Home Forums Gear Hunting Trucks and Four-Wheel Drives 305 question

I recently inherited my grandfather's truck, 84 gmc sierra classic 305 2wd 264,000 miles with zero engine work before now.

I've been having some carb issues out of it, but now I have a more serious problem.

Driving on the interstate the other day I lost power. Got off the road and popped the hood to find a belt broke.

Towed it home and changed out all the belts. Now at idle I have a horrible knock, also it is idling higher than it should. When you try to drive it, it has no power. At idle I have oil on the dipstick, but after turning it off and letting it sit, no oil is present on the dipstick. At idle I have between 30-40psi oil pressure and slightly higher under acceleration. In neutral it will accelerate up but will not in drive or reverse.


Any clues or directions to go in I'd love to hear. I'm afraid it may have thrown a rod.

Sorry to hear about your problems. I would try to find an independent garage and get an evaluation of your situation. If there is a community college near you that has an auto tech program there is a good chance that they take in outside work and it would be the cheapest route outside of doing the work yourself.If the engine is toast ,a donor is probably the best option. Good luck.

Sounds like the oil returns are gummed stopped up!!!!!!!!When it is running the oil on the dip stick is being thrown up there from the crank.....take the valve pans off....... I bet the top end is full of oil....It may have already damaged the crank bearings!!!!!!

I would dump a bottle of seafoam in the crank case and let it idle for a bit. If there is any sludge in there that should loosen it up. Change the oil to get the gunk out and use a good filter.

Hopefully you don't need a new engine. For what they charge, it is hard to beat a GM crate engine these days.

I bet you have water in your crankcase due to a blown head gasket. Take off the oil pan drain plug (after truck has sat overnight) and see if water or oil, or oil/water comes out. One thing is for sure, if it's knocking badly, your engine is shot. The knocking is likely a rod, which also (when it's knocking) destroys the crankshaft. THEN, if you do have water in the oil, and have run it a long time, the main bearings will be scored and the block could also have "spun mains", which means the block is junk. Well, it could be fixed, but it's cheaper to start a rebuild with an undamaged block, as it is cheaper that way. Good luck.

lets start simple. low oil can cause a lot of lifter noise. top it off with oil.

did the engine overheat?

was it working 100% before the belt popped? assuming so....
I would look at my electrical connections under hood. a coil wire barely touching can cause the same symptoms. any chance the belt moved the distributor enough to alter timing? I actually suspect this could be it as the raise in rpm is typical with a vacuum leak. I would go over my electrical and vacuum connections with a fine tooth comb.

the knock can be an effect of timing, low oil, low to no oil pressure (although you have enough to satisfy most engines at 40psi)or mechanical issues that will need to crack the valve covers off as a minimum.

to ease your fears, unless you ran it out of oil, it is dang near impossible to hold 40psi at idle with wasted rod or main bearings.....but overheating it can bring a can of worms from every angle.

I did add three quarts of oil and still nothing on the dipstick unlEss the eNgine is running. However when running that oil looks fine no sign of water.

Thinking about draining what oil is in the pan, inspecting it, then as long as No sign of water in in refilling with oil and some seafoam tI do a flush if you will draining again then changing filter and putting 5 good qUarts in and seeing what I have. Then moving on to vacuum lines and electrical.

3 quarts is a bunch in a 305....it only holds 5. I would save the mechanic in a can and find the problem.

Edit: My suggestion below is based on a problem with a 30 year old SBC with 264,000 miles, it's not worth agonizing over.

It depends on what you want to do with it, being your grandfathers I bet you want to hang on to it. But 305 was and always will be a turd, I owned several in cars and trucks.

Quick and easy is to grab a 350 long block and get back on the road in a weekend, new carb, distributor and wires while you are getting dirty.

A nice upgrade would be a 350 TBI out of a later model Chevy, 88-92 and get better drivability but not necessarily better fuel mileage and a tad more power.

Growing up with SBC's, I would jump right over them all and find a complete LS 5.3/4L60E, ECM, harness and pedal and make an engine swap worthwhile.

I always appreciate Dave's input on rifles and cartridges, he knows his chit. It appears he has a definitive knowledge of these older chevy's as well. Great suggestions there Dave. However, here's how I'd roll:

Chit can the 305. They are crap. Plain and simple...

