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Driveshaft? noise after Brat 5-speed swap
Posted 12 August 2012 - 04:59 PM
Found that I'd sprung a leak from one of the heater core hoses last night, fixed that this morning. For this build I just had one of my old radiators patched/cleaned up at local radiator shop for $80 I didn't feel great about paying, car still wants to run pretty damn hot sometimes in these hotter than 95 degree summer temps but not to the point of overheating, I'll try some redline water wetter, also may need to adapt a small coolant overflow bottle into this engine bay the radiator can take from/give. My old black Brat uses a bottle like that... Waiting for a new A/C condenser to come in like wednesday so that hopefully my A/C can work after that.
Trying to diagnose a vibration noise that comes and goes, pretty much above 60mph, would seem to be driveshaft (custom for swap, 51" long tube I believe about 10.5" longer than stock).
Driveshaft made & balanced at local Six States driveline shop.
From all external appearances, I don't think the driveshaft is rubbing against the exhaust pipe or anything close, everything is at least 3/4" away at its closest and exhaust pipe is mounted firm with two solid 'hangers' in the middle of car.
So my next question is, how much free-play is the driveshaft supposed to have to slide in and out of the trans? It's a long splined shaft on end of driveshaft that slides into trans.. if you remove the 4 driveshaft bolts mounted to the rear-diff. and slide the driveshaft all the way into the trans (with car on its 4 wheels), how much space is supposed to exist between the driveshaft and the surface of rear-diff. it mounts to? 1/2" gap or bigger? I would think if driveshaft is slightly too short it could cause a vibration issue like this..
I was going to unbolt driveshaft again to check that space next, and I was thinking about an AWD dyno run to help diagnose if I need to.
Also, if engine is just idling in neutral, I can hold the 4WD shift lever down slightly further towards the trans tunnel (in 2WD) and cause a slight trans noise to go away, like two sets of gears aren't slightly rubbing anymore.
I know for the 4WD shifting there are two rods, one that connects to the 4WD lever (modified for my swap), and another that is attached at two points coming out of the trans slightly ahead, connected together for shifting between 2hi-4hi-hlo.
Probably I need to make slight length-adjustments with adjusting nuts at the end of one of these rods to keep this slight-rubbing noise away when in 2WD??
Posted 13 August 2012 - 08:09 AM
how much free-play is the driveshaft supposed to have to slide in and out of the trans?.. if you remove the 4 driveshaft bolts mounted to the rear-diff. and slide the driveshaft all the way into the trans (with car on its 4 wheels), how much space is supposed to exist between the driveshaft and the surface of rear-diff.? 1/2" gap or bigger?
Also, 4WD shift lever slight noise? [Has some force on it in one direction now when it needs to be more 'neutral'?]
Thank you educated forum members, just need to reiterate my important questions.
If I could get any answer today that would be awesome, you guys are pros.
Posted 13 August 2012 - 10:24 AM
Posted 13 August 2012 - 11:30 AM
Posted 13 August 2012 - 12:05 PM
Is the rear differential itself acceptable to have so much play in it between the drive-shaft and the rear drive axles when you change directions?
It seems my problem occurs regardless of 4th or 5th gear pretty much above 60mph when I let off the throttle and so under deceleration or low engine output. Also I believe doesn't matter if 2WD or 4WD-HI would still do it in these deceleration situations at those speeds. Like a chatter that can come on stronger and stronger for a sec, driveshaft whipping back and forth at the trans snout near under the shifter? If I accelerate hard all the way past 75mph in 4th/5th gear I can prevent any major vibrations from occurring, BUT if I make it to 60mph then am just accelerating barely or maintaining speed, the chatter can come on. So.. I can drive this car even on the freeway, and feel like something bad is happening less than 5% of the time..
ONE-PIECE driveshaft made at Six-States driveline shop, 51" of new tubing.
I've had these wheels on two different brats here, 15" Pug alloys with newer Goodyear tires, problem shouldn't lie in any wheel balance alone..
This '86 car drove ok previously with no vibration issues on stock driveshaft/4spd trans..
Stock Brat height not lifted (rear does sit higher than front, must be at highest adjustment in rear), alignment of rear diff and tail of trans seems straight no bad angles..
Edited by TajMan, 13 August 2012 - 12:13 PM.
Posted 13 August 2012 - 01:17 PM
what's most important is that the angles between the driveshaft/rear diff and driveshaft/trans are the same or very close to each other and that must be measured with a special driveline tool! Even if angle is more or less than it was stock, I guess what matters more is that the two angles are close to the same?
I've got 4-speed and 5-speed Brats sitting right here, I can see with my eye that the angle is a little steeper with the 5-speed driveshaft than with the 4-speed (between rear diff. and driveshaft)...... so I can only imagine that this could be a possible problem until I get Brat on a lift somewhere that can measure with the correct driveline tools?
Posted 15 August 2012 - 09:36 AM
I'm just teaching myself about modifying 4X4 vehicles here..
At this point I am very confident that aligning my rear differential so it is about parallel with my transmission should fix this problem..
