The Stovebolt Site Forums The Parking Lot Big Bolts 1972 GMC 5500. Question about VIN and a few others!

Hello! So I just bought a 1972 GMC 5500. For the most part the truck is in good working order. It has typical age appropriate wear and tare problems. It has a hydraulic dump stake body that works fine.

I can't find a decryption key that matches my VIN. If anyone can tell me what it is I would appreciate it. Also since this is the oldest one I have ever owned, this number seems to be missing a few numbers but I could be wrong. TCE53WV500742

Does anyone know of a good vendor for replacement body parts or would it be easier to get them fabricated?

Also, it needs a brake master cylinder. Are there any vendors for replacement parts that I should be aware of?

Lastly, I am looking for a shop manual for it but all of the copies I have found are not a full mechanical break down.

Thanks a lot!

Hy comeaud, welcome, on the back of your glove compartment door there should be a plate which gives you the trucks model number and equipment list, could you post that on here. I have looked in my parts book and I can't find an exact match either.

Comeaud,

Welcome to the world of older GMC large trucks.

I have a 1966 GMC HM5500 and found the following site helpful in decoding the VIN. It is not easy to follow, and didn't work for my truck's wheelbase, but was otherwise helpful.

http://6066gmcguy.com/TwoTon.html

Finding parts has been a challenge for me. In some cases, I have needed to figure out what fits from other models. It helps to get a GM part number that can be cross-referenced to parts store numbers, such as NAPA. And there are dealers who specialize in some part types, such as master cylinders.

Good luck!

Thanks for the Welcome!

@3B, Ill take a look at that and see what I can find. If there is anything there I will post it!

@JRMunn, Thanks for the link! I'll be looking it up.

This is the largest truck I have ever owned so there is a bit of a learning curve for me. For example, the brakes on the truck "work" but you need to pump them up a few times to get any pressure. There are no fluid leaks to be found and when the pressure does build up it stops perfectly. Also there are two brake boosters under the driver's side of the cab. Unless there is some internal failure inside the boosters that I cannot see, I do not know how to test them. My first thought was the master cylinder because it mimics issues I have seen before on smaller trucks.

Anyone have any thoughts?

Hi,cumeaud! Welcome to the "'Bolt"! Front clips should be easy to come by. If you can find out who buys old buses,that may help. My friend has 4,'67-72's and front clips are all in great condition. Cabs are the same as a pick-up. vendors,such as L.M.C.,and Jim Carter,(just to name a few),sell just about everything for the cab,wiring,even engine overhaul kits. Check the "Swap Meet"section,to help find (Big Truck) parts. If you up-grade,and have parts to sell,please post them on the "Truck Parts For Sale" A good source for brake parts is N.A.P.A.From what I've read,they're able to order a hydrovac,and have it in their inventory,in three days,so I'd think the M.C. should be about the same turn-over rate. I see "Big Truck" shop manuals,all the time,on "E-Bay". once you're logged-in,try typing 1972 Chevrolet Medium And Heavy-Duty Truck Shop Manual,under Topic: "E-Bay Motors". Hope this helps. Good Luck,and please send some PIC's!!

I'm not so sure that the cab for a 67-72 big truck is the same as the pickups. I think that the cowl may be different at the bottom for the fender. I think that the front bottom of the door is also cut out for the fender.

So I located that panel in the glove box. According to it, the truck model number is CE 56403. There is obviously more information on it than just that number. I took a picture of the whole panel but can't find a way to attach it to a message thread. Is it possible to do that?

I did a little research and I can only partially Decode your VIN.

As you may know GMC's are not easy to Decode like Chevys are.

It looks like:

T = GMC
C = Conventional Cab
E = V-8 Engine
5 may mean 2-Ton
3 = Cab and Chassis (No Bed)
W ?
V = Plant (Pontiac, MI) ?
500742 = Serial Number starting with 500001

Double check the "W" as it looks like the next Number should be a "2" for 1972

Maybe someone out there can also add some more to my info.

Bill

Hy comeaud, thanks for the model number, that breaks down as follows, your truck has a 149" wheelbase a GVW of 24,000 lbs., the standard engine was a 350 cu. in.(small block) with a 366 cu. in. (big block) as an option, hope that helps.

