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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > Z Series > E36/7 Z3 (1996-2002)

E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 05-10-2005, 09:19 AM
TurnAround TurnAround is offline
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Location: Oregon
 
Join Date: Jan 2004
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Mein Auto: Z3C, Z3R, X5
Umm... Interstate MTP-91 Battery does not fit Z3 Coupe. Need options / advice

Sorry .. no pics.. Please bear with my descriptions.

The new Interstate MTP-91 battery I picked up for my 3.0i Coupe doesn't quite fit. The foot print is identical to the BMW battery. The overall height of the Interstate battery is 3/8" shorter. More importantly, the positive terminal post on the Interstate is 1/2" lower than the BMW Positive post.

This is a problem, because the positive lead coming from the car is not able to "seat" square on to the battery post. BMWs have the extra pyrotechnic de-coupler device built in to the cable / lead. It's bulky, and completely rigid. This assembly runs along side the edge of the battery well (frame of the car). It then has a "dog leg drop" shaped metal terminal lead sticking out at a right angle from the red cable. Like I said, the whole cable / lead assembly is very rigid and there is very little play in the cable.

The cable lead can "drop" about 1/4", but then it encounters / comes to rest on the battery well edge / car body-frame. It can't make it that last 1/4", so it won't seat firmly on the battery post. Sits at about a 10 degree angle. This is not good. I've always been taught, that with battery terminals you want a 100% solid tight connection. In fact, the terminal posts are just barely conical shaped, so that you can twist it on there a bit and get a super good purchase on the post. I'm no where near that. Visible .5 mm gaps on both sides.

There's a plastic shield under the positive cable lead assembly. Stoooopidly, I was thinking, "Hey, I'll just cut that outta there, for slack". Bzzzzz... That plastic is what insulates the positive cable from contacting the frame!

Next option is to raise the battery some. There are three fitment / tie down points. The side strap is no problem and a non-issue. The bumper side clamp foot has lots of threads and some play it... also not a problem.

The front most anchor point is the problem. A 6" long, 1/2" wide piece of 1/16" sheet steel formed into the universal 30 degree angle that would mate up with any batteries plastic molded bottom edge / foot. It's spot welded to the frame of the car. Fits the Interstate perfectly. I thought about taking a pair of channel lock pliers and straighten / pry up the bracket enough to get me 3/16" play, but still have just a little bit of an angle to it so it held the battery. Then I'd buy a sheet of 3/16" thick rubber (from Goodyear industrial rubber supply here in town), and place it under the battery.

The problem is, the sheet metal bracket has the typical "blips" formed into it (the trick for making sheet metal stronger). Three of them. I haven't tried to bend the bracket yet. Wanted to talk to you guys first. From just looking at it... I have a feeling I'd have to cut out the reinforcement blips to slightly weaken the bracket first, and then It would bend.

I double checked with Interstate. They say the MTP-91 is the right battery. I asked, "For the Z3 Coupe.. not Roadster.. not M Coupe". He said, yes. Definitely Z3 Coupe, all years. They have no post adapters to make the post taller.

He also says there is NO Optima battery that will fit my car (They are an Optima dealer as well). This is odd, as I've read on this board that Optima was the other choice to go with. He says the foot print is completely different. Do you guys know of an adapter or something?

I don't particularly want to go with a BMW battery. only a 2 year warranty, and clearly... they're not nearly as tuff. They only last 3 to 4 years. Plus like Ron said, they weigh 9 pounds more than the Interstate. The Interstate has an 8 year warranty and they're just as available across the US as BMW.

Modifying the bracket feels wrong. But... what choice do I have.

Also, thinking of the community here.. most Z3 owners aren't going to want to, or necessarily have the skills to.. modify their car's bracket. Need an easier solution. Tell me I've overlooked something here.

Any ideas?

