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#1 |
Registered User
Join Date: May 2017
Location: Inman/Boiling Springs, SC
Posts: 420
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Driveshaft length question
I have a 69 shortbed 350/th400 combo and am on my third carrier bearing. I only have a 2.5/4 drop on my truck, does anyone have the measurements for a full length shaft?
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1985 C10 shortbed, current project. Member of the Upstate SC GM Truck Club. |
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#2 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,158
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Re: Driveshaft length question
So many questions so little information. It is a factory short box? Coil or leaf springs? What rear end? Will the cross member hit the drive shaft? All these things affect your decision to convert to a one piece drive shaft. It would be better to have the measurement taken from your truck. If you're not comfortable making the measurements then a competent drive line shop can do it and then would be responsible if they came out incorrect.
Personally I would find the problem with what you have and fix it. It may take having your rear shaft modified and using an aftermarket carrier bearing. (Which is what I did on my Burban.)
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#3 |
Registered User
Join Date: May 2017
Location: Inman/Boiling Springs, SC
Posts: 420
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Re: Driveshaft length question
Factory shortbed, factory 12 bolt rear, coil spring. I've been told this combo came with either a full length driveshaft or a two piece thats why I'm asking.
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1985 C10 shortbed, current project. Member of the Upstate SC GM Truck Club. |
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#4 |
Senior Member
![]() Join Date: Sep 2014
Location: Wenatchee, Wa
Posts: 910
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Re: Driveshaft length question
When I went from the TH400 to the the 700R4 the driveshaft shop had me measure the span from from the u-jojnt center line of both yokes bottomed out. He then deducted from that dimension to account for suspension movement.
I don't know if this helps but it is what I did and it works great. |
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#5 |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,193
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Re: Driveshaft length question
A 2.5/4 drop should be ok with a split shaft....
Biggest issue I have come across with center bearing failures is incorrect setup of the mount bolts...or the shaft is bottoming out in end of trans... The center bearing carrier bolts should be loosely installed finger tight. The truck MUST be on all wheels and the rear suspension should be bounced up and down a few times.... Only then should the center bearing bolts be fully tightened... There are also several aftermarket center bearing carriers available that seem to be more reliable than the stock units. Finally, the rear shock angle changes substantially with a 4 drop...and raer shock relocation kits should be used to correct the shock angle...too much rear end bouncing around on a bad shock angle truck is sure death to a carrier bearing... ![]() ![]() ![]()
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#6 | |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,158
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Re: Driveshaft length question
Quote:
I'm pretty sure I know why your eating carrier bearings but it sounds like your heart is set on the single shaft swap so I won't go into it. Here is a link to a low buck shock mount modification to get more vertical shock mounts. http://67-72chevytrucks.com/vboard/s...d.php?t=359399 Good luck!
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#7 | |
Registered User
Join Date: May 2017
Location: Inman/Boiling Springs, SC
Posts: 420
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Re: Driveshaft length question
Quote:
As for the eating of the carrier bearing do tell.
__________________
1985 C10 shortbed, current project. Member of the Upstate SC GM Truck Club. |
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#8 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,158
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Re: Driveshaft length question
As it left the factory the 1/2 ton coil spring suspension has two solid shafts ( i.e. no sliding spline). When the axle moves up and down the drive shaft has to move back and forth. The yoke on the output of the transmission slides to accommodate this movement. The factory carrier bearing's rubber bushing holds the bearing in position vertically, side to side but allows movement fore and aft as needed. The aftermarket bearings I have seen seem to allow much less movement fore and aft than any factory carrier I have seen. Admittedly I have not found a NOS carrier to inspect.
