The 1978 Sierra Build - I NEED YOUR HELP
 

Hey Guys,

I am new to the site- but already it's providing me a tonne of info.

I just picked up a 78 GMC sierra 305. 125,000km's

Everything works, no rust, straight as an arrow but there are, as expected, some quirks that I will be working through and will need your help!

I picked it up from a guy who bought it for his daughter 3 weeks ago, she didn't like it - my gain! Apparently it lived its life as a farm truck and was always barn parked. It sure looks like it, like I said 0 rust!

Anyway, I cruised it home in the middle of a heavy rain storm and found my first issue- water on the floor soaked up in the dampening pad: I hope that it came from the doors (They're not straight) but understand that it could've come from a multitude of places. I will be pulling the floor this saturday and bucket testing everything this weekend. If anyone has anything I should be looking out for please post it below.

2nd quirk - the "Fasten Belts" light comes on and off - does anyone know where the sensor is? or why this is happening?

3rd quirk - the stereo and CB make noise through the speakers but theres no tuning them into a station- I'm thinking the antenna is disconnected- but it also looks like it's in the windshield- can anyone confirm that that's what is in the windshield (it's all original glass)?

I'm planning on becoming an active member on the site and any help is greatly appreciated.



Thanks,

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

Good looking truck. I'll look forward to seeing more pictures and progress.

Regarding the leak (water on floor), I finally found the cause of my similar issue a couple of weeks ago after months of no success - the windshield seal is leaking at the top of the windshield. To test the windshield seal, remove all interior trim around the windshield, spray the outside with soapy water, then use a leaf blower from inside to force a whack load of pressure on the inside of the seal - you'll get bubbles on the exterior where any leaks are present.

I know there are many other causes of leaks, but that's my experience. Other things to check are the floor vents, if you've got them, and inside the cowl.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

My trucks an 85 GMC and my antenna is in the windshield. I do know from experience installing an aftermarket head unit, the antenna cord isn't long so it may be unplugged. I got tired of how short mine was and bought an extension. It was so short I had to put in my radio then feel for the cord and hole from under the dash. It's a good place to start though, check for your antenna being plugged up and let us know.

As for the other problems, I'm not sure. Doing the bucket method as you said should find it, get a helper one to pour one to watch! Goodluck

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

Welcome
the leak could be the kick vents seals(79 shown),
could be the area leaking under the fender(87 shown).
I understand the seat belt light/buzzer has a little timer built in,
I think my light and buzzer go for a bit only when starting... not if belt is on.
Stock antenna is in the glass,
some find the fender mounted ones are better in poor reception areas.
Is the radio stock/with CB (a lucky find)?
they need separate antennas,or at least a splitter.
some non- stock radios the antenna plugin hole is smaller

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

The windshield antenna actually works quite well if it's plugged in properly.
I lived in some very rural areas of upstate NY and Northern NH. I used the windshield antenna and got decent reception.
It's actually two cables and the wires embedded in the windshield.
There's a pigtail that snaps onto a connector button at the base of the windshield dead center like shirts from the 70's. This is the piece that most often gets fouled up by improper installation.
http://static.summitracing.com/globa...661pt_w_ml.jpg

The coaxial cable bolts to the steel dash just under the button and pigtail on the windshield. This portion of the antenna system is the only section that's shielded. If you remove the dash pad and speaker you'll find it's very easy to access and replace both parts or just plug in the pigtail.

Keith Seymore posted the following pictures. Click on the pictures and they'll take you to the original thread. Windshield Antenna Adapter

Looking forward at the windshield:
http://i23.photobucket.com/albums/b3...k/100_7736.jpg

Looking down through the speaker hole (disappears in the ductwork making it's way to the back of the radio:
http://i23.photobucket.com/albums/b3...k/100_7737.jpg

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

I wasn't sure if you have the combo radio cb, or a separate aftermarket one. If it is an aftermarket, or you are not sure if the antenna is attached, be careful not to push transmit until you have the antenna attached and ideally set up using a swr meter. Otherwise it could damage the unit.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

Hey Everyone, here is a small essay about my progress thus far!

Thanks for all the help and advice so far. My journey to have an amazing Daily really got underway yesterday; albeit with a few too many beers with friends in my parkade.

