TH350 Help Needed!

SG7874 · 07-16-2022, 04:12 PM

Hi Class Racer,

Hoping someone can hep with my transmission problem. The short of it is there is no drive shaft RPM distinction between 1st and 2nd gear. 3rd gear is 1:1 but 1st and 2nd are about 1.5:1 each. Gears installed are 1st, 2.52:1, 2nd 1.52:1, 3rd 1:1.

Backstory:
-Purchased a car with the transmission, previous owner had no idea what is was composed of.
-Took it to a S/SS transmission builder to go through it, installed new Coan TH350 TB clean neutral valve body, new front drum, planetary, and new JW bellhousing.
-Installed the transmission and observed the issue mentioned above while in the garage on jack stands.
-Note, prior to this there were additional issues with the new valve body not holding the trans brake, modifications were required. Works well now.
-Took the transmission back to builder he took it a part and could not find anything wrong and has given up trying to find the problem. The shop does not have a transmission dyno.
-Reinstalled the transmission this morning (with only a hope and a prayer) and sure enough it did the same thing.

Troubleshooting I have done:
-Verified the drive shaft RPM ratio is the same at low and high RPMs under load and not under a load in the garage. Note, I still have never been able to make a pass in the car the last two years I have had it!
-Verified via Racepak data there is no drop in RPM when going from 1st to 2nd, there is a drop when going from 2nd to 3rd.
-Verified that the trans brake functions in 1st and verified that the trans brake does not function in 2nd.
-Done the above tests with the shifter installed and having removed the linkage. Verified that there is no issue with the shifter or linkage.
-Verified that reverse has the correct gear ratio, about 2:1.

Note this is for a 2002 SS Firebird.

If there is anyone out there that has any insight or can point me in a direction that might help, would love to hear from you!

Thanks,
-John

Mike Jones · 07-16-2022, 05:36 PM

Not an expert, but if it were mine, to start with....
I would take it down the street, shift it twice, and see what happens.
Good luck
MJ

mike britt · 07-16-2022, 05:39 PM

I can't hear, feel, or see any difference in my car on jackstands but when I drive it down the road it feels fine.

SG7874 · 07-16-2022, 05:46 PM

Thanks guys, for the suggestions. I will take it out for a spin on the street tomorrow and see what happens. I am basing this on Racepak data, specifically driveshaft to RPM ratio.

Mark Yacavone · 07-16-2022, 05:49 PM

Was the intermediate sprag looked at..not just turned by hand? Does it have the Coan light, small components?

SG7874 · 07-16-2022, 05:52 PM

Quote:

Originally Posted by Mark Yacavone

Was the intermediate sprag looked at..not just turned by hand? Does it have the Coan light, small components?

Hi Mark, it does not have the lite version. I will have to ask how the intermediate sprag was checked. Thanks for the suggestion!

e vassar · 07-16-2022, 11:04 PM

Not a expert either but I also have a T350 and a fairly loose converter. My tach will drop more on the 2-3 shift than the 1-2 shift.

Eman · 07-17-2022, 01:14 PM

When I had my T-350 it didn't feel like it shifted 1st to 2nd on the lift. As other said road test it.
You mention a new drum, you said front drum. The drum at the front of the transmission is the direct or high gear drum. It's the one without the shaft, the one with the input shaft is the forward clutch drum. The direct drum is the one usually replaced as it is the one that holds the intermediate sprag. The drum with sprag is generally replaced so you get the better 36 elemant sprag. https://www.tsr-racing.com/th350-dru...ent-sprag.html
If this was replaced I'd like to think it's good.

ss3011 · 07-17-2022, 04:39 PM

Quote:

Originally Posted by Mark Yacavone

Was the intermediate sprag looked at..not just turned by hand? Does it have the Coan light, small components?

Mark , Are you thinking the one way clutch on the direct clutch drum is locked up so it starts up in 2nd gear ratio ? There have been some sprag conversions that don't have the end caps and flip the sprag almost instantly .

SG7874 · 07-19-2022, 03:34 PM

Hi All,

Update time. Took it our for a spin this morning and was able to feel the shift! You can even see it in the data logger. Appreciate everyone's input. Long of it is, just go out and test!

