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Please Help Me With A Diff Problem

SRE30

By SRE30,
in Queensland

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SRE30 Rookie

SRE30

Posted
Posted

Ok, I have a E30 BMW with a Nissan SR20DET. I recently replaced the weak open wheel BMW diff with a second hand R32 Skyline LSD diff. To put it in I had to get a new 3" single piece tailshaft made up, two new Mazda half shafts, new Magna outer CV's, and the original R32 inner CV's.

Now between 3-4000 RPM (~110kmh) there is a horrid shudder that shakes the whole car and you can feel it most through the seat of you pants.

Now, since it's all new and most of it custom it's proving difficult to track down what's causing it. The place that made the driveshaft had a look at it and ran a dial guage over everything and couldn't see what could be causing it, so suggested the diff could be the problem.

I have replaced the rear wheels and tyres, same problem...

Removed left hand half shaft, same problem...

Remover right hand half shaft, same problem...

All that's left is tailshaft and diff so I have two questions:

1. Has aonyone had this sort of problem with their diff?

2. Does anyone in Brisbane have a known good R32 LSD diff with 4.1 ratio that they would like to sell on the basis that it is the diff at fault (ie, I pay you after I fit your diff and problem goes away, or I give it back if it doesn't :)

Any opinions?

Cheers

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SteveL Mentor

SteveL

Posted
Posted (edited)

It's unlikely to be the diff, BUT if the input pinion bearings are shagged it could cause the tailshaft to float around sufficiently to cause this sort of problem. I've never seen an R200 that was that bad and usually they get quite noisy well beforehand. A badly worn slipjoint at the gearbox can give a similar problem, although in that case oil leaks preceed other signs.

To me it sounds like tailshaft whip, which can occur when there is too much 'offset' between the connection of the tailshaft to the gearbox and its connection to the diff. IOW the imaginary line drawn between the centre of the gearbox to the centre of the diff should be as straight as possible. Shimming the gearbox mount can help but it depends on which way you need to go.

I had a similar problem with an Oz spec R31 Skyline sedan when I replace the tailshaft with a single piece unit that was quite long. Had bad shudders at similar speeds to yours and ended up modifying the gearbox mount. The problem is still there but nowhere near as great.

Generally the longer the tailshaft the more sensitive it will be.

Edited by SteveL
Oz Grand Master

Oz

Posted
Posted

the R31s are well knowen for the sort problem it sound like you might have, the tail shafts throw the balance weights off & @ around 80 too 100 k it shudders might be worth taking the shaft out & have it balanced....

SRE30 Rookie

SRE30

Posted
  • Author
Posted

I can't detect any movement/play at either the gearbox or pinion end. I first thought whip, but the gearbox and pinion are pretty well lined up. The rotational speed of the driveshaft is only about 4000rpm and they guaranteed no problems up to 9000rpm. I also can't detect any significant vibration from the gear leaver (I expect I would if it was the tailshaft whipping).

If I can't get a diff to try I guess I can take it to a diff lapping place and get them to inspect the internals of the diff, if it's all OK, I will take the tailshaft to some where else to have it inspected/rebalanced.

Ahh, the cost of doing something different...

SRE30 Rookie

SRE30

Posted
  • Author
Posted
the R31s are well knowen for the sort problem it sound like you might have, the tail shafts throw the balance weights off & @ around 80 too 100 k it shudders might be worth taking the shaft out & have it balanced....

I took it out last night, it's still got the weight on it, and it's brand new so it should be balanced...

dangerous_daveo Grand Master

dangerous_daveo

Posted
Posted

Uni joints. I had the same prob with mine when I got the rb25 box put in. We went to a 1 piece tailshaft. The place said the angle was too much, so we jacked the box up didnt help. Did a few other things. Then put it on a dyno. Shaft shacked to the s-house. Went back and said fix it. Low and behold they used cheap uni's. Had them replaced within about 3hours.

Thats my bet anyway.

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