I'm going to convert my O type open 3:08 to a posi using a powertrax type locker. I also want to upgrade the rear suspension and add a sway bar. Anyone use this kit from UMI or something similar.

 

I have UMI rectangular lowers and adjustable uppers in my 71. Been in there about five or more years now. Got no issues with them, I think its good stuff. Part # 402125. I'm running a stock 442 rear sway bar.

FYI, they have always ran a black Friday special on their stuff. If you're not in a hurry you might wait and see if you can save a few bucks.

 

This is a timely post. I'm going to upgrade both the front & rear suspension on my '71 CS convertible & add a rear sway bar. I plan to retain both the front UCA's & LCA's & replace the bushings (completely dry rotted). I've been on the UMI site and I'm nearly positive I'm going to purchase my items from UMI, including front & rear springs.

Eric - I have a general question. I noticed both round tubular and boxed rear control arms (including adjustable upper). I notice in the set you're considering they are round tubular and you're installing a rear sway bar. I've always suspected and intended I was going to purchase rear boxed LCA's since I thought I had to have boxed (as opposed to round tubular) to accommodate the sway bar. Is there a reason and/or advantage to round tubular rear LCA's versus rear boxed LCA's?

 

To be honest Norm, I'm still looking at the differences and gathering info on the control arms and sway bar.. I am fairly certain I'm going to go with a powertrax type locker. The only thing that remains on my car is the rear suspension, I'm reusing the rear springs, everything else will be changed or rebuilt.

 

Fair enough. Thanks.

 

I have the UMI adjustable uppers with roto-joints and tubular lowers. They have been in my 71 for about 5 years and have been great. I am also using UMI 1" lowering springs, their tubular upper front control arms with .5" longer ball joint, and their front and rear sway bars. Everything I have purchased from them has been of nice quality and Ramey is great to deal with if you should ever have questions.

 

I used a Powertrax locker in one of my old Jeeps and really liked it. I beat the living hell out of it and it never broke. One thing some people didn't like was that it would kick the rear end out with a 1-2 shift on wet pavement when making a left turn at an intersection. This was because there wasn't enough side load to disengage the locker...personally, I thought it added a bit of fun to driving the Jeep.

 

I decided to change up a little, this is the locker that Monzaz is recommending a modified version of this for my type O rear, from Nitro Gear and Axle. Powertrax does not support the type O.

And I think I'm going to go with UMI for the control arms and rear 1" sway bar. I spoke with UMI and they said there was no real difference in strength between the tubular and the boxed lowers, mainly a cosmetic preference. I don't think I need the frame braces in the kit posted above, an am leaning towards this one and a separate sway bar. I'm really starting to like the red. I thought about getting the adjustable but my current pinion angle is perfect with no wheel hop.
Going to wait until the end of the month to see what the holiday prices are.






The sway bar

 

Eric - Thanks for the follow-up. Regarding adjustable vs. non-adjustable upper &/or lower rear CA's I suspect I will obtain the non-adjustable, as well. It's my understanding if my '71 CS convertible is stock differential/axle, stock driveshaft, stock transmission, stock ride height & stock transmission cross-member there shouldn't be any requirement to re-evaluate pinion angle &/or change from stock configuration. I suspect had there been some previous incorporation of changes to the drive train or changes I might be making then I might re-evaluate the pinion angle. With that said, that will save me some money. I originally suspected the adjustable styles might afford better fine-tuning but I can see where the adjustable type won't necessarily provide any benefit if the drive train is stock. I'm going to stick w/ the boxed lower CA's instead of the tubular & I'll be installing the same sway bar. I do like the red for cosmetics.

I'm hoping we might see a Black Friday sale.

https://www.umiperformance.com/home/...trol-arms-kit/
https://www.umiperformance.com/home/...ment-bushings/
https://www.umiperformance.com/home/...rear-sway-bar/

 

I have a PowerTrax in the front diff on my Jeep. One thing to keep in mind is that, by design, it locks whenever there is torque applied from the driveshaft (as in whenever you are applying throttle). It unlocks only when you let off the throttle and are coasting. This means it is almost always locked while driving and can be annoying in situations such as accelerating while making a turn.

This is a big reason why I have one in the front diff only.

The good thing is if you don't like it, just remove it and reinstall your original side gears.

