Hi all, Not sure if I'm in the right forum for this but everyone here seems to be helpful anyway so here goes. This afternoon I noticed the advance timing is not working on my 1958 chevy 3800 1 ton truck. 235 engine, everyrhing stock from factory. I have a couple older posts here but couldn't find the "create new post" link, so this is where I ended up. Can anyone tell Me why tge advance timing (attached to distributor) would not be moving as I move the accelerator? Doing this under the hood by hand obviously, and as I'm pulling the accelerator linkage I'm warching the dist not moving at all. Concerned as to why this may be. I appreciate any help with this, thank you in advance.
Either there is no vacuum getting to the advance unit, or the diaphragm in the advance unit has a hole in it. Disconnect the tube, see if you get suction as you open the throttle. And manually actuate the advance, to make sure it's not stuck. If it passes these tests, then get a new vacuum unit. for those who don't know, the 235 has an external vacuum advance, and internal mechanical advance
Hi squirrel, I did move it manually and it worked by hand. I pulled the hose and metal tube off and looked through.. Saw sunlight through the hose. Will start it and plug tube with my finger to see if there is suction... One moment.. Brb
Ok just started it and yes I do have vaccume from the carb going to hose. Am pulling the end of line at the advance unit to see if I also feel vacuum at that end as well. If there is vacuum at the unit does that mean the unit is faulty?
Ok update.. Air lines are all free flowing clean and clear .. Good vacuum pressure and no leaks. Anybody know where I can buy one of these vacuum advance units? I've called around auto parts stores and they don't seem to know. Now if I was back home I could probably find this stuff a dime a dozen!!
I think it's like this. I replaced one on wife's '55 a couple years ago, 235, I'm thinking from Bob's Trucks... Bob's Chevy Trucks - The Ultimate Source for restoration parts, styling, and performance upgrades for your Chevy Truck https://www.bobschevytrucks.com/ Sent from my SM-S320VL using Tapatalk
Well, I ordered online through LMC, not the other parts merchant I had mentioned. Will have to wait til it arrives, but as soon as I'm able to install it I'm sure the truck will be back to normal!
ok so I installed the vacuum advance this afternoon, and its turning clockwise instead of counter-clockwise like the original one did. What gives? I hooked up the vacuum line where its supposed to go , and made sure of no leaks, but still does the opposite of what I need.
It's right side up? And under what conditions, does it turn which way? Pictures? video? would be a big help.
It turns clockwise, yes it is right side up (only fits one way). Under Idle it runs fine, under driving conditions it has been bogging down to about 15 - 20 mph , not wanting to move.. I have adjusted it multiple times to try to get it to function correctly and it seems to only want to work with the dizzy advanced max, and air fuel mixture set on the lean side. Fuel air mixture screw adjusted about 1 full turn from bottomed out.
I do know that it is meant to advance / or retard the timing on the engine (depending on the setting)..
Yes, it is designed to advance timing when the engine is under light load, as this will help fuel mileage. At wide open throttle, it will "back off" and not advance the timing. This happens because engine vacuum drops to near zero when the throttle is wide open.
Yes I noticed this, but I am not nearly maxing out throttle, and before installing the new V/A (also before old one died) I would rev engine and watch it move the dizzy counter-clockwise. Now it wants to move clockwise when I rev engine
Does the new one look the same as the old one? And if the old one was moving the distributor, why did you need to change it?
Yes the new one looks the same as the old one... the old one was NOT working at all! Would not move in any way. I checked the air line going to and from the carb and have plenty of vacuum suction so reconnected the line and instead of the advance unit turning counter-clockwise it turns opposite. I have no idea why!
Later this afternoon I'll take pictures of the shop manual tune up section. By your video it looks like it's working ok. Sent from my SM-S320VL using Tapatalk
It was confusing. First: "before installing the new V/A (also before old one died) I would rev engine and watch it move the dizzy counter-clockwise. Now it wants to move clockwise when I rev engine" Then:"the old one was NOT working at all! Would not move in any way." I assumed video was yours, now I see it's not. Here's wife's 55, her Mom bought new. Over the years I've changed minor things but basically stock. Distributor (rotor) turns clockwise. The body moves ccw (notice how vacuum advance is mounted). I would disconnect vacuum advance. On her '55, I assume '58 the same, timing Mark is on flywheel, a dot as seen through opening near back, #6 plug. A pointer line up at lowest idle TDC (dot/pointer align). Mechanical advance starts at 375rpm, 1 degree. It should advance 13 degrees at 1750rpm. Then connect vacuum advance. That should advance another 7 1/2 degrees, so about 20 degrees total all in by about 1800rpm, full vacuum. Vacuum advance has marks on it so you can adjust by way of how it's attached to dist body exactly how you want it. With engine off you should be able to move distributor body by hand ccw a little. They may have sent you the wrong advance, it should look like one on wife's distributor. About 20 years ago we rebuilt the motor. Wife decided on a Howard's cam thinking more performance. I could never get it to run right although I double checked with degree wheel. Powerglide shifted rough, etc. I called Comp Cams (they're fantastic). They had original grind specs for factory cam. Found out 235 had at least 3 different size lifters! So Comp cam & lifters, installed straight up, set lash. Car drives, shifts like new again. Smooth idle, great acceleration (For what it is!). I have more information if you need it. Sent from my SM-S320VL using Tapatalk
Yes it is pilled in already. But when I adjust the distributor adjusting screw on the (I'm assuming its called a timing plate) on the VA it then starts to relax and then pull as I accelerate the engine but at same time it fluctuates counter & clockwise at same time. (Back and forth) So I am at a loss thus far. The VA had markings for advancing and rwtarding the timing.. I have set it at a couple different settings and doesnt seem to make a difference. How would I go about this from scratch with the new VA .. Having to start with no markings to go by other than the flywheel being set at tdc and the rotor set at #1 then using the markings on VA timing plate and someone said something about unplug the vacuum line?? Does this sound right so far? Or am I off base?? Thanks in advance
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