Find a long block as Dave suggested and make sure it's a 350 (5.7 litre). I've had (and rebuilt) plenty SBC's myself and currently have a vortec 5.7 litre in my wife's 99 suburban and a 5.3 LS1 in my 04 GMC sierra 4x4. The VORTEC 350 gets better fuel mileage, even though the suburban is much heavier. The 5.3 is snappy as hell, but I like the low grunt of the vortec 350 better. I would also not suggest going to a 4l60E unless you know how to build them right. They are weak and very vulnerable to failure with weak clutch packs and bad reaction sun shells. Trust me, I've been into mine and replaced such parts. Both 4L60E's have been torn apart. The 04 GMC 4l60E had to be completely gone thru at 111,000 miles.

Back to the venerable SBC 350: There's nothing out there that is as easy to build and parts are dirt cheap. The sky is the limit when it comes to all the performance mods you can get for these. This is how I'd roll:

1. Long block 350
2. New weiand 8004 (if I remember correctly) or edelbrock dual plane intake manifold
3. Edelbrock 1406 (600 CFM) 4 barrel carburetor.
4. Upgraded HEI distributor.


Stay away from the quadrapuke carb. They are great if you know how to work on them.....

Another way to roll:

1. Locate a computer from a 96 or newer Chevy and do a Vortec transplant into grand dad's pu. You'll have the best of both worlds: Good mileage, great power, dependability. You'll appreciate it in the cold weather when the carbed engine will want to warm up first before operating.... Hope this helps Matt and hope things are going well for you buddy...

Update for any that were/are interested. When the belt on the secondary air compressor/charger thing broke the engine jumped time. Found multiple vacuum leaks, once timing was set and vacuum leaks fixed truck still had very bad bottom end knock. Ended up being a couple of rod bearings.

Got a sweet deal on a Goodwrench longblock 350, put it in along with new water pump radiator and muffler. Reused everything else from the stock setup. This spring when I have a little money saved up I plan on upgrading the cam, getting vortech heads and intake, new carb and headers.

Truck is running great with the new engine, i'm just about at the 500 mile mark of the break in process. I have some suspension and brake areas that need some attention, but over all the old girl is doing great.

Sounds like you did good Matt. Nice to see you posting here again. How have you been???

Be aware of one thing with these rebuilt engines - many rebuilders won't honor the warranty unless it's installed by a professional mechanic.

Got a 3yr warranty on it and had it installed by a shop, just been too busy to do it my self.

BSA, it's good to be back! The last year has been rough but things are really good now and the futures looking bright. Not sure how much time I'll have in the woods this fall, but coworker and I are starting to plan an elk hunt for 2016 and I'm looking for a local club to join for next season.

When I bought my new 350 it came with a 100k warrenty no matter what I put it in...sell a lot to hot rodeos and such...the good wrench is a good choice

When I was raising holy hell as a youth in Oregon I had a chevy truck and my buddies were into the whole dirt track scene (they still are) they told me how to build a good sbc as long as you wanted to put the money in it. It all started with a 4 bolt main sbc 350. then I would pop the heads off a 305 onto it. Always made for one hell of a motor. then my bud offered me a deal on a BBC 454 holy [bleep] talk about a lot of ass.. I said this before I think I was getting maybe 8 MPG but man was that truck fun.

Good to hear Matt, and even better you are driving your grandpa's truck!

My '81 was totaled around 1992, by that time the '88+ was growing on me and I bought a shortbed 4x2 Texas Oklahoma package with a 4.3 V6.

Nowadays, I have no interest in the old slab sides but darn sure would not mind another square body!

Thanks , I got her all cleaned up this evening.

Nice looking truck, I love those old Chevy trucks.

Yep, that is a clean truck, and I bet it feels a lot better with the 350.

It does, I can't wait for headers, flow masters , vortec heads and a new cam. Should be around 300hp and 375ftlbs makes for a nice daily driver with some punch!

Looks great Matt. Pretty clean looking... 300 HP will scoot that one down the road pretty good..

Those I would avoid. When I bought my '73 Mach 1 the previous owner installed headers and Flowmaster 40's when he had the 351 Cleveland rebuilt. It roared and had a drone at highway speeds that was absolutely unbearable. I installed Magnaflow XL's and all is good. A few weeks ago I bought a 2014 Tundra. Among other tweaks the previous owner had a Flowmaster cat-back dual exhaust system installed. It, too, roared with an even worse drone due to a single two in two out muffler. I replaced the muffler with the largest Magnaflow Straight Through and, again, all is good.