 

Check the price at Matts classic bowties. http://mattsclassicbowties.com/
They were cheaper than most vendors and they have a black friday sale going on now.

 

Well, whoever you spoke to is definitely NOT an engineer, at least not a mechanical engineer. The first problem is that the rear control arms are designed for stiffness, not strength. Non-engineers get confused by this, but it's like saying that a car is "fast" when you really mean it's "quick" in the quarter mile. "Fast" means top speed, like at Bonneville. In the case of your rear control arms, the sway bar imparts a bending load into the arms. The stiffer the arm, the more effective the sway bar is - if the control arm deflects, it "wastes" some of the stiffness of the larger rear bar. The stock boxed rectangular arms are about 2" tall by 1.5" wide. I'll ignore the flanges to make the math easier, but they just increase the bending stiffness even more. The UMI tubular arms appear to be about 1.5" in diameter. Assuming the same thickness metal (say, 0.090"), the boxed arms are 50% stiffer in the up/down bending direction (the one that matters) and about 13% stiffer in the side-to-side bending stiffness. If the UMI arms are actually thicker wall (say 0.125" thickness), the boxed arms are STILL about 12% stiffer in up/down bending.

And whichever way you go, do not use polyurethane bushings in the forward location of the upper arms. Use either stock rubber or the metal "monoball" style bushings. These arms are required to twist slightly under cornering deflections and the stock rubber is soft enough to allow this. Poly bushings are stiffer and will bind. The monoball bushings allow free rotation and are the right solution.

 

I've looked on their site and pricing is comparable to everywhere else at the moment.

 

The arms use thick wall tubing, .125 thick whether the rectangular or the round. The real question is the round tubing substantial enough to do the job intended and is the difference enough to go one way or another. As for the poly vs rubber, I've spoken to people who actually used this product with the poly bushings and had no binding issues. As an engineer, I respect your opinion greatly.

 

For the same wall thickness, the rectangular is considerably stiffer. Again, any deflection will negate the larger rear bar because the stiffness of the bar goes into deflecting the LCA, not stabilizing the car.

 

The binding only comes into play during cornering or body roll situations.... nothing you would feel during normal driving.
Poly bushings tend to limit the suspensions ability to articulate or twist. This can lead to an oversteer situation during hard cornering.

Drag racers will not know the difference.
Using a mono-ball on at least 1 end is the way to go here for the best of both worlds.

As stated above, square is better for stiffness since you are attaching a sway bar, otherwise the round will be lighter & sufficiently strong for all applications.

It all depends on how you drive if the extra $50 for the roto-joint option is worth it.

You may not like the locker... I've always found them to be a bit harsh & clunky in a car.
Binding & chirping ties when trying to park etc. You have to learn not to accelerate in turns as it wants to lock.... terrible for handling if you like to play road racer.
I tolerate it in a heavy truck, but do not want my car to do this.

 

Sorry, but you are still confusing stiffness with strength. "Strong enough" is not the issue. The crappy stock open channel arms are strong enough. While the sway bar clearly adds deflection, even without the sway bar, any deflection in the control arms adds to uncertainty in the motion of the rear suspension. Yeah, the tubular are stiffer than the stock open-channel arms. Whether they are "good enough" depends on how the car is used and driven.

 

Hypothetically thinking, lets look at the lower tubulars one more time and consider the overall length of the arm in general with the addition of the bolt on stabilizer bar tab section to the assembly, how much actual deflection is really going to happen? Isn't the stabilizer bar mounting tab going to act as a doubler for added strength to keep the tube from bending?

 

What tab? The UMI arms have holes right through the tube. Look, you can rationalize all you want. I prefer to do the math.

 

No I am not confused.... I'm an engineer also & I understand the difference.
I try to word things in common terms as this is car forum, not an engineering discussion.
I took into account the type of car & its power level.... any of the UMI offerings are stronger than the stamped factory ones.

I stated the tubular arms are good enough WITHOUT the need for a sway bar attachment.,, in this case I would prefer a more substantial rectangular arm.
Additional stiffness/ less deflection will allow the sway bar to work efficiently.
Remember the factory bushings deflect more than the arms ever did, so there is no comparison there.

Strength wise, I doubt you could break one of those tubular arms in a street car without being in a severe crash.

