PC 7424xp backing plate wobble.

[choijw2]

I just noticed my backing plate on PC wobbles little bit...

how should I explain this.... umm
if i put my PC with backing plate, flat on the desk, it will tilt left and right little bit. ..

is this normal??

I am using LC 6" backing plate and counter weight says use 6"
and used it on only 1 car with meg's MF pad and yellow pad.
it worked fine while vibrating my hands to numb at speed 6

[Mike Phillips]

I just noticed my backing plate on PC wobbles little bit...

how should I explain this.... umm
if i put my PC with backing plate, flat on the desk, it will tilt left and right little bit. ..

is this normal??

I am using LC 6" backing plate and counter weight says use 6"
and used it on only 1 car with meg's MF pad and yellow pad.
it worked fine while vibrating my hands to numb at speed 6

Is the compression washer installed? People sometimes lose it when they remove the backing plate as it can fall off and get lost on the ground.


Here's my article on this important little piece of the tool.


Don't use your polisher without it!


That is... the Compression Washer



If you don't use a compression washer, the rivets on the backing plate attachment base will come into contact with the counterweight assembly on your DA Polisher.

Damage caused by not using the Compression Washer



Damaged and Gouged Metal
The rivets have gouged the metal because the compression washer was left off. Not only does it gouge the metal it will usually make a horrible noise and that should be your first clue to turn the polisher off and inspect for issues.




Treat the compression washer like GOLD. Don't lose it.


Keep the little rubber nut to lock it into place when not using that backing plate. It's probably more likely you'll own more backing plates into the future than less likely.

The Rubber Nut - Keeps the Compression Washer from getting lost and protects the threads when the backing plate is not in use.


I have scads of backing plates in drawer in the studio and it's nice reaching for a backing plate and having the spacer washer intact with the backing plate.



The Purpose of the Compression Washer

The compression washer performs multiple functions,


Crushable Interface
The compression washer provides a crushable or malleable interface between two pieces of metal that are going to see a lot of pressure from being tightened together with a wrench and my guess is a lot of punishment from the operator. I punish all my tools... so it's not a reach to think others are going to punish their's too. Add to the above mix, the violent oscillating action of the tool on the highest speed setting and add to that t-i-m-e...

By time, I mean putting your polisher to work buffing out a car section-by-section, panel-after-panel. As Pros know and anyone that wants to get the job in a decent amount of time, when you start buffing out a car you have to keep the tool running and buffing on paint. There's no breaks. That's time of endured punishment.

Point being is you want and need the crushable interface between two pieces of metal on an electric tool capable of running at high OPM's.


Spacer
They also act as an actual spacer between the arbor or stud seat where there are the raised heads of a type of rivet or brad that anchors the arbor base to the the backing plate and the threaded portion of the Free Rotating Spindle Bearing Assembly.


Free Rotating Spindle Bearing Assembly




Here you can see a compression washer seated at the base or seat of the 5/16" arbor or stud where it's attached into the backing plate surrounded by the raised heads of the rivets or attachment anchors.




So keep track of both the compression washer and the rubber nut and don't use your DA Polisher, be it a Porter Cable, Meguiar's or Griot's without it.


Compression washers do wear out with use, that is if you remove and replace backing plates often you're going to wear your compression washer out.



Autogeek carries replacements...

Lake Country Compression Washers 5-Pack

[Mike Phillips]

If the compression wash is in place then make sure the backing plate is tightened down snug using your PC wrench.

If after doing the above the backing plate still wobbles it sounds like the bearing for the spindle is wearing out.

[ski2]

Once you get this wobble sorted out you might want to consider switching to a 5" backing plate and 5 or 5.5" pads. The Megs new THIN pads are excellent on the PC. You'll get better performance with less stalling when you put one some pressure. With the smaller backing plate and smaller lighter pads there is less mass for the motor to move. And there is no need to change the counter weight.

[choijw2]

If the compression wash is in place then make sure the backing plate is tightened down snug using your PC wrench.

If after doing the above the backing plate still wobbles it sounds like the bearing for the spindle is wearing out.

yes I do have compression wash in place....
oh man sounds like maybe i got bad unit, time to exchange i guess D:

[xan]

My plate did the same thing after about 3 yrs, anyplace to get repaired?

[MarkD51]

My plate did the same thing after about 3 yrs, anyplace to get repaired?

Sure, the PC can be repaired, and if you are adept at such repair, there are online parts suppliers in which you can purchase any needed parts, and do the repair yourself if the unit is out of warrantee.

Further investigation might be needed to determine the exact source of this "wobble".

Be prepared for some sticker shock with the prices on some of those parts though. Consider that cost for parts, and the additional labor costs, etc if you take-send the unit to a repair facility.

One day, I might get brave, and rip down my PC Machine. Sometimes poor lubrication, or lack of such can cause accelerated wear. Lube is good!

I tore into my baby Griots 3" DA some months back to find tons of grease where it wasn't doing one bit of good, not even on any drive gears, and two cracked in 1/2 motor brushes. Was getting louder than usual on a second use.

The unit didn't even have an hour's worth of use on it, and sure, I could've returned it to Griots, but I corrected such issues myself in a 1/2 hour's time, and no need to waste my money on shipping costs. Was nice that that machine did come with a pair of new motor brushes.

[dlc95]

it worked fine while vibrating my hands to numb at speed 6

I never have vibration problems with the PC, and a 5" plate.

Just for the heck of it I installed the 6" plate, and a 6.5" pad... It felt it then, and it was pretty intense! Dropping down to speed 5 took care of it, but I'd just as soon stay with the 5" set up.

Keep that 6" counterweight though. I had 2 PC's, one with the 5, and one with the 6. The heavier weight seems to give the spin more inertia. After selling the PC with the 6" weight, I got out the machine with the 5, and it felt like it was significantly weaker.

[mridan]

I have the older 7424 not the xp. There is also a small metal washer that came with the 7424. I use both the compression washer and the metal one, is this ok? Should I just use the compression washer that came with the 5" backing plate?