Vibration over 70 please help!

[78Delta88]

Pull the pan. And see what metal is there. With the clicking in neutral you might see if the parking support is tight. You can see with pan off. TH350 can crack the race on the over running clutch. Sonnex has a hardened unit. Could be anyone's guess of what let loose, but if there is metal in the pan, (meaning pieces of aluminum or steel) you will need to pull the trans and pull apart.

 

[SamJam05]

If the vibration is only present under load as you described, then it’s in the driveline FER SURE. If it were a tire, front end component, axle, driveshaft, etc, then the vibration would be consistent regardless of load.

Since the only thing that is different from what you’ve described, is the the differential/ring and pinion. My guess is the backlash is too tight. A cheap, and relatively easy test is to increase the backlash by .002 - .004”. Pull the axles, then pull out the differential/ring gear and move .003-.006” of shim from the left side and put it into the right.

Gear setup is like rod and main bearings clearance - a little too loose and no one will know, but too tight and everyone (and you) will know. I run the backlash at the top of the spec or .001-.002” too much. The gears will be fine a little, repeat a little, too loose. Considering I’ve been doing this in the 800-1000hp range, I’m sure you’ll be fine. If you feel that this adjustment is over your head, but you can do basic repairs, then you’re wrong. The only tool needed is a budget caliper. The only parts needed are a rear shim kit (less than $50) and some silicone.

When I originally set backlash it was at .011 from what I read, spec is .006-.010. I am at the upper end of tolerance/thousandth too high currently. I can pull the cover and double check though

 

[SamJam05]

Pull the pan. And see what metal is there. With the clicking in neutral you might see if the parking support is tight. You can see with pan off. TH350 can crack the race on the over running clutch. Sonnex has a hardened unit. Could be anyone's guess of what let loose, but if there is metal in the pan, (meaning pieces of aluminum or steel) you will need to pull the trans and pull apart.

Have a family member with a spare th350, just found out last night. I’ll drop the pan on mine check it, and probably just take it out and throw his in to see if that fixes the issue as well.

 

[78Delta88]

If/when you do, don't toss the other TH350, as they are getting harder to find.

If possible go through the replacement TH350 first. The banner kit is up in price, but you can still get around $100.

You will need the press for the Forward and Direct Drum pistons, and the other tool for the Low Reverse unit which is in the back of the trans.

You will need a fairly stout long straight pick to get the snap ring off that holds the output shaft to the front and rear planets. Other than that you don't need any other special tools.

If you don't open it up, make sure to check the two bushings at the back of the trans. There is one at the rear of the case and one at rear of output housing.

The one at Rear of the case will be difficult to see with the shaft still installed, but check to see that it is not worn out. Hard to explain here on the forum, but remove the governor and speedometer gear. You should be able to visualize some or most of the surface with a flash light. Check for obvious scratches, wear, bearing material wiped off.

On the output you can just buy the bushing as a separate item, Rock Auto or Oregon Performance Transmission carries it and just replace. If those two are worn out it can cause output shaft to wobble and you are back to same problem.

TH350 can be built up to 800HP range but it's not the HP that wears them out, it's the Torque and hard launches. The 350 is only rated for about 350 pound feet. And the 74 and later were only built for Federal 55 MPH Highway Speed mandates, and you are driving over 70 without overdrive. The good thing is, that they were originally designed pre-70, for heavy cars and 80+ highway speed.

 

[SamJam05]

If/when you do, don't toss the other TH350, as they are getting harder to find.

If possible go through the replacement TH350 first. The banner kit is up in price, but you can still get around $100.

You will need the press for the Forward and Direct Drum pistons, and the other tool for the Low Reverse unit which is in the back of the trans.

You will need a fairly stout long straight pick to get the snap ring off that holds the output shaft to the front and rear planets. Other than that you don't need any other special tools.

If you don't open it up, make sure to check the two bushings at the back of the trans. There is one at the rear of the case and one at rear of output housing.

The one at Rear of the case will be difficult to see with the shaft still installed, but check to see that it is not worn out. Hard to explain here on the forum, but remove the governor and speedometer gear. You should be able to visualize some or most of the surface with a flash light. Check for obvious scratches, wear, bearing material wiped off.

On the output you can just buy the bushing as a separate item, Rock Auto or Oregon Performance Transmission carries it and just replace. If those two are worn out it can cause output shaft to wobble and you are back to same problem.

TH350 can be built up to 800HP range but it's not the HP that wears them out, it's the Torque and hard launches. The 350 is only rated for about 350 pound feet. And the 74 and later were only built for Federal 55 MPH Highway Speed mandates, and you are driving over 70 without overdrive. The good thing is, that they were originally designed pre-70, for heavy cars and 80+ highway speed.

