Crap, th350 emergency

JP1738 · 02-15-2024, 05:25 PM

Ran great testing at Darlington last weekend, unloaded it today in Orlando to roll it across the scales and I have NO REVERSE. Trans is not low on fluid. It was a touch low when I checked it, I added about 3/4 of a quart, It's dead on now.

The car will snap into reverse and will pull itself backwards at an idle, but as soon as you give it some throttle to either back up over a hump or just go a little quicker, it just drives through the clutches and stops moving.

As far as I can tell, the forward gears have not been effected. It pulls hard at WOT in all 3 gears, but I was not able to make the test session today so I can't be certain it's still running as good as it was last week.

My question is, will the transmission be ok without reverse? Are there separate clutches that control reverse vs the forward gears? What could cause me to lose reverse?

Any input would be great. I'm asking around at the track as well.

Eman · 02-15-2024, 05:33 PM

What does the fluid look and smell like? Anyone have a pressure gauge? Sounds like reverse section is bad which means disassembly.

JP1738 · 02-15-2024, 05:43 PM

Quote:

Originally Posted by Eman

What does the fluid look and smell like? Anyone have a pressure gauge? Sounds like reverse section is bad which means disassembly.

I have not drained the pan, but what fluid is on the stick looks pretty good. I’ll run the car without reverse, but I don’t want to jeopardize the rest of the transmission by doing so.

ss3011 · 02-15-2024, 06:42 PM

It would be great if you could hook up a pressure gauge to the line pressure tap on the transmission case. Jack the rear tires off the ground, put on jack stands. If the line pressure is consistent in first gear, 2nd gear , and third gear, say 160 psi . Check pressure in Reverse. If that pressure is lower than the forward range, you might have a leak in the Low/Rev clutch, but if the pressures are the same in the forward gears, you could probably run some time trials. If it won't hold WOT in 3rd gear then the Direct clutch has a problem. If all is well during forward operation during time trials then you could probably get through the weekend, but stay out of reverse. Good luck !

BTR69 · 02-15-2024, 06:46 PM

I can't speak on a Chevy perspective with this, but back in the 90's, the 727 behind my 440 mopar lost reverse. lost 2nd as well. Still had 1st and 3rd though. Trash in the pan, looked a little bit like cardboard. Didn't have time to rebuild it before the bracket finals, so I changed fluid and raced it as it was. Picked up about .2 in the 8th mile.

Mark Yacavone · 02-15-2024, 10:25 PM

Not enough frictions in the lo/rev, or not enough lining left on the one's there.
You may or may not be leaving on the lo/rev and the forward. Depends on who built it.
If it has an auto 1-2 , then it should be on the forward clutch pack only.
In your situation ,I'd say try it pay close attention to low and high gear.
Find a place to drive in and out without using reverse, and hope for the best.

Mark Ugrich · 02-15-2024, 10:33 PM

In addition to the above , if it has a modulator check to make sure the valve isn’t stuck, Recheck to make sure the transmission linkage or cable is shifting fully into reverse.a pressure check will tell you a lot if you can do one.Its straining my memory, but i believe a stuck band can cause slipping in reverse too. Loose filter is a possible too.

Mark Yacavone · 02-15-2024, 10:39 PM

Quote:

Originally Posted by Mark Ugrich

In addition to the above , if it has a modulator check to make sure the valve isn’t stuck, Recheck to make sure the transmission linkage or cable is shifting fully into reverse.a pressure check will tell you a lot if you can do one.Its straining my memory, but i believe a stuck band can cause slipping in reverse too. Loose filter is a possible too.

No band in a th350, except for intermediate braking.. Should be long gone in a race trans.

Mark Ugrich · 02-15-2024, 10:44 PM

Quote:

Originally Posted by Mark Yacavone

No band in a th350, except for intermediate braking.. Should be long gone in a race trans.

If it’s there, the band is manual 2nd. correct?

Mark Yacavone · 02-15-2024, 11:31 PM

Quote:

Originally Posted by Mark Ugrich

If it’s there, the band is manual 2nd. correct?

