Powermaster motor cycling

[meanchicken]

I just finished overhauling my rear drums and front disks. I used ll NAPA stock replacement parts and used Dot 4 synthetic fluid. I bled the system thoroughly after pumpin it down and also syphoned off the old fluid from the bowls and replaced it. Peddle is firm after bleeding and the car stops great.

...but...
During my test drive, when slowing down or when sitting at a stop, I could feel the peddle vibrate slightly every once in awhile. While sitting at a stop with my foot on the peddle when the peddle would vibrate, I could hear the Powermaster motor run for a few seconds. The frequency of the power master motor turning on and off was as often as every 5 seconds or so (5 on....5 off for several cycles). Most often it would cycle once for a few seconds every minute or so while sitting with my foot on the peddle. The peddle only vibrates for 1-2 seconds when the power master motor first turns on.

Is this normal or do I have a new problem?

Thanks!
Tim

 

["Turbo-T"]

...but...
During my test drive, when slowing down or when sitting at a stop, I could feel the peddle vibrate slightly every once in awhile.

Does it feel like you're stepping on a plum when you apply pedal?

 

[meanchicken]

I'll have to find a plum and stomp on it to let you know.


The peddle doesn't seem to sink, it feels firm, but when the motor runs I just get that slight buzz on my foot for a second or two.

I'm mostly worried about when it was cycling on and off every 5 seconds or so.

What happens if the motor burns out....do the brakes still work manually?

 

[8UWITH6]

My WE4 does this. Its not as often as you say yours does. But about every other brake application I can feel the motor cycle once. The BRAKE light has never come on in this car.......... Brakes otherwise feel great.......

 

[POWERBRAKEBOB]

Hydroboost Vs Vacuum Vs Powermaster

Either the accumulator or the hydraulic check valve inside the P/M is not holding pressure, or the motor pump vanes are going away. The pump has to build up enough pressure to charge the accum, then open the switch to shut off the pump. When you pumped the booster/ master to bleed the brakes, it could have been on the ragged edge of the seals going away, and that finished it off. This happens with a lot of brake jobs, when the master is not replaced at the time.

 

[zeus87gn]

I'll have to find a plum and stomp on it to let you know.


The peddle doesn't seem to sink, it feels firm, but when the motor runs I just get that slight buzz on my foot for a second or two.

I'm mostly worried about when it was cycling on and off every 5 seconds or so.

What happens if the motor burns out....do the brakes still work manually?

I have a friend's P/M that vibrates like this. I haven't investigated yet, but I think his P/M motor mounts are rotten. His motor runs quite a bit but his unit needs rebuilding (internal leak caused by sitting too much). That doesn't mean to say yours is gone.

If the motor is only running for a second or two, the motor itself fine. If it keeps happening it won't be. You need to cycle your acc and time your system - aka Diagnostic test. You can determine the health of your internal seals and most likely eliminate the air that is probably in your acc.

Brake System

Yes, the brakes will work manually. BUT, they will be harder than a manual system to operate because they were designed to work at a very high pressure. The pedal will be very stiff. You will experience the dreaded "no brakes!" syndrome and run into a stationary object....like a mustang.

Z

 

[meanchicken]

I have a friend's P/M that vibrates like this. I haven't investigated yet, but I think his P/M motor mounts are rotten. His motor runs quite a bit but his unit needs rebuilding (internal leak caused by sitting too much). That doesn't mean to say yours is gone.

If the motor is only running for a second or two, the motor itself fine. If it keeps happening it won't be. You need to cycle your acc and time your system - aka Diagnostic test. You can determine the health of your internal seals and most likely eliminate the air that is probably in your acc.

Brake System

Yes, the brakes will work manually. BUT, they will be harder than a manual system to operate because they were designed to work at a very high pressure. The pedal will be very stiff. You will experience the dreaded "no brakes!" syndrome and run into a stationary object....like a mustang.

Z

Thanks, guys.
It's doing it far less fequently now, so maybe some air was trapped in my accumulator. I talked to a few guys during a Southwestern area turbo buick cruise yesterday, and they all agreed it's most likely the accumulator ball. I defintiely did not feel it before doing my brakes.

I also grabbed a few grapes...next best thing to a plum...from our kitchen fruit basket and stepped on them one at a time with varied levels of enthusiasm. Wife got pissed, but I can now say that the feeling I get in my foot when the PM motor first runs feels vaguely like stepping on a plump, ripe grape with slow pressure until it's skin bursts. At the point the skin bursts....that ddd feeling in the bottom of my shoe kinda feels the same as what I feel through my peddle.

Add that to the tech...

 

[POWERBRAKEBOB]

Hydroboost Vs Vacuum Vs Powermaster

Have you read the info on Hydroboost? If the engine is running, the hydroboost will stop the car, and better than it ever did . If th eengine is not running, then the accumulator comes in ewith pressure for 3 stops. If you are still traveling after that, The smaller master we use on the H/B is easier to push than the 1.250" piston used in the P/M. That thing about the plum was when a customer (country boy) used that term about his car, before he brought it in my shop. It's just something you never forget.

 

[meanchicken]

Have you read the info on Hydroboost? If the engine is running, the hydroboost will stop the car, and better than it ever did . If th eengine is not running, then the accumulator comes in ewith pressure for 3 stops. If you are still traveling after that, The smaller master we use on the H/B is easier to push than the 1.250" piston used in the P/M. That thing about the plum was when a customer (country boy) used that term about his car, before he brought it in my shop. It's just something you never forget.

When the PM goes out for good, I'm thinking about upgrading to a Hydroboost. How much do they cost and how difficult is the install? Do they come with a line kit for the GN, or do you have to build your own?

Thanks!
Tim

 

[POWERBRAKEBOB]

Hydroboost Vs Vacuum Vs Powermaster

The install is straightforward. Pretty much remove the P/M, and bolt the H/B in its place. The master lines are switched, but go right in. The unit bolts right up. If the car has been converted to vacuum, it takes one kind of mounting/pedal rod, and if it still has the P/M pedal, we re-use the P/M pedal with the angle bracket. We normally use stainless hoses to connect. There are 2 types. S.S. pressure, with 2 rubber type return hoses, or all stainless hoses, for a little extra. The hoses have the H/B end crimped on, and the other end is left long, to route where you want it. You can cut it easily with a cut-off wheel. We might offer the hoses preassmbled with a fixed length, if people want. We also offer an alum master, for extra cost, and powdercoat/chrome is available. I'm not supposed to list prices on the forum, but you can p/m, or call 800 504 1060 for prices

 

[meanchicken]

Thanks!

I'll give you a call when I'm ready...might have you hook me up for my 68 Camaro too. It's vacuum system is working well, but I have a buddy who installed a Hydroboost on his 69 Camaro and keeps raving about how much better it is than his old vacuum power booster.