Howdy from the Pacific Northwest

[mech0001]

Twenty years ago I was working as a tech in Salem, OR when I met the GMC Motorhome. The low access height and fantastic visibility grabbed me right away. Plus, a definite cuteness factor. Definitely a change from the rest of the motorhome crowd. Of course, there is the "slight" drawback that crawling under it is, um, difficult. "Real" trucks are so much easier...

About a year ago, I went on my last backpacking trip. The mountain informed me that I could no longer haul 30 lbs of gear on my back for very long without having to rest. Then there was the couple, looking fresh as daisies, who, I learned, were hiking back to their RV at the park campground. Somehow, sleeping on the ground was much less fun after that.

It wasn't long before I was looking into other options and perusing want ads. I remembered the GMC and researched its history, watched some videos. You know the drill.

Suddenly, there it was, a GMC Motorhome for sale! Olds 455 - check. 26 foot - check. Rear bed - check. Needs work - check.
In fact, the dash had been broken out in preparation for a CIP dash install. Turns out, it was a project that the owner, sadly, died in the middle of. It also appeared the vehicle received a thorough mechanical rehab prior to his purchase as well as numerous appearance upgrades. In other words, a medium risk, high gain opportunity to own a GM classic for someone with my unique set of automotive technician skills. Plus, I got to do it!

It took 8 months of weekends and other spare time and I learned a great deal about a "great many things", most of which I fixed or modified. I have just returned for my first real outing - an overnight to the Washington coast over the 4th. Motorhome ran very well, though I am still messing with the timing. For some reason, FiTech's ported vacuum doesn't appear until about 1/4 throttle, making it worthless for vacuum advance profile. Still, performance was everything I could hope for, just have to get rid of that ping.

I did notice something, though, that I'm hoping you all can help me with. I notice a low rumbling noise that appears at around 50 mph and gets quite loud at 60. At first, I thought it was my new front tires (agressive tread as I have a VERY steep, gravel drive), but then I noticed that my front air dam (above windshield) was vibrating and I believe that is the source of the noise. The fasteners appear to be tight. Have any of you encountered this and is there a fix?


Cheers!

 

[pvfjr]

Welcome! It looks like you've got a great start on that one. I work in Salem myself, though I live to the east up in the foothills. Are you still in the area, or are you in Washington now?

Add some more pics when you can, I'd be curious to see your dash.

 

[kbeefy]

Welcome!

I'm also in the PNW, close to Idaho.

 

[mech0001]

I moved from Salem to the Kitsap peninsula over 10 years ago. Love being near the Olympic National Forest!
Here are a few more dash pictures. It's a Custom Instrument Panels product. You might note that there are no screws in the holes. After the initial setup (with screws), I realized the fiberglass housing would not stand more than one screw insertion, so I used velcro strips to secure the panels in place. Not quite as pretty, but the ease of access is too good to pass up. If you have any questions, ask away.

 

[1976GMC]

We just returned after spending almost a week on the Olympic Peninsulla with our GMC. Such a beautiful area. Almost got overesaturated by all the greenery
Anyhow, welcome to the community

 

[tmsnyder]

Congrats on the first successful outing! Very exciting!

On the timing, check to make sure your mechanical weights are swinging freely.

Personally, I like the aftermarket sets of weights and springs that give me a known amount of mechanical advance. Who knows what a PO did in there? Set it at 30-34 degrees at 3000 rpm and leave the vacuum advance disconnected for a while. Run as much mechanical advance as you can without hearing preignition while climbing hills. Keep adding advance until it pings under load or kicks back on the starter when cranking.

Once you're happy with that, hook the vacuum advance back up. Again, who knows what vacuum can is on there, I would put on an aftermarket one that's adjustable, so you actually know what the thing is doing.

 

[mech0001]

Nice tip regarding timing. It's been a while since I've worked on this GM setup, spoiled by knock sensors and computer controlled timing, I suppose. I have verified springs/weights and vac advance operation. Back in the day, you'd verify those, set it to spec and then tweak to get that slight ping on hard accel. FiTech's lousy ported vacuum response is irritating me at the moment. Can't really get the OEM response without valid inputs.

When I got home, I pulled out the timing light and set the up-rpm timing to around 32. We'll see how that does. My combination of tires/rear end has me around 60 mph @ 2400 rpm, so that will be a factor.

 

[tmsnyder]

I have a mechanic friend that swears by mechanical-only advance.

FiTech uses ported vacuum only for control of its efi? That's weird, seems like they would use the manifold vacuum......

 

[mech0001]

I'm referring to the ported vacuum output from the FiTech unit. It doesn't begin to register vacuum until the throttle is about 1/4 open. Not what you need for a standard dist vac setup. After next outing, I will evaluate whether to go to another advance strategy. There's at least one ignition option out there with a timing dial, though I prefer to stick to GM when possible due to replacement part availability. Never modified spring/weight setup (usually just freeing them up) but that will be on the list.

 

[tmsnyder]

I'm referring to the ported vacuum output from the FiTech unit. It doesn't begin to register vacuum until the throttle is about 1/4 open. Not what you need for a standard dist vac setup. After next outing, I will evaluate whether to go to another advance strategy. There's at least one ignition option out there with a timing dial, though I prefer to stick to GM when possible due to replacement part availability. Never modified spring/weight setup (usually just freeing them up) but that will be on the list.

Ah, the ported signal on the FiTech is being funny, got it.

Why not connect the distributor to manifold vacuum?

