What can I do with my power disc brakes if I have poor vacuum?-UPDATE-FIXED!!!

[Mfr426]

Hey folks it's been a while since I posted. I had another daughter 3 weeks ago, finished a 6 month home addition and had a 9 month business project FINALLY come to an end so I've been doing everything but playing with my Charger. I currently have a dilemma that I need some assistance with.

I have a 69 Charger SE with a 71 383 "G" motor. I made the mistake years ago of buying the Mopar Performance "Road Runner cam" with the following specs: Hyd. - 284 / 284 Duration - 484 / 484 Lift. Keep in mind that this is a low compression motor (but is in very good shape). I have power disc brakes and they require a ton of pressure to stop the car. My buddy with a 68 RT with power DRUM brakes drove my car and said that the car was downright dangerous. He said that there is clearly something wrong. He seems to think it's the lack of vacuum from the aggressive cam. I'm inclined to agree.

Here's an interesting twist, I just got my stroker motor back after 5 months at the machine shop and soon I'll be installing this in my car. However, I will still be driving my car this summer until I can get the stroker installed. So, I need the brakes to work reasonably well until the stroker is installed.

My question is:  Do you folks agree that that cam in that motor would cause issues with power disc brakes? Keep in mind that all componets of the system are new (lines, booster, MC, calipers, pads, etc).  Second, does anyone have any ideas for a stopgap fix for this without replacing the cam in this soon to be replaced motor? I'll most likely take a vacuum reading this weekend but wanted to bounce this situation off the forum and the "experts".

I'll post stroker photos and details later this month.

Thanks all for any comments!

Mike R in Reading PA
69 Charger R/T Clone Project

[Charger-Bodie]

that cam really shoulnt create that much of a vaccum problem unless the gine is pretty warn out

[pandamarie]

I run that same cam in my 440 6 pack challenger and still have 21 inches of vacuum. with everything new I sounds like either a vacuum leak somewhere, check the whole headlight vacuum system, or if you didnt buy the MC and booster together the rod between them might be out of adjustment causing the loss of pressure due to a short stroke. open your MC cover and have someone push the pedal down and watch the piston through the holes, the seals should go past them, if its not its an easy fix, also did you bench bleed the MC to make sure there was no air in the system?

[Mfr426]

Thanks guys for the quick help. The booster and MC was not purchased as one and there have been several threads about that rod adjustment on this forum. The new MC's have plugs and new directions that indicate that you no longer have to bench bleed the MCs like you use to do. I'm hoping that it was the MC companies attempt to short cut the proceedure? I'll check for the range of that piston this weekend.

Thanks for the ideas!

[BrianShaughnessy]

What's the pedal like?    Long stroke? Does it go to the floor almost?   Does it pump up?     

[Just 6T9 CHGR]

I dont know how pandamarie got 21" of vacuum with the .484 purple shaft cam........myself including a lot of others were lucky to get 10" the most at idle

Mike did you actually check the vacuum at the booster?  "They" say a min of 19" will be sufficient to run the booster.

With my .501" Engle cam I am getting around 14-16" of vacuum and my brakes work beautifully.

I also agree with panda about the booster rod adjustment.  The way I did mine was to adjust the rod to get the slightest amount of movement in the master piston when bolting it to the booster.

In your situation I have heard of some 68-69 Charger owners tapping into the headlight vacuum can acting like a reserve...

if your manifold vacuum is not sufficent enough & the vac can trick doesnt work,  your next recourse would be to buy a vacuum pump.  MP brakes sells them but they are very pricey though


PS---ALWAYS bench bleed the master...trust no one! 

[Ghoste]

I have that cam in my 383 as well and I agree with Chris, 10 inches of vacuum is about the most.  That being said, it seems to stop my factory disc setup okay.  Nail the brakes a few times in a row and it becomes a little dicey, but...
No vacuum leaks anywhere, right?

[8WHEELER]

I have that cam in my 383 as well and I agree with Chris, 10 inches of vacuum is about the most.  That being said, it seems to stop my factory disc setup okay.  Nail the brakes a few times in a row and it becomes a little dicey, but...
No vacuum leaks anywhere, right?

  You are very lucky to get 12-13-lbs of vacuum out of that cam. I have run that cam most
of the years I have had my red car. I can't get 21-lbs out of some stock cams. I have tried the
vacuum can, did not notice any improvement at all, so MPB got my money for a vacuum pump.
Brakes will give you as many pumps as you need for great brakes, even if the engine dies,
of coarse, I would not know about that 

Dan

[Mfr426]

Hey Guys, when I checked vacuum on this about a year ago I had around 8 inches. I hope to recheck the travel of the piston in the MC this weekend. Pedal travel is about average and not to the floor. I bought an "EZ BLeeder" a few months ago and have yet to use it although I did the old "pump, pump, pump...HOLD" method several times. I may bench bleed it (again) but I dont have much hope that that is the issue as I did that (with the newer method) when I got the MC. I'd had this issue with the older MC too and I did the traditional bench bleed with that one as well.

Thanks for all the comments.

[Ghoste]

That sounds about right.  BTW, those specs aren't for the Road Runner cam, that's from the Street Hemi.  The Road Runner cam had more lift and less duration I believe.  Irrelevant to your question but in case you want to know.