@C10-C90 Bill, I just looked at the VIN again, it is a W. I'm not sure what that W means at all.

@3B, Thanks! I am pretty sure it's a 350 but 100% sure. I'm sure there are casting markings to look up. I do know that the timing is not the same as what the standard 350 calls for. It is off my one position, counter clockwise.

I do know that the brake parts are proving to be challenging. When I look up a 1972 GMC CE, CG, CS, SE, SE, SG, SM, SS, TE, TG, or TM 5500, the only master cylinder I can find doesn't resemble mine at all. Mine is much bigger than the one they call for. I found one that looks like it by looking up tucks in the series such as the HM, JM, RM, TM, AND WM 7500. It comes up as a Raybestos part number MC36346. Does anyone know why my truck as a 2 ton would would have a larger master cylinder?

Also if anyone knows how to upload pictures to the forum, I would be glad to share the progress I'm making!

Hy comeaud, does your truck have a single braking system or a dual braking system? The Raybestos website lists two different single system master cylinders possible for your truck, MC36229 1 1/2" bore and MC36289 1 1/4" bore, hope that helps.

Comeaud,

Brake parts can be a challenge. I had a hard time finding a new master cylinder for my 1966 GMC HM5500 because it combined the brakes and hydraulic clutch in the same housing, the size is larger than what was used in lighter trucks, and the original part numbers led to discontinued parts. I finally had to resort to finding a housing with the same bore and "stroke" measurements as were given for the original parts and the same bolt pattern based on available pictures. But it does work. You can also have your current unit rebuilt, with a sleeve if needed.

Since you have a big truck, it must have some sort of brake booster, which can further complicate your search for parts. Also, your truck is newer, so it may have a dual system that separates front and rear brake lines (this is a good thing). Mine is a single line system where the master cylinder line goes to a hydrovac booster located under the driver's side step.

Good luck! You are not alone. Others on this site probably have first hand experience with your year and model and can provide more advice about parts availability and dealer locations.

@3B, it is a dual piston master cylinder with a, 1 3/4" cylinder bore. I can only find it on the 7500 series trucks. I've noticed it has some pretty heavy parts for a 2 ton.

@JRMunn, it definitely is a challenge. I have found out that many of the part numbers that cross to the cylinder are discontinued. I haven't been able to find a new one but I did just this second locate a re-manufactured one through NAPA. I used the Raybestos link that someone posted as a reply.

As far as the boosters are concerned, there are 2 boosters mounted to the frame under the cab. I know the master cylinder is weak so I will find out shortly if it doesn't fix the problem!

So does anyone know if you can post photos to this forum? I'd love to share the progress.

You need to put your pictures on a photo hosting site like Photobucket or Flicker and then give us the link to them. On the bottom left of this page you will find a link to "Posting Images"...check it out.

Mike B

Comeaud,

I changed my master cylinder because it was leaking onto the firewall. If your master cylinder is not leaking, and even if it is, this is probably not the cause of weak braking. In the system you describe, with boosters located elsewhere, the master cylinder only needs to activate the brake boosters that do the real work of stopping the truck, so weak stopping performance is probably caused by problems in the boosters or downstream trouble with brake lines or wheel cylinders? As usual, others know more about this than I do, so I hope this will be corrected if I am wrong about it.

Hy comeaud, the GM part number is 685223 that translates to Napa p/n NMC P8568 $79.65 + $15.56 core, this master has ports 1/2"X 20 t.p.i. and 7/16"X 24 t.p.i.and is a 1 3/4" bore. My old United parts book lists p/n 39457 which translates to Napa p/n NMC P8551 $107.10 + $50.00 core this master has ports 1/2"X20 t.p.i. and 9/16"X 18 t.p.i. and is a 1 3/4" bore. Both these master cylinders have a four bolt flange mount, hope that helps.

@JRMunn, I'm getting braking power only if I pump the brakes 5 or 6 times. It doesn't seem to be making any hydraulic pressure. If you stand on the brakes The truck does start to come to a stop but it takes a while.

I figured that I would start with the master cylinder because its the cheaper option. All of the other components seem fine as far as the wheel cylinders are concerned and there are no leaks in any of the lines. Since the boosters cost 2 times as much as the master cylinder, and there are two of them I figured I would start cheap. Either way at least I will know all of the brake parts are solid.

