Makita 4" grinder Model 9501B / rebuild

[RickP330]

Hey Gang,
I am a born again mechanic planning on starting an automotive project in a year or so while I finish up grad school. So I am going through my tool box taking inventory and re-stocking where necessary. I pulled out my old 4" grinder and become a little sad at all the abuse I put it through in the past 30 years. I had been accused of being stingy and should just buy a new one, but I have a tool list a mile long already - Plus this was one of the first real tools I bought myself back in the day. Of particular frustration was that I lent it to my best friend during that time and it came back with a taped up cord. Oh yea, just nicked it on you. Every time I put it away I cursed him for it LOL. also the detent in the switch lever broke very early on. Item 17 below. Probably very common.

Okay, so I bought a new SJ cord for the grinder and tried to find the switch lever but it is obsolete. I did find one parts warehouse that claimed to have it in stock but it backordered after I ordered it and I presume I'll never see it.

So the cord is relatively easy. To get the switch lever out requires total disassembly as it must have been the first thing installed. Pressing the stator out of the housing was the most difficult part. I thought I could do it with just a brass drift from the back end but I damaged a few of the laminations on the back of the stator in doing so, so I stopped. I made a cross bar and pressed it out properly. That Stator is really pressed in there.

So since I cannot seem to find the switch lever, I embarked on trying to restore it. The "detent" pad was worn flat. I put two small holes in it with a pin vise and carburetor jetting kit. Then I used a high performance epoxy (Loktite 9304) to build it up. I'll file it to size and cross my fingers. I mean it does work but you have to hold it in the on position. It would be nice if I didn't have to any more. Epoxy is drying now - 24hours.

Also I'll clean the years of grinding dust out of it and there is not much left to the brushes. I'll change those.

A question to the group. I did have to open the right angle gear case to take it apart. The old grease is solid as a rock and it's obviously running dry. I could use a synthetic wheel bearing grease. What should I put in there and how much?

I'll update on the completed project as I move forward. Please comments and suggestions welcome.

Am I nuts for wanting to restore an old faithful tool?

Rick

 

[RickP330]

Here is the cord gee don't do me any more favors dude LOL. That's a "nick"? I hate dumb *** repairs like this. Hiding under electrical tape for who knows how many years....

 

[American Locomotive]

I have yet to find a good grease for grinders. Seems like every grease I try just flings off the crown wheel and that's it.

 

[RickP330]

I have yet to find a good grease for grinders. Seems like every grease I try just flings off the crown wheel and that's it.

Yep, seems like exactly what happened. I was thinking perhaps synthetic grease might not harden up and flow back onto the gear.
RP

 

[The Cobbler]

actually a thin grease with a lower melt temperature so when it heats up it flows a bit . don't overfill the cavity thinking you're doing a good thing, it's not.
I have an old can of water pump grease meant for lubricating car water pumps, yes, at one time that was real... it seems to work well.
If you watch ( and it might be worth it for OP) Dean Doherty on you tube, he does tons of grinder repairs, he uses a very thin grease too
you do know that 4" discs are getting harder to find, the standard is 4-1/2" now, with a larger center bore

 

[jayemm]

actually a thin grease with a lower melt temperature so when it heats up it flows a bit . don't overfill the cavity thinking you're doing a good thing, it's not.
I have an old can of water pump grease meant for lubricating car water pumps, yes, at one time that was real... it seems to work well.
If you watch ( and it might be worth it for OP) Dean Doherty on you tube, he does tons of grinder repairs, he uses a very thin grease too
you do know that 4" discs are getting harder to find, the standard is 4-1/2" now, with a larger center bore

While not a great selection, for 4" discs, I've had best results locally at Ace Hardware. Not real cheap but get it now. I believe Menards carries a few also. May find cutting wheels but no flap discs/grinding wheels at Lowe's and HD.

 

[Wamsutta]

You might find that switch lever on eBay. That's where all the discontinued parts end up at. You gotta have the exact Makita part number though. Enter that part number into the eBay search box. From my experience with right angle grinders, the armature bearings are always the first to go.

 

[The Cobbler]

it does show as available here

 

[neophyte]

Here is the cord gee don't do me any more favors dude LOL. That's a "nick"? I hate dumb *** repairs like this. Hiding under electrical tape for who knows how many years....

All the older Makita tools I have, have had the cord sheathing go crispy over time.

 

[The Cobbler]

All the older Makita tools I have, have had the cord sheathing go crispy over time.

that's a trade mark of Makita, the cords are nice & flexible , but the outer shell deteriorates and splits apart

 

[RickP330]

While not a great selection, for 4" discs, I've had best results locally at Ace Hardware. Not real cheap but get it now. I believe Menards carries a few also. May find cutting wheels but no flap discs/grinding wheels at Lowe's and HD.

I am now noticing that. I picked up a two at Home Depot that's all they had. I guess I'll try to buy as many as I can find for now. Maybe it's time to replace it....

