Driveline vibration on over run

I have the same problem, bad vibration on coasting. I am running a supra conversion though. have changed the gearbox, been through 2 tailshafts aswell all professionally built and balanced. Still cant find what the issue is

quote:

---

Originally posted by robertverhey

Hmm these things can be buggers to track down....neither of you mention engine / gearbox mounts....worth checking?

---

Gearbox rear mount I use is the original celica one bolted to an escort auto crossmember with the rubber cut out and a plate welded across the bottom. Engine mounts are fine and have been changed over the years.

quote:

---

Also turning the driveshaft through 180 degrees on the diff flange might change the nature of the vibration, thus assisting in tracking it down.

---

Tried that one, didn't make a difference but I like your thinking. I have had that when CV joints are reassembled not lined up as per original.

quote:

---

I've been known to put the rear end on stands and run a car through the gears to find noises.....but needs to be well chocked at the front! Risky but if you're desperate....

---

I have done that too but the noise just seems to come from everywhere!. I also did this on a 4 post hoist. Was scary!

Fordsy just sent me a link to a toyota website that has a Celica with the same problem. It was solved by changing the angle of the diff to gearbox. Gonna get some spacers made up of varying thicknesses and space the crossmember and see if it makes any difference.

It is one of those things that makes the car unpleasant to drive for long periods.

Craig.

quote:

---

Originally posted by spigot

Go to bunnings and get a magnetic angle finder/protractor. Find out the angles of the diff flange and output yoke w.r.t level ground, the angles should be equal but opposite. If the uni's are not offset and are perfectly straight to each other you will get a severe vibration which will destroy them quickly.

I reckon you must have a little play in your driveline to cause it on overrun. Try spacing down the gearbox mount first.

---

Thanks Spigot, just reading about this now on some american websites. Does Bunnings sell the magnetic angle gauges? I have found them on ebay but a quick trip to Bunnings would be better. Might have to look into it tomorrow lunch time.

Craig.

my escort did the same. the difference between the pinion angle and that of the gear box was 7deg, raised the box a bit and got it down to 3deg and this fixed the problem. if you cant get on the rear of ya gearbox easy to measure the angle the front of ya crank pulley is just as good and easier.

quote:

---

Originally posted by fordsy

Just incase you lose the link somehow...

http://www.buickperformance.com/Pinion.htm

---

Thanks Steve, what would I do without you?

Got one of these today so will see how I go. Looks like it might have to wait until the weekend though.



Craig.

This is probably more of the same but also discussed here...

http://www.cortina-mk1classifieds.com/forum/showthread.php?2030-Diff-pinion-angle

Shaun

Well, finally got some time this afternoon to rip the tailshaft out of the Escort and take some measurements. Only problem is that I found some bad news. It is good in a way though as now I know for sure what is causing the vibration.

The diff pinion is sitting at 0 degrees (as I suspected) but the gearbox in it's current untouched position is -5 degrees. I also found that I could check it by sitting the gauge on the top of the rocker cover.

So now the problem is how to adjust it. I removed the spacers from the gearbox mount and raised it 10mm which brought it back to 3.5 degrees. The gearbox and exhaust now hit the body so I think I am gonna have to adjust it at the diff end.

Can anyone see anything wrong doing it this way, so that the diff is pointing up +5 degrees and the gearbox is down -5 degrees.

Thanks for all your help so far.

Craig.