vacuum brakes

[mechanical73]

hey guys, wanted some input from those of you who have converted over to vacuum.

I found an early eighties cutlass supreme vacuum booster and master cylinder. Then I tee'd into the PCV valve and bought a new check valve and filter and proceeded to install it in my 84 T-Type.

I've heard that the pedal should be changed as well but I didn't have one so I had to drill the pushrod on the master cylinder to get it to fit on the t-type's pedal.

After bleeding the master on the car, then bleeding each wheel (i've done it using both methods: farthest wheel to closest and vice versa) the pedal goes right down to the floor even w/ the car off. There were no bubbles left when I was done w/ the bleeding and I actually wound up flushing the entire system w/ new fluid due to the extensive bleeding.

I didn't check the booster prior to installing but if it had a bad diaphram it would give a firm pedal with the car off then get soft when the engine is running.

At this point, I'm really frustrated as to what the problem could be. Does it really matter if I didn't bench bleed the master if I bleed it in the car ?

Am I incorrect in my assumption regarding the booster diaphram ?
I actually stopped by Sears and picked up a vacuum tester unit to check the unit on the car; can this be done while on the car ? I would imagine so right ?

Did I tee in at the wrong place ?

Could the proportioning valve be shot ? how do you trouble shoot it ?

Is the fact that I used the t-type pedal causing incorrect master cylinder functioning ?

One thing I'm not too comfortable w/ is that even after all the bleeding i've done - i keep noticing some small specs of dirt/rust in the reservoir.

I forgot to mention that I installed new brake lines from the proportioning valve all the way to each rear wheel cylinder as I had a leak and wanted to be sure it was corrected. The fronts are fine.

Anyway - let me know what you guys think

thanks

Nelson

 

[bruce]

Originally posted by mechanical73

I found an early eighties cutlass supreme vacuum booster and master cylinder. Then I tee'd into the PCV valve and bought a new check valve and filter and proceeded to install it in my 84 T-Type.

I've heard that the pedal should be changed as well but I didn't have one so I had to drill the pushrod on the master cylinder to get it to fit on the t-type's pedal.

The booster has to have it's own line/ source for vacuum.

You have to use the correct pedal, to have the right ratio, and geometry.

 

[mechanical73]

pedal

do you know this for a fact ? have you had both pedals side by side to see what the difference is ? and if so, what is the difference ?

what exactly is the problem if the stock PM pedal is used w/ the NA booster/MC ?

 

[bruce]

Re: pedal

Originally posted by mechanical73
do you know this for a fact ? have you had both pedals side by side to see what the difference is ? and if so, what is the difference ?

what exactly is the problem if the stock PM pedal is used w/ the NA booster/MC ?

Yes, I've looked at both, side to side.

The pivot pin, for the pushrod is in a different location. So the pedal ratios are different.

 

[Red Regal T]

It is a mistake to use the PM pedal unless you move the pivot. Much easier to get an NA pedal. The pivot pin is around two inches higher on the PM pedal, so a vacuum cannister rod does not line up with a PM pedal pivot pin. Also, the diameter of the pin on the PM pedal is larger than the hole in the push rod on the vacuum cannister. If you break the plastic collar on the booster, which may happen with the rod in improper position, you can toss the cannister, because it won't hold vacuum.

 

[mechanical73]

pedal

Thanks for the info.

I picked up a NA pedal today and hopefully that solves the problem. If not, then I don't know what else it could be ?

how do you check for a bad booster or proportioning valve ?

 

[mechanical73]

I got a new booster and finally have brakes !

As for my question on where to tee in for the vacuum line to the booster - it seems that you can tee into the pcv hose. No need for a TTA block as some of you pointed out.

so a quick summary of what I did was:

MC, booster (along w/ new check valve and filter) and pedal from 87 NA Regal.


thanks guys

 

[bruce]

Originally posted by mechanical73
- it seems that you can tee into the pcv hose. No need for a TTA block as some of you pointed out.

Wait a while. As your engine ages, and you have more blow-by, you'll be adding the TTA vacuum block, due to the lose of vacuum signal.

If you want to ignore advise, that's fine, but you might be sure of the long term results, before saying what you were told, wasn't true.

Justa FWIW...

 

[mechanical73]

tta vacuum block

have you had such a problem ? where did you get this info ?

What difference can it make to tap in at the PCV or at a junction block ?

If an engine has that much blow-by that it would cause such a drastic situation as to substantially reduce the vacuum signal then its time for a rebuild.

if you know something for a fact then please by all means state what you know and what its based on other than just assumptions.

 

[bruce]

Re: tta vacuum block

Originally posted by mechanical73
have you had such a problem ? where did you get this info ?

What difference can it make to tap in at the PCV or at a junction block ?

If an engine has that much blow-by that it would cause such a drastic situation as to substantially reduce the vacuum signal then its time for a rebuild.

if you know something for a fact then please by all means state what you know and what its based on other than just assumptions.

Yes, I've had the problem.

The PCV is a controlled vacuum leak.

Not really.

An actual observation, no speculation was involved.



****
If an engine has that much blow-by that it would cause such a drastic situation as to substantially reduce the vacuum signal then its time for a rebuild.
****
Interesting that you can speculate, and express this opinion, as being fact, and then ask me *for what I know*.

Now, do you have anything to support your claim?.


BTW, I have a small collection of torched pistons, that still ran pretty well, and that had alot of blow by.


BTW, why do you think Pontiac redesigned the Vacuum block when a simple *T* fitting would have supposedly worked?.