1976 Auto Trans noise in first and third
10-19-2018, 03:55 PM
#1
1976 Auto Trans noise in first and third
I've recently gotten a 76 corvette L48 with i believe a TH400. Thing was parked for a long time before, been restored to large degree and now driving. As of a few days ago, it won't upshift in auto. i can manual shift to any gear. it will downshift if i stomp the gas. And now there is a strange sound in first and third, coming from the cowl [gear shift/parking brake area] but not second. The sound is not persistent. Sounds more like something floating around and occasionally hitting, or maybe something spinning that is loose. When i first start the car, may not hear it. but after driving a little, its back. I'm a novice, so i just tried different things to see if the sound changes. I can leave in second and never hear it. I can place in third and then shift to neutral, the sound continues. Before this shifting and noise started i was riding around and stepped on the gas. When the car went to shift from 1st to 2nd (I think it was) it was like the car missed the gear. I let off the gas and everything seemed OK. But, then i started hearing sounds... then it stopped shifting. Any ideas on what i should be looking at? [Apologies if too much or too little info... and thanks, this group has already been helpful].
10-19-2018, 04:17 PM
#2
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Have you checked the tranny fluid level?
10-24-2018, 09:14 PM
#4
Went to a local transmission shop. Technician drove it around, said he believed it was something in the planetary gears, but he would have to drop the pan and filter to check it out. He guessed at a price of $1400 to rebuild. We were thinking it is a TH400, but looking around online seems only the TH350 was used on L48s. Anyway, I don't know pricing... so just checking your experiences. Part cost versus labor cost... i don't mind getting dirty to fix something, but i've seen some people claim this is not a job for a novice. Price reasonable? can a novice pull it off?
10-25-2018, 05:39 AM
#5
I would recommend avoiding diy trans rebuild. I am not speaking from personal
experience but have seen 2 or 3 people fail trying to rebuild transmissions. That said the th350 is one of the best candidates for rebuild because it is much simpler than newer tranys.
I would buy one from a catalogue like summitt and diy install. Local shop rebuild probably not a bad option either. Local shop will probably void warranty if you diy install.
experience but have seen 2 or 3 people fail trying to rebuild transmissions. That said the th350 is one of the best candidates for rebuild because it is much simpler than newer tranys.
I would buy one from a catalogue like summitt and diy install. Local shop rebuild probably not a bad option either. Local shop will probably void warranty if you diy install.
Last edited by Greengear; 10-25-2018 at 05:40 AM.
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Al Garrett (10-25-2018)
10-25-2018, 08:22 AM
#6
We were thinking it is a TH400, but looking around online seems only the TH350 was used on L48s.
10-26-2018, 08:03 AM
#7
Fair enough. They said it was a TH400. I didn't challenge them. Research online implies it should be a 350. My best guess is that they didnt take or have the time to 'look' at it. They merely drove it around and answered based on sounds, responsiveness, and experience. They have a good reputation in town. Just doesn't feel like $1400 is a good answer. Some have said i should change out to a 4-speed if i'm gonna work on the transmission... opened a whole new can of worms.