No. 2nd gear clutches are attached the case ,behind the front pump. No band necessary for forward motion.
400s work similarly for 2nd. They do have a band for lo/rev , rather than clutches though.

02-15-2024, 05:25 PM	#1
JP1738 Member Join Date: Jan 2024 Location: Charlotte, NC Posts: 311 Likes: 737 Liked 543 Times in 166 Posts	Crap, th350 emergency Ran great testing at Darlington last weekend, unloaded it today in Orlando to roll it across the scales and I have NO REVERSE. Trans is not low on fluid. It was a touch low when I checked it, I added about 3/4 of a quart, It's dead on now. The car will snap into reverse and will pull itself backwards at an idle, but as soon as you give it some throttle to either back up over a hump or just go a little quicker, it just drives through the clutches and stops moving. As far as I can tell, the forward gears have not been effected. It pulls hard at WOT in all 3 gears, but I was not able to make the test session today so I can't be certain it's still running as good as it was last week. My question is, will the transmission be ok without reverse? Are there separate clutches that control reverse vs the forward gears? What could cause me to lose reverse? Any input would be great. I'm asking around at the track as well. __________________ Dawson Pauley #2827 N/SA 1980 Malibu SW 2S 305/180 #2827 S/ST 1978 Mazda RX7 w/ 383 sbc/glide

02-15-2024, 05:33 PM	#2
Eman Member Join Date: May 2014 Location: E TN Posts: 456 Likes: 14 Liked 117 Times in 67 Posts	Re: Crap, th350 emergency What does the fluid look and smell like? Anyone have a pressure gauge? Sounds like reverse section is bad which means disassembly.

02-15-2024, 06:42 PM	#4
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 900 Likes: 67 Liked 238 Times in 112 Posts	Re: Crap, th350 emergency It would be great if you could hook up a pressure gauge to the line pressure tap on the transmission case. Jack the rear tires off the ground, put on jack stands. If the line pressure is consistent in first gear, 2nd gear , and third gear, say 160 psi . Check pressure in Reverse. If that pressure is lower than the forward range, you might have a leak in the Low/Rev clutch, but if the pressures are the same in the forward gears, you could probably run some time trials. If it won't hold WOT in 3rd gear then the Direct clutch has a problem. If all is well during forward operation during time trials then you could probably get through the weekend, but stay out of reverse. Good luck !

02-15-2024, 06:46 PM	#5
BTR69 Junior Member Join Date: May 2014 Location: Wilmington NC Posts: 90 Likes: 128 Liked 60 Times in 17 Posts	Re: Crap, th350 emergency I can't speak on a Chevy perspective with this, but back in the 90's, the 727 behind my 440 mopar lost reverse. lost 2nd as well. Still had 1st and 3rd though. Trash in the pan, looked a little bit like cardboard. Didn't have time to rebuild it before the bracket finals, so I changed fluid and raced it as it was. Picked up about .2 in the 8th mile. __________________ William Kilduff 1970 Barracuda (still under construction, indefinitely) 1968 Camaro SS/C

02-15-2024, 10:25 PM	#6
Mark Yacavone Veteran Member Join Date: Mar 2002 Location: Miles From Nowhere Posts: 7,667 Likes: 2,776 Liked 4,857 Times in 1,848 Posts	Re: Crap, th350 emergency Not enough frictions in the lo/rev, or not enough lining left on the one's there. You may or may not be leaving on the lo/rev and the forward. Depends on who built it. If it has an auto 1-2 , then it should be on the forward clutch pack only. In your situation ,I'd say try it pay close attention to low and high gear. Find a place to drive in and out without using reverse, and hope for the best. __________________ Real life never quite adds up.... Jay Farrar

02-15-2024, 10:33 PM	#7
Mark Ugrich Member Join Date: May 2011 Location: Auburndale,Florida Posts: 211 Likes: 22 Liked 60 Times in 34 Posts	Re: Crap, th350 emergency In addition to the above , if it has a modulator check to make sure the valve isn’t stuck, Recheck to make sure the transmission linkage or cable is shifting fully into reverse.a pressure check will tell you a lot if you can do one.Its straining my memory, but i believe a stuck band can cause slipping in reverse too. Loose filter is a possible too.