To shim or not to shim

[jonstine]

My starter on my M1028 died over the weekend. I checked voltage, wires, etc, everything was fine. I removed the ACDelco 28MT 12V starter that the PO had installed a decade or more ago. Based on the way it looks and after reading that some folks replace them more frequently than I plan to, I splurged for the POWERMASTER 9052. Didn't feel like messing with a decade old starter/solenoid and possibly have to replace it again in a year or two. No judgement for those that go that route, just not for me with something as important as a starter. The 9052 is arriving today, and before I crawl under and mess with it I have a question about shims.

The ACDelco 28MT that I pulled out had a shim on it. I know the original guidelines were to never shim, but I read on here while researching this that GM updated that to say it was acceptable if needed. Should I put the shim back on with the new Powermaster 9052 since the previous starter was shimmed, or should I try it without the shim first? It's such a tight PITA to work on that I'd rather only do it once, but I'm just curious if the consensus is that it should be shimmed initially or left off at first.

I will add that while I prefer to only do it once, it is more important to do it correctly, for the long haul. So, I will do what it takes to get it right. Just looking for some advice.

Thanks!

 

[TGP (IL)]

Pull the dust shield with the starter bolted up, engage the starter drive into the flywheel by prying it out and check the tooth engagement clearance.
A paper clip wire is close.
If you can't get it in between the teeth add a shim. If it fits leave it alone.
There are TB's and numerous threads about doing it and with the correct spec.
Search!
Tom

 

[smurph]

The short answer is shim if it needs it.

And how do you know if it needs shims? You have to measure! Listening doesn't cut it. Pull the solenoid off the starter where you can engage the bendix by hand. Mount the starter. Engage the bendix into the ring gear and measure the space between a ring gear tooth and two teeth on the bendix drive gear. It should be .030" to .040" Shoot for the middle at .035". Wire gauge feelers are the ticket.

If you are lucky, it will be there and no shim is required. But if shims are required, a shim on the outer bolt closes the gap and shims across both bolts open it up. Find the correct shim combination and take the starter back down, replace the solenoid, and bolt it back up with the shims.

There was a time when shims were never needed. The blocks and starters were machined close enough to spec that all you had to do was bolt it up. But something changed in the late 70's and it became shim-a-geddon.

Also, there may be a hanger bracket that attaches to the rear of the starter and the block. It has been a while since I have seen one of these trucks, so I can't remember if they used them or not. But most of the civilian trucks did. If it is there, put it back on!!! Especially if shims are used only on the outer bolt that reduces the starter to block contact.

 

[jonstine]

Got it. Thanks for the replies! Sounds like I'm going to leave off the shim at first, pull the dust shield and see how it looks. If it's good then put it all back together and see how she works.

Now I need to go find the starter bracket to engine bolt/nut combination from some hardware store and I can get this process going. That's still a M8 x 1.25 x 20 bolt, correct?

 

[smurph]

Not sure on the bolt size. I thought it was a 5/16 NC thread. I don't believe I ever really looked to tell you the truth. I just put the one that came out back in. Sorry.

 

[jonstine]

I bought several bolts at Lowe's last night.

This worked for me, found it listed on another thread here on SS: grade 8, 1/2" hex head, 5/16x18 thread.

Since it's not a combination bolt/stud I don't have to worry about the nut, but not sure what the overall depth of the new bolt should be. Bought 1", 1.5", and 2". I suspect after threading the 1" bolt in that it will be the one I use.

 

[jonstine]

Update.

I put the starter in, got everything bolted down tight, and the drive wheel on the starter wouldn't even fit into the teeth on the flywheel. So I pulled everything back off, replaced the original shim that had been in there, bolted it all back up, starter bracket and all, and it cranked right over. Sounds great, cranks immediately and starts so much faster than the previous 28MT GR starter. Big difference with the Powermaster 9052. Looking forward to the long term evaluation of this.

Thanks all that offered assistance.

 

[scottladdy]

Update.

I put the starter in, got everything bolted down tight, and the drive wheel on the starter wouldn't even fit into the teeth on the flywheel. So I pulled everything back off, replaced the original shim that had been in there, bolted it all back up, starter bracket and all, and it cranked right over. Sounds great, cranks immediately and starts so much faster than the previous 28MT GR starter. Big difference with the Powermaster 9052. Looking forward to the long term evaluation of this.

Thanks all that offered assistance.

Is your truck 12 volt or the original 24 volt? I know you stated the PO had installed a 12 volt starter. If your truck is still 24 volt I believe that powermaster you bought is 12 volt.

 

[Barrman]

Glad you got it running.

What are you going to do with the old starter? I like the old direct drive units and would be interested since you are so close by.

 

[edpdx]

I spent a lot of timje and money trying to figure out my starter problems. My 09 came with a 12v where there should have been a 28.

I ended up going through three starters and when I finally broke down and bought a WILSON I thought that would be the end of it... it wasn't. My starter needed shimming. A guy I talked to at the starter shop pointed out that some shops during the refurbishing process actually mill the mating surface of them and don't bother XXX'ing out the stamp that says DO NOT SHIP. The reduction of surface puts the starter too close to the flexplate and then you get clearance jams. My WILSON came with a shim so thick I thought it was some kind of wrench for application other than mine and tossed it.

I ended up with sticking problems so I began shimming. Measuring with a gauge was a ROYAL PITA so I just started with a medium shim as a stating point. Less sticking, but better. I added another shim nearly gone. Finally upped it to a single thick shim. All problems fell away... mostly. Once or twice a year I have to loosen the mounting bolts about 5 turn until I hear the jam free. Then I tighen everything up and I am GTG. I keep a rolled sleeping bag mat and a 14mm socket on and extension in my console so the whole procedure takes about two minutes.

REMEMBER: If you go to start the vehicle and all you hear is a single "CLACK", you may need to shim- carry the 14mm (maybe it's 15mm) wrench and you won't have to call the tow truck.

Good luck.

 

[smurph]

There is more to it than just clearance jams. If there is not enough clearance, the bendix drive gear may or may not jam into the ring gear. If it doesn't, and you think all if fine, you may be wearing that ring gear out! And one fine day it will bite you when the paper thin gear teeth just strip off. And then you will find yourself pulling the transmission out and replacing the ring gear! Which is the mother of all royal PITAs. I have seen it many times.

Too much clearance can also wear the ring gear and bindix drive gear.

I do agree that checking with gauges is a PITA. There is no two ways around that! But it is the only sure way to ensure the correct fitment. Well... other than pure luck.

I'm just saying that it might be a good idea to look at the condition of the ring gear and make sure it is not wearing. Your sticking bendix drive may be just from starter movement. The rear starter brace prevents this, but sometimes they don't get put back on. So if your starter brace is missing and your ring gear clearance is good, then that could actually be the sticking problem. But if the clearance is not right, ring gear wear IS happening.

If the starter clearance is good, and the brace is on, there should be no reason to ever have to touch the starter until it just wears out.