Posted 16 August 2012 - 10:41 AM
Posted 16 August 2012 - 11:14 AM
You're saying you have 5-speed swap, with a one-piece driveshaft, and steep driveshaft angles, AND you say your trans and rear diff are not parallel?
I don't know what to think about that..
but I talked to guys a six-states here who had built my custom driveshaft. I am very disappointed how little help the offered, basically just left me on my own zero help (because they don't know how Subaru Brats are built or what changing the rear diff angle would take)
My problem now is, The angles seem to be multiple vertical & horizontal- I need some kind of tool to properly calculate these angles, a pro-tractor/level under the car on a lift measuring the vertical rise/drop is NOT sufficient enough. What point of relation do I have to go off of on the trans to tell what is 'straight'!? Its a big odd shape without a flat plate on bottom that looks parallel with the driveshaft yolk, difficult to measure..
It seems I could add washers to the 4 bolts/nuts on rear diff mounting, and change the angle more in the WRONG direction pretty easily... but it seems to change angle in the right direction may take some cutting/drilling/modifying to the bar that runs BEHIND the diff and mounts with two bolts. With those two bolts mounted lower the angle between driveshaft/diff could be less-steep.
I KNOW the angles are not steep now! I just thought the difference in angles was surely causing this..
Edited by TajMan, 16 August 2012 - 11:17 AM.
Posted 16 August 2012 - 01:10 PM
Posted 17 August 2012 - 09:44 AM
Driveline angle only changed because driveline slightly longer now...
I know you'd think the angle slightly less steep now, with the longer driveshaft..
HOWEVER, if you look under both the 4-speed and 5-speed brats, just judging by eye, it appears the angle between driveshaft/rear diff is slightly steeper on the 5-speed car!?
Posted 17 August 2012 - 10:59 AM
Posted 17 August 2012 - 11:15 AM
Posted 20 August 2012 - 10:45 AM
but yet to diagnose properly..
With this 5-speed swap, one part of the rear of trans tail shaft is basically touching the body sheet metal on the side of trans tunnel (tight fit w/ these custom trans mounts) SO... if something causes the driveshaft to vibrate, its just going to shake the trans and AMPLIFY the sound/vibration.
I am going to try to hit the body underneath with a bar and a big sledge, try to bend a little and create a bigger gap there.
AND then my next task will be to try and measure/re-mount the rear diff at a slightly different angle.
If I'm unable to stop this issue with the 1-piece, I suppose I may always try a Loyale 2-piece driveshaft..
Posted 24 August 2012 - 10:04 AM
I may snag a 2-piece driveshaft and try to install/fabricate a center section mount.. to see if it fixes my issue.. because it may be the simplest way of attempting to do so first.
Posted 24 August 2012 - 11:18 AM
Posted 27 August 2012 - 06:19 AM
Most driveshafts need about 1 inch of clearance to allow the movement into the extension housing on a conventional live axle as the suspension compresses and the drive shaft slides into the box,Obviously with a Subaru with the rear Differential solidly mounted and Independant rear arms that does not occur to the same degree so leave at least 1/2 inch to 3/4 inch minimum to allow easy R&R.
However Uni joints must be in line on the driveshaft perfectly or it will vibrate,they cannot be out of line so check alignment between both Uni joints with a string line or better if available a laser pointer.
Remember Uni's must align at each end of the Propellor or Driveshaft but when bolted up must not line up between the Gearbox and differential unit,Usually just vertical differences in alignment is enough but being out side to side should pose no issues either.
Edited by coxy, 27 August 2012 - 06:21 AM.
Posted 27 August 2012 - 01:42 PM
.. but the point is- no extreme angles! Stock car height stock mounting, driveshaft only longer causing slight difference from 4spd angles.
my name on the driveshaft built by six states
difficult to adjust anything..
sooo I just bought a '94 Loyale 2-piece driveshaft for $50 and I'm going to see how easily I can weld some mounts for the center section and give that a try instead
Posted 27 August 2012 - 04:42 PM
That will give a vibration.
Angles are OK up to a point,but ,you want the trans and rear end parallel.
Posted 28 August 2012 - 08:50 PM
There are still times between 60-65mph off-throttle that I can feel the beginnings of a faint vibration similar to before but nowhere near as bad as the past at times..
I'd call it 99.9% fixed, and know the things required to perfect it to feel like a 'completely stock car always'...
Posted 29 August 2012 - 10:32 AM
Posted 29 August 2012 - 04:38 PM
besides that there is a slight driveshaft issue sometimes still, which means at the same time I fix the exhaust hangers I'm going to cut the center section of my exhaust out, fix driveshaft center mounting for an even more centered location, then afterward I'll fix all those slight bends in the middle of my exhaust with a new straight section of piping..
Posted 27 September 2012 - 10:11 AM
What is ridiculous I'm surprised nobody mentioned before, is that its very easy to alter the angle of the rear diff in the direction I wanted, just by stacking some large washers(19mm nuts) on the two ends of the bar mounted transversely which is bolted to the back of the rear diff. Move those two mounting points down, the front of rear diff that driveshaft mounts to then angles up slightly. If you don't have enough movement yet with 3 large washers, then you could unbolt those 2 brackets from the body under the bed, and also add washers/maybe longer bolts which mount those brackets to the body..
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