 

[neophyte]

4” cutting discs are a standard industrial size, although nowadays, usually used for pneumatic cut off tool grinders with a guard, rather than for angle grinders.
The 4” angle grinder size is more of an Asian grinder size, rather than a standard US size, since the grinders made by US tool manufacturers used to be 4-1/2” for the standard small size.
Still, 4” cutting discs should be available from industrial suppliers, and there are now longer life diamond grit cutting discs made for cutting metal, that might be a bit slower, but which also retain their outer diameter size, and which are far less likely yo fracture in use.

 

[jayemm]

I am now noticing that. I picked up a two at Home Depot that's all they had. I guess I'll try to buy as many as I can find for now. Maybe it's time to replace it....

If you like Makita with a slide switch, both the current GA4030 (4") and GA 4530 (4-1/2") have a slim barrel that's comfortable to grip. I have the 4" and like the grip in addition to low vibration, good balance and not too noisy. Shop around a bit and you might save $20-$30 off big box store prices.

 

[RTM]

I have a 4" Makita, and used to get my supplies here. They've restructured their page so my link isn't working to get just the 4-in abrasives and I'm on my phone so I can't really search right now.

Abrasives - Discs - Flap Discs - Page 1 - Klingspor's Woodworking Shop

www.woodworkingshop.com

 

[lotus_esprit]

If you like Makita with a slide switch, both the current GA4030 (4") and GA 4530 (4-1/2") have a slim barrel that's comfortable to grip. I have the 4" and like the grip in addition to low vibration, good balance and not too noisy. Shop around a bit and you might save $20-$30 off big box store prices.

The GA4530 is the lower end homeowner grinder. The GA9557 is the heavy duty industrial 4-1/2” grinder, it’s usually not much more expensive than the 4530.

 

[Boilerhouse]

Your story is similar to mine. I bought my 4 inch Makita sometime around 1984, then used it very hard for many years. Around 2020, it needed the same TLC as yours, brushes, cord and the switch no longer latched "on". I decided to keep old faithful, so for the switch I retrofitted a toggle switch, cleaned up the innards, new brushes and replaced the cord. I bought it when I was 27, and am now 67. I am sure it will likely outlast me.

Grinding, cutting and sanding discs aren't quite as common as they once were, but, for me, the easiest and quickest source is to go to my local hardware store that sells Makita tools. and have whatever I need ordered through Makita which I usually pick up a few days later at the store.

 

[The Cobbler]

I bought it when I was 27, and am now 67

I have similar stories, people won't be saying that with cordless tools

 

[RickP330]

actually a thin grease with a lower melt temperature so when it heats up it flows a bit . don't overfill the cavity thinking you're doing a good thing, it's not.
I have an old can of water pump grease meant for lubricating car water pumps, yes, at one time that was real... it seems to work well.
If you watch ( and it might be worth it for OP) Dean Doherty on you tube, he does tons of grinder repairs, he uses a very thin grease too
you do know that 4" discs are getting harder to find, the standard is 4-1/2" now, with a larger center bore

Hey,
I found Dean's you tube page - It's addicting can't stop watching - All I pretty much watch on TV is YouTube now. my wife thanks you LOL

However, I have not found one where he has repacked a gearbox yet. So, no mention on the grease he is using, but a simple search seems to indicate the following:

* Makita Grease SG No. 0, which is part number 042016-9A which is insanely expensive if you can find it ($50)
* NLGI a grade of 00 or 2 is a common substitute. Super Lube is a grade 2 grease for ($16).

Apparently weel bearing grease is not a suitable substitute. If you guys can think of anything simpler, please let me know.
RP

 

[RickP330]

Your story is similar to mine. I bought my 4 inch Makita sometime around 1984, then used it very hard for many years. Around 2020, it needed the same TLC as yours, brushes, cord and the switch no longer latched "on". I decided to keep old faithful, so for the switch I retrofitted a toggle switch, cleaned up the innards, new brushes and replaced the cord. I bought it when I was 27, and am now 67. I am sure it will likely outlast me.

Grinding, cutting and sanding discs aren't quite as common as they once were, but, for me, the easiest and quickest source is to go to my local hardware store that sells Makita tools. and have whatever I need ordered through Makita which I usually pick up a few days later at the store.

Boilerhouse: bought mine in '91 we are in good company. Local Hardware Store? They still have those?

I have similar stories, people won't be saying that with cordless tools

Cobbler: I am with you. I'll reach for a corded tool or a pneumatic tool first. My mentors told me they will never buy a car without a solid rear axle and an oil pressure gauge. History repeats itself. They will be laughing at me one day with my corded tools - but old age and treachery beats youth and enthusiasm every day of the week. Bring it on....
RP

 

[jayemm]

Hey,
I found Dean's you tube page - It's addicting can't stop watching - All I pretty much watch on TV is YouTube now. my wife thanks you LOL

However, I have not found one where he has repacked a gearbox yet. So, no mention on the grease he is using, but a simple search seems to indicate the following:

* Makita Grease SG No. 0, which is part number 042016-9A which is insanely expensive if you can find it ($50)
* NLGI a grade of 00 or 2 is a common substitute. Super Lube is a grade 2 grease for ($16).

