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timing drag, strange shift points, and other wonderful mysteries...

5K views 35 replies 9 participants last post by  bowtietruck 
#1 ·
Hi all!

Before I begin, I want to let you know that yes - I had tried to search these boards as well as google, but keywords like "Drag" don't really bring up the correct articles lol...

SO... I've got this issue, started happening randomly, maybe sometime after I installed a 2400 stall, or rebuilt the top end. Now I don't have extensive knowledge of engine building, so I lay the trust on a mechanic, but he does fill me in on what he does.

The issue I experience is when driving highways, if I am accelerating, and reach, per se, 3000RPM, then let off the gas pedal, the RPMs drop to around 2800 and I feel the car getting pulled back - something I discovered is classified as "timing drag"? I am 100% sure this is not normal, since I've owned the car for over 10 years, and before, the RPM's would drop somewhere lower, and it would coast like it was in neutral - almost as if the engine disengages from the tranny (not sure what thats called).

We have tried to advance the timing on the vacuum advance, I remember at one point mechanic replaced the dist spring for a heavier one, ive got an MSD ignition box and coil, going to a 454 bored over with a comp cam 228 lift @ .50, 870 holley carb, 2400 stall, TH400 and fresh 3.42 out in the rear.

with all of this strangeness going on, ive also noticed shift points during cruising are off a bit (1 to 2 shifts at 2400 but only drops to 22) and etc. I would imagine there being a wider band between gears when switching.

would appreciate any help and advice - perhaps someone has dealt with this in the past? More than happy to answer any supporting questions.

Cheers guys!!!:banana:
 
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#2 ·
I am not positive BUT it could be the converter. Not that there is anything wrong with it but your shift points will change with a stall speed converter. Never heard of timing drag??? I have run a few stalls before and they change every thing shift points to rpm at certain speeds.
 
#3 ·
after doing more research, im thinking maybe my throttle return spring is too loose, or too big? gonna try a stiffer spring and maybe a dual spring setup to see if it helps whatever is going on?

thing is, when we installed the converter, everything was fine. i cant really remember when the problem occured, but just around the same time, my throttle return spring snapped on the highway, so i pulled over at pepboys and bought some unversal springs and installed one that KIND of resembled the OEM one. would that affect it?
 
#5 ·
its a TH400, the kickdown is hooked up, but I have a feeling its not functioning as well as it should be either. My educated guess says that when the gas pedal is slammed, it should hit the floor, and have the kickdown switch engaged fully. For some reason there is a bolt connected to the side of the pedal, that engages the kickdown lever before the pedal is fully to the floor. In any case, I do believe the pedal still achieves WOT, but I actually plan on yanking that bolt out to see what happens.

The kickdown does engage, as I feel it. But with my motor and 3.42 rear, I've heard that im supposed to get whiplash and burning tires when stomping on it at cruise speeds... :sad2:
 
#6 ·
I've heard that im supposed to get whiplash and burning tires when stomping on it at cruise speeds... :sad2:
Not with a 228 lift cam. :poke:

...I'm sure that is your duration not your lift.
 
#7 ·
never heard of "timing drag" before.. got a link??

what you feel when you let off the throttle "getting pulled back "
is engine braking, or compression braking
what makes the biggest difference is rpm and what gear your in,
2nd gear will have a lot more braking than 3rd,
3000rpm in 3rd gear would feel more like coasting and less braking..
ignition timing has little effect on this,
you would get about the same amount of engine braking or more with the ignition switch off..
as for the randomness check the vacuum modulator, or governor??
it may be sticky or starting to leak?? just a guess?? I don't know??

as for the 2400 converter, is this a stock transmission??
just as a kinda generalization [usually street converters are not that loose]
anything under 2400 and its slipping, if you shift at or below 2400 you unload the converter,
the rpm could go up instead of down..
a stock trans could be setup to part throttle shift as low as 18-2000rpm,
shifting at under 30-3400rpm is just slipping the converter and building heat..

:texas:
 
#10 ·
I have a 2800-3000 converter in my Willys. I don't use a kick down....don't need it with blower and 2800 pounds.

I'd guess you get about 400 rpm drop between " gears" at part throttle. As you increase the rate of acceleration you will get a little slippage from the converter. As you go faster say over 3000-3500 the converter doesn't slip as much, maybe 200 rpm. If you are cruising at about 3000 rpm (75 or so ) I'd expect only 200 rpm drop as you let up a little. This is about as close to lock up as these converters get.

