Intermittent drag at 10-40 mph

[keymonkey]

Just got my truck back from an engine swap and perhaps from sitting or random failure, I can feel an intermittent drag when cruising around town. Feels a bit like varying wind resistance but with no wind. Brakes seem fine, pedal five is good and the vac booster seems to be working. What are some diag steps I can take to narrow where this might be coming from?

 

[Yeller]

Dragging brake caliper, carry an infrared heat gun. Check rotor temps as you drive. If one is much hotter, or both are much hotter there is a sticking caliper or the master cylinder and brake booster are not matched and the booster push rod is too long not allowing the brakes to fully retract.

Other option is much deeper, if auto trans, it has an internal leak or converter failing. Brakes are far more likely.

 

[keymonkey]

Dragging brake caliper, carry an infrared heat gun. Check rotor temps as you drive. If one is much hotter, or both are much hotter there is a sticking caliper or the master cylinder and brake booster are not matched and the booster push rod is too long not allowing the brakes to fully retract.

Other option is much deeper, if auto trans, it has an internal leak or converter failing. Brakes are far more likely.

Will the same method work on 4 drums?

 

[Yeller]

Will the same method work on 4 drums?

Yes it will in the same manner.

 

[keymonkey]

Yes it will in the same manner.

Ok.....was going to jack it up tomorrow and see if I can feel or hear resistance when manually turning the tires. The tranny is auto, bit fluid level is fine and it is a Monster AOD with under 10k on it.

 

[phred]

Remember with drum brakes, if properly adjusted, there should be some minor drag/resistance as the shoes should just barely be touching the drum at rest.

 

[keymonkey]

Remember with drum brakes, if properly adjusted, there should be some minor drag/resistance as the shoes should just barely be touching the drum at rest.

So driver rear needed adjustment as it was not dragging at all, but heat test showed fronts 140-150 and rear 115-135 degrees after a 40 minute city drive. So not convinced its brakes, but now not sure what it could be. Everything else in drivetrain is new or rebuilt. Itis very subtle.....gonna make sure my driveshaft u-joints are greased. Otherwise, might be wind resistance? Very strange.

 

[DirtDonk]

You can certainly get a lot of wind resistance in a bronco!
But when you rebuilt the drivetrain, did that include replacing the front and rear wheel bearings?
They act up most often at speed, when they heat up, so that’s something to at least think about.

When you checked the temperature on the brakes, where did you measure? Did you also happen to measure the hub temperature at the same time?
Inconsistent, or large variances in heat in the hubs could mean a wheel bearing issue.
Although, if you were getting drag from a front brake or bearing, you would think that it would also be a noticeable pull.
The rear too, but may be more subtle.

 

[keymonkey]

You can certainly get a lot of wind resistance in a bronco!
But when you rebuilt the drivetrain, did that include replacing the front and rear wheel bearings?
They act up most often at speed, when they heat up, so that’s something to at least think about.

When you checked the temperature on the brakes, where did you measure? Did you also happen to measure the hub temperature at the same time?
Inconsistent, or large variances in heat in the hubs could mean a wheel bearing issue.
Although, if you were getting drag from a front brake or bearing, you would think that it would also be a noticeable pull.
The rear too, but may be more subtle.

Ah! I only checked the drum through the gap in the rim.....ok.....next drive hub temp up front as I replaced the rears last year. Thanks!

 

[Timmy390]

Power drums......be careful as in mindful of keeping the brakes adjusted properly. I had a few major puckers over the years with that combo.

Disconnect the booster and give it a drive. See if it acts differently. Be sure to plug the vacuum line engine side or ypu will have a huge vacuum leak. Booster side don't matter.

Tim

 

[keymonkey]

Thanks for all the suggestions...but I think I figured it out.....did a little carb tuning and dropped my timing back down to around 5 degrees and that made the issue much more pronounced on flat road with steady petal pressure. It feels like drag, but it is actually very subtle fluctuation in the fuel mix. I called Edelbrock and they knew right away. With the new Stroker 306 I have in there now the existing setup spring is not enough so the needle bounces ever so slightly in the carb causing a barely perceptible chug that is not enough to even hear in the motor running rpm, but just enough to cause a weight shift in the vehicle when cruising. Man....that was a fun one! Thanks again everyone...could not have done it without the help narrowing it down. BTW I did also find that my driver rear brake shoes are in need of adjustment but increase in contact with the drum...not too much!

 

[DirtDonk]

Wow, good catch! Makes sense too, since most of the other things I could think of would have resulted in a pull to one side or the other as well. Unless somehow something was working against you on both sides.
But the engine will certainly do that. Glad you got it figured out.

Or do you? Have you already fixed the issue? Or have you still yet to fully resolve it with new parts?

Paul

 

[keymonkey]

Wow, good catch! Makes sense too, since most of the other things I could think of would have resulted in a pull to one side or the other as well. Unless somehow something was working against you on both sides.
But the engine will certainly do that. Glad you got it figured out.

