The Stovebolt Site Forums The Shop Area Engine Shop sm420 drive shaft parking brake

I'm waiting on a shop manual for my truck (1955.2 GMC 150). It has an sm420 and what appears to be a drive shaft parking brake.

There is no shoe in the drum and without the manual I'm not sure what, if any, parts are missing. Is there any place that makes replacement parts for these? I'm not having much luck finding anything online.

thanks
Jeremy

There are no shoes. There's a metal band that wraps around the outside of the drum, with brake lining material riveted to it, and the long lever that's pivoted to the right side of the transmission squeezes the band down around the outside. Good parking/emergency brake, as long as it's kept adjusted properly!
Jerry

I disagree,
It should have an inner and an outer shoe, not a band around the outside.

Finding used parts is you best bet, you can have shoes relined, but as far as I know you won't find any of the hard parts new.

Grigg

Grigg,

According to the 1955-2nd Chevrolet Truck Shop Manual, Jerry seems to be correct. The 3/4 and 1-ton prop-shaft brakes are different in comparison to the 1.5 and 2-ton prop-shaft brakes.

A GMC 150 is a 3/4 ton truck. I would suppose (guess?) that 3/4 ton Blue Chip GMC and Task Force Chevrolet trucks are similar with respect to the prop-shaft brake set-up?

Thanks Tim,
I was unaware of a band type brake on an SM420.
Of the three I have and the countless others I've seen all have the double shoe.
I (incorrectly) assumed they were all the same.

What I've read about and never seen is supposedly some AD school buses used a "Tru-Stop" brake on the transmission, which I think is a disc brake, so far I haven't spotted one, but check under every AD bus I see.

Grigg

My 59 model 3800 had the external-contracting band brake. I was unaware there was a shoe-type brake on the bigger rigs! Nothing like answering from our own unique perspective, is there? I believe a serviceable parking brake could be fabricated from a rear disc setup with the parking brake shoes integral with it with a little adapting for a long-lever linkage and a short piece of cable. The disc section could be retained, or machined off at the user's discretion.
Jerry

thanks for the info and the link to the manual, now that I have an idea what it's supposed to look like I can get an idea of what exactly is missing.

I have a 1951 1 ton. It has ALL e-brake parts missing. I just purchased the hand lever. I have been trying to figure out how the system was set up, but I just learned today about the prop brake system, and I believe that is the type mine had. NONE of the pieces are there. I have been searching just this evening for a parts truck, but can't locate anything. Does anyone know the answer to Peterson's original question: Is there a place to get such parts? I have doubts that there is. The prop brake system seems interesting to me, as I have never seen such. But, I cannot figure how to get it back to working condition. Furthermore, I found an online shop manual that explains the system. It says there is an outer and inner shoe that should work to stop the prop.

Thanks for any advice!
Mike

Welcome to the Stovebolt

When viewing the rear of the transmission is there a a square or round peg at the 9-o'clock position (drivers side). If it's the square peg than it had the exteranal band, if it's a round peg it had the Dual Shoe brake.

These parts have been out of production for decades. Place an ad in the "Parts Wanted" section here on the Bolt or search your local bone yard...you might get lucky

Mike B

Thanks for that! I will check it tomorrow to see. I have searched the internet so many hours looking for parts. I will place an ad here! I can't find anything online.
Mike

I checked today, and it is definitely round!
Thanks for all of the information and help!!
Mike

Here are some pictures of Sm420 band type driveshaft brake. Also page 6-11 of the 1960 Chevrolet truck shop manual fig 24 has a picture

Just a suggestion- - - -I'll bet one of our talented tinkerers could adapt a hydraulic rear disc brake from a 3/4 ton or 1 ton truck to the output flange of an SM-420, and use a small master cylinder operated by a ratcheting hand lever to apply it. Since OEM parts are either missing or broken on a lot of trucks, a tech tip on how to fabricate one might be a good idea.
Jerry

The one I have looks like the pretty one up there. I have no idea what it came out of. None of the parts look too hard to make. After looking again mine has a different looking top. It came with 3 292's I bought.

Might just have to scrounge through yards.

Ed

Then it's a Dual Shoe type...the one's pictures in the above posts are Band type...completely different.

Post a picture of what you have so we can see what's missing...

Mike B

Search Ebay for "Chevy truck parking brake". There's a used drum, internal/external shoes, and some linkage for sale today for $75.00. No handle or ratchet, however. It's on about page 6 or 7 of the listings.
Jerry

Thanks! Yep--Mine is the drum set-up!
I just learned how to link up pictures. I hope these are clear enough for you. You will see that I have a mess to clean off of the transmission. But, I hope you can see how the lever (which I recently bought) is missing from the cab through the floor, as well as everything else.
Thanks again, guys!

Mike

Thanks Hotrod Lincoln! I will check that out!!! It is not easy to locate, that is for sure.
Mike

Mike, I have seen a few trucks in this yard with all the parts you are inquiring about.
http://ronsautowrecking.weebly.com/store/c1/Featured_Products.html

I imagine getting someone to take them all off is going to be the issue

Thanks sstock! I will check into that!!!!
Mike

I’m new to this forum but here’s some pictures of my e-brake that seems similar to your set up. Hopefully it helps.

Thanks Wedgele!!!
Mike

It's been a few years since I needed this, but I was able to locate and get the parts on the truck.

However, I had to remove the PTO shaft to the dump bed. I set it aside to work on it later. Well, later is coming this weekend or the next. So, Any advice on getting this thing back on? The brake on the drive shaft did not allow room for the PTO shaft to be there. I was even thinking about grinding off a bit of it to make it allow for the shaft. Someone told me that the drive shaft braking system has to be adjusted "just right" in order for everything to fit. Is there a particular piece I should concentrate on?

The drive shaft brake "shoes" had been re-done. They have a thick amount of lining on them. I wonder if that is a problem?

Any advice, as usual, is always very-much appreciated!