When you lower the truck the range of movement of the shaft is shifted forward from the factory range of movement. The factory bushing sometimes will accommodate the new range of movement. At other times it fails from operating at the limit of its forward range of movement. And of course it's old. When the factory bushings go bad is is usually noticed as a vibration in the truck as the rubber is no longer able to hold the bearing in vertically and/or side to side, not a catastrophic failure of the mount. Replacement carriers are designed to do the job as cheap as possible and no GM specifications are used. Thus the reduced amount of travel that they seem to allow. (And don't get me started on the "Engineered to Fail" traits of modern day rubber products. Like rubber bands). Due to tolerance stacking and how much the truck has been lowered sometimes the replacement carrier will survive. The trick of making sure the new carrier is as far forward as possible will work on some trucks. On other trucks the shaft is too far forward and when the carrier is bolted down the bushing is preloaded at or close to its limit of travel. When the limit is reached the carrier mount has to flex and eventually it breaks. The same thing will happen if you use a aftermarket billet carrier with the stock 1/2 ton coil spring driveshaft. The billet carriers have no provision to allow fore and aft movement and they require a slider in the rear shaft. On 3/4 ton and leaf spring trucks the carrier bearing is different and the rear driveshaft has a slider just behind the carrier. The carrier holds the front shaft in one place and the fore and aft movement is taken up by the slider in the rear shaft. There is very little movement of the yoke at the output of the transmission. The photo shows the factory driveshaft I removed and the new one with a billet carrier and the slider in the rear shaft. I hope this helps.
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#9 | |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
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Re: Driveshaft length question
Quote:
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Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox ![]() ![]() ![]() |
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#10 |
Registered User
Join Date: May 2017
Location: Inman/Boiling Springs, SC
Posts: 420
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Re: Driveshaft length question
I'm doing away with the carrier bearing! I've spent enough money on them. The shaft is not bottoming out on the trans and I know the trick for setting the carrier mount. As for the shocks there is no need to relocate them, if I had went with more than 4" drop then it is needed.
I'm surprised no one has a similar setup that has went to a full length shaft, everything I have found was with a th350 and not a th400.
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1985 C10 shortbed, current project. Member of the Upstate SC GM Truck Club. |
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#11 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,940
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Re: Driveshaft length question
I dropped my coil sprung rear 4" and I absolutely needed the rear shock relocation mounts. It helps so the shocks aren't laying almost flat parallel and in a bind. You'll really like having them installed.
![]() Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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#12 |
Registered User
Join Date: May 2017
Location: Inman/Boiling Springs, SC
Posts: 420
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Re: Driveshaft length question
That will go on the to do list, for now i'm really wanting to do the driveshaft swap.
__________________
1985 C10 shortbed, current project. Member of the Upstate SC GM Truck Club. |
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#13 |
Senior Member
![]() Join Date: Jun 2017
Location: burlington north carolina
Posts: 1,030
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Re: Driveshaft length question
if you want to do away with it and have a one piece made all measurement must be made at ride highth measure from center of input on diff. to back of tail shaft then measure to output shaft on transmission thoese 2 measurement should be all you need to make a shaft . that will correct a lot of problems. just my 2 Cents
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#14 |
Registered User
Join Date: May 2017
Location: Inman/Boiling Springs, SC
Posts: 420
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Re: Driveshaft length question
HO455 I completely agree with your assessment. I've had my share of 4wd's and never understood why GM didn't do the slip yoke on all two piece shafts. At present I have a full length shaft that only has to be shortened vs building a slip yoke setup, I'm pretty much looking at it from a cost standpoint.
I did solve some of the problems today by installing a shock relocation kit which has made the ride a bit better and it seems more stable of sorts.
__________________
1985 C10 shortbed, current project. Member of the Upstate SC GM Truck Club. |
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#15 | |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,158
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Re: Driveshaft length question
Quote:
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__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#16 |
Registered User
Join Date: May 2017
Location: Inman/Boiling Springs, SC
Posts: 420
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Re: Driveshaft length question
I wouldn't doubt that.
__________________
1985 C10 shortbed, current project. Member of the Upstate SC GM Truck Club. |
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