@3B, I think that is the part I found and put on order. I will keep you posted.

@Mike B, Thanks! I'll set it up!

Comeaud,

You are beyond me at this point. I can think of only two suggestions, both of which you probably have already looked into. First, are you certain that all the air is out of the master cylinder line? This was easy in my case because there is a bleeding fitting on the master cylinder to let air out, and it is all downhill to the booster slave cylinder. Second, if you have vacuum operated boosters, is the vacuum line dis-connected, plugged, or leaking? My truck came with a big hole burned in the vacuum line hose where it had been touching the exhaust manifold (this was the worst of several vacuum leaks). I agree with starting at the master cylinder so that you know what's new from the start. If weather permits, I will be removing my hydrovac unit this week for rebuilding before fixing wheel cylinders - since I only have one, it has to keep working so the truck will stop!

You might want to get a pressure bleeder to bleed the system. You should also make sure that the brake shoes are all adjusted and also make sure all the return springs are good.

I agree with Don, adjust the brake shoes. If they are too far away from the drum it takes more fluid than can be pumped out in one push to make contact, hence you have to double pump. Make sure the MC is full of fluid or you will pump air into the lines which can cause the same feeling in the pedal.

To test the Hydrovac's put your foot on the brake pedal with medium foot pressure and then start the engine...as the engine builds vacuum you will feel the brake pedal fade just a little bit if they are working. If you try this after just having the engine running you'll need to pump the pedal 6 or 8 times with the engine off to bled off the vacuum reserve tank...

Hope this helps,

Mike B

Thanks everyone for all of the suggestions! Just as an update, before changing the master cylinder I lifted the dump to soak the 4 bleeders in the rear end in PB blaster. Upon inspection, the vacuum plate on one side has effectively been destroyed by rust. Something not all that surprising for a truck that has spent all 42 years of its life in New England. That being said, I have put the master cylinder project on hold. I now need to locate part numbers to replace all of the rear brake components. I am still going to attempt to bleed the system anyway to check the integrity of the rest of the system.
So if I cannot find part numbers for the parts I will have to disassemble the rear brakes and bring them to Fleetpride to see if they can match them up, that is unless someone has a better suggestion.

I will create a photo sharing account tonight and get some pictures it up!

If it were me, I'd replace all of the steel and rubber brake lines 100% front to back. The lines fail from the inside out...not worth the risk for an inexpensive and easy weekends work.

Be safe...

Mike B

Absolutely! It's getting the full treatment now. I was going to do some work on the body but I'm going to hold off and just get it mechanically solid.

Hy comeaud, are you saying that one of the vacuum booster steel shells is rusted through, or is it some other part? As to the other parts are you looking for wheel cylinder p/ns brake shoes and return spring kits?

@3B, As far as I can tell the vacuum booster is fine. The casing is in great shape too. I put a vacuum gauge on it and it was where it should be. The rusted parts I was referring to was the vacuum plate that attaches to the axle tube and holds all of the components. I will be needing to completely rebuild the rear brakes from the plate to the shoes, springs, cylinders, lines and hoses. Everything must go!

Hy comeaud, I think you are referring to the backing plate, if you are talking about the plate to which the wheel cylinders and brake shoes are mounted.In order to help you find the correct parts I will need to know the width of your brake shoes minimum, the diameter of your wheel cylinder bores will also be helpful. There are many possible options listed for your truck, from 15" X 4" brakes to 15" X 7" brakes. This is all assuming that no one has swapped the rear axle sometime in the last forty something years

As if this point I know it is a GM T130 rear end with the casting number 3873551. I am going to probably have to rip it apart in the spring. At this very moment I don't have a heated pace to work on this pig.

Just wanted to let you know that I set up the photo sharing site. There are only a few up at the moment but I'll keep updating.

Quick update. After further exploration, I found out that the previous owner replaced a brake line. That line supplies the pressure for both lower rear wheel cylinders, and those were the ones with the seized up bleeders. So obviously there was no way to bleed out the air. So as a cheat, i disconnected that line and bled it using a plug at the end of the line. Now the truck stops on a dime. The rear brakes are still going to need to be replaced in the Spring but at least I know that the master cylinder and the boosters are functioning. Until then, at least it can be putted around the farm.