Making the switch to a 9", new driveshaft or can it be cut?

bustedknuckle

Dragway Regular
Mar 4, 2008
959
0
16
St. Louis-Missouri
making the switch to a 9". when switching from an 8.5 does the driveshaft need to be cut or do i need a new shaft?

trying to get an idea of expenses
tia
 

lilbowtie

Pro Stocker
Oct 5, 2004
1,736
0
0
Canton Mi.
Re: Making the switch to a 9", new driveshaft or can it be c

Do your home work on drive shaft critical speed before your decide.
The Mark Williams sight has a nice chart.
 

bustedknuckle

Dragway Regular
Thread starter
Mar 4, 2008
959
0
16
St. Louis-Missouri
Re: Making the switch to a 9", new driveshaft or can it be c

I've done research on driveshaft critical speed vs rpm and length. but what im asking is, do i need to cut my driveshaft and have it rebalanced or or do i need a longer driveshaft when switching rear ends? i think the pinion sits closer to the front of car on a 9" then a 8.5 does.

what the difference in length for driveshafts when comparing 9" to 8.5"?

BTW i already have a 3.5" mark williams bonded mmc driveshaft. as mark williams suggested it beings my shaft needed to be 62-3/8" long.
 

bustedknuckle

Dragway Regular
Thread starter
Mar 4, 2008
959
0
16
St. Louis-Missouri
Re: Making the switch to a 9", new driveshaft or can it be c

im not sure your understanding my question correctly. i originally had the mark williams driveshaft cut for an 8.5 grand national rearend but now im going to swap the 8.5 for a ford 9". will the driveshaft for the 8.5 be too long or short or will it bolt in.

i havnt been able to put the 9" in the car yet otherwise i would just measure. im sure somebody has swapped from a 7.5 or 8.5 to a 9" right?
 

lilbowtie

Pro Stocker
Oct 5, 2004
1,736
0
0
Canton Mi.
Re: Making the switch to a 9", new driveshaft or can it be c

It's been so long since I had the stock shaft I cann't remember thats why I posted the length with the 9 in 52.5 inches. I do believe it's shorter.
 

79Landau

Frequent Racer
Aug 28, 2005
372
0
0
Delhi Ontario,Canada
Re: Making the switch to a 9", new driveshaft or can it be c

I did the 9" swap from a 7.5 with a muncie. Used the same drive shaft but just changed the u-joint. Don't go by what everyone says.... measure yours to make sure its right.
 

SSedan64

Dragway Regular
Oct 5, 2009
948
0
0
MACON, GA.
Re: Making the switch to a 9", new driveshaft or can it be c

I agree^^, you will need to measure to be sure.
Engine/Trans/Rear mounting tolerance stack from car to car can be different, Aftermarket Control Arms are different lengths etc.. etc..

TH2004R/TH350 w/7.5" rear & Stock DS = 52.50", with 8.5" Rear = 51.50".
TH700R4 w/7.5" rear DS = 49.50", with 8.5" Rear = 48.50".
 

MalibuRacing.com Gear

Stickers & Shirts!!