2013 Mustang GT/V8. Just got done installing a one piece aluminum driveshaft, as the stock two piece is a major weak point of this car if you wish to go higher speeds.
Everything went smooth for the most part. Except 2 of the bolts on the rear driveshaft have a black washer on them (pic below) that i somehow managed to lose when removing them. I reinstalled those 2 bolts to the flange on the differential without the black piece and tightened them down as far as they would go and then tightened to manufacturer torque spec.
My question is, I reinstalled the bolts without the black piece which I suppose acts as a washer, but the threads bottom out slightly before the head of the bolt and the bolts won’t physically go in any further no matter how much force is applied after a certain point even if the head of the bolt is not sitting flush with the flange so on just 2 of the 6 bolts that bolt the driveshaft to the rear differential have the bolt heads sticking out maybe half a CM and the head not sitting flush with the mating rear diff surface due to that black piece not being there. Again, the threads on the 2 bolts bottomed out and they won’t physically turn any further even with ALOT of force, using a foot long 1/2 inch drive pushing very hard it wouldn’t turn further (and I suppose they’re not meant to turn further since the black piece would normally be there anyway) Plus there are 4 other flange bolts that didn’t use that black washer also holding the driveshaft on. The other bolts are all bottomed out the way down and torqued to spec.
Is not having that black piece on 2 of the bolts a major concern? Could the driveshaft fall off without them?
The bolts are supposed to cause the two parts to be mated against each other. They have a specific number of fasteners for a reason. Having two of them not doing what they were intended to do is risking failure. Would you leave two of your lug nuts loose? Especially since the whole idea of this upgrade is to apply more power to the driveline?
Bolts are designed to apply force at the head flange against a surface. Not at the threaded end of the bolt bottomed out in a threaded hole. Also a good way to distort the threads by applying torque them under this condition…
I would not leave 2 of my lug nuts loose. But in this case those 2 bolts aren’t loose at all. Like I said they are on VERY tight. With or without the washers the bolt would still be inside the flange the same amount and would also be the same tightness. The only difference would be the back of the bolt head would be touching the washer but the tightness of the bolt itself and the depth that the bolt is sitting in the flange would be exactly the same. The amount the 2 bolt is sticking out is almost null, basically only sticking out the amount of the thickness of the washer, like a few mm’s.
Not arguing with your logic but I really want to make sure it’s necessary before doing most of the job over again.
Those tabs act like washers. If you are missing one, use SAE washers under the head. You should then be able to tighten the bolts properly. Use threadlocker… blue not red.
Those look like new bolts? Was that just a screen grab from the web? At first I assumed the new drive shaft came with the bolts. But then, I guess not?
I can’t give you any technical reason for the black washer/spacer - because I honestly don’t know. But manufacturers don’t put stuff like that out without reason. (And do note the blue thread locker on those new bolts). I’d be going OEM spec.
Yep that picture was a screenshot, but that’s what the oem bolts look like. Basically I lost that black metal washer piece. And not sure why but the driveshaft came with new front bolts but no rear bolts so I guess they want you to just reuse the old rear ones. And the driveshaft was a ford performance part as well.
I’m just confused as to why those washers hold the bolts together like that and what purpose it serves and if it’s ok to just use a regular circular SAE washer without those hooks so I don’t have to spend $120 for 2 bolts
Don’t use any old hardware store washers. Use SAE washers. SAE metric sized washers. They are smaller in overall diameter and flatter as well as harder.
Yes, I think it would be ok to use them instead of the double washer plate. Space them 180 degrees apart from each other.
Do you happen to know the torque specs for the front and rear bolts? I’ve read a lot of inconsistent answers but what I found the general consensus to be was 76 foot pounds for the front bolts connecting driveshaft to tranny and 41 foot pounds for the rear end bolts. Does this seem right to you
You apparently don’t understand that the bolts are there to clamp two mating surfaces together. If you (over)tightened the bolts without causing any clamping force on the mating surfaces then the bolts are not performing their intended function. That concept is so basic that you should make sure you understand it completely before you attempt any other repairs, especially the removal of a major weak point so you can reach higher speeds. Removing the clamping force of one third of the driveshaft’s mounting points would CREATE a major weak point, wouldn’t you think? And make the car a danger to everyone on the road near you.
Question, since it is VERY critical to have a 0 balanced driveshaft, and the weights or welds are mostly very close if not at the end of the driveshaft, could having 4 bolts with 2 straps and 2 bolts with missing straps throw the balance and or harmonics of the driveshaft off and cause premature failure of the pinion bearing and or u-joints and maybe even the transmission output shaft bearing/bushing?? I would check with Summit or Jeg’s to see if they something like a set of ARP bolts that are all equal balanced and extra strength…
My drive shaft is 0 balanced with NO weights, it is all in the welds, very smooth, and I have a forged steel with U-bolts, I would never mix match the U-bolt nuts or anything that could throw the balance off…
And since you don’t understand the clamping force thing, remove (temporarily) the other 2 straps and tighten all 6 bolts down with NO washers/spacers to spec and see if the driveshaft is loose, that should show you how a tight bottomed out bolt does not hold the driveshaft in place… The washer not only spreads the clamping force over a wider load, it also acts like a spacer/shim…
Actually, you are arguing with the logic but from a place with a fundamental misconception of how that actually works. Please listen to others if not me. This is dangerous and needs to be corrected. You don’t have to do the entire job over, just replace the bolts that are bottomed out and make it like the manufacturer intended.
There are contributors here on this thread with mechanical engineering background. The advice being given has reasons that are not detailed here and might cause people’s eyes to glaze over and not pay attention. But just listen to Mustangman’s advice:
The washer, in the case of at least two of them, serves multiple purposes. What is also important is the material used. The dimensions to a degree, the alloy and the hardness are all important. All metal flows over time under pressure. That can allow the bolt to become loose over time and cause stress to fatigue or other failure modes of the parts bolted together. This is the reason for specifying the grade of washer as well as the use of threadlocker as a back up measure to ensure those bolts do not come loose.
If you’ve ever seen the result of a driveshaft coming loose at speed, you wouldn’t be considering half way measures on such a critical interface.
We’ve been focused on clamping force but you bring up another excellent concern. Of course the further from the centerline the imbalance is, the worse the effect on balance. There are bound to be certain rotational speeds that end up being harmonics of the imbalance and causing even more vibration.
I had a driveshaft custom made for one of my hotrods. It’s very short by comparison to OE due to the nature of my custom transmission. The place that made the driveshaft balanced it of course and the weights are not much bigger than washers. However, they are applied to the outside circumference of the shaft. Still, to your point, I wouldn’t be intentionally unbalancing the flanges or yoke by altering the connecting hardware mass…you might be able to get away with that under less stressful conditions but it’s still “getting away with it”
Yes, that is the factory spec for these bolts… the 4 front bolts at 76 ft-lbs and the rear 6 at 41 ft-lbs in a criss-cross pattern.
And given the $36 price for 2 new bolts and a strap, yes, buy one.
BTW you don’t need a single piece driveshaft for highest speed you’ll likely see in this car. The best reason to swap to the single piece driveshaft is that is it cheaper than the 2 piece complete assembly required if the center bearing goes bad. That’s why I installed a one piece driveshaft. It is lighter, too.
