TH 400 question
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
TH 400 question
When i put my car in reverse it really slams...
It feels like a large play somewere and there is a delay before reverse kicks in when car is hot..
Modulator issue or/and bad bushings somewere.
It feels like a large play somewere and there is a delay before reverse kicks in when car is hot..
Modulator issue or/and bad bushings somewere.
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,334
From: North of Toronto - Ontario
If it's only when the trans is hot I'd be tempted to say it's leaking between the clutch plates. When it warms up the fluid is thinner and it can leak where when it's cold it doesn't.
That said, is the fluid level up all the way? Checked when hot, in Neutral after running it through the gears a few times. (rev neutral drive neutral rev neutral then check)
If the fluid bright red or darker (clutches wearing)?
Does it smell burnt at all?
When was the fluid / filter changed last?
Not sure if there are many th400 service places over there, but I'd check the fluid level, if it's ok, I'd do a filter/fluid change and add some Lucas to help the seals.
Just my $.02
M
That said, is the fluid level up all the way? Checked when hot, in Neutral after running it through the gears a few times. (rev neutral drive neutral rev neutral then check)
If the fluid bright red or darker (clutches wearing)?
Does it smell burnt at all?
When was the fluid / filter changed last?
Not sure if there are many th400 service places over there, but I'd check the fluid level, if it's ok, I'd do a filter/fluid change and add some Lucas to help the seals.
Just my $.02
M
Pro
Joined: Mar 2015
Posts: 681
Likes: 31
From: Nebraska
I had the same problem with a '74 TH400. It evolved into a full-blown rebuild. Forward clutch was smoked. The reverse thing was the first symptom, then after a while it would not shift into 3rd. Hope that isn't what you get.
Instructor
Joined: Aug 2012
Posts: 164
Likes: 1
From: Lancaster Kentucky
I agree with most of what Mooser says, but just so you know, the TH400 is a relatively easy/straight forward rebuild that can be done by a non-professional. Buy a nice kit off Summit or something and get into the trans itself, its more intimidating sounding than it actually is.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
If it's only when the trans is hot I'd be tempted to say it's leaking between the clutch plates. When it warms up the fluid is thinner and it can leak where when it's cold it doesn't.
That said, is the fluid level up all the way? Checked when hot, in Neutral after running it through the gears a few times. (rev neutral drive neutral rev neutral then check)
If the fluid bright red or darker (clutches wearing)?
Does it smell burnt at all?
When was the fluid / filter changed last?
Not sure if there are many th400 service places over there, but I'd check the fluid level, if it's ok, I'd do a filter/fluid change and add some Lucas to help the seals.
Just my $.02
M
That said, is the fluid level up all the way? Checked when hot, in Neutral after running it through the gears a few times. (rev neutral drive neutral rev neutral then check)
If the fluid bright red or darker (clutches wearing)?
Does it smell burnt at all?
When was the fluid / filter changed last?
Not sure if there are many th400 service places over there, but I'd check the fluid level, if it's ok, I'd do a filter/fluid change and add some Lucas to help the seals.
Just my $.02
M
Strange thing, it slams in reverse gear a lot heavier than in drive.
Maybe a too large play in driveline, but it should be the same in drive and reverse.....
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,334
From: North of Toronto - Ontario
Rev. has higher pressure and less cushion.
Is the idle maybe a little high?
Low vacuum at idle can cause harder into gear shift but not usually that bad.
If there is clunking noise, check the nose mount on the diff (easy to see) and the rear trans mount (harder to tell)
M
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
Do you have your idle speed set higher than stock setting? The higher the idle speed, the more power put through the converter and the more torque is passed through the system. Also, there are rubber 'snubbers' on the differential that try to minimize that 'shift shock'. They may be deteriorated and not doing their job.
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Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Do you have your idle speed set higher than stock setting? The higher the idle speed, the more power put through the converter and the more torque is passed through the system. Also, there are rubber 'snubbers' on the differential that try to minimize that 'shift shock'. They may be deteriorated and not doing their job.
Pro
Joined: May 2013
Posts: 672
Likes: 31
From: Rapid City South Dakota
When was the transmission serviced last? How does the transmission fluid look compared to new? If you decide to service the trans, do a complete drain and use a good quality fluid and skip the additives.....
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
As seals and valves wear in an automatic tranny, internal leakages increase and time for clutches to engage increase because of that leakage. So, it may take a second (or less) for a clutch to engage when the shifter is relocated. But, that doesn't mean that the transmission has lost function. It's just not as good as it used to be.
See about lowering the idle speed. That will make the quickest improvement in 'shift shock' that is presently available to you.
Do you know if that trans has been modified with an aftermarket shift 'improvement' product? Those can have a pronounced effect on shift quality.
See about lowering the idle speed. That will make the quickest improvement in 'shift shock' that is presently available to you.
Do you know if that trans has been modified with an aftermarket shift 'improvement' product? Those can have a pronounced effect on shift quality.