Bad shake while in drive or reverse

[xoxoxobella]

I have a 1976 bronco and I just recently had the intake manifold gasket replaced at a shop. 4 days after picking it up I was driving and punched the gas to avoid an accident. When I took my foot off the gas it shuddered. Then it almost shut off at the light. I have replaced EVERYTHING except the engine or trans since January 2024. I thought perhaps the new fuel filter at the carb was possibly clogged so I replaced it myself. Didn’t fix the issue. Took it back to the shop and he said “I don’t really like working on carbs” so he referred me to the most expensive shop in my little desert town. He “claimed” there wasn’t a vacuum leak, I beg to differ, but I’m just a girl who does minimal work on my vehicle. I came home and did a ton of research. Had the timing checked and the carb readjusted by a neighbor. I have since driven all of the gas out and replaced it. At start up it does make a whining noise for about 15 seconds. It shudders horribly at first start up in the morning and almost shakes the paint off the entire vehicle when I am in drive or reverse if I’m idling or moving less than 15 mph. In other words if I’m not giving it gas it runs like crap. I feel Iike there is a vacuum leak with the new gasket he installed but I don’t know how to figure this out, I’m trying to avoid being bent over by another shop with their “diagnosis” since they see a woman driving a 76 bronco. I want to be educated on this before I go back to the shop that performed this repair because he was super quick to dismiss the possibility of a vacuum leak at the intake manifold


Sent from my iPhone using Tapatalk

 

[Oldtimer]

X,
Let us know what corner of the country you live in. There may be a Broncoholic in you neighborhood willing to lend a hand.

 

[73azbronco]

what is your vacuum at idle?

 

[xoxoxobella]

what is your vacuum at idle?

I’m not sure. I’ll ask the guy who check the timing and pulled the vacuum advance tube off and said it’s working properly.


Sent from my iPhone using Tapatalk

 

[xoxoxobella]

X,
Let us know what corner of the country you live in. There may be a Broncoholic in you neighborhood willing to lend a hand.

I’m in Southwestern New Mexico


Sent from my iPhone using Tapatalk

 

[73azbronco]

pretty cheap tool at autozone or harbor frieght, vacuum gauge. If you drive carb, good tool to start a diagnosis.

https://www.harborfreight.com/fuel-...1vTIfE3AW_WuGE1Y8rcsTCRLjRGfet_xoCSXYQAvD_BwE

If you have fuel injection, fuel pressure gauge next best tool.

 

[73azbronco]

I’m in Southwestern New Mexico


Sent from my iPhone using Tapatalk

Gotta be someone in Lordsburg/Deming who is a carb expert? Use my technique, go into the NAPA in your town, ask who they think can work on carbs.

 

[Jdgephar]

The vacuum advance tube that goes to the distributor is not where to check the engine vacuum.

We would like to know the engine vacuum from a constant vacuum source (like the brake booster). You should know if the needle stays steady, and how much vacuum it has.

 

[gnpenning]

Welcome.

Good information on testing for vacuum. Cheap and easy check you can do yourself.

Resist the urge to start throwing parts at it with out proving it first.

Take the air cleaner off and check choke operation from cold to warmed up. After it's warmed up shine a light down the throat while it is idling and see if you can see gas drops.

Check all the plug wires the entire length looking for wear or melting.

These are all tests you can do without spending money. Report back

I'm sure others will more other suggestions.

 

[xoxoxobella]

The vacuum advance tube that goes to the distributor is not where to check the engine vacuum.

We would like to know the engine vacuum from a constant vacuum source (like the brake booster). You should know if the needle stays steady, and how much vacuum it has.

I don’t have a brake booster, no power brakes. I’ll check with the neighbor who corrected the timing etc to see if he knows. Thanks! I’ll keep y’all posted.


Sent from my iPhone using Tapatalk

 

[xoxoxobella]

Welcome.

Good information on testing for vacuum. Cheap and easy check you can do yourself.

Resist the urge to start throwing parts at it with out proving it first.

Take the air cleaner off and check choke operation from cold to warmed up. After it's warmed up shine a light down the throat while it is idling and see if you can see gas drops.

Check all the plug wires the entire length looking for wear or melting.

These are all tests you can do without spending money. Report back

I'm sure others will more other suggestions.

Thanks for this info. I’ll do it this weekend and report back with info!


Sent from my iPhone using Tapatalk

 

[xoxoxobella]

Gotta be someone in Lordsburg/Deming who is a carb expert? Use my technique, go into the NAPA in your town, ask who they think can work on carbs.

