Hot Rods TH350 seems to be snatching at low speed

I have a 350/350 combo in my hot rod, yes, it's not Hamb trad, it is about the only thing available where I live. Anyway, the trans has always played up, so I had it fully overhauled a few month ago.

It always had this odd thing when going really slow, it was like something was dragging or snatching, and pulling the car along in little jerks. not too hard, just not smooth. Even now, after a full overhaul and a lot of new parts, plates, bushes, hard parts etc, it is doing it still. Converter???

Oil seems a bit dark, (I drained and filtered it) but no metal in it or bits of stuff, smells a touch burned, but why???? I have low miles on the trans since overhaul, no racing, very little hard use. Cooler is in front the radiator. I will be going out for a drive soon, will take my heat gun and check the oil pan temp afterwards.

There is no way to simply buy a new trans, which I would love to do, as everything has to be shipped in from the USA.

I also have a BW T10, but no accessories, no housebuilding,. clutch, shift linkages etc, or that would be going in right now.

Been building this car for so long and the trans has always been a pain in the ass. This will be the 5th time it has been out!

 

Are you sure the linkage is adjusted properly?
Interesting description, snatching.
I've got a fresh AOD that does something along those lines. I've decided to ignore it for now.

 

Maybe something caused by bad transmission or engine mounts? Funny drive-line angles? Rear axle and/or suspension binding or moving around where it shouldn't? Linkage adjustment as already mentioned? Something sticking or missing in the valve body? Guess it could be something in the convertor like the sprag going out, but I don't think of that as slipping and grabbing. It seems like they usually fail completely, don't they? I'm just grabbing at straws here...

 

Something wrong in the rear end? did you try turning the rear wheels, when the trans was out?

 

I should have added that I have an engine plate and four bar with heim joints, which was a line of thought that I am merely feeling drive-line vibration/roughness.

I went to see the trans builder and he checked the oil, colour, smell, level, temp etc, and said he can't really imagine what was causing it. Obviously we both don't want to pull the trans and tear it down with no real indication of a problem within.

He suggested I find a hill and drive slowly against it, so the brakes were not involved, and I did that. There is definitely a sort of 'rumbling' feeling and slight physical jerking,coming from somewhere.

Maybe it is drive-line rumble, which is why manufacturers use rubber everywhere?

There is a bit of a noise in the diff from old gears, when driving, but this problem is happening when the car is virtually at a standstill.

 

So it could be rearend bearings, or a wheel bearing, or something?

I was mainly asking if you'd really checked out the rest of the parts of the car that move when it's driving.

 

So has the car ever accelerated away from a stop and run at lower speeds smoothly? If not it may be time to look elsewhere for potential problems, like Squirrel suggests.

Having a lot of stuff mounted solidly and not isolated with rubber mounts can really magnify normally minor imperfections. Plenty of other things to consider beyond the trans, especially if this is an issue you've experienced since day one.

U-joint phasing? Prop shaft out of balance? Rear differential, bent axle flange, bent wheel, warped drum or rotor with a brake dragging? Is this a standard TH350 or does it have a TH350C with a lock-up convertor? Mismatch of flexplate and/or damper with engine relating to internal or external balancing requirements?

 

I doubt any of that will induce vibration when the car is actually sat still against something, in drive and idling, without moving forward, and the rumble/jerk is still there. That is what I discovered a couple of days ago.

But it does drive smooth and steady, accelerates okay etc when it is not hot. I can drive for 20 minutes and it is okay, seems to be just when it has really completely warmed up. But, trans temp is not more than 185f measured with infra-red heat gun on oil pan.

 

If the trans has time to warm up so does the rear end, the brakes, etc. As squirrel said, check every thing
it is easy to think you have a problem in one area and miss others, I have done it myself.

 

What cam is in the engine, what torque converter is in the TH350.

Do you need a higher stall speed converter for a larger cam?

 

What kind of Converter thrust clearance do you have? A good tranny guy would have checked that and will answer that for you. Your saying it only happens when at full run temp. Heat expands everything and converters need space. While your at it check your Crankshaft end play. However from what your describing I would look into the diff first.
The Wizzard

 

Just to clarify. Did you mean earlier that you can feel it without the car even moving? Like when you're up against a hill in drive but not moving?
Also, have you only noticed this issue since the trans was done this time? Or has this been ongoing?

