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Discussion Starter · #1 ·
I've been working on a 1969 Chevy C/10 with a LG 250 engine and a THM350 automatic Trans. I'm having issues with it stalling out while driving. I can hit the gas and go, but when it gets to about 40-45 ish MPH, it starts dragging (almost feels like your downshifting) and will eventually stall if you don't let off the gas and slow down a bit. If you slow down to about 30-35 MPH you can hit the gas again up to the same 40-45 MPH and the same thing happens all over again. Just to get more info, I took it to a nice straight downhill grade and can get it to accelerate to more than 45 when going downhill.

It has also been wanting to stall while slowing/stopping. Note, I can throw it in reverse and haven't been able to get it to stall, I'm only having these issues going forward.

I am assuming that it's a bad torque converter. I am not noticing any odd sounds, vibrations or other weird things coming from the motor/trans, so I don't think the problem is there, but I'm more of an engine guy, I don't know as much about transmissions.

Any ideas would be greatly appreciated. I've already pulled the trans out. I'm not against buying a new TC, but I don't want to if that's not going to fix the problem.
 

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I've been working on a 1969 Chevy C/10 with a LG 250 engine and a THM350 automatic Trans. I'm having issues with it stalling out while driving. I can hit the gas and go, but when it gets to about 40-45 ish MPH, it starts dragging (almost feels like your downshifting) and will eventually stall if you don't let off the gas and slow down a bit. If you slow down to about 30-35 MPH you can hit the gas again up to the same 40-45 MPH and the same thing happens all over again. Just to get more info, I took it to a nice straight downhill grade and can get it to accelerate to more than 45 when going downhill.

It has also been wanting to stall while slowing/stopping. Note, I can throw it in reverse and haven't been able to get it to stall, I'm only having these issues going forward.

I am assuming that it's a bad torque converter. I am not noticing any odd sounds, vibrations or other weird things coming from the motor/trans, so I don't think the problem is there, but I'm more of an engine guy, I don't know as much about transmissions.

Any ideas would be greatly appreciated. I've already pulled the trans out. I'm not against buying a new TC, but I don't want to if that's not going to fix the problem.

You have an engine problem , not torque converter problem.

You describe a fuel delivery problem with the engine.

What is the condition of the engine? Age, rebuilt, high mileage?

:cool:
 

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Discussion Starter · #4 ·
The engine is original. I've changed out the water pump and all the gaskets. Other than that, it hasn't been touched. It's got 150,000-ish miles on it.

My thinking for it not being an engine problem is that when it's not in gear, I do pretty much anything I want to it and I never have an issue. The same applies to when I'm in gear, until I get to 40-45 MPH. I can floor it or ease into it and don't have any issues whatsoever until I hit that certain speed.
 

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x2 on Crosley's advice.

Just do a fuel pump delivery and pressure test.
At 150K ... that fuel pump is way past due for replacement.

Any fuel coming out of the atmospheric vent holes in the diaphragm housing?
 

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Wrench Turner
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Does it happen @ that speed in other gears? 40 to 45 in 2nd vs 40 to 45 in 3rd.This would help to determine if it is actually vehicle speed related vs engine rpm related.
 

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Discussion Starter · #7 ·
x2 on Crosley's advice.

Just do a fuel pump delivery and pressure test.
At 150K ... that fuel pump is way past due for replacement.

Any fuel coming out of the atmospheric vent holes in the diaphragm housing?
I will check. I don't remember seeing anything out of the ordinary there.

Also, let's just say I did discover something fuel related. I would think that would just cause the engine to stall and I would keep coasting. When I most notice the problem, is while driving. It drags and feels almost like I'm downshifting to slow down (enough to make you lean forward) then the engine wants to stall. I have hit a higher RPM rate than what it takes to make it stall when at that specific 40 MPH. (That sentence barely makes sense to me either) Of couse the truck I have does not have a tachometer, so I can't give exact RPM rates. I have completely stalled out many a time while I was working on getting the engine running in the first place. When it died, although usually at less than 30 MPH, it just died and I never noticed the dragging feeling.
 

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Wrench Turner
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Just wondering if you can maintain the 40 to 45 or even faster in 2nd vs 3rd,it would tell me that it is more likely fuel,vacum,or tuning related vs convertor,trans..IMO.
 

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Discussion Starter · #9 ·
Just wondering if you can maintain the 40 to 45 or even faster in 2nd vs 3rd,it would tell me that it is more likely fuel,vacum,or tuning related vs convertor,trans..IMO.
If I drive in 2nd, it does the same thing at 40-45. It doesn't matter if I'm flooring it or just slowly accelerating at a lower RPM, it always happens at the same speed, regardless of engine RPM.
 

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Discussion Starter · #11 ·
That's weird.Is convertor a lockup type? Almost sounds like maybe brake or differential draggin it down.
I don't really know for sure. Again, although I'll be the first to admit I don't know everything, I'm more of an engine guy than a trans guy. I can't tell by looking at it and I can't dig up any information on it. The only number stamped on it turns up nothing according to google.
 

