Still pulling my hair out over this.

I pulled the MC and lengtheneed the rod between the booster and the MC. Now the pedal returns and the brkae lights go out with the motor off, but once the motor is running problems begin.

If I am driving slowly and lowly apply the brakes, the truck stops fine and the brake pedal returns to the top of its stroke. However, if I am going more than 20 MPH OR if I am park and the engine is idling higher than curb idle, I can step on the brakes and the pedal gets pulled to the floor away from my foot and stays there! Self-applying brakes! I can lightly pry up on the brake pedal and it will release, and sometimes it eventually comes back on its own. I am completely baffled.

The only thing I can think of is that somehow the booster (which is a remanufactured unit) has an internal failure that is applying way too much vacuum and somehow sucking the brake pedal down which actuates the master cylinder. The brakes are VERY easy to apply and it feels as if the booster is just too powerful.

Should I try putting the old booster back on? I hate just changing random parts and not doing true diagnosis, but I have bled the brakes many many times, verified that all calipers and wheel cylinders are working and not sticking, and measured the rod between the booster and the MC and adjusted it so it is the right length. Even though the booster is "new," the symptoms seem to be related to over-boosting, in other words the booster is over-assisting the brakes and actually sucking the brake pedal almost to the floor. I have never seen this before. Usually bake booster failure causes rough engine running when the brake is depressed or brakes that are difficult to use.

I might just go swap the old booster back on, but if anyone has any suggestions I would really appreciate it.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

it may seem asinine, but before swapping boosters again, I would pull the vacuum hose off the booster, plug the hose to the engine and see how the brakes feel.
it should take a lot of pedal pressure to stop but it should at least feel normal.

if the brakes are still goofy there is something else going on.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Well, I read your post too late. I went ahead and swapped boosters so I am back to the original Bendix booster in the truck. Unfortunately, during the swap the stoplight switch broke apart. And, of course, my truck has cruise control which uses a special switch that nobody stocks. Literally. I ordered what is apparently the last new one in the world from Rockauto. I can find a few NOS switches on eBay but prices START at $30 and go up from there. But I digrees.

I couldn't take it for a test drive because the brake lights don't work, but the pedal felt better and didn't seem to stick when I ran the engine and applied the brakes. I am trying to glue my stoplight switch back together and if that works I can do a test drive tomorrow.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

You're a step ahead of me; I was going to throw shade at that "remanufactured" brake booster. Cardone, is it? Their stuff is junk.

You're a hop, skip, and coupla jumps from Portland, home of Booster Dewey, who makes brake boosters walk, talk, sing, and dance. I always buy from him, never "remanufactured" crapola from parts stores. Y'might talk to 'im; odds are reasonably good he'll say "Ohhhhh, yeah, those have a fault where [something something something] and then [something something something]. It can be fixed; when do you need it?".

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I hear you Dan, I think that will be my next step. I have had bad luck with parts store parts, and have watched the quality decline sharply in the last few years. I am now actively using NOS parts when I can find them or else I try and find experienced, reputable small-operator rebuilders like Booster Dewey.

I think my re-glue job is holding on my original brake switch, so I am going to reinstall it and see how the brakes are doing. If they are working right, huzzah! My quest will be complete. If I still have problems, I will likely be shipping a booster down to Oregon and have them go over it. I am fairly confident the problem is in the booster portion of the brakes and not the hydraulic portion.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

I agree. Keep careful eyes on that switch; do regular brake-lights checks.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Will do. I had to reglue the original factory switch because it wasn't working right. I am glad I took it back apart because I was able to re-align and clean the contacts for the brake lights and cruise control in the switch. Now I have to wait a few more hours for the Gorilla Glue to dry and try it again.

Hey! The picture uploading works!

_________________
Casually looking for a Clifford hyperpak intake for cheap.

A picture of the Ramcharger. A very forgiving picture. It doesn't show the badly faded paint, rusted out 1/4s, and the rusted out and failed original muffler line. Still, it has a lot of good going for it, not the mention the fact it was a surprise present from my family.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

Now that you have the brake problem sorted, when does the slant swap begin?

_________________
1976 Feather Duster /6 4sp
1984 W100 318 727 np241
1972 'Cuda 340 4sp
1985 D250 360 46RH

Update! Brake problem is, in fact, solved! The switch back to the original brake booster solved the self-application problem. Rebuilding the original stop lamp switch solved the taillamp problem. Zip ties and gorilla glue for the win!

As far as the engine goes, everything, and I do mean EVERYTHING on this truck is/was original Chrysler parts. OK- the engine belts were new, and the guy who had it before me had the brake system rebuilt, but everything else was factory parts. To be honest, I think a slant is a smidge too small to power this big heavy brick around, especially since it has four wheel drive. Plus, I would have to track down another slant six transmission case and swap guts to make it 4WD compatible. Not interested and don't have the time right now.

