E46Fanatics

E46Fanatics (http://forum.e46fanatics.com/index.php)
-   Suspension & Braking Forum by BimmerWorld (http://forum.e46fanatics.com/forumdisplay.php?f=97)
-   -   Tips for establishing ZERO preload on RTABs? (RTAB tool in SoCal?) (http://forum.e46fanatics.com/showthread.php?t=927014)

Mango 06-11-2012 12:27 PM

Tips for establishing ZERO preload on RTABs? (RTAB tool in SoCal?)
 
Very direct and simple question (hopefully)

I ordered M3 RTABs and I want to know if the best way to align the carrier. I know of the 8mm below hub centerline/straight edge rule, but that's on a stock ride height, correct? How bout being on H&R sport springs? Compensate a little? how much?

Am I overthinking it?

Also if anyone in SoCal (818) has the RTAB alignment tools that I can borrow/rent, that would be great.

ThatGuy_JZ 06-11-2012 12:34 PM

Might be over-thinking. I used a 2x4 following the straight edge rule to align mine prior to re-install

Mango 06-11-2012 12:52 PM

Thanks but I want some solid, accurate, experienced device. I installed RTABs on my E36 M3 before using the straight edge 8mm rule but i never felt right about it since my car was lowered.

mystert 06-11-2012 05:26 PM

Since the car is lowered, the angle of the trailing arm to the body mount will change. The 8mm stock offset will now be less since the body is closer to the ground but the center of the wheel didnt move. Either put your car together with the new bushings preloading it by eye to get it close (since your going to take it all apart again in a minute), then with all the weight on the car, measure and record the new angle that the trailing arm is situated at. Then take it apart, and install the bracket onto the bushing so that its the same angle it was when the car was put together with all the weight on it. That will cause zero preload on your lowered car. You could always measure another car that has the same springs allready installed instead of putting it together and taking it apart again.

Will it make your RTABS last longer, sure, will your really notice, probably not. These cars are about 10 years old and some driven hard. The bodies have shifted/settled due to their unibody construction, and its a rubber bushing, if your off by a few degrees, youll be fine, its called manufacturing tolerance.

As im sure you know, get it aligned after at that place up in Valencia and youll be good.

Its a car, not the space shuttle.

Mango 06-11-2012 05:42 PM

Quote:

Originally Posted by mystert (Post 14477944)
Since the car is lowered, the angle of the trailing arm to the body mount will change. The 8mm stock offset will now be less since the body is closer to the ground but the center of the wheel didnt move. Either put your car together with the new bushings preloading it by eye to get it close (since your going to take it all apart again in a minute), then with all the weight on the car, measure and record the new angle that the trailing arm is situated at. Then take it apart, and install the bracket onto the bushing so that its the same angle it was when the car was put together with all the weight on it. That will cause zero preload on your lowered car. You could always measure another car that has the same springs allready installed instead of putting it together and taking it apart again.

Will it make your RTABS last longer, sure, will your really notice, probably not. These cars are about 10 years old and some driven hard. The bodies have shifted/settled due to their unibody construction, and its a rubber bushing, if your off by a few degrees, youll be fine, its called manufacturing tolerance.

As im sure you know, get it aligned after at that place up in Valencia and youll be good.

Its a car, not the space shuttle.

Good answer. You're probably right about the manufacturing tolerances. I feel better now. And yep of course I'll be getting an alignment. Bjorn knows me (at least I hope) on a first name basis and I'm going to tell him about DMAX.

I like to think of my car as a space shuttle though. I like to achieve space shuttle results even if from dinky repairs. :lmao:

scottjoh 06-11-2012 06:41 PM

If you already have the springs on the car and are only replacing the RTABs then you can make marks on the arm & bracket as to where it is currently sitting (must be done on a level surface with all wheels on the ground. When it comes time to tighten the RTAB bolt, align it to the marks you made and then tighten. Not the most accurate, but, with non stock springs it's difficult to get the right preload. This is the whole reason I went with polyurethane RTABs! No need to adjust preload.

mystert 06-11-2012 09:33 PM

Something to add-

You would be amazed how much a unibody car will move. When buying an older unibody muscle car such as a 60's early 70's Camaro/Firebird, some people try to look for a factory 6 cyl car. The V8 cars usually have been abused and raced hard over the years and the unibody can get totally tweaked from the engine torque, sometimes causing the rear suspension to move/sag by up to an inch in places. I looked at a 98 camaro back in the day and the C-pillars had creases and cracks in the paint from the body moving.

