Author Topic: TH400 in an Altered  (Read 870 times)

Offline H.G. Wells

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TH400 in an Altered
« on: March 24, 2018, 02:45:37 PM »
Looking for some guidance on a trans issue.

Helping a friend with a new altered and he is looking to swap the powertrain from his other car into a new hardtail altered chassis.
Altered was running a PG, but we want to run the current TH400 as a two speed in the altered. This gives a more favorable gear ratio, + saves $$ from buying a new trans. Driveshaft is not an issue as there is only 1/2 difference, but he was concerned about having a rear trans mount.
Never ran mounts on a glide in dragsters that I have played with, but not sure if the added weight of the TH would be a concern?
Anyone experience running a TH400 in an altered?

Ultimately this car will have a clutch.
Racecar spelled backwards is racecaR

Offline Calkins

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Re: TH400 in an Altered
« Reply #1 on: March 24, 2018, 02:59:47 PM »
If you have a motor plate between the engine and transmission and mounting ears at the front of the engine, I believe you do not want to run a rear transmission mount.  If you do, the chassis will flex, and you start braking stuff.  Hopefully Roo or someone with more knowledge than me will add to this.

Personally, I think swapping out a Powerglide for a TH400 is a great idea.  I wouldn't be afraid of running it as a three speed either.  That would keep in engine RPM in the sweat spot (power band).
Justin Calkins - Iowa Falls, Iowa

Offline jeff/21

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Re: TH400 in an Altered
« Reply #2 on: March 24, 2018, 04:09:26 PM »
That is one heavy trans to hang from the bellhousing I would add a support but wouldn't bolt it solid
what motor are you running?
any pics?
have a nice season

Offline H.G. Wells

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Re: TH400 in an Altered
« Reply #3 on: March 24, 2018, 04:38:49 PM »
Jeff it is a BBC, initially aky injection then blown.
And yes the biggest concern was the weight. But I know in our FEDs you do not run a rear mount with a motor plate. When you tie it all together, if the chassis flexes the trans is going to be your weak point, that is why we leave the PG float.
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Offline BK

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Re: TH400 in an Altered
« Reply #4 on: March 25, 2018, 01:51:33 PM »
 I tried looking at Promods as a lot of them use 400s. It was hard to say for sure but I think they have rear mounts. I wouldnt worry about adding one if you decide to, my Spitzer Altered has a solid rear trans mount that doubles as the engine limiter. No breakage issues. I dont think you get a lot of flex with an Altered.

Offline H.G. Wells

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Re: TH400 in an Altered
« Reply #5 on: March 25, 2018, 03:17:06 PM »
BK, you say your Spritzer has a sold rear mount? does it use a rubber isolator, or is it actually mounted solid with no give?
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Offline Curly1

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Re: TH400 in an Altered
« Reply #6 on: April 03, 2018, 09:57:41 AM »
Mine has a rear trans mount but I just have rear of transmission sitting on it. I do not bolt it down on it.