I have my 76 D100 to scratch my slant itch. The Ramcharger is my daily driver, but the 76 D100 is my toy. I have big plans for it and its 225/727 drivetrain, it is just a matter of time and money. If you are familiar with Roadkill and Steve Dulcich's Mopar Muscle Truck, that is kind of what I am going for, just with a slant instead of a v-8. And Little Red Express exhaust stacks.

The Ramcharger's stock 318 will (eventually) be upgraded with a set of factory high-swirl "302" late 80s cylinder heads, an Edelbrock SP2P two barrel intake manifold (WITH EGR provisions), and possible a cam swap to a cam I got from Joshie225 years ago. The axles have 3.2 gears in them so this is never going to be a off-roading or racing vehicle. With 3.2 gears it will rarely get over 3000 RPM, even on the highway, so I am modifying the engine to maximize low-RPM torque. I have all the parts for this, it is, again, a matter of time and money. I want to get the heads checked out and possibly rebuilt before I install them.

I am happy that I can now actually drive this thing safely. But the next project is replacing the badly rusted out original exhaust system. Everything from the head pipe back has rusted out and failed internally. I think the backpressure is so bad that the engine only gets about 15-16 inches of vacuum at idle.

Thank you all for the input and assistance!

_________________
Casually looking for a Clifford hyperpak intake for cheap.

Ahh, time for another one of these, is it? Gonna run a cat? (meow!)

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Funny you should mention that. I have the last one of those that I bought sitting on the floor next to the Ramcharger and I have been puzzling how to fit it in there. It was last run on my brother's 83 Dodge van that had a spectacular catalytic converter meltdown. I saved the muffler, but there is still a little bit of converter matrix rattling around inside of it.

I am on the fence about installing another catalytic converter. Space is tight under a 4x4 Ramcharger. The short wheelbase, transfer case, and skid plate require careful measuring and planning to route the exhaust. I want to run the Walker quiet flow, but it is so long that I wouldn't have room to run the catalytic converter. The Walker 50051 is 38 inches long, almost twice the length of the stock Ramcharger muffler (21 inches). I am fairly confident the original (!) catalytic has failed, and I have a strong suspicion that one of the two check valves in the air aspirator system (no smog pump on this truck) has failed. Removing the lid on the air cleaner while the engine is running sounds like I have removed the muffler from the exhaust line. Anyway, we all know that catalytics and carbs don't play well together, and the last thing I want is another catalytic meltdown.

I need to get the old original parts out of the way and spend some more time test fitting and eyeballing things. I want to try and keep as much ground clearance as possible and use the stock muffler support points, if possible. I also would love to use those new type of exhaust clamps that actually use a thin metal sheet over the joints instead of the old u bolt style clamps, I just need to find a store that stocks them locally.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

This thread got me to thinking about the brakes on my 1980 D150. When I bought the truck the previous owner had disconnected vacuum from the booster making the pedal effort pretty high. I reconnected it and while pedal effort went way down the brakes became super sensitive. I learned to drive it this way but no one else can drive it without almost going through the windshield upon brake application. With the booster hooked up there is quite a bit of pedal travel but the truck does stop well. After reading this thread I suspect as I always have that the re-manufactured booster is faulty. I don't have the original to try so my question is, what is a good source for a new booster? Sure I could buy another rebuilt or if I can find one, a used one. Anyone have a trusted brand of rebuilt booster or other source for Nos?

_________________
“Buy the ticket, take the ride.”
― Hunter S. Thompson

Funny you should mention that. My 76D100 has brakes exatly like your 80 D150- any application of the brakes more aggressive than a light touch nearly locks up all four wheels and sends you through the windshield. My truck had the original MC and booster on it, so I replaced them both. The brakes got a little less touchy but are still over-sensitive. The problems got a little better when I got new tires. I had been running ten year old tires that had low mileage but the rubber had hardened and they had very little traction. Exciting in the rain with grabby brakes!

I still have the original MC and booster. I am eventually going to ship them to Booster Dewey (Dan provided a link in a post above) and have them rebuilt. If I were you, I would try to grab a booster out of a junkyard truck (MC, too, if you can find an original) and send them to Booster Dewey in Portland, OR, to be rebuilt. BOOSTER DEWEY LINK- CLICK ME

The only remanufactured units I could find were Cardone units, and they don't work. I am DONE with Cardone. You save money in the long run finding NOS parts or paying to have your originals rebuilt. Rockauto lists a "rebuild and return" service that costs the same as a Cardone booster unit, but I can't speak for the quality of that service.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

Reed, thanks for the good info!

_________________
“Buy the ticket, take the ride.”
― Hunter S. Thompson