Im not saying our 225hp cars have that much torque, but if you went and somehow measured where the original suspension mounting points were located, theres a chance they have moved. Just look at the early 3 series cars that tear the subframes apart!

Alex323Ci 06-12-2012 01:21 AM

^ i am rather doubtful the geometry plane that the rear trailing arm connect at would be changed. and if so nothing near where it would be that out of spec. we are talking about a wishbone system that is buffered by rubber bushing through-out.

as for the subframe mounting blocks cracking through the floor. that's from thin metal in those hollow areas. the whole floor does not show stress cracks.

dmax 06-12-2012 05:13 AM

Can't help, Mango, but came by to lend you moral support.

Hope you find out how to find out the proper location. Not having done this myself, I only have a vague understanding of it. Fortunately, though, when I do do it, I know where it'll go, coz, you know, I'm boring!

Mango 06-12-2012 09:45 AM

Thanks.. I'm mainly going to eyeball it, take pictures, etc. I.e., try to reinstall the carrier at the same angle which i found it.

mystert 06-12-2012 12:34 PM

Just make sure u measure it when the car is all assembled with the full weight of the car on all 4 tires. Since your lowered, it probably preloaded a lot more and will spring back to "normal" once you unbolt the bushing carrier and release the loads on the bushing.

BTW- how often do you get aligned to be on a first name basis with the guy! LOL i might try that place out when i get new tires in the next 6 months now that my suspension is all sorted out.

liquiddawn 06-12-2012 12:56 PM

Quote:

Originally Posted by mystert (Post 14480330)
Just make sure u measure it when the car is all assembled with the full weight of the car on all 4 tires. Since your lowered, it probably preloaded a lot more and will spring back to "normal" once you unbolt the bushing carrier and release the loads on the bushing.

BTW- how often do you get aligned to be on a first name basis with the guy! LOL i might try that place out when i get new tires in the next 6 months now that my suspension is all sorted out.

Bjorn is awesome!!!!!!!!!! He knows me on a first name basis as well! My first time meeting Mango was at Bjorn's shop! Pretty soon, we'll be having E46F meets at his garage!

Mango 06-12-2012 01:00 PM

Quote:

Originally Posted by mystert (Post 14480330)
Just make sure u measure it when the car is all assembled with the full weight of the car on all 4 tires. Since your lowered, it probably preloaded a lot more and will spring back to "normal" once you unbolt the bushing carrier and release the loads on the bushing.

BTW- how often do you get aligned to be on a first name basis with the guy! LOL i might try that place out when i get new tires in the next 6 months now that my suspension is all sorted out.

lol he's aligned my car two times so far. I also introduce other friends to him. I also have him do my tire/balancing work which I will now trust nobody else to do.

fiveightandten 06-12-2012 01:24 PM

You can put a straight edge, flat side down, on the carrier and mark the angle of the trailing arm itself up against the the carrier pretty accurately that way (let the straight edge extent to overlap the side of the RTA and mark a line on it that you can reproduce when torquing it down with the new bushings). Do this with the car either on level ground (if you can get under there), or with the rear end on ramps. The ride height shouldn't change significantly between those 2 scenarios.

Though, I will say that from my experience with doing this on E36's a few times, if you're running limiters, the 80 ft-lb torque spec on that car isn't enough to completely keep the carrier from rotating around the bushing. It will shift over time with vibration, making this entire process completely moot, as it preloads itself in a short amount of time. Any quick deflections from suspension movement aren't enough to rotate it in real time though. So, IMO, even the 8mm rule will be enough to get it in the range that it will correct itself. I actually go harder than the 80 ft-lbs torque spec, so I can prevent mine from twisting.

