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Thrust Arm - do I need to have the car in "Normal position"?

12K views 32 replies 15 participants last post by  bluebee 
#1 ·
Hi Everyone,

First Post!!! (actually second - I incorrectly posted in the DIY section - sorry guys - rookie mistake - asked for it to be deleted)

Love this site. Best information!

Will be doing the thrust arms replacement on car (E39 530). I've read a bunch of DIY threads on this and most times they refer to "normal position" for the suspension, which is used when you do the final tightening of the arm (see link below as an example):

http://www.beisansystems.com/procedu..._procedure.htm

Here's the question: Do I need to put weights in my car to get this "normal position" measurement, or does BMW use some sort of standard chart?

Thanks!
 
#4 ·
So would it be sufficient to just drop the car on ramps and tighten?

Or do I need to add the weights in the car, full tank of gas and take the measurement of the center hub to the fender and compress the suspension to this measurement and tighten?
 
#5 ·
No one uses the compression method that you talked about and IMO it's not consistant. If you can load sand bags would be ideal, but for me I have done them in the past without any sand bags, just the weight of the car is good enough for me.
 
#7 · (Edited)
This is known as "pre-loading" before torquing the control arms. This is because the bushing in the control arms of any car is made from polyurethane (or rubber) embedded in a metal sleeve, which by itself is squeezed by the bolts, so once the metal sleeve is squeezed, it does not move (supposedly). Every time you hit a pot hole or road imperfection, the control arm goes up and down twisting the polyurethane (or rubber) bushing up and down around the sleeve axis.
By preloading (having the car on the ground before torquing the bolts) as opposed to torquing the bolts while the car is up on the lift at the shop, the polyurethane (or rubber) is in a position similar to normal driving condition, and this "pre-loading" is supposed to make the bushing last longer.

FYI, my 1998 Volvo V70 procedure calls for torquing the control arm bolts car on the ground with full gas tank but no need for 150 lbs in each front seat.

BMW engineers are a whole bunch of an*l-paranoid people (seriously) and they aim for perfection. They want you to torque the bolts similar to real dynamic driving condition. To make things even more complicated, they make different torquing procedures for different cars, reflecting the income status and the profile of the buyers!

For example, who'd buy E39? Maybe single people, maybe married couple in their 30's and 40's with kid(s).

So the 'smart' BMW engineers say: for E39 torque the bolts with:
- full gas tank
- 150 lbs in each front seat (but they forgot that quite a few Americans are obese and weigh more than that hehe...:)) = couple in the front!
- 50 lbs in the rear center center (kid in the rear center seat)
- 50 lbs in trunk (maybe a golf bag!).
(This is again to reflect the profile of a couple with a single kid!)

Now you can guess that the 'smart' BMW engineers say: for Coupe or Z3 (just think of who would buy the Coupe?) torque the bolts with:
- full gas tank
- 150 lbs in each front seat (look it up but I think it is the case). Basically "double income no kids" = DINK!

So one day I decide to check this out, with 2 passengers in the front seats of my E39, the distance between the top of the front tire and the bottom of front fender goes down exactly 1 cm (check and you will see).
Then I did a calculation by placing 150lbs in each front seat, and since the length of the thrust arm is 45 cm long, the change in the angle at the bushing is:
Arctan(1 cm/45 cm) = 0.0222 degrees!
Not much to worry about!



So if anyone asks me how I torque my thrust arms, I'd say car on the ground with full gas tank is good enough for me (no need for 150 lbs in each front seat).
There are too many things in life to worry about than this extra an*l-paranoid crap from the BMW engineers.
 

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#19 ·
There are too many things in life to worry about than this extra an*l-paranoid crap from the BMW engineers.
The problem is they are selectively anal. They are NOT anal about:

- E39 coolling systems
- E39 hvac buttons
- E39 thrust arm bushings
- E39 valve cover gaskets and valley pan seals
- E39 dash pixels
- E36 upper rear shock bushing
- E36 rear suspensions tearing out of the frame

I could go on for a long time... :yikes:
 
#8 · (Edited)
Welcome!
Is your car a sport?
A sport version will have the M-sport suspension and 17" wheels and tires.
It will also have the sport steering wheel and sport seats.
According to the TIS manual (digital manual), the non-sports require to be weighted, but the sports do not.
My car is a sport.

The "Normal" ride position is similar to weighing the car down for an alignment.
It is:
1. 150 lbs in each front seat
2. 150 lbs in the center rear seat
3. 46 lbs in the trunk, and
4. A full tank of gas

I just make sure I have a full tank of gas.

The Bentley manual measures the lower wheel/ rim to the upper fender arch while the car is sitting flat on the ground.