After pulling up the rubber floor and taking a look at the jute-like material a few things were apparent. Firstly, a small amount of water was coming in through the fire wall on the drivers side and a large amount was somehow only on the floor of the passengers side. Secondly, wet jute-like flooring under a rubber mat most likely never dries, is disgusting, and when disintegrating into moldy sludge on your hands when you're hungover is gag inducing.

Once we got the sludge out I cleaned up any surface rust that was present- surprise surprise - there was a new plate welded on the passengers floor. As it is a single ply plate with some sort of silicone over the welds we deduced that it was most likely sweating some water in. I scraped the silicone and then re-sealed the entire plate a few times; not the prettiest but I think it'll be effective.

Then I bucket tested the truck, starting at the cowl drain and inner fenders and working my way up. I noticed some old silicone material in the drain on the drivers side where the weld for the firewall is. Sure enough water was coming down the firewall and through the red gasket around the brake line. New silicone on the drain and today no more leak on the drivers side :)

The passengers side is much more complicated. After a bunch of testing, and a few more beers, we noticed that the water coming off the silver rain deflector above the passenger door was shooting straight into the door seam at the roof weld, further inspection revealed some sort of filler in the doorjam at that location, the water appeared to pool on the door seal, get behind it, travel down to the rocker, then leech out to the floor- At least I found my problem. We 'adjusted' (see- bent) the deflector out by a few mm's and that seemed to direct the majority of the water back towards the hood, one step in the right direction, then I got out my knife, removed the filler in the door and put some new stuff in there. Back out today to bucket test and the water isn't running down to the foor..... because, well, its just dropping straight in. Just did a bit of reshaping.

I think I need new door seals as the ones on there are falling off, so I'll pick some up tomorrow. Also, I am wondering if anyone has the upper door seals installed and if you think that will help? It doesn't look like they were ever there. Lastly, it takes a really good slam to close the doors so I'm guessing they're a little out- anyone have experience with this.

Luckily the kick plates and the seals there looked great, theres no rust on my rockers and I just seem to have this one leak now - and its visible. I purchased some double sided heat shield as well, so that if (see- when) it leaks again I, hopefully, wont vomit.

Regarding the stereo - I removed the CB- not sure if it was stock but it looks pretty stock, it was on a bracket under the console but it also had an Audiovox sound expander connected to it. It was easy to take out, with the power and connections just unclipping in the dash, there is a separate antenna wire that runs out to the passengers side of the hood where it was neatly placed so I can reinstall an antenna after paint. I will most likely wire it back in when I do the stereo. I am thinking about a retrosound - does anyone have experience with it? My next step is to wire the speakers directly to the tape deck to see if I can get some temporary tunes working.

I have some crappy pictures included of the passengers door problem.

Again, thank you for all your help so far (and I need it), once I sort this it's on to new door panels and a dash cover, then hopefully paint.

The pics show :

-the gross Jute
-the old filler (where the water was coming in)
-the new filler
-where the water leeches over from (on to some shop towels)
-where the water is falling directly onto now (dash)



Cheers,

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

Don't know why the photos are 90 degrees rotated. Sorry,

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

The way I have always water tested as shown many years ago. If the vehicle has A/C, close everything up meaning all windows,vents. Turn A/C on high and on Recir. Engine running of course, then soap the body seals down with very soapy water. The A/C is building cabin pressure and will bubble at air gaps.

Also high mounted rear bed lamp gaskets will leak and run down both sides of the cab .

Ken

This truck has no AC , no dash speakers, no headliner, stock. Base model 78 Sierra with the 305


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Re: The 1978 Sierra Build - I NEED YOUR HELP
 

So, I was tinkering around late last night and decided to pull my poverty caps off. To my surprise, the rim was white....WHITE!!!! I saoked the caps in CLR for about 30 mins and scrubbed them clean, now I'm wondering how I am going to clean the rims. Anyone have a good suggestion? Anyone ever seen em this bad?