I have a 77 SS with 350 and T 350, 3.42 gears and 2400 converter. Mine drops 400 rpm between gears and has about 200 rpm slip at cruise speeds. I haven't tried coasting in 2nd gear, it's not a good idea unless necessary.

As for the "drag" never heard of such a thing. If it pulls down on the motor it's as was noted above. " compression drag" or what ever you want to call it. It happens on gas motors. Diesels don't have this, that's why they have exhaust brakes. Some modified transmissions do not have this " braking " feature. Modern cars often have the motor go almost to idle when you let off on the gas especially in OD. if yours never did this and now it is or random does it, I'd suspect some internal problems are happening. Not good. You may want to go to a good transmission shop for evaluation. T 400 are tough trans. But not totally bullet proof.

Fix the throttle spring. Dual springs area safety issue so use them.

If you have an MSD distributor ten years old I'd surely take the cap off and inspect the inside. Mine lasts two years and it's worn out. Remove the rotor and inspect the weights and springs. These can get corroded and stuck and make the motor do all kinds of strange things. The newer MSD caps have vent holes to relieve moisture build up as well as vent the ozone the spark creates.

As for the bolt on the gas pedal, I'm not sure with a T 400 but I think they have electric kick down so maybe this activates it. It may be just a throttle stop so you don't stress the carb stop.
 
#12 ·
Thank you so much for this - you've essentially hit the nail on the head with your response.. mine gets just about 400 rpm drop between gears, which is audibly different from what it used to be, but then again I didn't have a stall converter in there before. Sometimes its even less, if I really tried, I could probably catch it going through all 3 gears with only 100 rpm drop between each, which as you can imagine, is freakin obnoxious.

On the highway, I used to have that same "new car" concept, where the car would nearly go into idle when letting off the gas, and now I get this pull back, drag, whatever it might be called. The bigger issue with all of this is that the car runs noticeably hotter because of this, cause once I let off the pedal at 3000RPM doing 75, it drops to maybe 2700RPM and starts slowing down - unnecessary revving and pressure on the motor that was never there before.

Gonna take my car in on Monday, and perhaps it could be a transmission issue. was planning on putting a shift kit in there anyways.

Did the dual spring setup, that didnt solve the problem.

Definitely agree on the MSD distributor, I could probably use a new one.

Will let you know if I make any progress soon! ah i love these forums!
 
#13 ·
When you add higher stall converters I'd consider it mandatory to add an additional trans oil cooler. Your radiator cooler keeps the trans temp at 180 or what ever you running temp is. The converter adds a lot of heat that the radiator is not able to handle.

I run an external cooler without a rad cooler in my Willys. The temp normally runs about 150-170 al, the time. The excepting is idling through the crowd at cruise ins. It goes as high as 210 after 1/2-3/4 hour idling.and stop and go.

I'm going to add a cooler to my el Camino in the spring. I already have a port on the oil pan for a temp sender.

When you add a cooler put it in front of the rad or condenser. Also DO NOT use the usual through the radiator plastic tie downs. Go to the extra effort to make a permanent bracket. Keep it about 3/4-1" in front of the rad or condenser.

Byron
 
#14 ·
we do have an oil AND trans oil cooler installed in front of the radiator. We installed it on custom brackets to make sure its set and secure.

I will be taking the car in tomorrow to see about the possibility of timing being off. I know theres been a leak in the tranny for a long time now - coming from the speedometer cable i believe, but I'm not sure how this could result in such erradic RPM shift points and winding, or however else you would classify this as.

I just want this beast running at top notch... :(
 
#15 ·
I don't live far from you I'm in the City Of Commerce 5 FWY and Atlantic Blvd. If you want to stop by this weekend we can take a look at it.

When we started mine a my buddies shop.


Robert
 
#20 ·
You got way too much time on your hands.
 
#21 ·
Originally Posted by JJLT1 View Post
got a link for the "timing drag" and other research??

You got way too much time on your hands.

X2
 
#24 · (Edited)
Getting back to Nick's question.

Nick, Can I ask for a little clarification? This might help others add value to the discussion.

This weekend, you adjusted your initial timing and measured it at 26 degrees.

Correct these statements if they are wrong.
1) Total timing (initial plus mechanical) was not measured.
2) Vacuum advance was not measured.

