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AC/Power Steering Serpentine Belt - '91 S4

8K views 34 replies 6 participants last post by  srguy 
#1 ·
I imagine this has been discussed, but was unable to find a thread, so my apology if this is "old" subject....

When I operate the AC on my Spider, the belt slips at low RPM (Likely also slipping at higher RPM, but don't notice the resistance in steering effort at speeds above 25-30 mph). The adjustment is maxed out, so I purchased a new belt . . . . part # 25-050570 from NAPA which fits, but also slips. Once again the adjustment is maxed out, I can't do any better than maybe .5"-.75" deflection of the belt. I tried the next shorter belt from NAPA, but it's absolutely too short. Lengths are 1462mm (Too long) . . . and 1338mm (Too short) . . . .

I've owned the car for a bit less than a year, and previous owner said he had AC charged, and it seems to operate as designed . . (Blows cold air without drama or noise). I'm beginning to suspect that a new belt was installed at the time of service and recharge. (The one I changed out thinking the belt was worn rather than too long as it now appears.)

Now for my question:
Is there a U.S. domestic belt that is intermediate length that will work better. Also, is it possible that folks who serviced the system "overcharged" creating excessive torque requirement at the compressor?
 
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#2 ·
part # 25-050570 from NAPA which fits, but also slips. Once again the adjustment is maxed out
That is the correct belt number.

Can you show us what you mean by "adjustment is maxed out"?

My belt was also slipping. I found the grooves in the AC pulley and the crankshaft pulley were full of crap!

Here is the before and after of the AC pulley and crankshaft pulley.

Automotive lighting Tire Photography Wheel Metal


Red Metal Photography Wood Machine tool


Once I cleaned them up, no more slipping.

Good luck,

Vin
 
#3 · (Edited)
The adjustment is maxed out
Found this picture when I was doing an engine clean up.

This shows the adjustment height. See the large bolt on the right side, roughly half way up the adjustment groove.

Auto part Engine Vehicle Car Fuel line


Are you saying your bolt is at the very bottom of the slot?


Vin
 
#4 ·
I'm still novice enough I won't try to post a photo, however when the belt is tightened, the bolt is up solid against the bottom of the adjustment slot. I will uses some cleaner and clean out the groves, to see if that makes the belt any "stickier".

By the way . . for future reference . . . when I attach a photo here, is it necessary to dial back the resolution on photo settings? Or going thru a 3rd party (Photo Bucket maybe).

Thanks for your replies
 
#5 · (Edited)
If the bolt is up against the bottom of the slot, either you do not have the route correct or you might be missing the idler.

Here is a picture of the idler. It is the silver wheel in between the ac pulley and the crankshaft pulley.

Auto part Engine Automotive engine part Metal


Here is the route. I suspect you did not route the belt around the idler. The belt goes from the bottom of the ac pulley, up and over the idler, down under the crankshaft pulley, up and over the power steering pulley, back to the ac pulley.

Line art Drawing Locomotive Auto part Illustration


Good luck,

Vin
 
#6 ·
BB photo size

The jpeg size 249.0 KB 700 max width, I shot 640x480 for using BB software.
 
#8 · (Edited)
Following the helpful advice from this Forum . . . I've been out in the garage and #1. Double checked serpentine routing - is "OK" . . .#2. Check for build-up and residue in the machined slots on the pulleys - "OK" . . . . #3 Check deflection at location indicated . . . deflection is in the range of 20.320mm - 25.400mm (Excessive) . . . #4. Took some photos, adjusted resolution and will now attempt to attach.

 
#9 · (Edited)
To post a picture:

1. Click Reply or New Thread as appropriate. That brings up the familiar text box to type in your reply. Above the reply box you will see an icon for a paperclip. Click that.
2. Click on Manage Attachements. A new box will appear titled "Manage Attachments." Click on Browse.
3. Find the file on your computer's hard drive that you want to attach to your reply. Double click on it or select and click Open. That box will disappear and the previous on will show the file uploading to the ALFA BB server. It may take a few seconds to upload, depending on the speed on your connection.
4. This will return you to the main "Reply" and click the paperclip again and your attachment's file name will appear there, but the picture will not actually show in the text box.
5. Click Submit Reply and you're done.
 
#10 · (Edited)
Maybe the belt itself is the wrong length?