Thanks again.
-John

07-16-2022, 04:12 PM	#1
SG7874 Junior Member Join Date: Mar 2020 Posts: 16 Likes: 9 Liked 26 Times in 5 Posts	TH350 Help Needed! Hi Class Racer, Hoping someone can hep with my transmission problem. The short of it is there is no drive shaft RPM distinction between 1st and 2nd gear. 3rd gear is 1:1 but 1st and 2nd are about 1.5:1 each. Gears installed are 1st, 2.52:1, 2nd 1.52:1, 3rd 1:1. Backstory: -Purchased a car with the transmission, previous owner had no idea what is was composed of. -Took it to a S/SS transmission builder to go through it, installed new Coan TH350 TB clean neutral valve body, new front drum, planetary, and new JW bellhousing. -Installed the transmission and observed the issue mentioned above while in the garage on jack stands. -Note, prior to this there were additional issues with the new valve body not holding the trans brake, modifications were required. Works well now. -Took the transmission back to builder he took it a part and could not find anything wrong and has given up trying to find the problem. The shop does not have a transmission dyno. -Reinstalled the transmission this morning (with only a hope and a prayer) and sure enough it did the same thing. Troubleshooting I have done: -Verified the drive shaft RPM ratio is the same at low and high RPMs under load and not under a load in the garage. Note, I still have never been able to make a pass in the car the last two years I have had it! -Verified via Racepak data there is no drop in RPM when going from 1st to 2nd, there is a drop when going from 2nd to 3rd. -Verified that the trans brake functions in 1st and verified that the trans brake does not function in 2nd. -Done the above tests with the shifter installed and having removed the linkage. Verified that there is no issue with the shifter or linkage. -Verified that reverse has the correct gear ratio, about 2:1. Note this is for a 2002 SS Firebird. If there is anyone out there that has any insight or can point me in a direction that might help, would love to hear from you! Thanks, -John

07-16-2022, 05:36 PM	#2
Mike Jones VIP Member Join Date: Apr 2012 Location: Connecticut Posts: 1,125 Likes: 1,179 Liked 684 Times in 289 Posts	Re: TH350 Help Needed! Not an expert, but if it were mine, to start with.... I would take it down the street, shift it twice, and see what happens. Good luck MJ

07-16-2022, 05:39 PM	#3
mike britt Member Join Date: Mar 2013 Location: Italy, Texas Posts: 176 Likes: 365 Liked 66 Times in 31 Posts	Re: TH350 Help Needed! I can't hear, feel, or see any difference in my car on jackstands but when I drive it down the road it feels fine.

07-16-2022, 05:46 PM	#4
SG7874 Junior Member Join Date: Mar 2020 Posts: 16 Likes: 9 Liked 26 Times in 5 Posts	Re: TH350 Help Needed! Thanks guys, for the suggestions. I will take it out for a spin on the street tomorrow and see what happens. I am basing this on Racepak data, specifically driveshaft to RPM ratio.

07-16-2022, 05:49 PM	#5
Mark Yacavone Veteran Member Join Date: Mar 2002 Location: Miles From Nowhere Posts: 7,789 Likes: 2,881 Liked 5,077 Times in 1,935 Posts	Re: TH350 Help Needed! Was the intermediate sprag looked at..not just turned by hand? Does it have the Coan light, small components? __________________ "We are lucky we don't get as much Government as we pay for." Will Rogers

07-16-2022, 11:04 PM	#7
e vassar Member Join Date: Jul 2015 Posts: 377 Likes: 67 Liked 263 Times in 105 Posts	Re: TH350 Help Needed! Not a expert either but I also have a T350 and a fairly loose converter. My tach will drop more on the 2-3 shift than the 1-2 shift.

07-17-2022, 01:14 PM	#8
Eman Member Join Date: May 2014 Location: E TN Posts: 468 Likes: 16 Liked 133 Times in 76 Posts	Re: TH350 Help Needed! When I had my T-350 it didn't feel like it shifted 1st to 2nd on the lift. As other said road test it. You mention a new drum, you said front drum. The drum at the front of the transmission is the direct or high gear drum. It's the one without the shaft, the one with the input shaft is the forward clutch drum. The direct drum is the one usually replaced as it is the one that holds the intermediate sprag. The drum with sprag is generally replaced so you get the better 36 elemant sprag. https://www.tsr-racing.com/th350-dru...ent-sprag.html If this was replaced I'd like to think it's good.

07-19-2022, 03:34 PM	#10
SG7874 Junior Member Join Date: Mar 2020 Posts: 16 Likes: 9 Liked 26 Times in 5 Posts	Re: TH350 Help Needed! Hi All, Update time. Took it our for a spin this morning and was able to feel the shift! You can even see it in the data logger. Appreciate everyone's input. Long of it is, just go out and test! Thanks again. -John