We don’t have a Napa here in Truth or Consequences. I’ll check with the guys at carquest, they’re more likely to know before the guys at oriellys or auto zone. Thanks. I’ll keep you posted!


Sent from my iPhone using Tapatalk

 

[Broncobowsher]

What carburator are you running?

What I have done in the past with a 4-barrel Holley is get a piece of trash (rubber sliver from sliding the fuel hose over the fitting) make it to the secondary side of the carb. The engine ran fine for days. Get on it hard, the secondaries open up, that piece of trash makes it to the needle and seat causing it to hang open just a little bit. The secondary (rear) fuel bowl now has a slight leak of excess fuel that dribbles down the carburator. At speed there is enough air that it runs fine (very rich, but generally fine). At idle it just dribbles raw gas down the intake and it runs horrible.

Couple easy ways to check. With the engine running look down the carburator. Do you see fuel dripping off the secondary boosters? With a Holley check the fuel level in the rear fuel bowl. Remove the plug and there should be just a little drool down the side. Normally this is done running, but in this case try it with the engine off (but just run). If it gushes out, you feel like you just cut a fuel hose gush, the back side of the carb is overflowing into the engine. This has only happened to me with Holley 4-barrel carbs.

OR it could be something completely different. When you are completely sure it is a fuel issue, the fix will be in the ignition.

 

[xoxoxobella]

What carburator are you running?

What I have done in the past with a 4-barrel Holley is get a piece of trash (rubber sliver from sliding the fuel hose over the fitting) make it to the secondary side of the carb. The engine ran fine for days. Get on it hard, the secondaries open up, that piece of trash makes it to the needle and seat causing it to hang open just a little bit. The secondary (rear) fuel bowl now has a slight leak of excess fuel that dribbles down the carburator. At speed there is enough air that it runs fine (very rich, but generally fine). At idle it just dribbles raw gas down the intake and it runs horrible.

Couple easy ways to check. With the engine running look down the carburator. Do you see fuel dripping off the secondary boosters? With a Holley check the fuel level in the rear fuel bowl. Remove the plug and there should be just a little drool down the side. Normally this is done running, but in this case try it with the engine off (but just run). If it gushes out, you feel like you just cut a fuel hose gush, the back side of the carb is overflowing into the engine. This has only happened to me with Holley 4-barrel carbs.

OR it could be something completely different. When you are completely sure it is a fuel issue, the fix will be in the ignition.

Just had another mechanic look at it and it was the fact the shop that performed the work a week ago failed to put the firing order back correct. It now runs like a charm. I appreciate all of the input! Thanks!


Sent from my iPhone using Tapatalk

 

[xoxoxobella]

Thanks for this info. I’ll do it this weekend and report back with info!


Sent from my iPhone using Tapatalk

It was an incorrect firing order that the previous repair shop did incorrectly. She purrs like a kitten now! Thanks for the input!


Sent from my iPhone using Tapatalk

 

[xoxoxobella]

I don’t have a brake booster, no power brakes. I’ll check with the neighbor who corrected the timing etc to see if he knows. Thanks! I’ll keep y’all posted.


Sent from my iPhone using Tapatalk

The shop that originally worked on it a week ago did the firing order incorrectly. Thanks for your input to help solve the problem. She runs perfect now!


Sent from my iPhone using Tapatalk

 

[DirtDonk]

Well, thank goodness for quick fixes! Well, “quick“ as far as the actual work. Still took an annoying amount of time with it vibrating like that, for you I’m sure, to find someone that could easily narrow it down.
Semi-common issue though, wit two different orders used by Ford over the years.
It can even happen when someone’s not paying attention and they’re used to working on, say Chevys instead of Fords, and don’t bother to look up the correct orientation.

No matter what, glad you got it fixed!
Have fun!

Paul

 

[73azbronco]

Nice, as Bob Barker used to say,
I'll tell you one thing, in what I do for a living, there's no substitute for experience. I don't care how much natural talent you may have... In the type of show I do, you can depend on surprises. Bob Barker

 

[Broncobowsher]

... When you are completely sure it is a fuel issue, the fix will be in the ignition.

Once again

 

[DirtDonk]

Yep, as Chris Jacobs, of Jacobs ignition used to say “90% of ignition problems are carburetor related. And 90% of carburetor problems are ignition related and“ or something to that effect.