P.S. Just saw pictures of the M Coupe's battery well. Yeah.. the Z3 Coupe's battery well is completely different. It's over on the far passenger side, and the cables come out from the car at a different angle.
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'02 Z3 Coupe 3.0i [Hellröt II - Walnuß]
'03 X5 3.0i [GrauGrün - Beige]
'01 Z3 Roadster 3.0i [AlpenWeiß - TraumRöt]

Last edited by TurnAround; 05-10-2005 at 09:35 AM.
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  #2  
Old 05-10-2005, 09:22 AM
bob lindquist's Avatar
bob lindquist bob lindquist is offline
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search on the title "lets battery my" you will find Rons writeup.
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Last edited by bob lindquist; 05-10-2005 at 09:27 AM.
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  #3  
Old 05-10-2005, 10:30 AM
TurnAround TurnAround is offline
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Location: Oregon
 
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Mein Auto: Z3C, Z3R, X5
Quote:
Originally Posted by bob lindquist
search on the title "lets battery my" you will find Rons writeup.
.

That's where I initially learned about the Interstate MTP-91 and the Optima. But.. the install notes are specific to an M Coupe.

Thanks.
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'02 Z3 Coupe 3.0i [Hellröt II - Walnuß]
'03 X5 3.0i [GrauGrün - Beige]
'01 Z3 Roadster 3.0i [AlpenWeiß - TraumRöt]
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  #4  
Old 05-10-2005, 10:34 AM
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alpina22 alpina22 is offline
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Mein Auto: 2001 M Coupe
Quote:
Originally Posted by TurnAround
.

That's where I initially learned about the Interstate MTP-91 and the Optima. But.. the install notes are specific to an M Coupe.

Thanks.
Bill you have two options:
1) Get an MC
2) Get the BMW battery

Sorry. I have nothing productive to add. Just poking fun mate
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  #5  
Old 05-10-2005, 11:52 AM
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mng mng is offline
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Location: Houston, TX
 
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Posts: 1,396
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Quote:
Originally Posted by alpina22
Bill you have two options:
1) Get an MC
2) Get the BMW battery

Sorry. I have nothing productive to add. Just poking fun mate
always messing with us ZCers


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  #6  
Old 05-10-2005, 02:34 PM
TurnAround TurnAround is offline
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Location: Oregon
 
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Mein Auto: Z3C, Z3R, X5
Ship me yours.. and then I'll 'ave two Coupes. I wouldn't mind having an MC as a dedicated track car.

-------------------------------------------

I've decided to mod the bracket. What's the point in having a Z if you don't get to make sparks fly once in a while.
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'03 X5 3.0i [GrauGrün - Beige]
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  #7  
Old 05-11-2005, 07:02 AM
TurnAround TurnAround is offline
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Fixed it. The magic number is 3/8".
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'03 X5 3.0i [GrauGrün - Beige]
'01 Z3 Roadster 3.0i [AlpenWeiß - TraumRöt]
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  #8  
Old 05-11-2005, 08:31 AM
Steven540i Steven540i is offline
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How?

What did you do to fix it?
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  #9  
Old 05-11-2005, 11:40 AM
TurnAround TurnAround is offline
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Location: Oregon
 
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Quote:
Originally Posted by Steven540i
What did you do to fix it?
Bent the forward sheet metal flange "up" slightly. About half way. You still want some lean to it, or it won't catch an edge on the battery's base. Can be bent with channel lock pliers. "Pivot" your wrist and make small bends. Work your way across the bracket with small movements. If you just "pry" the whole thing foward, you may break the spot welds. Be patient. Slowly bend it up.

Go to your local industrial rubber supplier [ Yes, yes.. some comic sarcasim there, but really.. check around. You may be surprised that your area has a shop like this. Usually they make custom hydraulic and water hoses ]. Get a 1 foot square sheet of 3/8" thick rubber, and a small scrap piece of 3/16" rubber, and a small scrap piece of 1/2" rubber. The 1/2" one will likely measure out to 1/16" less than 1/2". That's normal. and that's what you actually want. The other two pieces should measure out to exact (and need to).

