Help needed with retensioning on 240D after v-belts replacement - PeachParts Mercedes-Benz Forum

rino · #1 12-29-2011, 12:01 PM

This was my first time replacing all belts on my 1979 240D.
Took the old belts out, put the new belts in. The power steering pump belt I was able to retension just fine.

However, when it came to the alternator-water pump belt, I'm having problems with the tensioning screw, it seems to be slipping, leaving the belt very loose. What to do?

Also, in the case of the refrigerant compressor belt, how do I put the tensioning roller in tension before tightening the fastening screw? I have no idea how that can be achieved.
I've followed the instructions from my service manual CD to the letter (job 13-340 Tensioning V-belts)...it simply says (when covering the refrigerant compressor belt), "Tension V-belt by swivelling tensioning roller" then "Tighten fastening screw." But how do you do that, specifically?

TIA very very much for your help. Right now I have the car sitting in my garage, and I really need to get it going ASAP.

vstech · #2 12-29-2011, 12:28 PM

if the alt tensioner is slipping, the bolt is hosed, and you will either need to replace it, or build yourself a replacement from an eye bolt... or use a prybar.

for the a/c tensioner, do you have the compressor removed from the motor?
there should be a 10mm nut between the oil cooler lines bracket, you tighten that nut to tighten up the belt... you also have to loosen the 3 17mm bolts on the rear of the compressor... this is assuming you have the R4 compressor, if you have the GIANT york compressor on top of the alternator... it's harder.

toomany MBZ · #3 12-29-2011, 12:45 PM

Depending on which tensioning bolt you have, the gear or "L" bolt.

I've seen the gear bolt need seemingly constant tightening. Inspect the other end for wear.

rino · #4 12-29-2011, 01:47 PM

Quote:

Originally Posted by toomany MBZ

Depending on which tensioning bolt you have, the gear or "L" bolt.

I've seen the gear bolt need seemingly constant tightening. Inspect the other end for wear.

I have the one at the bottom (V-belt A, Alternator-water pump, Version starting August 1973), but as I said some of the teeth of the tensioning screw are damaged and it slips.....does not allow me to tighten up the belt....

vstech · #5 12-29-2011, 01:49 PM

I have two sets of this style bracket, and gear sitting on a shelf...

rino · #6 12-29-2011, 01:58 PM

Quote:

Originally Posted by vstech

if the alt tensioner is slipping, the bolt is hosed, and you will either need to replace it, or build yourself a replacement from an eye bolt... or use a prybar.

for the a/c tensioner, do you have the compressor removed from the motor?
there should be a 10mm nut between the oil cooler lines bracket, you tighten that nut to tighten up the belt... you also have to loosen the 3 17mm bolts on the rear of the compressor... this is assuming you have the R4 compressor, if you have the GIANT york compressor on top of the alternator... it's harder.

Do you know of a DIY somewhere that teaches how to build a "replacement from an eye bolt?" How would I use a pry bar properly? Can you explain what to leverage against.....pictures would really be helpful...

I have the York on top of the alternator... I could easily free the old belt by unscrewing the 19 mm bolt (you can see it in the picture provided by
toomany MBZ - V-belt B, Refrigerant Compressor)... that's all I needed to do to release the belt..... now, as the manual says, I need to do that in reverse, push somehow on the tensioning roller and then tighten the fastening screw while the belt is under tension.....and my question is, how do I do that? What way could I push on the tensioning roller in order to achieve the needed tension so that I could then tighten the fastening screw and be done with it? Does it make sense to you?

rino · #7 12-29-2011, 02:04 PM

Quote:

Originally Posted by vstech

I have two sets of this style bracket, and gear sitting on a shelf...

How much would you want for one set? you can PM me that if you care to.
My concern, however, is to get the car functional ASAP.....so I'd gladly go for prying the alternator or quickly building some sort of replacement if someone would kindly enough show me how......
Something I could do tonight, as opposed to having to wait several days with something coming in the mail....

vstech · #8 12-29-2011, 02:38 PM

Hmm.
I would think a thin prybar on the top of the alternator would give you the leverage to tighten the belt if the alternator bolts are loose enough to let it move...

rino · #9 12-29-2011, 03:04 PM

Quote:

Originally Posted by vstech

Hmm.
I would think a thin prybar on the top of the alternator would give you the leverage to tighten the belt if the alternator bolts are loose enough to let it move...

The alternator bolts are loose....but I don't see what you leverage the pry bar against....I'll have to look underneath again.....

I'd really need someone who has actually done it to explain to me how to do it.

Also someone who has actually tightened the york compressor belt "by swiveling tensioning roller and then tightening fastening screw" - could such a kind soul please explain to me how it was done? I'm getting panicky here, really need use of the car soon......these seem pretty simple procedures, but obviously I'm overlooking something somewhere.... I'll keep alternating between searching old threads in this forum and coming back to this one, hoping to soon come up with something useful.

