Gents,

I put up a thread a while ago about my propshaft knocking on the tunnel of the car and it still hasent been resolved. I've just changed the prop again as the centre bearing was ruined.

I also had a new pitch stopper and diff outrigger bushes put on in an attempt stiffen up the driveline.

The prop bangs violently against the tunnel of the car when moving off from a standstill in first gear. It dosent do it when rolling. Only when theres maximum torque applied to the rear.

My question is what can be causing this? There appears to be no play in the rear diff.

Anybody with any ideas would be appreciated as me and a number of garages don't have a clue.

Thanks

PS car is a 2005 blob STI

 

my 04 blob sti knocks when pulling off but thats down to the rear shocks knocking, have you checked the struts?

 

is the gearbox mount ok ?
It has to be something along the lines of the box moving to make the shaft move enough to touch.

 

I get all sorts of knocks when stopping or setting off in my 2005 STI. I ruled out the shocks with the grease nipple mod, and that definitely solved one of my knocks.

I've replaced ARBs and links front and back, so next up will be transmission mounts. I've also identified a further knock which is the brake pads moving up and down in the calipers, only at slow speeds and only after a change of drive, ie 1st to reverse or reverse to 1st.

Just learning to love it as the subaru soundtrack tbh

 

Thanks for the replies lads.

The engine mount, gearbox mount and shocks are fine. It's like the prop is trying to put power into the rear diff and is facing resistance. looking at it earlier with someone outside the car watching the rear as I moved off in first quickly, it appears the rear off side wheel looses traction while the other one dosent. It maybe nothing but is an observation.

I'm at a loss. It has to be rear or centre diff related unless anyone else has a different theory. Would it be worth removing the back of the rear diff and having a look at the gears? Any tell tale signs somethings f****d?

Thanks for your help. Really really annoying this problem

 

When I bought my jdm blob it had a very similar knock to what your describing, it was the actual rear diff swinging around inside the housing on mine, I was told I could shim the play out of it but it wasn't something I wanted to do tbh, so I found a replacement diff and changed it over and it was problem solved for me, as you said above it had a violent knock when pulling away, but mine would also do it if you where a bit quick off the clutch on a gear change but never when driving under load, if your driving up the road and you were to go fully on and fully off the throttle repeatedly a few times does it make the noise then or any kind of knocking noise? As mine did if it helps at all

 

I get a very small knock if I go on and off throttle quickly. But like you say I'm sure thats rear diff related. It's what's causing the prop to smash against the tunnel I cant get my head round. I'm beginning to think my rear diff is the culprit. I need it confirmed before I get a new diff though. I've wasted enough money and time with "it could be" answers.

Thanks for the input. In all honesty I'd rather it was rear diff than centre diff. What a nightmare that would be.

 

Well from logical thinking if your prop is hitting the turret then something on the drivetrain is either loose or seriously worn, if the actual prop is hitting the turret it has to be going almost in to a 'v' so to speak where its flexing and causing it to hit, as the prop is solid as you know, so if your confident (working from the front back) that all the box mounts, pitch mounts, engine mounts etc are all in good working order and are not perished, you've said you have changed the centre bearing or the complete prop again then it has to be rear of the car related, is the rear subframe in good condition? Everything lines up correctly and is central? If so then i would be inclined to think its the rear diff that's causing your issues, when the prop was off I assume you checked the box end for any significant play on the flange, and does your gearbox give off any kind of unwanted noises? Again if no then its unlikely (but wouldn't definitively rule it out unless 100% confident) that its going to be gearbox related. So again its pointing to rear of the car, as if it was anything mount related on the engine you would clearly see the movement up front IMO as the box and engine are bolted together so if the one is going to move the other would as well so to speak within reason so would be pretty obvious, so if there is no movement there it has to be from the rear, I was the same as you bud when mine was like it, I worked through everything but my prop was not hitting the turret, but it would make one almighty thud.

Can you actually see the prop hitting the turret if you looked from underneath whilst someone is rocking the car on the clutch? As if you can then you should be able to see what is giving under load and is causing the flex on the drivetrain.

 

Everything at the front 'looks' to be fine. I had a new Pitch stopper installed just to be sure. The gerabox has very little play and nowhere near enough to cause the prop to vibrate. The rear subframe is now solid after I had new outrigger bushes put on.

One thing we did notice was you can rotate the prop by the rear diff by hand about an inch in either direction before the diff takes up the slack. If that makes sense. Does that sound normal?

You can't see it moving as the prop is hidden inside the tunnel above the exhaust and you need to get a bit of power down for it too happen.

I like that logical look at things. Makes a bit more sense. Going to another garage on friday to see what they think. I think I'll get them to strip the rear diff back plate off and look at the gearing.

 

You will have a little float on the rotation of the prop until it catches yes, I'm not sure of what is deemed "acceptable" tbh but mine has the same may not be quite an inch but yes I can rotate it by hand a little until it catches.

Have you checked all the rear diff hangers and all the bushes to make sure they are not perished or dead? Probably a silly question but you never know it does sound very similar to what I experienced, like I say I had a hell of a thud but it was not the prop hitting the turret it was the movement inside the rear diff housing, are you sure its definitely the prop hitting or is that what you believe it to be? As if I didn't know better mine could be felt on the underside and perhaps others would think it was the prop, like I say it was a thud and I also had a little clicking noise coming from the rear when I pulled off or reversed, it was all rear diff related, since I've changed it over its been a pleasure tbh, really hope you get to the bottom of it fella, nothing worse than having something you can't put your finger on, and I totally understand why you don't want to rush in to changing parts ***** nilly as its an expensive game to play if its wrong

 

Yes checked all diff bushes and hangers and they seem fine. Nothings a silly question at this point! lol

It is without doubt the prop hitting the tunnel as you can see where it has been happening. I also get a small knock/click from the rear on lift-off or when reversing. The more about your problem I read, the more it sounds like mine with a few exceptions.

Like i say I'll get an expert to have a look to confirm. Thanks very much for your input. You've been a big help. I dread to think how much a rear diff will cost! haha

 

You will pick a rear diff up for around £150 slightly more from the breakers, mine was a little more as its a jdm with the different ratios and are a bit harder to come across by all accounts.

I would say its the backlash in the diff that's causing your problems at a guess, and the entire crown an pinion Is moving/swinging which is what was happening with mine, yours sounds a bit worse than mine, and mine made a thud so if its defo hitting the underside then I bet that's a bit noisier

Have you dropped the flange off the rear diff to check behind it, I would have thought if it was causing the prop to move then you would have some kind of oil seepage from the seals, you just undo the nut an tap it off, the flange is splined and slips on to the shaft if it helps

 

Yes mines JDM aswell. Coincidence maybe?
No not checked the flange properly yet. That's a job I can get the garage to do aswell.

 

There is a 3.9 rear diff advertised for £200 in the for sale section, I'm going to be getting my old one overhauled to go back on eventually, I think the guy who's selling the diff is finnigan or fin something like that.

Perhaps you may want to think of overhauling yours, I had a price of £380 but that was depending on something or another being usable, I'm not to up to speed with the internals of it all so forgive my ignorance but it may be an option to you

 

Ok nice one. Thanks for that. Dosen't seem too expensive if I have to replace it. I know sod all about diffs so you're not alone. lol