Do you know if your mechanical advance, sometimes called centrifugal advance is locked down?
There are several cars in our area that run a mechanical advance locked down. I am not encouraging this for you, yet say it is not rare to find.

My situation is different from yours (see my garage). I run initial advance of 28 degrees and lock out mechanical advance. I know other older GMs running this way, even without the concerns of boost. I am not recommending the lock down, yet for someone looking at my MSD Streetfire, they would think I am adding 22 degrees mechanical. Only with checking with a timing light at high RPM (or seeing the mech advance disabled inside the distributor) would they know that it is adding zero.

If total advance (initial + mechanical) was not measured, you might not have much mechanical coming into play. Sometimes the distributor mech advance binds and does not come into play or limits that part of the equation.
 
#25 · (Edited)
This just happened two weeks ago to me it's the MSD Box. I ran fine all the way to Fontana drags in the morning . Once temp outside went up and I was waiting in line to run with the engine on it died. It would crank perfect but wouldn't even pop. Got towed back to my pits and started checking. The thing I checked was to see if I had spark but nothing. after about an hour of checking wires it fired up. I thought I had a loose connection. After the engine warmed up again in line it died again. This went on till I started thinking vapor lock. Got towed home and went on line to see how to test the box. after the engine warmed up in the hot afternoon truck wouldn't start so I pulled the blaster 2 out of the 69 swapped coils still no start. Jumped the box wires no spark. Ran up and got a new box fixed it. His is doing the exact same thing when hot. I pulled the dist. to see if the pin on the dist. shaft gear broke but it was fine then re-timed the engine at the track but that didn't help.
 
#26 ·
I didn't see Nick mention that his truck was dying/not starting, only not accellerating well.
I know you likely have spoken with him and have heard more than I.

I did see that there is a different thread open by another member with an MSD and his car is either dying or not starting when hot.
 
#31 ·
my bad wrong thread sorry.
 
#27 ·
Hey guys, thanks so much for all your feedback and help. Still dealing with all of this, and it's getting more and more confusing lol...

Old Bear, we measured initial + mechanical advance with the vacuum plugged. The mechanical gave it an additional 24 degrees, vacuum advance we measured at 10 degrees

Is it possible that MSD ignition does read correctly with regular timing lights? Maybe its reading at half (or double) than what it really is? We were messing with the distributor and when I first had it installed, my mechanic made a mark for 12 degrees, which is where the dist is sitting now, but timing light is reading 24..

I also researched online and saw that someone else was having issues with their MSD setup and was getting crazy readings, and apparently if polarity on the pickup wire is reversed, it would read 20-30 degrees off, but my plug only fits one way.

Just to clarify, my truck is not dying, has no issues starting, no backfire, no pinging whatsoever. Once we advanced the timing as mentioned, the acceleration / engine response improved by a substantial amount. I am currently idling around 950RPM, 750RPM when in Drive. Engine sounds healthy, so theres that.

To add another layer of complexity, which I assume might tie in: I replaced the rear diff with a 3.42, and am running a TH400 trans. This obviously means I am revving higher on the highway (around 3000RPM at 65MPH). Well, last night I got a little excited and maaaaybe was going a bit above the speed limit, running the engine at 4000RPM for no more than 10-15 seconds, just to hear it. All of a sudden I smell burning oil, let go of the accelerator pedal, and see a good amount of white smoke out of my pipes. Obviously freak out a bit, pull over, examine the oil, everything is fine. Driving home everything was fine and the instance didn't repeat itself (granted I didn't do 4000RPM anymore)...

all this help and advice is extremely appreciated guys. I just feel like I've built this monster over the past decade, and something like timing is preventing it from really breaking free haha... I want to take this thing to the strip!:dontknow:
 
#28 · (Edited)
Thanks for the feedback Nick.

MSD - Understanding Ignition Timing - Reynolds with Freiberger for Summit

To help avoid confusion. My use of "locked down" in threads above refers to the mechanical advance being locked to add no more timing. Presenters in this video refer to 'locking down distributor" which in their language means to tighten distributor hold-down clamp bolt so the distributor body does not shift positions.
 
#29 ·
Hey Old Bear,

Yeah so we are definitely on the same page. The distributor is not locked down (mechanical advance exists), but we have tightened it down so that it does not move or wiggle in place.