Or do you? Have you already fixed the issue? Or have you still yet to fully resolve it with new parts?

Paul

New springs and re-adjusted the mix and idle....took it out for a spin and it still does it.....I'm beginning to think it is a misfiring cylinder. It does not rough idle but it seems to skip a fire every once in a while so the motor visibly randomly shimmies. I wonder if at a higher rpm this "skip" causes just enough power loss to make it seem like the truck lags. Bought new plug wires, to see if the brand new ones on it have a bad wire.

 

[m_m70]

With the new Stroker 306 I have in there now the existing setup spring is not enough so the needle bounces ever so slightly in the carb causing a barely perceptible chug that is not enough to even hear in the motor running rpm, but just enough to cause a weight shift in the vehicle when cruising

Since this issue happened right after the motor swap I would say you should look there first.

Can you share a bit more about your motor swap?? High HP?? Not familiar with this one.
New carb as well?? Even if it's the original carb, will still need to be tuned to your swapped engine.

I'm going to agree with Edelbrock that your springs and metering rods need to be changed changed out to tune your carb. This can take some time and lots of variables. I think I used the #1487 kit when I was running the 1406 carb.

Bump your timing back up. 5* is not right.

I think if it were your brakes dragging to the point you can feel it they'd be smoking....

 

[gr8scott]

I called Edelbrock

What model Edelbbrock do you have? Kind of sounds like fuel starvation.

And I agree about the timing. That 306 Stroker needs 12-15.

 

[m_m70]

That 306 Stroker needs 12-15.

Totally agree here. Isn't the 306 just a rebuilt stock 302 that the bore has been opened +.030"? Not knocking anything, just want to make sure I'm on the same page.

The issue I had, when I had similar symptoms to yours, cleared up by leaning the carb out via metering rods and springs a couple steps. This was with a 1406 right out of the box. I've since put in AFR gauges to make adjustments.

Good luck with this!

 

[DirtDonk]

Good point. Unless you started with a 289 instead of a 302, then it probably isn't really a "stroker" engine at just 306 cubic inches. Your original was a 302 (you have a '74, correct?) so unless the engine was a different one swapped in, and used a 289 core, then it was just a re-bore to 306.
Big difference in just a re-bore and re-stroking an engine. But it's still only 306, so isn't really a huge change from stock.

But more important perhaps, is what cylinder heads, pistons, cam, exhaust, and ignition are in play at this point?
I'm with the others that, even a stock '74 would benefit from at least 10° advance, if not 12° instead. Even with a Thermactor system present, it could probably use more than your 5 degrees.
Do you have a Thermactor/air pump system installed?

And verify that your distributor is actually advancing and retarding as it should. Not just bouncing around willy-nilly or not advancing at all.
Then check your jetting and re-jet or tweak the springs and needles to get your fuel mixture playing nice with the ignition.

Paul

 

[keymonkey]

Good point. Unless you started with a 289 instead of a 302, then it probably isn't really a "stroker" engine at just 306 cubic inches. Your original was a 302 (you have a '74, correct?) so unless the engine was a different one swapped in, and used a 289 core, then it was just a re-bore to 306.
Big difference in just a re-bore and re-stroking an engine. But it's still only 306, so isn't really a huge change from stock.

But more important perhaps, is what cylinder heads, pistons, cam, exhaust, and ignition are in play at this point?
I'm with the others that, even a stock '74 would benefit from at least 10° advance, if not 12° instead. Even with a Thermactor system present, it could probably use more than your 5 degrees.
Do you have a Thermactor/air pump system installed?

And verify that your distributor is actually advancing and retarding as it should. Not just bouncing around willy-nilly or not advancing at all.
Then check your jetting and re-jet or tweak the springs and needles to get your fuel mixture playing nice with the ignition.

Paul

So...... checked the timing and advanced to 14. Then when no improvement I thought maybe a bad wire somewhere so started with the coil. When changing the coil wire I leaned in the distributor cap and it slid back toward my air cleaner easily. Looked inside and it looks like the cap has been vibrating off center. I rotated it until it locked in and then locked it down. Idle smoothed out and the test drive went equally smooth. Never would have guessed. Just for answers to questions above the motor is a Blueprint Max 306 with the Edelbrock AVS2 off road 650 cfm. New setup springs didn't solve a loose distributor but I do feel like I'm getting a bit better idle now. Anyway......you guys are great with suggestions and ideas. Love it. Thanks.

 

[DirtDonk]

Great! Glad you found the main culprit.
It’s just goes to show that the forum is here to give ideas, advice and ideas from experience, and shoot-from-the-hip possibilities. But only the people right there on the scene can ultimately pinpoint what’s wrong.
Sometimes multiple things!

Good catch on the cap. You might keep an eye on it in the future as well, to make sure either it’s not doing it again, or it hasn’t received some advanced wear from its running out of position like that.
It might have shortened it’s, and maybe even the rotor’s lives. But it sounds like it’s working pretty good for now.