Track only driveshaft travel

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chillent

chillent

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I've searched all over and can't seem to find a consistent answer.

I've lowered my ride height in the rear and now have only 1/2" slip yoke travel before it bottoms on the trans output shaft. I've always heard 3/4-1" is the magic amount but wondering if I can get away with 1/2" or not. This is a strip only car.

If not, is my option to just get a new shaft or would it be cost effective to have the existing shortened?

Thanks in advance!
 
chillent said:
I've searched all over and can't seem to find a consistent answer.

I've lowered my ride height in the rear and now have only 1/2" slip yoke travel before it bottoms on the trans output shaft. I've always heard 3/4-1" is the magic amount but wondering if I can get away with 1/2" or not. This is a strip only car.

If not, is my option to just get a new shaft or would it be cost effective to have the existing shortened?

Thanks in advance!
Click to expand...
If you are using rubber bushings in your front leaf spring mounts you could experience too much forward travel in the rear axle for only 1/2" of play. Take it to a drive shaft shop and have them cut some off and balance it, it's really not that expensive. $75-$100 should do it.
 
RockinRobin said:
If you are using rubber bushings in your front leaf spring mounts you could experience too much forward travel in the rear axle for only 1/2" of play. Take it to a drive shaft shop and have them cut some off and balance it, it's really not that expensive. $75-$100 should do it.
Click to expand...

Thank you! I didn't know what kind of money I was talking about for shortening ... is 1" travel what I'm shooting for?
 
Assuming that you still have leaf springs and rubber engine mounts consider two facts.

#1 when launching at the strip the nose (pinion) of rhe differential rotates upwards driving the slip yoke into the transmission, more so than normal street driving would.

#2 when launching at the track your engine and transmission want to stay where they are (physics) and move back in their mounts driving the slip yoke farther into the transmission.

If anything I would suggest that you need more, not less clearance for your slip yoke at the track.
 
The amount of slip yoke travel (standard 3/4" - 1") is based on your rear suspension (vertical travel). If your rear end is shoved up into the body so that it has limited travel then you don't need as much yoke travel. Normally the rear end can travel "vertically" about 12 inches in the streets. When the rear end travels towards the body the yoke goes further into the transmission. If your body is lowered you have limited the amount of "yoke" movement.

Treblig
 
I run 3/4" and at the track set the adjustable snubber 1/4 from the body. No issues and the spring extension pushes the tires into the track.
Instead of shortening the shaft you can also move the rear axle back using shim plates on the forward spring mounts.
 
d55dave said:
#1 when launching at the strip the nose (pinion) of rhe differential rotates upwards driving the slip yoke into the transmission, more so than normal street driving would.

#2 when launching at the track your engine and transmission want to stay where they are (physics) and move back in their mounts driving the slip yoke farther into the transmission.
Click to expand...

Understood, but what is also true is that the suspension wants to separate from the chassis during acceleration on a leaf spring car, so my thought was set the pinion snubber close and the lack of 'bumpy' streets could allow me to get away with it ... except for the bumpy return roads lol!

mderoy340 said:
Instead of shortening the shaft you can also move the rear axle back using shim plates on the forward spring mounts.
Click to expand...

Thought about this but, to me, that's a bandaid for the real solution which is to make the shaft the correct length ... although the added shim would probably strengthen the mounting location on the chassis.?! Maybe that is a good option!
 
Look at the wheel well/ tire location, before you plan on adding a 1/2"spacer on you spring mount........
 
chillent said:
I've searched all over and can't seem to find a consistent answer.
I've lowered my ride height in the rear and now have only 1/2" slip yoke travel before it bottoms on the trans output shaft.
Click to expand...

Could I ask ? How much did you lower your ride and how much travel did you have before ?
Did you use the front mount to lower or did you use spacers ?

Your screw length, on your front spring mount, may only allow @ 3/8" spacers and still have a full nut on the threads. I just did mine, and used two 1/8" spacers and a 1/8" backing plate . So I gained 1/4".

I don't have the stock mount, I have the lowering 2 hole mount.
If I lower it, I may have to shorten it anyway, since I'm at 3/4".
 
Last edited:
70 DUSTER CRATE said:
Could I ask ? How much did you lower your ride and how much travel did you have before ?
Did you use the front mount to lower or did you use spacers ?

Your screw length, on your front spring mount, may only allow @ 3/8" spacers and still have a full nut on the threads. I just did mine, and used two 1/8" spacers and a 1/8" backing plate . So I gained 1/4".

I don't have the stock mount, I have the lowering 2 hole mount.
If I lower it, I may have to shorten it anyway, since I'm at 3/4".
Click to expand...


I lowered mine using the PST two hole brackets, and using the upper hole. I will have to measure but I think it's 1 1/2" lower than stock. I had 1" travel before. I also had to adjust the pinion angle.

Pretty sure I'm gonna have the driveshaft shortened instead of spacers.
 
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