Huge "thump" selecting reverse (TH400 Auto)
Thread Starter
Advanced
Joined: Oct 2019
Posts: 85
Likes: 7
From: UK
Huge "thump" selecting reverse (TH400 Auto)
Hi Guys,
When I select reverse, I get one hell of a thump...but only when warm or hot. Fluid level is good.
Any suggestions?... I admit to knowing very little about auto boxes so it's a mystery to me. I had a short video here...make sure you "unmute" to hear it.
When I select reverse, I get one hell of a thump...but only when warm or hot. Fluid level is good.
Any suggestions?... I admit to knowing very little about auto boxes so it's a mystery to me. I had a short video here...make sure you "unmute" to hear it.
Last edited by Specialbrew; Mar 23, 2021 at 01:46 PM.
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
Could be a couple different things, but when I developed that exact same problem, it was my rear end (believe it or not). Have someone outside the car listen closely, since it's hard to pinpoint from inside the car. Could be a mount loose or internal trans line pressure too high.
Thread Starter
Advanced
Joined: Oct 2019
Posts: 85
Likes: 7
From: UK
Could be a couple different things, but when I developed that exact same problem, it was my rear end (believe it or not). Have someone outside the car listen closely, since it's hard to pinpoint from inside the car. Could be a mount loose or internal trans line pressure too high.
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
To me, that sounds like the front differential mount is shot, or maybe the rear transmission mount? Easy fix for either if that is the case. It could be happening only when it's warm because the transmission probably slips a little more when cold, so no 'snap' when it goes into reverse.
http://repairs.willcoxcorvette.com/1...-instructions/
http://repairs.willcoxcorvette.com/1...-instructions/
Safety Car
Joined: Oct 2004
Posts: 3,926
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From: Youngstown Ohio
I'm aware......mine didn't do it cold, either......and only in reverse. I was convinced it was the trans, but a rear end expert assured me it was in the rear and showed me the loose parts when he took it apart....he was correct and the problem was solved.
Racer
Joined: Jun 2017
Posts: 495
Likes: 85
What is your idle rpm when the car is hot?
What i noticed is when my car is cold, my idle is around 850 rpm, and shifting into reverse is no issue.
After it's fully up to temp the idle goes a bit higher, maybe 1000rpm, and creates a much bigger thump when going into reverse because at that higher rpm the torque converter has more resistance and thus slows the engine down more.
What i noticed is when my car is cold, my idle is around 850 rpm, and shifting into reverse is no issue.
After it's fully up to temp the idle goes a bit higher, maybe 1000rpm, and creates a much bigger thump when going into reverse because at that higher rpm the torque converter has more resistance and thus slows the engine down more.
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
What is the idle rpm of the engine? {I assume it is an automatic car.} The reverse shift 'thump' results from too much available torque coming from the engine during the shift and can be enhanced when the rubber 'snubber' mount is missing/worn out/damaged. If you have an upgraded engine with a relatively high idle speed, that will definitely cause a thump.
Thread Starter
Advanced
Joined: Oct 2019
Posts: 85
Likes: 7
From: UK
What is your idle rpm when the car is hot?
What i noticed is when my car is cold, my idle is around 850 rpm, and shifting into reverse is no issue.
After it's fully up to temp the idle goes a bit higher, maybe 1000rpm, and creates a much bigger thump when going into reverse because at that higher rpm the torque converter has more resistance and thus slows the engine down more.
What i noticed is when my car is cold, my idle is around 850 rpm, and shifting into reverse is no issue.
After it's fully up to temp the idle goes a bit higher, maybe 1000rpm, and creates a much bigger thump when going into reverse because at that higher rpm the torque converter has more resistance and thus slows the engine down more.
Thread Starter
Advanced
Joined: Oct 2019
Posts: 85
Likes: 7
From: UK
Racer
Joined: Jun 2017
Posts: 495
Likes: 85
The point is, if you have a higher idle, expect more of a thump getting into reverse, or really putting into either drive or reverse.