Syncro Rattle and Pulse

[FloAK]

We are bringing an 87 tin top syncro back into working order.

Two things to figure out, 1-rattling noise underneath and 2-slight pulsing.

We purchased the van with the prop shaft out and a bad final drive. Transmission drove smooth and quiet, but when we drained and looked inside it needs a new R&P. There was a tow hitch welded from the bumper to the mustache bar. We swapped a different trans, prop shaft and final drive in. Then replaced coolant hoses and new stabilizer bar links. It has a stock 2.1 with GW EFI.

1- A rattle type sound, at first sounded like near the front right, but as I drove more hard to say it is from front. Sound tends to happen at higher rpm when under load and in 2, 3, 4 gear. Examples driving at 4,000 rpm uphill it will rattle when in third then it will go away if road transitions to flat. It also rattles when driving at 65 mph in the wind, if drop to 50-55 mph sound goes away. Also if under load and go over the right type of bump. It will also happen at high rpm, ie 4500-5000. Sounds goes away as soon as load is reduced. The rattle type sound at high rpm was there before swapping trans and install prop shaft and final drive.

2- Light pulsing: Feels like van is not entirely free when in gear on flat roads, it bounces between propulsion and being restricted forward even when throttle is steady. Another place if feels like it pulses is when in 1st gear climbing steady, there are small pulses where postive power then minute breaks in power. In both cases you can feel it if you are paying attention and aware, it is a small bobble as you hold steady power. Passengers not paying attention do not notice. It is subtle.

Temp sensor tested ok, but reads low on gauge always under 194F and IAC is normal between 13-18 momentarily but drops low to 6.1 when it idles. Screw on throttle is near max clockwise position, so no more to adjust up. Cleaned and greased all CV’s. They show wear on the cages.

Appreciate ideas on how to resolve. Thank you.

[Sodo]

Not a lot of action on this post. I gotta say its kinda hard to get a grip on.

Sone unexplained noises can be attributed to a worn out front diff.
Its getting to be about that time for front diffs. Folks should make sure they have clean oil in those valuable, No Longer Available drivetrain components.

If the front diff oil is real black it could be contaminated by the VC fluid. Which likely wears out bearings and gears sooner.

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That’s my one beef about Swepco oils, they are dyed so dark they impede diagnosis. At least for me. I can’t think of a good reason for the dark dye except maybe it looks more substantial or valuable. I wonder what Swepco says is the reason.
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[DanHoug]

[pemz0r]

For the rattle sound... does the van have the bash guards installed? See if the the bash guards are touching the trans or engine cases.

Last weekend, I went off road pretty hard and hit some rocks, when I got back on the road I noticed the car started vibrating, I thought I broke some ish, but once I got home I noticed the bash guard was pressed against the block. The vibrations would change depending RPM and how fast I was going.

Just something to check..

[FloAK]

Appreciate replies, sorry if post is not clear.

The rattle noise is reproducible above 4000 rpm going uphill. The noise was present with prop shaft removed, original Front final drive and original transmission. Swapped in a different front final drive and transmission then installed prop shaft. The noise is the same.

The swapped in Front final drive has new oil. I don’t have a history on it. The oil that came out looked reasonable and no considerable metal on plug. I made a viscous coupler test, both by jacking up one wheel at a time and lifting the back end on a jack. When lifting each wheel, I was able to turn the wheel by hand with some effort. On the test were lift the back end with a jack with a 2x4 in front of the front tires and in g gear. I was able to spin the rear wheels with clutch 1/2 out before front wheels engaged, when I let the clutch full out engine stall. Idle is 950. It seems like that is a ‘pass’ on the viscous coupler working properly. I did same test with another Front final drive, swapped it in and had the same result.

I will double check bash guards. When I am driving it sounds like it could be coming from below me, maybe related to suspension or front final drive, when I ride in back, it is hard to tell where it is coming from, maybe right underneath.

Thanks for replies.

[FloAK]

Checked out the bash guards on the prop shaft, it looked like all was in proper order.

Test drive to get an audio. The noise starts in higher rpm while under load in all gears and when under load over bumps. The first run up is on gravel, after turn right on pavement-both gradual uphill to create load.


Link

[MarkWard]

On my phone, that’s an ugly sound.
Step one. Is it mph or rpm? Have you tested the VC yet? There are videos how to test using a floor jack and a 2x4 in front of the front tires.

I’d drive it just enough to pinpoint. Spare out cv’s would let you drive the van with the front cv shafts removed. With the driveshaft removed and the front cvs removed, but with spare outer cvs installed, that will isolate the front differential. Short of spare cvs. You can remove the outer CVs from the front shafts and use those. That’s a bigger job. Don’t drive the van with the front CVs removed without securing the outer hubs. Sorry

Edit, my new to me syncro made a similar noise. It failed the 2x4 test. Here is what I found. Not cheap to fix.

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[FloAK]

MarkWard

Wow! The picture of the front diff…Thanks for share and thoughts. This gave me a boost to start taking parts off again.

VC- I did the 2X4 test and the test were jack one wheel off the ground. On the 2X4 test, (There is a video of my test below) the rear wheels would spin with the clutch pedal 1/2 out. When clutch pedal is full out engine stalled. If I added rpm van climbed over the 2X4. When I jacked up one wheel, I could turn the wheel by hand with significant resistance. As long as I went slow the wheel turns. I think that is a ‘pass’ on both tests. I had similar results with a different VC. Hopefully VC is not too tight.

-RPM or Speed: If the drivetrain load is low I don’t get the noise at any speed or RPM. The noise happens when drivetrain is under load in all gears (have not tried low or reverse). The noise starts around 4000 rpm on uphill or at lower rpms if driving over bumpy road, ie 2500 rpm. No noise driving any speed on downhills or if clutch is released. Hard to tell, noise is more frequent at higher rpm, not sure if it follows rpm.


Link

[MarkWard]

Little hard for me to follow along. Going forward with driveshaft installed , the front pinion is loading one side of the ring gear. Coasting down hill, the pinion loads the opposite side of the ring gear.

What’s confusing is the noise is there with the driveshaft removed. At that point, the front ring and pinion are along for the ride. The wheels are turning the ring gear which in turn is spinning the pinion shaft. Forward motion would have the same affect going up and down hills. So, I’m at a loss at this point.

I sold our syncro once I realized the cost and headaches. Our 2wd Vanagon takes us anywhere we’ve gone so far.

If I had our syncro, I would have spent the money for new outer front CVs and carried the used ones for spares or a situation like this. I’ve seen heavy duty bolts, and custom washers to install in place of an outer cv, but it’s custom = more money than new CVs likely.

Sorry I can’t be of more help. Plenty of Syncro experts here to help. This bumps your thread to the top.
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[FloAK]

Thanks MarkWard

I had time to remove prop shaft and test drive, still same noise. CV’s next on list.

[FloAK]

I found the source of the noise A deep breath of relief it was not the transmission.

When I removed the prop shaft I went for a short test drive. The noise moved towards the transmission rear and center. On closer inspection, there was only 1-2 mm space between the bash plate and the exhaust. It turns out that the exhaust would make contact with the plate when the engine was under load.

PemzOr…You had the right advice, it just took looking further than I had.

Thanks for everyone’s patience and help!

[dobryan]

Glad you found such an inexpen$ive fix!
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

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