[firefighter3931]

You will need to add a reservoir to help with vacuum as mentioned above. The 284/484 is larger than the old "street hemi" grind and has more overlap and a tighter lsa....both of which reduce manifold vacuum. The roadrunner cam will produce the best vacuum out of those three ;

Roadrunner cam specs :

268*/284* advertised duration
115* lsa
46* overlap
.450/.458 lift


Street Hemi cam specs :

280*/280* advertised
110* lsa
60* overlap
.474/.474 lift


484 purpleshaft cam specs :

284*/284* advertised
108* lsa
68* overlap
.484/.484 lift



As you can see....when the lsa is tightened up and the duration is increased the overlap also increases. The more overlap you have the less manifold vacuum it will make.  Other factors such as engine displacement, static compression and intake manifold selection will also influence manifold vacuum readings but the cam is a big "player" in the overall result. 



Ron

[bull]

Get rid of the booster and run manual brakes. Problem solved.

[daytonalo]

PIECE OF CAKE , THEY OFFER A  SMALL ELECTRO -VAC PUMP FOR THIS PROBLEM ! NOW FOR A REAL DELEMA , WORLD PEACE !!!!!!!!!

[Rolling_Thunder]

the .484 MP cam doesn't make vacumme at all...     i had one...    summarily removed it...        installed a bigger camshaft and went with a hydroboost unit...       maybe a vacumme pump is in your future ?

[Mfr426]

Hey all, thanks for the post and for the clarification on the cam name.

Now for the good news; I took a vacuum reading at the booster at idle with a warm motor and got a solid 15" of vacuum. I see that as good news!!! I know the motor has good compression (new rings, etc.) and this number tells me that my motor is in good shape and that vacuum is not my issue. My next step will be to make sure the piston is making the fulll travel (I'll need the wife for this test). The booster itself is new.

The only other adjustment is the rod that pushes in the piston. I remember we went over this months ago on this forum and many said that this was most likely NOT the isssue. At this point I'm going to check everything.

Thanks all for the comments...

[Just 6T9 CHGR]

Good news Mike.....read my post above on how I adjusted mine....

[Mfr426]

Hey Chris, I saw that comment about getting the slightest amount of movement when you bolt on the MC. The only problem that I had was trying to actually get that acorn style nut to turn on the rod. I didnt want to bugger up the rod with vice grips and that nut was pretty tight (perhaps tightened all the way in). Any suggestions?

[Just 6T9 CHGR]

The rod is knurled for the purpose of using pliers to hold it while turning the acorn nut....you wont damage it at all.

Do you have any threads showing?  IIRC when I had my "correct" master on I had about 2-3 threads showing.......they are all different though you have to adjust to your master

See here as well

http://www.dodgecharger.com/forum/index.php/topic,27395.0.html

[Mfr426]

Yep, I saw the knurl but had a hell of a time getting it to loosen. I'll try it again this week. The directions on the other post are much better than the ones in the FSM. They are way to basic and general.

Thanks

Mike

[is_it_EVER_done?]

15" of vacuum should be plenty to operate power brakes properly, so it sounds like you have either a bad booster, or a M/C with to big a bore.

Is there a difference in pedal effort between running and a shut off engine? Are you certain that the booster is actually getting vacuum?

Just to save you the time and trouble, adding a vacuum reservoir will not help anything as it can only store the amount of vacuum you already have (15"), so if it isn't enough now, a larger reserve won't change anything.

If you are certain that your booster is working and have access to any other M/C's, try a power drum brake one (1" bore), or an A-body disc unit that's 15/16th" bore.

[Mfr426]

One item that I neglected to mention is that years ago I put on A-body spindels from a 73 dart and did the swap from y 69 discs. I could not afford the calipers for the 69 so I had to do something. I did put on a new booster but referenced one for a 69 with power disc brakes. Dont know if that makes any difference here?

Thanks for the continued help...

[is_it_EVER_done?]

The conversion makes no difference. Did the stock system work before you changed over? After you changed the booster, did the brakes work properly?

What exactly do the brakes feel like. is the pedal hard but firm, or is it spongy. is the pedal high, or does it go close to the floor?

My guess is that you have a bad booster, but it's possible that if/when you changed the M/C that you got a big bore unit by accident.

[Mfr426]

The pedal is stiff and does not go to the floor. Christ, if I have to climb under that dash one more time for those 4 nuts I'm going to welll....welll...I'm going to have to do it...

[8WHEELER]

I just put a new booster on last year, the one before that lasted one year. The diaphragm was completely blown.

The rebuild shops these days can be good, or they turn out junk, they will admit to it. They told me
last year, they can go through 10 rebuilds, check them a week later, and only 7 out of the 10
are still working properly.

edit: OK you answered this while I was slowly typing.
Yes, How hard is you pedal? more often than not, if you loose your booster, your pedal gets harder.

Dan

[Mfr426]

OK...no laughing at this question...

I can go onto Advance Auto and they have boosters for my car (disc) for about $90.00. I think they were Cardone but am wondering if they are correct for my car??? I mean that from a functional as well as a visual standpoint...