Apparently weel bearing grease is not a suitable substitute. If you guys can think of anything simpler, please let me know.
RP

I'd be careful about using Superlube and verify that it can handle high contact pressure on the gears.

 

[RickP330]

Well this is back to the point where I need to pack the gearbox and run it. Settling the grease question has not been simple. I found an old thread here that is two pages long and spans a few years and basically goes nowhere.

What I have surmised is that it should be a NLGI-00 or -2 grease for high speed / pressure application.

It appears the grade 00 grease is more like an oil, where the grade 2 is thicker like a wax. The grade 2 melts as the gearbox heats up and lubricates the gears. I am afraid using the lighter grease in a very well seasoned gear box will lead to leaks at the seals.

I found the following. NLGI-2 with Moly additive. This has to fit the bill and seems reasonably priced. It is grade 2 and the moly additive should satisfy the high speed pressure requirements. I am going to use this and finish this project up.
RP

https://www.amazon.com/gp/product/B000KKJQL4/?tag=atomicindus08-20

 

[RickP330]

Okay Gang,
Just a follow up to this topic. Like I mentioned before there seems to be no consensus for the grease to use, so I'll document this here in case a future member digs it up.

I purchased the StayLube Moly grease and new brushes as well. I tried to use the same amount of grease I saw when I took the gearbox apart. I will say that old grease looked more like wax and was very hard. This grease is NGLI - 2, but it is very fluid. I did use it a bit and it seems fine, but time will tell. I'll try to report back in a month and update the thread.

Here's what I did:

1. Totally disassembled the housing and built up the detent switch lever with epoxy and sanded to shape. This part seems to be unavailable everywhere and even on Ebay. This involved pressing out the stator, which was a chore, I damaged it in the process and tried to repair it as best I could.
2. Replaced the electrical cord.
3. Totally cleaned out the unit and repacked the gearbox with NGLI-2 Moly lube
4. Replaced the brushes
5. Probably spent $20 - $30 bucks

In the end I still have a 30-year-old grinder where 4" disks are becoming hard to find. Jury is out if I should have just purchased a new one. I'll use this one till it drops now, let's see if has the guts to last. The detent switch is working but it's very stiff. I've been passing sandpaper under it trying to get it to break in a little faster, but so far, it's still not perfect.

Thanks for following.

Rick

 

[PFSard]

Great write-up. Hope you live a long life and that your effort on this tool outlives you.

 

[RickP330]

Great write-up. Hope you live a long life and that your effort on this tool outlives you.

I ask a lot of questions here and try to give back where I can. Thanks for following. I'm sure it will die in the middle of a big job - then I'll replace it. But at least I tried!!!

 

[Steve_P]

There have been multiple threads here about the gearbox grease and per them the "real deal" stuff is insanely expensive. You apparently need a 00 grease as the thicker stuff just sticks to the gearbox cavity wall once it's slinged off. 00 grease was used in the old Snapper riding mowers, and it's cheap, or used to be, but that makes me skeptical that it'd be suitable for this application; there's also a similar product from John Deere.

 

[dnschmidt]

The best grease I have found for grinders and polishers is either the 00 grease from Tractor Supply or Corn Head Grease from John Deere. Both are thin and the John Deere is thixotropic meaning it goes from semi-solid to liquid when under pressure. Any thick grease simply ends up on the walls of the gear case doing nothing.

 

[RickP330]

There have been multiple threads here about the gearbox grease and per them the "real deal" stuff is insanely expensive. ...

Yes, and that's if you can find it. I'd buy a new grinder first I think it's on the order of $30 - $50.

thicker stuff just sticks to the gearbox cavity wall once it's slinged off. ...

I believe that when the gearbox heats up It may melt and drop back into the mix of moving parts. Keeps the bulk of the grease off the gears maximizing efficiency. But that's just a guess.

As a compromise I bought this $9 tube. On first use it seems to work well. Last night I made 2 dozen weld coupons. I don't have a shear, so I cut up 16 ga sheet metal with a wiz wheel. I probably spent 15 - 20 min deburring the parts using the Makita. It worked just liked it always did, nothing seemed to overheat or run improperly. The grinder sound sounded like it was the same exact speed although I have no way of quantifying that. and I didn't notice any leaks. I'll double back here in a few months to follow up, but for 9 bucks in an old tool it seems to work just fine.
RP

PS the switch is breaking in nicely, the question will be will it last once it works normally again....

 

[RickP330]

Just a quick follow up on this grinder. I've been through two disks since last posted and it's humming along perfectly. Yes, finding the 4" disks is becoming a problem now. I found a sleeve on E-bay and should probably pull the trigger before they are gone.

Suprisingly the brushes took some time to break in. I just kept getting more and more powerful till it settled in. Grease stayed inside and it just barely stays warm after a long hard use. Switch isn't perfect, but it stays on when clicked in.

In general real happy with it for the moment. We have to keep these old school tools going.....
RP