Thank you all.

rino · #10 12-29-2011, 08:06 PM

OK, I've read *extensively* some of the old threads on V-belts and I think I understand where I got stuck now...

My Mercedes factory manual apparently gives the wrong procedure for tightening the A/C compressor belt (you can also see the image provided by TooMany MBZ, which is an exact copy of my manual page for that job).
The manual gives an oversimplified procedure for the A/C compressor belt:
"1) Loosen fastening screw.
2) Tension V-belt by swivelling tensioning roller [MIND you, this is at the idler pulley, NOT the A/C compressor...The factory manual does not mention messing with the A/C compressor at all in order to tighten that belt]
3) Tighten fastening screw."

The several posts I've read on this just now say otherwise...they say all the A/C compressor bolts need to be loosened along with the metal clamp holding the freon lines and then play with the adjusting strap in order to tension this belt, and nowhere do they mention to do anything to the tensioning roller (idler pulley) which is the only focus of the factory manual for this job. Here's the best explanation I've found, by vstech: http://www.peachparts.com/shopforum/2104453-post11.html

Loosening the tensioning roller (idler pulley) bolt worked perfectly to free the belt.....but I was right when I saw no easy way to do the reverse procedure for tensioning it.

So, I'll try this approach tomorrow early morning. If someone has some experience with the york compressor and thinks there are additional things I should know working on this, please contribute your knowledge here.

Tomorrow I'll also use PB Blaster on the tensioning mechanism for the alternator belt....after completely loosening the three bolts....let's see if this leads to a different outcome.

Any thoughts/advice/suggestion you might have please contribute here. I'll read whatever was posted tomorrow morning before attempting these tasks again.

God bless...

EDIT: Actually that procedure from the manual is perfect for my 1979 240D with York A/C compressor. I was able to use an adjustable wrench on the rectangular structure on which the idler pulley is bolted and tension the belt that way while tightening the fastening bolt behind the idler pulley with my other hand.

vstech · #11 12-29-2011, 08:18 PM

... my instructions are ONLY if you have the GM R4 pancake compressor under the IP...
if you have the York compressor mounted above the alternator, then you need to adjust the Idler pulley...

rino · #12 12-30-2011, 12:37 AM

Quote:

Originally Posted by vstech

... my instructions are ONLY if you have the GM R4 pancake compressor under the IP...
if you have the York compressor mounted above the alternator, then you need to adjust the Idler pulley...

Then back to my initial question: how do you do that, how do you cause the idler pulley to extend the belt, properly tensioning it, before tightening the bolt behind it? With a prying bar? This is what I have not yet managed to understand in the least.....

vstech · #13 12-30-2011, 12:44 AM

gotcha... I think there is an adjustment bolt that moves the pulley... I'll look over the bracket on my 78300D...

rino · #14 12-30-2011, 09:56 AM

No adjustment bolt that moves the idler pulley on my car... I studied it early this morning and was able to use an adjustable wrench on the rectangular-shaped structure on which the idler pulley is bolted - I think it's maybe 19 mm or 20 mm wide.
It worked like a charm, while pulling on that with one hand I was able to tighten the fastening bolt behind the pulley with a 19 mm wrench + breaker bar with the other hand. Very satisfactory outcome and the belt is now tightened properly. Actually, the A/C compressor belt on a 1979 240D (York A/C compressor) is the easiest of all belts to replace or adjust, once you understand how to do it right. You don't even have to go near the compressor at all, it is all done from the idler pulley and yep, the instructions from the FSM were right on target (just a bit obscure, I wish it would expand a bit more on the details of how to do things).

I still have to deal with the alternator belt - not enough time on my hands this morning. I checked again and the tensioning teethed bolt is definitely shot....it slips... Someone very ignorant must have tried to use it without first loosening the three bolts behind the alternator, thus ruining it...what a shame. Can you provide a bit more information on using an eye bolt to fix it? Thanks...

Phillytwotank · #15 12-30-2011, 10:09 AM

That toothed bold is pretty tricky. if its shot then its shot and you'll never be able to tighten it up. try to find one in salvage if you can or you can order a new one from various sources. I find the trick that works for me is.... to have all three nut and bolt points on the alt loose to the point where there almost tight, then while laying under the front of the car, get two wrenches one the head of the toothed and another on the nut of the toothed, rotate the toothed towards the tightening direction then clamp down the nut in the back. then tighten the other two. it's tricky. be patient and maybe move the whole setup back and forth to kinda get a feel of the mechanics. One tooth can be the difference between a squealing belt and a tight belt.