Another way to do this is to make a tool. I bought an aluminum L-bar at the hardware store and cut it to size. I notched out part of the L on the ends and drilled holes to mount it to the carrier on one end, and to mount a small L-bracket on the other end with a bolt in it that goes into the center of the hub. I measured my ride height with the car on the ground. Then I pulled the wheel off and used a jack under the RTA to get it to the same position with the wheel off. I bolted the tool to the carrier and saw how far down the other end would have to go in order to have the bolt/stud be in the center of the hub. I took note of that measurement and drilled a hole in the small L bracket far enough down to offset it.

I'm probably not explaining it well, but I basically made this, but without the fixed reference point on the hub side...I marked my reference point based on my ride height:
http://i22.photobucket.com/albums/b3...C00887copy.jpg

The end that goes into the hub is offset a specific height from the carrier end. Just let your tool hang wherever it lies with the RTA jacked up to "ride height", and mark your small L bracket where the center of the hub is. Now you have your reference point to set the angle when you put it together. If i'm not explaining this well enough, I can take a picture of the tool I made. It would probably make more sense.

Alex323Ci 06-12-2012 01:52 PM

^ not sure about the others but reading this on my phone and I'm lost.
But really curious to see what tool you made. So I'm in for pictures.:hi:

Mango 06-12-2012 02:31 PM

fiveeightandten, thanks for the awesome explanation. Also in for pics. Good idea about jacking up the RTA. Couple of questions:

Maybe its self-explanatory (haven't received the parts in my hands yet) but when I install the limiters, does the beveled edge FACE the rtab? (flat side out?)

Last time I did this, it was on a lift. This time I'll be doing it on the ground with jackstands. I'm guessing it's easier if I lift the entire rear end with the wheels off? (so the swaybar doesn't load one side up, making it impossible to drop the trailing arm?)

I know you've done this a few times, so I appreciate your feedback!

mystert 06-12-2012 04:09 PM

The beveled edge goes away from the bushing. It should be pretty self explanatory once you have it all apart. I did mine in the carport under my apartment by jacking up the car from the jackpad next to the RTAB i was doing. Was pretty easy, I wouldnt reccomend starting it at 530pm on a Tuesday when you have to go to work in the morning.......

Make sure you buy 6 or more hose clamps. I used them to compress the split bushing prior to pressing them in. I used 2 hose clamps at a time, and really had to crank on them to fully compress the bushing. I ended up stripping/damaging the clamps and had to find someone to take me to the autoparts store minutes before they closed to get a couple more.

Mango 06-12-2012 04:21 PM

Why do i need to compress the split bushing? isnt that what the MIS RTAB tool is for?

Alex323Ci 06-12-2012 05:08 PM

Quote:

Originally Posted by E46Mango (Post 14481143)
Why do i need to compress the split bushing? isnt that what the MIS RTAB tool is for?

my split bushing were able to be tapped in by hand. on one i just used a C clamp to help press in all the way.

The rtab tool is mostly for taking stock out. it also will work on pressing in a stock one piece in. but on split two piece bushings that have the "brims' on the outside the tool doesn't really work as well. as the bushing is wider and covers the rta hub where the tool would rest on. so instead of metal tool "feet" on the metal of the rta, it would be on the bushing. split two piece bushing are easy to fit. a rubber mallet is all that would be needed.

fiveightandten 06-12-2012 05:09 PM

Here ya go...I did up a short video, as it's probably easier to explain in words with the tool in front of me:

http://www.youtube.com/watch?v=-k8Vu...ature=youtu.be

The only thing you may have issue with is getting the RTA up to ride height with the car off the ground. If it's an issue, unbolt the sway bar and you should be able to get there. You can always just remove the spring as well, which only takes a second. Make sure the e-brake isn't engaged.

Hope that helps.


All times are GMT -5. The time now is 08:18 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
(c) 1999 - 2011 performanceIX Inc - privacy policy - terms of use