said you went to oring seals.

Peterbuilt

Here's a picture I found in the 74 Service Manual. I've never taken a booster apart but if one of the 3 springs broke could that have been the 'clunk' you heard?

Also where is the seal you changed to stop the leak?

wcsinx

The only non-oem part he has is the MC. I've never had any experience with Wilwood. Is this an issue others have had with their MCs?

wcsinx

Can you describe for us in detail your bleed process? Did you beat the crap out of those calipers with a rubber mallet? Air loves to hide in the cylinder wells when you're bringing up a dry system.