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

If thats dirt and grease ,diesel,it will break down,or engine shampoo

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

On having to slam your doors so hard, I would suggest checking to see if the plastic has broken off the strikers. I bet it has.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

I use #0000 steel wool and simple green or Castrol super clean for wheels like that. Spray them down, let sit, maybe have a warm bucket of water with a bit of Dawn in it and a comfy stool.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

This worked amazingly well, a few wraps of electrical tape and a kindergartner could've shut the doors with their pinky... Of course I bought new Counterpart Door Seals to finalize my leak issue and now my doors barely close when i summon the strength of Thor! The new seals are definitely a different shape than the old rotten ones but I mean the door doesn't want to shut. About two inches before the latch reaches the striker the door is rebounding off the inner seal at the hinge.... I slammed er good and now it looks like the the top of the door isn't sitting right. Good News though, no more leak: I guess I'll just wait and see if the new seal beds in. I'll keep that door shut for a week and see how it goes. :waah:

Thanks everyone for all the help.

As always, here's a question someone is bound to know.

Does anyone know the paint colour of red in the "GMC" badge I am repainting those god dishes and want them to match the grill!

Cheers,

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

not trying to thread jack but pastic on strikers? Mine don't have any and the doors don't close right - wondering if this s why?

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

Jack away, honestly a few wraps of electrical tape and they were money until the new door seals.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

There should be plastic bushings on the striker pins. With the hinge pins and bushings in good shape, the door aligned to the the cab, and the latch not riding across the striker, the door should shut smoothly. I would suggest using the correct bushing as opposed to tape, I foresee the tape shredding and gumming up the latch. I also DO NOT recommend the Dorman/Help/CRAP striker bushings that are found at most auto parts stores, they split after a short time. Last time I needed them I went to the dealership and bought new strikers.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

Damn, thanks for the input guys! Mine are just metal and I have 3 big ass washers acting as shims. The door doesn't close unless it's slammed and doesn't sit anywhere close to flush. I haven't addressed this issue yet as I'm still ironing out my brake issues.

When you go to the dealer do you ask for your year (78) they still carry parts that way back?

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

I spend the time to find the part number myself; one of our members, hatzie (I think) has a link in his signature to a lot of the parts manuals: http://gmpartswiki.com/ and I have a whole lot more success at the dealer if I walk up with the number in hand. Also, searching the part number on ebay generally yields good results too. For instance, from Parts Catalog P&A 51/51A for the 73-78 trucks it says that the striker bolt p/n is 9601750...there are 87 search results in ebay for that number. I see at least one where someone removed the plastic bushing from the bolt and is selling an incomplete assembly, there are also cheapy Dorman results in there, just gotta shop wisely.

Edit: You mentioned having three washers on yours, one is part of the assembly (pictured) and it's entirely possible they added the other two at the factory for alignment purposes. I'm sure Keith Seymore could confirm/correct my assumption. The actual hole in the body that the bolt passes through is much larger than the bolt, allowing you to raise, lower, shift in/out the striker for latch and door close alignment.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

Well, I've had a blast the last couple days, driving around in the rain and seeing almost no water make it in and then as if a sign that my water problems were behind me.... FIRE!!!

I started her up this am and when waiting for her to warm up I noticed some smoke coming up behind the cab, I immediately turned the truck off and jumped out to investigate (I was in a sprinklerd garage and needed to get that smoke to stop asap!) popped the hood and had a wire fire coming from a mess of wires about 6'' off the + post. This is my first project truck, and as you can guess by now I'm really new at this but am having fun tackling these situations. I will post a video so you can see what I'm talking about and hopefully help me not light my apartment building on fire.

Any help would be appreciated as I need to get the truck to the mechanics on Monday... I'd rather not tow it.

Some info that might help. I took out my CB radio and i may have broken the red power wire behind the dash when remouving it. Yesterday one of my blinkers stopped working and the truck was running generally rough. I don't know much but my assumption would be I'm grounding out a live wire somewhere pretty bad.

https://youtu.be/s3UiP37-17Y

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

If you have the space and bandwidth you can download the parts books on the manual page. :D

What material is the GM striker bushing made from?
It sounds like the Dorman part is just not the right material. Too hard and brittle. Softer stuff like HDPE, Nylon or, Delrin might work fine. You can buy rounds of different plastic varieties in various diameters and bore the centre to fit the striker. I'd get a few types in the right OD and give em a shot.

Re: The 1978 Sierra Build - I NEED YOUR HELP
 

83 GMC thank you so much for the info - will check the parts book out shortly.

Great info in here as always.

Hatzie thanks for including all those links in your sig. it will make it a snap to find everything now....One thing at a time :)

Thanks again