 

[mech0001]

Well, yes, that's what I've done but my base timing was more advanced than expected, so my on-road adjustments never got to the ballpark they needed to be in. It'll get there, just not sure how yet. Unfortunately, I have an extremely steep drive to scramble up, so I don't go out for short test drives.

 

[tmsnyder]

Well, yes, that's what I've done but my base timing was more advanced than expected, so my on-road adjustments never got to the ballpark they needed to be in. It'll get there, just not sure how yet. Unfortunately, I have an extremely steep drive to scramble up, so I don't go out for short test drives.

This is why personally I prefer to take out the old weights and springs and vac advance can, throw them away, and put in new aftermarket ones that return the timing to pre-smog settings.

 

[kbeefy]

Well, yes, that's what I've done but my base timing was more advanced than expected, so my on-road adjustments never got to the ballpark they needed to be in. It'll get there, just not sure how yet. Unfortunately, I have an extremely steep drive to scramble up, so I don't go out for short test drives.

You are checking Base timing without vacuum hooked up, right? The vacuum advance doesn't really do anything under load, it's mostly there for idle, startup, and very light throttle applications.

The way I was taught to set timing was to disconnect and plug vacuum advance. remove springs from mechanical advance and run engine up to wherever your mechanical advance maxes out. Adjust timing until you have 36 degrees peak advance, depending on compression, fuel, boost etc.

Reinstall centrifugal springs and rev engine up to 3000 rpm, monitoring the timing. If you don't get the same max advance as set without springs (36 degrees) before 3k, your springs are too stiff. Adjust accordingly.

Connect vacuum and test drive. Retard timing and/or adjust fuel octane or boost to correct for knocking.
When I'm making my final timing adjustment I do it on the road, just leave the distributor not quite snug so you can turn it by hand without tools. Check timing when done (back at home) then tighten distributor holddown and recheck timing.

 

[mech0001]

I don't think I'm at the "remove the springs" level. I'm seeing my timing max out at low to mid 2000's so I think that's fine.

System isn't really that complicated and I'm not adding boost (lol). I'll check back if it doesn't resolve fairly simply.

 

[tmsnyder]

You are checking Base timing without vacuum hooked up, right? The vacuum advance doesn't really do anything under load, it's mostly there for idle, startup, and very light throttle applications.

The way I was taught to set timing was to disconnect and plug vacuum advance. remove springs from mechanical advance and run engine up to wherever your mechanical advance maxes out. Adjust timing until you have 36 degrees peak advance, depending on compression, fuel, boost etc.

Reinstall centrifugal springs and rev engine up to 3000 rpm, monitoring the timing. If you don't get the same max advance as set without springs (36 degrees) before 3k, your springs are too stiff. Adjust accordingly.

Connect vacuum and test drive. Retard timing and/or adjust fuel octane or boost to correct for knocking.
When I'm making my final timing adjustment I do it on the road, just leave the distributor not quite snug so you can turn it by hand without tools. Check timing when done (back at home) then tighten distributor holddown and recheck timing.

That's an interesting way to do it, never heard of taking off the springs. Neat.

After putting the vacuum back on, if it pings at partial throttle if an aftermarket vacuum can is used; those are adjustable. You can back off the amount of additional timing added by the vacuum signal, so it allows one to leave the base + mechanical timing where it belongs and only adjust the advance added by vacuum. It's also easy to do as well and since it's immediately under the hatch, it's easy to get to. Just takes a allen key.

 

[pvfjr]

After putting the vacuum back on, if it pings at partial throttle if an aftermarket vacuum can is used;

That's right where I'm at with the Glenbrook. If I set timing according to the manual, I end up with pinging at part-throttle. If I back off, or put my foot into it, the pinging goes away. I'll have to look into this. You got a good part number for the adjustable vacuum advance?

 

[tmsnyder]

That's right where I'm at with the Glenbrook. If I set timing according to the manual, I end up with pinging at part-throttle. If I back off, or put my foot into it, the pinging goes away. I'll have to look into this. You got a good part number for the adjustable vacuum advance?

I used this one: ACCEL 31035 Adjustable Vacuum Advance
but there's a pertronix version: Pertronix D9006 Flame-Thrower Adjustable Vacuum Advance Canister for HEI Distributor as well on Amazon that's supposed to fit 1976 Olds Toronado

 

[Tybalt39]

View attachment 9069I moved from Salem to the Kitsap peninsula over 10 years ago. Love being near the Olympic National Forest!
Here are a few more dash pictures. It's a Custom Instrument Panels product. You might note that there are no screws in the holes. After the initial setup (with screws), I realized the fiberglass housing would not stand more than one screw insertion, so I used velcro strips to secure the panels in place. Not quite as pretty, but the ease of access is too good to pass up. If you have any questions, ask away.View attachment 9070

Thank you for photo #2!

I'm happy to see the "right/accessory" face sits flush with the bezel rather than being recessed like the main instrument cluster. My intended double-DIN android system has a 9.5" vertical screen that will sit proud of the top of the dash (handy for GPS maps). I was concerned I would have to modify the top of the dash to clear it. Looks like that won't be an issue.

 

[Henzlerpl]

I have a 1974 someone did a complete restoration
I will be travelling south from Canada on the I5 sometime next week and was hoping for a recommendation of a shop that can check out my Fitech installation and install the 2 wire distributor plus run my radiator fan with the fitech system
My mechanic in Calgary had limited Fitech knowledge

 

[Wheelock]

Welcome!

I'm also in the PNW, close to Idaho.

You in Clarkston?