Cut the 3/8" sheet to fit the base of the battery. 7" x 11" rectangle. Now, cut out another inner rectangle inside of it, leaving a 1" boundry all around. This is to dump off excess weight. only the outside edges of the battery touch anyway (look at the battery well). Yes.. you could do this rubber shim with several little pieces, but then they could move around. It's cleaner and more "Stygar / Forbes" like to make the single piece and cut it down to make it light.

Put it down in the battery well. Set the battery in. Unlike the M Coupe, the Z3 Coupe (or Roadster) has plenty of the light grey original BMW battery vent tube hose to reach the new location for the vent (don't need to buy more). Hook up the vent tube kit that you got with the battery. Couple it to the car's hose. Gently stuff it down along side the battery (don't leave it where it could get crimped). Center the battery so the Pos connector will reach nicely.

Put the cross strap over the battery. Carefull.. don't drop the little bolt down inside the well. Place a 1" x 2" piece of the 1/2" thick rubber underneath the left side of the cross strap. This will take up the remaining slack, give plenty of threads for the cross strap bolt to bite, and will provide a very secure locked down fit.

Use the 3/16" thick rubber to make a 1" x 2" piece that will go down where the back end clamp goes. Make a little half round cut out to allow the bolt to pass through to the threads in the car. Without this shim, you could bend or break this particular bracket. It needs "a foot" to help it deal with the fact that the battery is now 3/8" higher in the air.

Put the positive lead on. Note, that the 3/8" pad provides juuuusst baaarely enough for the positive lead to go on squarely and tightly. Why not use an even thicker piece of rubber underneath the battery (after all.. the battery is a half inch shorter). 'Cuz.. if you did this, then the front base of the battery would slip past the spot welded on bracket. It's only "so high".

So, 3/8" inch is the magic number. Any more, the battery slips past the front bracket. Any less, and the positive terminal lead will not fit well.

Without the proper fit on the terminal lead, not only could it lead (arr .arrr.. lead) to a problematic "mysterious" battery drain problem, but, that odd angle fit and the bar resting on the car frame.. and a tens of thousands of miles of minute vibrations... could crack the positive terminal post. Much worse problem.

This combo of rubber parts should work forever. "Interstate MTP-91 infinitum".

The ROadster went well too, although interestingly.. there is no cross strap. Unfortunate, but.. the back end clamp seemed to be enough to apply pressure against the front bracket. I'll have to check it in 4 months. But really, we should all be checking out batteries every 4 to 6 months anyway. I've had a cracked and leaking battery before (no other reason than a defective battery case). Bad enough in the engine bay. But to have that happen in the boot...

Hope this helps others.
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'02 Z3 Coupe 3.0i [Hellröt II - Walnuß]
'03 X5 3.0i [GrauGrün - Beige]
'01 Z3 Roadster 3.0i [AlpenWeiß - TraumRöt]

Last edited by TurnAround; 05-11-2005 at 11:44 AM.
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  #10  
Old 05-11-2005, 03:21 PM
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bob lindquist bob lindquist is offline
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How much did the MTP-91 cost ?
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2000 Imola Red M Coupe

Dinan suspension, M rotors /Axxis pads
Eurosport Cam Kit 1, touch lane change
Zaino polish, Beach Sand
Garys mirror adapter, S54 Oil Cooler
seat tilt coupling nuts, spare tire

"life's to short to drink cheap beer"


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  #11  
Old 05-17-2005, 07:51 AM
TurnAround TurnAround is offline
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Quote:
Originally Posted by bob lindquist
How much did the MTP-91 cost ?
Gosh.. now I can't remember exactly. I want to say $87.
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'02 Z3 Coupe 3.0i [Hellröt II - Walnuß]
'03 X5 3.0i [GrauGrün - Beige]
'01 Z3 Roadster 3.0i [AlpenWeiß - TraumRöt]
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