 

I might have a look at the brakes not the trans. I would guess that your front brakes are binding up a bit when they get warm. Rotors are slightly warping with the heat in them. It will cause an effect you are describing. When you have this problem stop and jack up the front and try to spin the front wheels. You might be surprised.

 

Couple things from experience.

Converter and cooler should be redone and fresh with a new Trans. Otherwise the new Trans starts life off contaminated.

Friend of mine swore his Trans was bad and hit skip slipping. Turned out to be a faulty ignition component. A $3.00 part fixed the problem after the $800.00 Trans rebuild.

 

31 Vicky makes a good point. Quite often trans complaints are ignition.
Wasn't sure if your converter was new at rebuild? Understand getting parts is an issue for you.

 

Quote; "Converter and cooler should be redone and fresh with a new Trans. Otherwise the new Trans starts life off contaminated. 31 Vicky".

This is a must do. You also say this is the 5th time you had the trans out. Is that for the same issue? Did it go to a shop each time? If yes to each then you are probably looking in the wrong place.
The Wizzard

 

It makes this weird jerking when stood still, so diff or brakes are nothing to do with it.

Trans was swapped out for another 3rd time out of the car, a used one was installed, which was when the problem started. I almost lost reverse after a few months, which was when I had the overhaul done, lots of damage inside, but all was supposedly fixed.

While it was apart I drained the converter through a plug that has been drilled and tapped by someone at some stage. Swilled some clean fluid through it too.

Converter is stock.

Motor has a mild cam, not sure the specs.

I have a tunnel ram, twin Holleys, but I seem to recall it did the same things with a stock manifold and edelbrock carb.

Idling along in traffic no throttle, no brakes, I can actually feel the motor running a little unevenly, so I'm starting to think it may well just be vibration or engine pulses coming through the frame. I have no insulation, carpet, upholstery or Dynomat type stuff inside the body.

 

Presumably the idle is lower when the motor is warmed up? Might be as simple as a pulse / roughness / shake when idling? I guess you could feel for the source somehow?
Chris

 

Ck your driveline angles. My lowered truck pulses when pulling up a hill at low speed. A wedge helped but still not perfect.

 

Be more specific on you mild cam please. Was this cam in the engine all along? With solid mounts,you will feel everything

 

Yes, it has been in since I built the car. No idea of the profile, just a mild Lunati bumpstick.

 

And Neither does the transmission nor slow speeds.

 

The transmission is moving, rotating, clutches and plates are engaged, and holding the car still on the hill, so yes, it does have something to do with it.

 

Sounds like maybe a convertor problem ? Reason I say that is the fluid seemed slightly burnt on a pretty fresh trans. I'm just thinking out loud. Lippy

 

When your sitting still only the pump in the trans is turning.

 

But it is physically trying to pull the car along, holding it on a hill, so things must be working and moving inside the tran, surely? If not then the only moving parts that could be doing anything are the pump and converter.

 

The wrong fluid or dirty or contaminated fluid can cause a Trans to be grabby. You can read post 14 and maybe tell the same story from experience about fresh rebuilds and old converter.

If the Trans had plenty of internal damage as you say then the converter is full of junk too. Swishing fresh fluid around in a converter to clean it is equivalent to pissing in the ocean with intent to change the amount of water.

 

I could change out the fluid again. There is a drain hole in the converter so I could drain that too.

How about refilling, without taking it all apart I can't pour the customary quart or two directly into the converter.

 

I am no expert, but I have been thinking oil pump or convertor from the beginning of this thread.
The other thing could be as simple as incorrect oil level in the trans.
I had huge problems with a T700R4 tranny and every thing seemed right but still had issues.
A tranny guy suggested adding more fluid in a measured kind of way and driving and then if no change or little change, then add a small amount again.
Turned out we added over a 1 litre more and it has run fine since without issue.
Upon reflection I was of the opinion that the dipstick was not right for the tranny or the advise I was given regarding fill quantities was not accurate.
All the same it is the 1%ers you need to look out for.

My other thoughts early on was that the pinion shaft/bearings in the diff may have been an issue or if you are running a brake booster the shaft measurement between the booster and the master cylinder is not quite correct and when the brakes heat up they are binding due heat activation.

 

Did you solve this problem in the end???