I keep a spare and just measured it.

When doubled the belt is 28.5" long.

Just thinking.

Vin
 
#11 ·
Thanks Vin . . . I'm also thinking the belts too long. It measures closely to 28.5" when doubled, but as you can see by the photos, the upper hydraulic line is uncomfortably stressed. I can't see what may be peculiar about my Spider, but I'd like to find a belt that is 20mm - 40mm shorter than the ones I've got.
 

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#13 ·
How are your motor mounts?

I know the picture on the left is on a bit of an angle, and our engines are designed to be on a slight angle towards the driver side, but yours looks to be too much.

If your motor mounts are shot, the whole engine will be low and could cause this.

The driver side mount is easily accessible for a picture.

Could you post a picture of that?

Vin
 
#14 ·
Hello again . . . Here is a photo of Driver Side Motor mount, however it appears in good order. I will look to see if I can find a full picture of the Engine bay to get the decent perspective . . . . if the engine is not sitting at the correct angle, or not.

By the way, I spent some time today researching and found a slightly shorter Gates Belt, but ordered the Alfa Belt from I.A.P. Should be here Thursday and it's dimensions were shorter than the NAPA Belt.
 

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#15 ·
Motor mount looks ok. Certainly not so deformed so much to cause the issue.

Engine bay looks nice.

It's so strange because I use the Gates belt with the same part number and the same length.

Let us know how it works out.

It's still bugging me to figure out what is going on.

Good luck,

Vin
 
#16 ·
Yeah, it is a puzzler . . . . I will let you know how it goes. The Belt from Gates is on back order, but the Belt that's available from I.A.P. was available and I went ahead and ordered it. It's Length measurement is shorter than the new Belt I bought from NAPA, but only about 15mm shorter . . . if it doesn't center the adjustment to my satisfaction, I can order the Belt from Gates, as its about 20mm shorter.

Thanks for sharing your ideas with me.
 
#17 ·
OK . . since my last post, the new belt has arrived from I.A.P. (Mfg in Germany by a company named Rofan . . . part # 5625 1000). It is better but still not right. Adjustment slot should be more centered and with this belt, I've used nearly all the slot to tighten. The belt is not slipping, but I'm pretty certain that it will, once I've run it for a few miles, particularly in the summer heat. This belt is 12mm shorter than the NAPA belt, but still longer than the Gates belt (which I still haven't ordered.) It doesn't make sense to me, to keep up the trial and error route I've been following.

Having purchased the car from an Estate Auction, I've gotten only partial and incomplete maintenance records for the vehicle. I'm suspicious that the idler pulley may have been replaced in the past with an aftermarket pulley having a smaller Dia. than original. Its pretty confined for space, but maybe 1/2" larger pulley would make the difference. Just thinking out loud, so to speak.

If someone has the dimension for what the idler pulley should be, please let me know. It doesn't appear that the pulley has worn significantly.

Still puzzled.
Don
 
#18 ·
If someone has the dimension for what the idler pulley should be, please let me know. It doesn't appear that the pulley has worn significantly.

Still puzzled.
Don
Thats a good idea.

Mine measures 75mm.

Vin
 
#19 ·
Thanks Vin,
My pulley measures 74.295mm . . . . smaller for sure, however not so much smaller as a percentage . . . is it enough? I won't know until I've tried the Gates Belt. At times, in the past I've been fooled by a small variation creating a misfit. As closely engineered as these cars are, I suppose its possible.
Don
 
#20 ·
No that is not enough of a difference. I think you have the original pulley.

I go back to the picture you posted that looks like the engine is really tilted to the driver side.

Can you try to take another picture?

Vin
 
#21 ·
Moderator,

Could you please move to Spider section.

Maybe, we can get more help there.

Vin
 
#22 ·
Ok, lets try this.

I just measured the distance between the oil cap and the hood.

Take a loosely packed ball of tin foil. Make a ball with it, loose, not tight.

Put a piece of tape on the oil cap and tape the ball to it.

Close the hood.

The hood is angled up so the ball should be pressed into a wedge.

In the middle, I measure 24mm.

Lets see where yours ends up. I am going to guess the engine is low.

Vin
 
#24 ·
"Take a loosely packed ball of tin foil. Make a ball with it, loose, not tight.