Was your Mach 1 true Dual mufflers as in two mufflers both single in single out?

Matt, flowmasters aren't bad if you go duals dumping into a single. Nothing wrong with doing that either because it helps to equalize back pressure anyway. I run a flowmaster on my 04 GMC and it sounds pretty good. It's a cat back system with bigger pipe from the cats back... With this set-up, it sounds great at idle, nice and throaty when you get on it, and not annoying on the freeway... The best I have for you as far as sound is this short video. I was playing around in 2wd in about 9" of snow after shooting at my spot....:


[img]http://i1180.photobucket.com/albums/x401/chiefbsa/th_009-11.mp4[/img]

Bud of mine had an '81 K10 pickup bought used around '84 with high mileage for it's age (50K). Stock 305 was always a dog, began causing problems at around 110,000 miles (cam, oil consumption).

He put a rebuilt four bolt main 350 in it. TRW/RV grind cam, better pistons, etc. Someone suggested he use the aluminum intake/RQJ from the 305 and that worked out well. Ran like a bear, got fairly good fuel mileage.

That engine had well over 300K on it before it was ever replaced by the next owner, years after my bud had sold it around '94.

Only 305 that I ever owned, was in an '83 work van. Fuel pump lobe went to hell at about 95,000 miles. Installed an external "pusher" elec. pump back near the tank in the "supply" line. Anytime it got balky for fuel, hit the pump switch and off she went again. Yeah I know, shade tree but it worked.

Knew another guy that had a new Blazer w/305 that dropped a valve into a piston in less than three years.

Come ta think of it, never heard any "good" reports on any 305s?

Same here. I can't stand Flowmasters.

I like the distinctive sound of flowmasters, had the original two-chamber on two Mustang 5.0's, no drone to be honest but the dynomax cat-back was absolutely horrible.

I was also in my late 20's to early 30's and enjoyed loud mufflers and straight exhaust on my cummins.

From what I can hear on youtube, I would be looking at 50 series now.

I had a good experience with the 305 in an 1984 K5 Blazer that I used for plowing snow in far NE Minnesota.

I used it from 1984 to 1993 as my recreational and work vehicle, added the plow for my own road, then picked up other jobs to keep me in some extra cash all winter. I switched out the clutch fan for a direct drive fan for cooling, and switched out the automatic hubs for manual lockers.

In addition to it being my weekend hunting/fishing rig, involving light towing, I ran about 14 plow jobs with it through some really tough winters, including 1995/1996, with over 150" of snowfall at our house, and record cold down to -45f actual air temperature (the same night Tower set the MN record of -60f Feb 2 1996).

That year in particular I can't count how many times I was either stuck due to snow falling down off the banks back into the road and piling up to stop the truck. I shoveled what seemed like over 100 tons of snow from in front of that straight plow blade. There were a lot of narrow roads on my route so I had to subcontract late winter with my neighbor to bring in a bobcat to push the snow back between the trees to make room for all the snow, which never melted much at all that winter until well into April, with snow piles in the shaded woods until after Memorial day.

Anyways that truck never used much oil, ran smooth, never made any bad engine noise, never left me stranded, always started in on the coldest mornings after sitting outside all night, and was just powerful enough to get the job done, but not so powerful that I was able to damage the front end or drivetrain.

I sold it with over 150,000 hard miles. The truck did not have a straight piece of metal on it, but the old 305 was still running strong. To this day I like it better than the 5.3 in my Suburban which consumes oil, smokes on start up, and has a piston slap on cold start up.

My BIL's Uncle has raced NHRA super stock since the 60's. Don't know what class but i do know he has to run stock displacement, iron heads and stock type carb (quadrajet), and manual trans. He's been running a 84 Firebird since the 80's. Builds his own 305's and it will snatch the tires quite handily. He's won his class at years end 10 plus times with those turd 305's. I've never owned one worth a damn but he can make them talk that's for sure.

I had an 85 GMC that puked the rear main at 83K in 1988. I dropped in a crate 350 longblock, rejetted the Quadrajet, Edelbrock headers and straight 2" exhaust with 18" glasspacks. Unbelievable difference....