Transmission Problem or Engine Problem?

[flyboy1100]

so truck was running great for about 100 miles after carb rebuild and tune up. timing set to 12 degrees (maybe that is too much, will probably back it down to 8, emissions sticker says 4 @ 550 and my idle is set to 700). 305 engine, 700r4, 3.42 gears, 265/70r15 tires

anyway, after a lively accleration today it shifted to OD at about 55mph and then shuddered and bucked a bit. let off the gas, it stopped, hit the gas did it again. shifted to D and it went away. a few miles later shifted back to OD and all was well for the rest of the day (about 20 miles of mixed driving)

fast forward to this evening leaving work, hit the interstate and it started again, speeds 75mph, shuddered and bucked no matter what I did, had to drive home in D (40 miles)

closer I got to home and slower speeds i tried OD again. it would shift normally and run OK @55mph, but as soon as I hit the gas, it would sound a bit like a diesel and shudder. even when in Drive.

like i stated earlier, timing set to 12, i checked it tonight thinking maybe it backed off again, and it is still set to 11, unless i read the timing marks wrong, then it could be a lot lower. going to check tomorrow when the light is better.

so transmission problem or engine problem? also, other than bringing to a transmission shop, where do I go from here? kinda bummed out as i was just thinking I had all the mechanical issues pretty well squared away

 

[flyboy1100]

could it be the stupid ESC distributor. how do I test that out

 

[chengny]

I'm certainly no expert - mostly just stop by the Transmission/Transfer Case area to learn - but based on what you report, I would say it is a transmission issue. And since you seem to be okay other than when the TCC locks in, I would suspect a control system component is at fault.

If for example, the contacts inside your vacuum switch are not snapping open and closed as designed, but rather they are chattering - the 12 volt signal to the TCC solenoid will be fluctuating as well. Consequently, the actuator and valve will not cleanly open and close. This could cause an erratic hydraulic signal in the circuit that locks the OD in.

The fact that the transmission is operating normally until OD kicks in would support this "theory". You might try hot wiring the TCC through a temporary switch and bypassing the automation for a test.

Get up to the normal engaging speed, close the switch and note whether the shuddering effect is still there. If it goes away when a good steady power supply is provided to the TCC solenoid, it's a control problem.

Check your vacuum switch, inspect the sensing line for leaks and be sure the associated wiring is intact and tight at the connections. The TCC solenoid only has one wire going to it (sometimes two). So it is easy to test with a jumper. Somebody wrote this:

At it's most basic, the only thing the TCC system requires to lock up the power train is 12VDC to the solenoid.

The solenoid is internally grounded through the transmission casing. So, if the coil is good and you supply a hot wire to it, the valve will operate.

I have looked at a lot of wiring diagrams over the past couple of days and, while there are many variations of the wiring harness into the transmission, one thing is consistent. The lead that supplies power to the TCC solenoid is always light green.

Take 12 volts from anywhere, run it through a switch and feed the solenoid coil (via the light green wire). When you want overdrive, flip the switch closed and the torque converter will lock up.

Go read this thread:

http://www.gmsquarebody.com/forum/showthread.php?t=10090


When you're done reading, you'll know a lot about TCC/OD systems - probably more than most people would consider healthy.

BTW - I would forget about the ignition timing for now. I seriously doubt that is the issue. A SBC can tolerate even a very badly mis-timed spark without causing the truck to shudder and buck.

 

[flyboy1100]

Read that thread. Maybe before i try a switch, i Will just unplug the brake switch or vacuum switch then i won't have lockup. I seem to remember tapping the brake last night and watching the rpm and it increased like it should, but it is definitely a starting point

Sent from my SCH-I605 using Tapatalk

 

[flyboy1100]

I disconnected the vacuum switch which should have killed power to the TCC if i understand it correctly, no change

Checked timing, it was off just a bit as i used the wrong mark yesterday when i checked, no change but does idle better, need to retune carb idle, unrelated..