Put a piece of tape on the oil cap and tape the ball to it.

Close the hood.

The hood is angled up so the ball should be pressed into a wedge.

In the middle, I measure 24mm."


OK . . having done that, I measure 1.050" (26.67mm)
 
#26 ·
I'm not all that familiar with the S4 model, but here are a couple of things that might be worth investigating.

1. Is it possible that a couple of the bolts that hold the compressor to the sump are loose (or unnecessary washers have been placed under the compressor/on the mounting pads)?

2. Is it possible that the idler pulley is not bolted tightly?

3. Can the positioning of the compressor and idler pulley be adjusted, even slightly, at their secure points? In other words, have you tried loosening the bolts that hold both of these items in place (with the belt off), and then moving them as far "out" as possible, and then re-tightening their bolts?

4. Is it possible that the idler pulley bracket is bent and thereby not providing the designed amount of tension on the serpentine belt?

5. Were different methods used to secure the AC compressor in the different years/models, and some PO installed an earlier version mounting setup on your car, i.e., replaced the motor (which changed the compressor mounting setup)?

6. I know you checked the diameter of the idler pulley, but did you check the diameter of the compressor clutch pulley? Many aftermarket or rebuild compressors are available that will "work" on these cars but do they all have the same sized clutch pulleys? What if your PO replaced the compressor or clutch pulley and the diameter of the replacement clutch pulley was incorrect?

I dunno, perhaps I'm grasping at straws here, but I'm following this thread with interest, and hope you figure it out.
 
#29 ·
Lots of good ideas.

1. Has to be checked by OP but I doubt it.
2. Has to be checked by OP but I doubt it.
3. No adjustments.
4. Has to be checked by OP but I doubt it.
5. Same set up for S4's
6. Interesting. It wasnt the easiest measurement but I get 4.1" or 104mm.

Vin
 
#27 ·
I'm glad I'm not the only one who's perplexed. I've checked the idler pulley checking for play, or noise (worn bearing). The belt "tracks" centered over the idler while operating at a range of RPM . . . (not likely to do so if mount plate or bearing axle was bent or otherwise mis-alligned). The crank gang pulley appears to be original to the engine (as best I can see without engine removed). Same with the pulley on the power steering and compressor. However . . . A/C Compressor is difficult to assess because of it's location. Maybe ? ?

Anyway, the belt is not slipping for now, so I took it out, washed it, towel dried it, then took a very pleasant drive in the country on a warm and balmy summer evening.

Life is good, (For the moment), so will continue to drive it while I contemplate the problem.

I will certainly keep you posted on my progress. I think I might return to the 1st belt from NAPA (the one that was marginally too short). I want to see if I can gain a bit by completely removing the adjustment bolt, then re-install the bolt after installing the shorter belt.
 
#28 ·
I think that Norseman is on the right track about the compressor mount. The s4's have 4 rubber bushings on the compressor mounts that become mush over time. You can see them by jacking up the passenger front side of the car. The mounting bracket to block bolts were also loose on mine. Replacing the bushings and tightening the bolts will test your patience but it's doable by us home mechanics without disconnecting the refrigerant lines.
 
#30 ·
#31 ·
Thanks guys, I think maybe, we're narrowing it down. . . I'm needing to correct another issue with a leaking seal on the Speedometer sending unit. I've been waiting to get it up on a friend's lift, so while I've got it up in the air, I can look at the compressor mounts . . . I'll bet I can fabricate new bushings if the ones under the mounting plate are mushy.

This car shows 50,000 miles and by appearance and general condition, even with the incomplete maintenance records that I have, I believe it to be original mileage. As I'm working thru these relatively minor issues, I wonder if it would be prudent to go in a bit deeper, and change the timing belt? The car runs great, and I've no reason to suspect an imminent failure, but I'd rather perform a preemptive maintenance, then a later necessary one . . . maybe with associated valve damage.
 
#34 ·
Hi srguy,

I'm not seeing any pictures, but when the motor mounts get old and worn, they can compress and allow the crankshaft pulley (that drives the AC belt) to move down and make contact with the black suspension rod that runs across underneath it, just aft of the radiator. I'm guessing that if your serpentine belt is touching the round rod that spans from side to side underneath it, your motor mounts need to be replaced.

Cheers,
 
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