In the case of the video explanation, my initial timing seems to be at 12* with an additional 24 degrees of advance, giving it a total of 36* which seems right. Wondering if I should perhaps raise the initial and decrease the advance with heavier springs?

I also read on a different thread on this forum about an old school method of setting timing without light, where you put the car in drive, hold down the brake and rev the engine to 2400RPM (thats where my stall is) and advance the timing until it starts pinging, then roll it back 2-3* and that is where the ideal total timing should be? Does that sound about right? I don't mind testing this out to see what it does.

All info points to the fact that the timing gun we are using is showing incorrect numbers...
 
#30 · (Edited)
"All info points to the fact that the timing gun we are using is showing incorrect numbers... "

It might be good to meet up with HkdUp87 (Robert) just down the 5 fwy.
I believe he has a relatively new timing light.

One more set of experienced eyes on the MSD weights for centrifugal advance would not hurt.
If Dale is around...even better with that set of eyes too.
in his earlier post,Bryon suggested giving it a good look since he has experienced failures with his MSD.

Also, since you like the track, Robert likes company when he goes to Irwindale on many Thursday nights. It is east of you in Inglewood. He could be back at the track in late April or May.
 
#32 ·
you have changed shift points and might even have shift kit
if your trans is kicking into nuetral around 70 or 80 i had stock truck
doing that and radiator was plugged its a trans fluid heating thing
have air ? you have to have to have regulated 12 psi so you dont pop radiator
ajustable nob on air nozzle
I forget what you spay in out line call tranny shop
you blow it out in reverse
and by all means add Bent wings oil cooler
and if that still kicks in nuetral you need to check trans pump.
a lots of the time trans mechanics will have hole in backing plate
and pump gear will get caught on hole
if their good repuable shop theyl pay fore used good hard part pump.
and pass cost to you .
first he bragged to me.
then he sanded down a hole bigger than a silver dollar
so pump gear would not catch on it .
for about 100 miles LOL
just passed his warranty
I got so mad I knocked him down made him open up trans and pump to show me
the pump was good on tranny he just sold me FOR 800$
pulled out a hunk of his hair too.LOL
SORRY about the rant.
Im with Bent wing And it doesnt take much but breaking tranny lines loose to flush raiator. :secret:
 
#35 ·
WOW guys you got issues
I never had so manyLOL
I run single carb blower and have desent knowledge about basics
never even timed cam before
but can maybe see from outside your boxes
BASICS
its spring change your fuel filters water in gas plugs filters giving idle step on gas and it just dies.
fuel pumps and coils when there tired take a dump when they get hot.
superchargers make a little compression but actualy make more horsepower thru RPMS and in doing so run harder spark and fuel thru rpm and mine always
melts diode in distributor cap msd hyperteck so watch those carefully.
might be reasonable to get cheap new stock coil on hand cause you forgot the reeson you shelfed that coil to begin with
i keep whole distributor on hand for anilizing that hasnt been tortured LOL
one poof white smoke smell oil usualy isnt bad
but might run compression check to make sure it wasnt new higher rpm
spitting out stock head gasket thats why they machine steel rings in block
copper gaskets or ring that comes in gasket
I just run rings in gasket 5-7 psi single carb but if i crank it over 10000
itl hit hp like i dont usualy do und spit out headgasket
timed at 12 degrees with advance coming in before 2000 rpm with or without vac.
you run big blowers but im sure you got my problems too
main blog kicking out of gear on freeway is trans overheating
reverse blow out your tranny lines call a trans shop find out what to spray in line
and dont go over 12 psi or youl blow radiator and add cooler tork converter
rode hard makes more heat on trans fluid
and blow in trans modulato with mouth if it leaks thats what made white smoke.
antifreeze and trans fluid white smoke
black smoke rings and valves seats
hope i helped some times ask the fifth grader LOL
thru rpm new tork convertor has raised you hp quite a bit new problems
THINGS WILL TEND to BREAK so reinforse them
I run 308s so it saves alot keeps rpms road racer
but did sand drags hillclimb racing 2 years
daily driver but loves to get up 5 till 7.00 and be to work 2 till 7.00
25 miles away from my house
cops will never take me alive LOL they try
had to buy the mechanics lunch to hide my truck in shop
on many occasions than they blackmail me to not tell when cops are driving thru yard LOL
 
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