You and everyone else have been incredibly helpful and it’s much appreciated. I definitely won’t be throwing it out, just trying to be cost effective in my diagnostics vs throwing a ton of new parts at it (which I’ve done). I already replaced the tail shaft housing bushing and seal, I will make sure to check the other one as well. The tail shaft doesn’t have a lot of play If any at all, so that’s why my brain keeps bouncing between rear end and trans. I figured cost effective just throw the other trans in in a few hours and drive it, if it’s not fixed then it would more than likely be the rear, if it is fixed then I know I have to tackle the trans. I’d rather not get too far into it without knowing if it’s the problem.

 

[64nailhead]

When I originally set backlash it was at .011 from what I read, spec is .006-.010. I am at the upper end of tolerance/thousandth too high currently. I can pull the cover and double check though

If you pull the cover and recheck gear lash, then check it on opposite sides of the ring gear to make sure the ring gear is straight. Also recheck your carrier preload.

 

[86LK]

If/when you do, don't toss the other TH350, as they are getting harder to find.

If possible go through the replacement TH350 first. The banner kit is up in price, but you can still get around $100.

You will need the press for the Forward and Direct Drum pistons, and the other tool for the Low Reverse unit which is in the back of the trans.

You will need a fairly stout long straight pick to get the snap ring off that holds the output shaft to the front and rear planets. Other than that you don't need any other special tools.

If you don't open it up, make sure to check the two bushings at the back of the trans. There is one at the rear of the case and one at rear of output housing.

The one at Rear of the case will be difficult to see with the shaft still installed, but check to see that it is not worn out. Hard to explain here on the forum, but remove the governor and speedometer gear. You should be able to visualize some or most of the surface with a flash light. Check for obvious scratches, wear, bearing material wiped off.

On the output you can just buy the bushing as a separate item, Rock Auto or Oregon Performance Transmission carries it and just replace. If those two are worn out it can cause output shaft to wobble and you are back to same problem.

TH350 can be built up to 800HP range but it's not the HP that wears them out, it's the Torque and hard launches. The 350 is only rated for about 350 pound feet. And the 74 and later were only built for Federal 55 MPH Highway Speed mandates, and you are driving over 70 without overdrive. The good thing is, that they were originally designed pre-70, for heavy cars and 80+ highway speed.

and here's some reference videos...

https://www.youtube.com/@PrecisionTransmission

 

[78Delta88]

Precision Transmissions has by far some of the best videos out there.

I was wrong on one of the specs. Originally I was going say 425 was the rating, now I'm looking at 410 being the factory rating, but I said 350 pound feet, conservatively not to lead anyone astray. Basically the TH350 can handle 300 to 425 or a little more pound feet of torque rated engine with little or no problem.

On the output bushing... Those were changed so would be ok. The slip yoke actually rides on the bushing and as long as that is all tight as far as spec, you shouldn't have much "wobble".

The following is a guess, but pic attached is the rear planet and these do fail and can cause the problem you have. Not a guarantee, just a possibility.



The pic below is the high performance unit that has the five pinion setup, plus a lower gear. This unit can handle more power and changes 2.52 first gear to a lower 2.75 first gear. The 1.52 second gear ratio will stay the same. Third gear is still one to one.

 

[SamJam05]

If you pull the cover and recheck gear lash, then check it on opposite sides of the ring gear to make sure the ring gear is straight. Also recheck your carrier preload.

I’ll make sure to do this, I am going to start at the trans when I get to a day off. Drop the pan maybe even change the converter. Drove it today, downshifting to second causes the vibration to come back. It’s seemingly due to rpm not mph, so I was very mistaken.

 

[SamJam05]

Precision Transmissions has by far some of the best videos out there.

I was wrong on one of the specs. Originally I was going say 425 was the rating, now I'm looking at 410 being the factory rating, but I said 350 pound feet, conservatively not to lead anyone astray. Basically the TH350 can handle 300 to 425 or a little more pound feet of torque rated engine with little or no problem.

On the output bushing... Those were changed so would be ok. The slip yoke actually rides on the bushing and as long as that is all tight as far as spec, you shouldn't have much "wobble".

The following is a guess, but pic attached is the rear planet and these do fail and can cause the problem you have. Not a guarantee, just a possibility.

View attachment 222446

The pic below is the high performance unit that has the five pinion setup, plus a lower gear. This unit can handle more power and changes 2.52 first gear to a lower 2.75 first gear. The 1.52 second gear ratio will stay the same. Third gear is still one to one.

View attachment 222447

Will these being faulty show up in the pan? I know little to nothing about transmissions, I will watch those videos in my down time. But judging by the fact that down shifting makes it worse it seems as though it would be more related to the transmission would it not? Again, much appreciated for all the information you guys are amazing