What does it take to put an 8.5 into a 7.5 car?

MrSony

Comic Book Super Hero
Nov 15, 2014
3,606
1,191
113
Des Moines, Iowa
#1
Is it literally a drop in swap? Do I need a shorter driveshaft, or is that only when going to a 200r4? What codes on the rear should I look for? Asking for a friend... ;);)
 

Injectedcutty

Comic Book Super Hero
Nov 24, 2014
2,771
4,249
113
34
KY
#2
Unbolt the 7.5, unhook brake line, remove. Bolt in 8.5 and reattach brake line.
Shorten driveshaft by 1 inch and rebalance.
Th350 and 200-4R are the same length.
Check fluids, and do burnouts :cool:!!!
 

-83MONTESS-

Moderator
Moderator
Silver
Nov 4, 2010
4,397
312
83
26
Bellevue, Ohio
#3
Mine required a 1" shorter driveshaft but I have heard others say 1.5" depending on car. Doesnt make sense to me but whatever
 

MrSony

Comic Book Super Hero
Nov 15, 2014
3,606
1,191
113
Des Moines, Iowa
#4
Unbolt the 7.5, unhook brake line, remove. Bolt in 8.5 and reattach brake line.
Shorten driveshaft by 1 inch and rebalance.
Th350 and 200-4R are the same length.
Check fluids, and do burnouts :cool:!!!
:D
 

MrSony

Comic Book Super Hero
Nov 15, 2014
3,606
1,191
113
Des Moines, Iowa
#5
I doubt the DS would care about that extra half inch. Unlike some girls I used to know....
 

64nailhead

G-Body Guru
Dec 1, 2014
609
331
63
51
Upstate NY
#7
Mine required a 1" shorter driveshaft but I have heard others say 1.5" depending on car. Doesnt make sense to me but whatever
The driveshaft length is affected by several variables - yoke on rear, suspension height, trans/engine angle, transmission model,etc. I do agree that it should be relatively standard, but if you're swapping the rear or transmission that is going to result in a driveshaft length change, then that is the time to optimize the length rather than dropping off an inch and 'calling it good' IMHO.

It's also a great time to upgrade to a heavier shaft (tube) and u-joints if you're making alot of power, or plan to in the future.
 

lilbowtie

Royal Smart Person
Jan 7, 2006
1,960
900
113
Canton Mi
#8
I'll get on my soap box again and ask you to take a look at "drive shaft critical rpm". Depending on the rpm range your planning on running it can have devastating results. Google - drive shaft critical rpm, Precision Shaft Technologies has a nice chart.

IMG_4130.JPG

IMG_4133.JPG
 

foxtrot

Royal Smart Person
Dec 19, 2008
1,345
176
63
USA
#9
Holly cow, that's gruesome! Hopefully nobody was injured with that carnage.

Definitely a good tip to take to heart.

I'll get on my soap box again and ask you to take a look at "drive shaft critical rpm". Depending on the rpm range your planning on running it can have devastating results. Google - drive shaft critical rpm, Precision Shaft Technologies has a nice chart.

View attachment 75317
View attachment 75318
 

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,222
660
113
Melville,Saskatchewan
#10
Another reason to use the factory, shorter heavier duty 8.5" drive shaft if you can get it with the rear.
 

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