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Ford Restomod: Rear Suspension Guide - DIY Ford

As with the front suspension, the rear suspension is very important when you’re building a performance Restomod. These cars are supposed to be driven, and driven hard. This chapter will go over different factory and custom rear suspension systems for your Restomods. It will also explain how to...

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Thank you for the article. One of the main things I understood was that I should aim to be more like -3deg @ Tranny & +1.5deg at the pinion due to axle wrap. Does this sound right? Thus, a 2 deg shim at the front of the axle perch should get me closer to where I need to be?

 

Have you had your driveshaft checked for balance? I dealt with a similar issue and I was chasing pinion angles for a long time. Finally, I had a local driveline shop look at and balance my driveshaft. Turns out this new driveshaft was horribly out of balance

 

I wouldn't think you'd have a vibration now........... while at the same time 1-degree up at the pinion location (static) is only going to "climb"
to a bigger number under acceleration, so that isn't really ideal anyhow. Did you ever replace the tailshaft bushing? (assuming it wasn't new to begin with)
What are all the angles? You're missing the driveshaft angle.
I like Spicer's tool on their webpage....

Spicer Driveline Operating Angle Calculator

Measure the angles of each component in your drivetrain, then use the Spicer Driveline Operating Angle Calculator to find the operating angle of each u-joint in your drivetrain.

spicerparts.com

 

That looks like a used driveshaft. How did you go about measuring for it to fit properly?

 

As @GT289 wrote, you need to measure also the driveshaft angle too. It might be possible you have too much angle on the pinions.
The pinion angle will go up under acceleration. How much depends on your driving style and on your rear suspension.
What kind of bushings are you using on the cross member? Friend of mine also had vibrations, switching to rubber bushings solved the problem.

 

All good questions. Driveshaft was built for and balanced a few years ago. It was rebalanced within the last year. The length of the driveshaft is also within spec. Believe has around .75" runout. The transmission was purchased new and the tailhouse bushing doesn't have any noticable play. I also switched from poly bushings to rubber bushings (with a noticable reduction in vibrations).

New Developments:

I added the +2degree shim to the rear. Unfortunately the vibrations persisted. When I took measurements again off another location, I ended up getting 5.5 degree down (previously 3deg down) on the transmission, and 3.5 degree up on the pinion yoke (Previously got around 1.5deg up + 2deg shim. I am waiting on another more accurate inclinometer to verify the results. I also used the tremec app and got around 5deg down on the transmission.

This all means that I will have to shim my axle perches nearly 4deg. I feel like this is a problem because of the stress on the u joints?

 

You can’t shim the pinion up 4 degrees and expect to fix this issue.

 

Please elaborate more on this if you don't mind.

 

You can buy 1* shims. I bought a box of 6 of them and was able to fine tune my pinion angle to get rid of the vibration. I don't do 6000 RPM launches so a downward angle of about 3.5* on my T5 and an upward angle of about 2.5* on my pinion worked out. The bottom of the tailshaft housing on the T5 is not parallel to the output shaft. I actually found it easier to measure the transmission angle by putting the level on the crankshaft pulley.

 

I just finished installing in a 4 degree shim. There is a noticable difference in vibration reduction while on the throttle. The car does drive smoother.

However, the only time I feel them now is coasting at high speed 50 mph+ with tranny in neutral. Any amount of throttle in gear clears up the vibrations.

Any thoughts?

 

Do you need to have the car on a level surface when taking these measurements? It seems like it wouldn't matter, since it's the relationship of angles between the trans, driveshaft, and pinion that matters. Any thoughts?

 

So I referred the angles in relation to a level part of the frame rails. From what I understand if you don't necessarily need a level surface as the transmission yoke and pinion angle are in reference to each other.

 

Some more results:

I checked my u joints for any loose needle bearings at the rear pinion and confirmed that it moves freely. I aIso checked the torque on the u joint straps and made sure they were 14-17 ft lbs. Turns out one strap was a bit loose.

Thus far there has been a dramatic reduction in vibrations, especially vibrations felt through the shifter handle. At this point the vibration feels like it's coming from the driveshaft backwards.

I'm wondering if it's my driveshaft?? It's a 3" mild steel driveshaft @ 49.875" long, .083 wall thickness. Perhaps the gearing is causing the driveshaft to spin faster than what it was balanced for??

 

By the Spicer calculator, just cruising down the road there shouldn't be any vibration where you're at now......
Probably not a problem when the pinion climbs either.

 

5 degrees at the motor/transmission seems like a lot. I believe less than 3 degree working angle on the ujoints is recommended. You’d be at over 5 at the front u joint and 4.7 at the rear. May be causing some vibrations.

 

The sweet spot "rule" is to be within 2 degrees....... which he is.

 

I thought the ideal setup was less than a degree difference between between the front and rear but less than 3 degree working angle. If I’m wrong forgive me but that’s how I set mine up after my t5 swap. I ended up shimming the trans and rear end.

 

For what it’s worth, when I swapped in an 8.8 rear end on my 67 with T5 I messed up the angle of the leaf spring pads when I welded them on, and was off a few degrees. I had a bad vibration during acceleration, which disappeared during heavy deceleration. I played with shims for a bit tweaking the angle and then going for a drive. I finally found a good compromise where it would be smooth during acceleration and cruising, and an ever so slight vibration during HEAVY engine braking deceleration. I wasn’t able to eliminate it completely without the aid of traction bars to limit axle rotation... so after those were added, all is well now.

I’m not sure how much power you are putting down to the ground, but something to think about with the floppy leaf springs.

 

Good recommendation on the traction bars. I will look into that.

 

Hey All,

What are some symptoms of an unbalanced driveshaft? I currently have a steel 3" driveshaft and maybe I'm hitting critical speed rpm limit of it with the overdrive in there ??

I'm trying to figure out what are some things I can rule out. My thought process is that since I am not feeling the vibrations in the shifter handle of my transmission, the problem is likely behind the transmission. Does that seem logical to you ?

 

My driveshaft was fine in all gears except for 5th where it would vibrate the car like crazy. With the .64 OD and 3.80s my driveshaft was spinning pretty fast. Also +1 for the traction bars, they really help with the climbing of the pinion angle among other pros/cons

 

OP, you said the driveshaft was balanced in the past, was it also shortened? Reason I ask, and I can’t tell from your pics, but if the yokes on the shaft are slightly out of alignment or phase, you will get vibrations. This is typically only an issue with multi-piece driveshafts in trucks and such that can be separated and reinstalled incorrectly by the average joe. But if the shop goofed up welding the yoke back on not clocked correctly, I don’t want you chasing your tail any more than necessary! 😉

 

I'll take the driveshaft to a shop this week and see what they say.

 

5* down is also a bit more than I’d like my carb fuel bowls to sit at, all things being equal. Is the tunnel prohibiting you from obtaining a slighter angle? I thought the 71/72/73 cars had the most tunnel room of all of them.

 

I have this trans shimmed up as high as I can go without touching the tunnel. These TKOs are really big in width in comparison to the toploader that was in there....

And I have a throttle body fuel injection system on there 😏

 

Ok so here's an update. I think the issue has finally been resolved!! After 2 years. I decided to take the driveshaft in to shop and they found that it was not balanced properly. I think the shop sho shortened it did not so a good job balancing it. Also, the transmission yoke u joint bearing cap wasn't seated properly. I didn't notice any play on the yoke. You had to remove the u joint there to find this issue... FML

Now I am running veryyyyyyyy smooth. Thanks all for the recommendations and help.