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

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