71 340 Cuda, BRAKE BOOSTER ROD TRAVEL

[Manuel]

Hi,

Kindly request your help.

Mechanic said brake master cylinder had to be replaced, so we did buy a new one.

He opened up the original Midland Ross brake booster, changed some seals and the vacuum check valve,   diaphragm was still good.
He did NOT disasemble the center section because of not knowing how and suspecting it was not needed.

All was put back in the car but never able to make the brake pedal get hard when bleeding.

Bought another new pump!    I bench bleeded it,   same thing.   Bleeded again the 4 brakes,     Pedal goes to the bottom.
He adjusted the forward tip and it does get better but the wheels start to be locked with brake peddal out

I am not a mechanic but yesterday asked him to push the pedal with no master cylinder installed and noticed that its pushing rod will only move forward 3/8¨.
It only moves say the length of the nut that is at the tip.   Maybe 2 mm more than that.

Q. Is that not to short of a travel to really push the plunger as to create good preassure?
Plunger seems to have a travel lenght of maybe 1 1/4 inch?   So, that does not sound matching.

Q. If he did not disassemble the center section, what can be wrong?

Its been maybe 2 months,  two mechanics have seen it.    No luck...
Forward rod sleeve does not move with the rod, for some reason it looks like it was damaged ar the forward end and made a little shorter, would that affect??
Rear part of the booster has the rod that connects to the pedal, that rod has a plastic housing, that was broked and glued, dont think taht could affect something or??

Thanks for your ideas before I burn the car.      It was 6 months at the shop for paint!

[anlauto]

Did they mess with any of the linkage at the pedal ? Is it all back in correctly ?

[Manuel]

Thanks for helping out Anlauto.

I insisted on that and yesterday they assured me again everything on the pedal to booster rod attachment was correct.
They also said it could not be assembled incorrectly but will go today and check it myself to verify the travel range at the attaching point.

[Manuel]

Back from the shop.

Surprised to see that the attaching point from the pedal to the booster rod travels some 2 1/2 inches.   
Understand that the pedal needs to be pressed to obtain alignment, some travel is lost.

Booster is out so I could not measure actual booster pushrod travel at that point.

[anlauto]

So with the booster on the bench...on the input side, how much travel does the rod have inward, and is it directly equal to the outward rod travel on the output (master cylinder) side ? Or is travel being lost inside the brake booster ?

[Manuel]

Total plunger travel when bench bleeding must have been some 1 1/4 inch.

Booster pushrod to the plunger is only moving say 3/8" so we are missing about 7/8"

I asked the mechanic to measure the actual travel at the booster to pedal attaching point with the booster on to compare to what is going out in the front but he did not do it and booster is out right now.
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I just went back again to see the car and confirmed,  brake pedal is well assembled.   

[Manuel]

This is all the travel we are getting. 

Is it not too short??

[Dakota]

I can't answer your question about pushrod travel distance, but I do wonder about whether the gap between the end of the pushrod and the cup on the inside of the master cylinder has been checked.  After changing my master cylinder,  I had a lot of pedal travel before the brakes engaged.   It turned out that the gap was too large.   

https://forum.e-bodies.org/wheels-tires-brakes-suspension-and-steering/12/is-the-brake-booster-pushrod-adjustable-70-challenger/18970/msg242566#msg242566

I ended up buying this tool for the final adjustment:

https://www.zip-corvette.com/68-76-power-booster-to-master-cylinder-pin-adjustment-tool.html?gclid=CjwKCAjwt8uGBhBAEiwAayu_9R2xvwUGV3ULvLUv6-SYX0Fp4s3K8P1C8e3NXwDll8h0PciDiTDeOhoCrNkQAvD_BwE

[Manuel]

Thanks a lot Dakota

We did adjust the tip many times even making the rear tires become draging but never were able to get the pedal hard. 
We would feel a little at the bottom but still reach the carpet. 

All I can think of is to be loosing some travel inside the booster or that once the pedal mechanism is connected to the rear pushrod from the booster the travel is to short which I doubt. 

I will see again the booster since it is disasembled to figure out if something can bend inside. 

Muat say that the sleeve for the front rod is broken at the base and that the brown housing around the rear rod is also broken. 
Dont think that should affect the travel but may be an indication of sometthing not being rightly assembled. 
Mainly believe they broke those at the shop. 

Any ideas are more than welcome and thanks again. 

[Manuel]

This is the back side with the broken part. 

Forgot to mention Dakota, what a nice instrument, will see if they sell it here in Guatemala. Thx

[Manuel]

Would you all agree that the distance the back rod is pushed inn the front rod should go out?

[Dakota]

I have never looked inside a Mopar power brake booster, so what I'm about to write may not apply to our brand of vehicles. Based on this generic diagram of a power brake booster that I found on the internet, it shows a gap inside the booster between the input rod and the master cylinder push rod.  If this applies to Mopars, then the answer to your question is "no". 

[Manuel]

Have this one disassembled almost completely and it looks like rear and front rods of the booster reach a metal plate at the center.
Nothing to be compressed there.

   

[Manuel]

Well,  I had never seen the brake pedal mechanism under the dashboard until I wrote here and all looked normal.

Today we went and put the booster again in order to measure travels, magically the front rod of the booster moved some 1 1/2" instead of the 3/8".
I will never know if the mechanic had something wrongly attached and corrected it when I insisted on travels.

Must say that the front rod sleeve was broken almost at its base and the rod might have been slipping to the side but I don't see any marks from that happening.
I use epoxy and fixed that before assembling the booster.

Now the booster is not working but that will be chapter II   

Here some pics.

[Manuel]

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Seriously doubt that if the rod was getting out of center it could make for a 1" travel difference.