The triangulated uppers (which are very short) are now carrying the side loads
With a roto-joint & no sway bar there is no torsional stiffness needed... it is free to rotate.
Now, the sole load is compression/tension on lower arms, due to acceleration & braking. The car in question is not producing 1000hp so it will not warrant any load induced deflection worth discussing.
My 9 second Camaro has withstood hundreds of 6000RPM launches on slicks with a set of UMI Roto-Joint tubular arms, so I stand by my statement that they are OK for his application.

 

I am the one who suggested the ball joint upper control arm bushings back in post #12. I also said that the stock stamped arms are more than strong enough, so obviously the tubular ones should be stronger. My point is that stiffness of the arms is what matters, with or without a sway bar. Any deflections in the control arms will cause unwanted motion of the rear axle housing and thus produce unintended and likely undesirable rear axle motion relative to the rest of the car. The stock boxed LCAs are stiffer than the UMI tubulars. I didn't say stronger, I said stiffer.

 

Blazing slide rules !!!!!!!!!!!

 

All of my rear bushings are 50+ years old and shot. My lower arms are not boxed since I have no sway bar, so this stuff will probably be an improvement. I'll follow up with what I think when they show up at the house. Decided to go with the black.

I went with this:


And this:


I'm still deciding on whether I want to go with the lunch box locker or not.

 

You won't be disappointed. Great quality parts.

 

Eric, my springs are shot, as well. This is what I ordered. I opted for the red.


1968-1972 GM A-Body Boxed Lower & Tubular Upper Control Arms Kit

1965-1972 GM A-Body Polyurethane Rear End Housing Replacement Bushings


1964-1972 GM A-Body 1″ Solid Chromoly Rear Sway Bar


1964-1972 GM A-Body Complete Rear Control Arm Bolt Upgrade Kit


1967-1972 GM A-Body Factory Height Spring Set

 

Looks you got a handle on it Norm. I just couldn't get my arms around the red, everything under my car is black, mixed with dirt, and some minor surface rust. Its not pretty under there at all.

 

Eric, I went with Spohn Performance , black adjustable uppers and black boxed arms for the lowers with urethane bushings, no squeaks .... No issues, I would use them again.
Jeff

 

Got all the UMI stuff in, looks to be very good quality and pretty strong. I also ordered the locker from monzaz, Jim is really helpful and knowledgeable. Next up install time.

 

Eric, is this referred to as a 'lunchbox locker'?

 

Yes, its supposed to drop in place of the spider gears.

 

OK
Thanks

 

I just re-read this thread & I missed the fact you already stated it’s a lunch box locker (above). My bad.

 

No issues, I think I'll start this project next week. I'm trying to keep this from snowballing and become a complete under car cleanup job.

 

Started tearing it apart today, finally. Got the rear end out, and the brakes apart. With the stubborn bolts about 4 hours. Going to have to loosen up the exhaust to get the lower arm forward bolts out because they hit the mufflers.

 

Very good. A nice Holiday project. I had to loosen my exhaust and drop it down to remove the bolts, also. I love your Cutlass. My first car was a 1967 4-4-2. Merry Christmas, Eric.

 

I'm hoping I can just disconnect the collector joint without having to drop the hangers, the exhaust is completely welded. I'm surprised the aluminized pipe is holding up really well, its about 10 years old. Luckily this is the last of the bushings that need replaced. Did the body bushings, front upper Aframes and springs/shocks back in 2010, and the rest of the front end about 3 years ago including all the steering gear and ball joints. Also looks like a new set of shocks are in order, the gas charge is gone. I just hope the locker goes in as easy as the videos and what monzaz described.

 

Got the exhaust disconnected from the headers which allowed clearance for the control arm bolts to come out and removed all 4 from the body. Got the locker installed, wasn't that hard at all. Just pull the pin, remove spider gears, transfer thrust washers, install unit and reinstall the new pin.

 

Good to see things are going your way with the project, enjoy.

 

Played around in the garage today while waiting for some other parts to this project. Everything is now removed off the car ready to install all the new control arms, started cleaning on the diff. and installed the new bushings, and took some pictures to compare the new to old arms. Going to pick up some paint and RTV tomorrow to finish assembling the rear.

 

Eric, I am sure you are one happy camper having removed the rear end providing you w/ plenty of room to clean & refinish the axle housing, differential, etc. So much easier. Not long before you're bolting up the new rear sway bar & dropping it to the ground.