I measure the center of the hub to the upper fender arch.

Then when I have whatever end jacked up and resting on jack stands, I use a jack to push up/ jack up the wheel hub to similate the resting position of the car.

I measure the center of the hub to the fender arch, to make sure it matches the first time I measured.

Then, I torque the control arms.

You can also hand tighten the control arms, and try torquing them when the car is flat/ resting on ground, if you have enough room.
However, my car is much too low to torque anything while the car is on the ground.
That is why I torque the suspension with the car up in the air with jacks.

I hope this helps!
Thanks!
Jason
 
#15 ·
I think there's Jiffy Lube in Canada***8230;but they're few and far between; Mr Lube's squeezing them out***8230;$50 for a dino oil change in a 4-banger is almost as bad as BMW prices though; dunno how long they'll last :p

Interesting post about how much the preloading affects the car's dynamics. However, the smallest things can affect the car***8230;I'll probably stick with the recommended weight in the car, or adjust it to my weight as I'm usually driving alone (as per the Z4 specs).
 
#17 · (Edited)
Further to my post above, I am attaching the BMW TIS so you can see the difference between E39 and Z3 Coupe etc.:

The main difference is that:

- E39 owners have a single kid (actually grown up kid weighing 68 kg) in the REAR seat and have 7 kg more in the trunk!!!
- And guess what: the difference in cargo weight 21 kg (E39) vs 14 kg (Z3 coupe).
Basically too much crap from BMW engineering perfectionism (Oh, they try to be perfect in the torquing department but they can't even get the AM radio station done right!!!):



As I mentioned previously, for me: car with full gas tank and on the ground (i.e., no extra weights) is good enough for me.
 

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#18 ·
You guys rock!

cn90...geez...you are a legend...didn't expect the university take on BMW and thrust arm replacement...love it!

I have a stock (non-sport) suspension. My mechanic buddy just puts the cars on ramps to do the final tightening. I'll have a full tank and go from there...depending on my paranoia.

As for Jiffy lube...we have...but I only let my buddy touch the car...to many scams out there...BMW wanted 3k CAD to do the thrust arms, control arms and sway bar links. I've already done the sway bar links...now the thrust arms. I should be changing everything at once, but I just wait for the part to go. Now I think I'm hearing my front wheel bearings go. Only hear it at over 100 km/hr and only going straight. It may be my tires as I'm down to wear bars. Once I put the winters on, I'll be able to determine better.

Boys - Thanks so much!

I'll keep you posted as I'm also doing the CCV swap and valve cover gasket this Friday.
 
#27 ·
Thrust Arms finally installed!

Boys...took forever, but my buddy was finally able to install the thrust arms. Well, let me tell you that I was so impressed with the handling improvements. It did fix the steering wheel shake when braking hard at 50-60km/hr, but the icing on the cake was that everything was tighter and I am now able to corner much flatter at higher speeds. It's like the car is brand new again! I didn't expect such a difference so I guess the gradual decline in suspension performance got me used to the set up. I only have the stock suspension, but now I roll over bumps smoother with less "noise" coming up into the cabin.

I was going to lower the car by getting like the OEM sport suspension or an aftermarket kit, plus the M5 rear sway bar, but now I can wait a while and enjoy.

Thanks for everyones input on this!

Paul
 
#28 ·
Torque Thrust Arm

How do you guys get the torque wrench on the front thrust arm bushing side bolt, especially with the car in normal position?
 
#31 ·
azbimmer, torque the nut, counterhold the bolt head. Easy to do on the i6 cars, not sure about your space constraints with the v8 suspension bits.

firehawk17, if by "not correctly" you mean not torqued in 'normal' position with the wheels (and bushings) under proper load... the bushings fail much much sooner.
 
#33 · (Edited)
Just by way of suggestion, there is an easy way to weight the car:
- One users quest to diagnose uneven tire wear on the inside edge due to excessive and uneven alignment camber & toe (1) (2)





See also:
- Which of the dozen alignment specs are adjustable on the BMW E39 (1) (pdf) & cn90's front (1) (2) and rear (1) wheel alignment DIYs & how to keep the steering wheel (SW) straight during home alignment (1) (2) & what tools measure rear camber at home (1) (2) and what tools measure front/rear toe at home (1) & what tools lock the steering wheel & brake pedal at home (1) & the theory of alignment with weights (1) or without adding weight (1) (2) (3) & philosophically why most people prefer to let a professional alignment shop align their suspension (1) & what expensive equipment is used at the stealer to align your suspension (1) (pdf) & Internet references for how to DIY caster, camber & toe at home (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39)
 
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