Ross Nicol
GT40s Supporter
I've had an interesting time with the ZF and thought I should share some of it with you.I had my order placed for a porsche G50 when the ZF popped up and I snapped it up.The history known was that it came out of a BMW M1.I was able to split the box in my workshop to check condition prepurchase.I wish I had taken the time to count gear teeth at this point but I'd only just seen inside my 1st gearbox.However I did count the crown wheel and pinion teeth and found the Ratio to be 3.2:1 instead of the side plate saying it was 4.0:1. Over the next few months parts were purchased to change gearshift shaft from left to right, worn bearings replaced and the reverse idler gear shaft (an alloy quickfix) replaced with a hardened shaft.This work was carried out by Will Croll (formerley foreman at Roaring Forties) and myself.
The first race meeting at Sandown in July 2003 was the first time I recognized a big drop in ratio between 4th and fifth gear and how tall 1st gear seemed to be.Other matters for car's development had to take priority so I lived with the gear ratio problem for a while, not to mention the money it had soaked up already.Finally mid 2004 I got stuck into the 4th / 5th ratio jump and I started to think changing gear ratios and the C&P but at $US3000 for C&P and$US850 per gear Ratio I had a reality check.Went back to the gear ratio calculator and determined that if I changed 5th gear to the ratio on the plate (returning to original .791 ratio)and combined with 3.2:1 diff ratio, I would have a fantastic close ratio 5 speed box with top speed in 5th gear at 6500 rpm rev limit right in the ball park.I had limited time before the next race and to save time on the gear purchase and shipping I put a call out for help on this Forum.Tim Kay (he's on the forum)answered the call and drove for miles to RBT, picked up the gear set and delivered to a hotel nearby where another friend of mine bought it back to OZ for me all within a week.In the car for the next race and it was fantastic.
The next step was to strengthen the clutch to help overcome
slippage at race start.Pulled transaxle again (only 2 hr job now)and purchased scintered iron plate and stronger springs in pressure plate.All went well until I proved, after 3 hrs of trying to put box back on the motor plastic alignment tools are shit.pull apart again.Sorted the clutch
all together again and output shaft locked solid grrrr@@#%^^^$%@#.Back out again.Splir gearbox to find reverse Idler gear in mesh.That's not meant to happen I thought.Traced the problem to not enough spring tension on the reverse Idler lever.Gulp imagine if that gear had fallen into mesh at high forward speed? ok don't think about it. Back together and to date is all ok and now I'm working on making the shift better.I think I qualify now as a ZF guru now.
Ross
The first race meeting at Sandown in July 2003 was the first time I recognized a big drop in ratio between 4th and fifth gear and how tall 1st gear seemed to be.Other matters for car's development had to take priority so I lived with the gear ratio problem for a while, not to mention the money it had soaked up already.Finally mid 2004 I got stuck into the 4th / 5th ratio jump and I started to think changing gear ratios and the C&P but at $US3000 for C&P and$US850 per gear Ratio I had a reality check.Went back to the gear ratio calculator and determined that if I changed 5th gear to the ratio on the plate (returning to original .791 ratio)and combined with 3.2:1 diff ratio, I would have a fantastic close ratio 5 speed box with top speed in 5th gear at 6500 rpm rev limit right in the ball park.I had limited time before the next race and to save time on the gear purchase and shipping I put a call out for help on this Forum.Tim Kay (he's on the forum)answered the call and drove for miles to RBT, picked up the gear set and delivered to a hotel nearby where another friend of mine bought it back to OZ for me all within a week.In the car for the next race and it was fantastic.
The next step was to strengthen the clutch to help overcome
slippage at race start.Pulled transaxle again (only 2 hr job now)and purchased scintered iron plate and stronger springs in pressure plate.All went well until I proved, after 3 hrs of trying to put box back on the motor plastic alignment tools are shit.pull apart again.Sorted the clutch
all together again and output shaft locked solid grrrr@@#%^^^$%@#.Back out again.Splir gearbox to find reverse Idler gear in mesh.That's not meant to happen I thought.Traced the problem to not enough spring tension on the reverse Idler lever.Gulp imagine if that gear had fallen into mesh at high forward speed? ok don't think about it. Back together and to date is all ok and now I'm working on making the shift better.I think I qualify now as a ZF guru now.
Ross