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Wrench Turner
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I doubt it is.Just remembered you said truck wuz basically stock.It would have to have been added.You would have wires from the trans if it were.I wuz just thinkin that most lockup @ about 40 to 45.Just thinkin somethin could have been goin on there.My mind workin too much again.I smell wood burnin.LOL.
 

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Discussion Starter · #13 ·
I don't know why I never checked, but when I turn the spindles on the trans, it sounds normal, but after I put the tc on and rotate the tc on the trans, it whines a bit. Its not bad, but its there.
 

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Discussion Starter · #14 ·
I think I'm going to just replace the TC. If I'm wrong, it can't hurt to have a new one on there. The priciest one I can find is only $350-ish, could be worse.

I've narrowed it down to three that are compatible with my trans:

B & M Torque Converter, Holeshot 2000 Series - 1900 - 2100 rpm

B & M Torque Converter, Tork Master 3000 Series - 2800 - 3200 rpm

B & M Tork Master 2000 Torque Converter - 1900 - 2100 rpm

B & M Torque Converter, Tork Master Series 2400 - 2300 - 2500 rpm


Which one seems logical. I get the concept behind the stall speeds, but don't know which is the best fit for my truck.
 

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Wrench Turner
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With the stock 250 inline 6 you have,I would just get a good stock convertor.I think the stall on any you listed are gonna be a little high for your use.
 

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Discussion Starter · #16 ·
I just got a new tc. From what I found, a stock converter didn't have toom different of specs from the B & M Torque Converter, Holeshot 2000 Series - 1900 - 2100 rpm converter. Difference is that I bought the B&M from JCwhitney and the other "stock" ones were ebay, etc. I trust JCW a lot more.

Anyway, I got it replaced and nothing happens now. I shift into any gear and either idle or floor it and I don't move an inch. I checked everything twice now and can't find anything I missed. I really have no idea what's going on now....
 

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Part Number? Is it the correct convertor for your application?

How much fluid in total have you put in there?
I cant look up the specs for a 1969 C10, but an educated guess would be about 10 litres (or US quarts)

How did the installation of the converter go?

It's usually pretty easy to get the convertor into the front bushing, but a little tougher to get the front pump drive engaged. You should feel a definite click when it slides in, and it should spin relatively easy and straight with very little wobble.
Once you are SURE that the convertor hub has engaged the front pump, align the bellhousing with the dowels on the block and insert the bolts. Tighten them up alternately to ensure the trans is pulling up evenly to the block. You shouldn't require a lot of force on the bolts while drawing it in.

The convertor usually has a hub on the back side of it that fits into a pilot hole in the back of the crankshaft. Once the bellhousing bolts have been snugged up, the convertor tabs should now be in very close proximity to the flexplate. Insert and tighten those 3 convertor bolts.

IF you haven't properly engaged that front pump and have been running the engine ... there's a good chance that you have caused some damage to either or both the convertor and the front pump.

Let's hope not ...
 

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Discussion Starter · #18 ·
According to what I could find, it is compatible with my engine/trans combo.

GM Torque Converter – B&M Tork Master 2000 for GM

If you're thinking 10 Litres if fluid, then I went a bit low. I'll add some more.

I got the TC on the trans and seemed to fit fine. It sank all the way from what I could tell. I got it lifted back up to the engine block and bolted it in just fine. When I was bolting the TC to the flexplate, there was about a 1/8~1/4 inch gap and when I tightened the bolts it pulled the TC off the trans that gap. The bell housing is perfectly flush with the block, so I know that's tightened how it's supposed to be.

The engine has run maybe 5 minutes since it's been back together.

Also, what is the function of (according to google) a detent cable? There is a cable coming off the transmission, but ever since I bought the truck that has been just floating around the engine compartment, and never bolted down to pull on the cable. Could that be an issue?
 

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Sounds like you're OK on the convertor installation, IMO.

Don't just blindly throw in 10 litres of fluid though. Keep checking the stick until it's near the mark. It usually says "check hot, idling in park"

A TH350 "detent cable" is really not much more than a "kickdown cable" and is nowhere near as important as a "detent cable" on a 700R4.

I was able to find a thread on the 67-72 truck site that includes pictures. It sounds like some "Red Green"-ing may have nessecary, using parts off of a 70's Nova in this case.


Holley makes the correct linkage stud for a TH350 downshift cable.
Part # 20-40

Just as an aside ... a 70's Nova 250 HEI setup works on these old trucks. I had converted my 66 GMC to HEI using one.:thumbup:
 

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Discussion Starter · #20 ·
I wasnt planning on blindly adding. i thought i had typed check and more. I did add more, and it starting working as usual. i couldnt do a true test, I ran out of gas.....

I will try again once i get gas
 
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