Checked transmission fluid, i am 1/2pint low, could that be it, not very much considering the full capacity. Will get a new filter and fluid tomorrow and drain/refill again. Just did it like 1000 miles ago, but i know that doesn't change entire capacity. Color is medium red and smells slightly burnt (it was dark red and burnt smelling before i changed it).

Also plan to order a transmission pressure gauge to check tv system.

But it surges/bucks when trying to shift from 4-3 at light throttle applications, larger throttle and it downshifts correctly. So to me with limited transmission knowledge or seems like either 4 or 3 clutchpack( wrong term perhaps) or tv system.

But really i have no idea

Sent from my SCH-I605 using Tapatalk

 

[flyboy1100]

I called a recommended transmission shop in my area and he said it sounds like a plug or wire issue. He said he could tell me exactly what it is with s test drive, so maybe next Monday i will go do that

Sent from my SCH-I605 using Tapatalk

 

[350runner]

Very well could be a plug wire (easy) just buy a single wire from your nearest part store and swap em, but to me sounds like the clutch packs aren't getting the fluid they need (hints the burnt fluid) after you get that pressure gauge setup post up your readings.

Sent from the dust in front of you!

 

[350runner]

Also do you have a cooler installed yet?

Sent from the dust in front of you!

 

[flyboy1100]

Also do you have a cooler installed yet?

Sent from the dust in front of you!

pretty sure i do. I didn't install it however but there is definetly a smaller cooler installed in front of the radiator with lines that look like they go towards transmission lines. I will admit I didn't follow them 100%

 

[flyboy1100]

should add plugs/wires/i think cap and possibly rotor are new as of about 12 months ago according to PO. they certainly looked ok when i pulled everything apart a few months back, but that doesn't really mean anything either.

 

[350runner]

If really be more concerned about keeping that trans cool and tv cable adjusted at this point. Burnt smelling fluid is never a good thing.

Sent from the dust in front of you!

 

[flyboy1100]

If really be more concerned about keeping that trans cool and tv cable adjusted at this point. Burnt smelling fluid is never a good thing.

Sent from the dust in front of you!

It is definitely better adjusted now that my throttle cable issues were fixed.

I am going to pick up some plugs and maybe wires tomorrow they are easy enough to check.

And the fluid was really bad before I changed it before, but the TV cable was Fayed and binding.

Sent from my Nexus 7 using Tapatalk

 

[flyboy1100]

http://auto-repair.yoexpert.com/tro...se-my-car-to-misfire-under-load-like-758.html

i'm all for learning how to troubleshoot this stuff w/o a computer, but man sometimes it is just nice to pull the code, see "misfire cylinder number 5" and go from there.

 

[350runner]

http://auto-repair.yoexpert.com/tro...se-my-car-to-misfire-under-load-like-758.html

i'm all for learning how to troubleshoot this stuff w/o a computer, but man sometimes it is just nice to pull the code, see "misfire cylinder number 5" and go from there.

Lol yea maybe it's time to go Ls I know the feeling. Idk but at first when I got into carbed engines it was cool as Heck... then came the trouble shooting. Ugh I've never had a break down thank God. Here lately with the price of an Ls swap being bout the same as a complete fresh carbed rebuild with all new parts under the hood I'm thinning what life wild be like. To just crank and go.

Sent from the dust in front of you!

 

[flyboy1100]

Lol yea maybe it's time to go Ls I know the feeling. Idk but at first when I got into carbed engines it was cool as Heck... then came the trouble shooting. Ugh I've never had a break down thank God. Here lately with the price of an Ls swap being bout the same as a complete fresh carbed rebuild with all new parts under the hood I'm thinning what life wild be like. To just crank and go.

Sent from the dust in front of you!

there is a complete 5.3 near me for 1300...just don't have 1300 currently. would like something different though, need more torque and a different engine could give me that

just weird that it is part throttle, only in OD, and only once there is a load on the engine. been trying to research this, but it is tough for sure. so many possiblities.