Hey guys,
I am looking for the best clutch for my 25 Hour race project car ('84 GTI with a 1.6lTD engine). The clutch needs to last for a 25 Hour all-out race. I know that the clutch should fit the trans, and not neccessarily the engine. So what is the strongest clutch available for the GTI? Under the rules in my class I have to keep the original, unlightened flywheel , but the clutch is open. Options...opinions?
The trans in the car shows signs of worn 2nd gear synchros, as does the spare trans I was given yesterday (from an '83 GTI). My question is, how important is this? My race experience is with dogring race boxes, where a worn dogring can quickly lead to toal loss of that gear, and even the gearbox, ending one's race. Is it the same with synchros? Or is it merely a matter of it making a little noise? If it
IS important to fix prior to racing the box, what should be done to the gearbox to make it race-ready, and is this something a reasonably skilled home mechanic can do?
TIA!!!
Stan
BTW, here are NASA's rules for the clutch and associated equipment:
7.26. Clutch
Any clutch disc and an all steel pressure plate of the stock diameter may be used provided that they bolt directly to an unmodified flywheel. Multiple disc clutches are prohibited.
7.27. Flywheel
Any stock VW 190mm or 210mm flywheel may be used. Flywheels may not be modified.
(I have a 210mm clutch from an 83/84 GTI...from what car do I get a 190mm clutch?)
7.28. Transmission
Any stock four or five speed transmission from a 75-84 gas powered Rabbit may be used. No automatics or semi-automatics are allowed. Transmissions may not be modified. Shift linkages may be modified by installing short throw shifters such as offered by Neuspeed.
7.29. Differential (Final Drive)
The differential must be a stock unit from a 75-84 Rabbit. The differential and transmission is considered to be one assembly (no mixing and matching, see update rules). No welding, shimming, or limited slips of any kind are allowed. Final drive ratios may not be changed. Electronically controlled traction control devices are prohibited.
some rabbit pickups had a 4 speed with a 4.17 r&p. as far as i know, a worn synchro makes it hard to get in gear before the main and pinion shafts speeds are matched. shouldn't cause gear failure.
Thanks!
Normally on the track one only uses second gear once in a while, and it's not imperative that the synchro be fixed, but it's nice to know...!
Stan - I'm pretty sure that in stock form, the 190mm flywheels are as heavy as boat anchors, so they would not be well suited for performance use without lightening. They have a very big weight of mass near the starter gear ring that needs to be peeled off to get their weight down. I'm pretty sure that if you can't lighten the flywheel, a 210mm setup would be the lightest, especially if you could find or make a lightweight pressure plate that can bolt onto it. I would however, turn the 210mm flywheel down to it's minimum thickenss (IE: blueprint it for lightest weight) to save as much weight there as you can.
It looks like you are allowed to bolt any pressure plate to the 210mm. Sachs racing makes a very light aluminum alloy 210mm pressure plate, however because it is ultra expensive, you may be ruling that one out. Since a 210mm flywheel and pressure plate has a different "bolt pattern" than a 190mm or 200mm setup, you'd need to use a 210mm pressure plate to go with the 210mm flywheel. You might however, be able to lighten a stock 210mm pressure plate by taking weight off the "friction ring" (IE: face it to make it thinner, and turn down it's OD to 190mm, which would work if you ran it with a 190mm clutch disc....)
For the clutch friction material, the stock material of clutch disc would work fine as long as you had it pre-loaded with enough pressure plate spring, and didn't abuse it to the point of overheating it. It also requires a lot of clutch pedal travel to completely disengage it due to it's "sprung" marcel. A 4-puck or even lighter, 3-puck clutch disc with solid (non-sprung) center would save some weight and would give more holding power than you'd need, and also since it has no sprung marcel, you can disengage it with something like 1/4 of the clutch pedal travel. This ability to get the clutch disengaged/engaged IMO makes for fewer "gear crunch - oops" shifts, so it adds reliability for shifting. Taking off from a stop, they are shakier and more prone to stalling than a stock disc, but this isn't a problem for a racer.
I'm thinking that a close-ratio transmission like one from a GTI would be ideal for your needs, assuming the fifth gear is tall enough for your needs, which will depend on how high you want to revv the motor and also how fast you go down your fastest straight.
As others have said, a bad synchro will just make it a little harder to get into that gear. If you only select 2nd gear once per racing event, and it's only during your warm-up lap when a slow shift would not effect your performance, it sounds like it might not be a problem at all! Your application sounds like it may be very hard on transmission fluid temps, and the chance of loosing fifth gear is very high if you run the transmission fluid level down too low if it leaks even a little bit, etc. Might want to ask MrDave about his low fluid warning / transmission temp sensor.
Got it! Now, who's MrDave...?
Got it! Now, who's MrDave...?
That would be me.
Link:
http://forums.vwvortex.com/zerothread?id=799985quote:
I've owned my GLI for 12 years, and have blown up a number of transmissions. The usual failure is baking 5th gear. The transmission leaks from the axle seals, and eventually 5th gear runs dry, bakes and fails. For this transmission, I mounted a VDO oil temperature sender in the 5th gear endcap, under 5th gear.
(see the link for images)
-Dave
Hey Dave...thanks for replying!
I'm at work right now (SF Bay Area), and our LAN police have the Vortex blocked, so I can't read the entire thread... :?
But I follow the point you make about 5th gear. A few questions if I may... :wink:
Does this leakage happen quickly? Is it something that could be a factor in a 25 hour race? If so I can add checking trans fluid level to the pitstop checklist.
Do you race, Dave? Where abouts?
Thanks, Stan
The leakage is usually an 'over time' thing, unless you really blow a seal or gasket, at which point the race would be over anyway.
Checking the tranny fluid level on the manual gearbox really isn't an easy thing, unless you rig something up.
The usual way things go for the VW 020 5-spd are that they develop slow leaks, a drip now and again, and over time the low levels of fluid, combined with 5th gear being way out on the end, in it's own seperate case add-on, with the shallowest oil, things get hot and the plastic bearing carrier melts. Then the main shaft can move around a little, the brass syncro for 5th soften, and the tranny starts popping out of 5th gear.
Search the forums over at VWVortex for 'pops' or forms of the verb 'to pop'. It comes up quite often.
Anywho, I installed the sensor and a temp gauge just to keep an eye on things. It's a good indicator of how hard the engine/tranny are really working. My peak is about 90 Celcius, on a hot day (33+ degrees) climbing the Coquahalla in BC.
No, I don't race. I'd love to, but I don't have enough time or finances to finish or fully accomplish the things I'm already waist deep into.
-Dave
Cool...thanks!
When I get home tonight I'll look at the pics and read the thread., and if I have any other questions I'll drop you a line.
BTW, I drove the car briefly yesterday after rolling it off the trailer. The engine ran fine, but the clutch pedal needed to come nearly all the way up before the gear engaged. IIRC these cars need to have the clutches adjusted periodically (it's been a decade since I owned an A1).