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Change gear ratios...

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I'm looking at changing the 5th gear set on an FFV box (that goes with an SDI). The existing ratio is 1:1.35 or 1:0.74 depending which way you look at it. I'd like to move the RPM from 3000 at 80 to 2400. So I think the gear set from an FLE will be about right. They are 1:0.64

Which cars use the FLE variant? Is it the tdi?

IMG_1081.PNG

Edited by mk2

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FLE FJD show as dual clutch gearboxes so those are 3L TDI yes.

Can your 60HP chuffer pull those revs with that wind resistance in that gear? You might find if it is a big jump from 4th you dont get to use 5th as much as you'd like to. Check out the 3L ratios and see what jump 4th to 5th is in them. They are lighter, better aero, more torque and have a turbo power band.

Edited by Sausage

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40 minutes ago, Sausage said:

FLE FJD show as dual clutch gearboxes so those are 3L TDI yes.

Can your 60HP chuffer pull those revs with that wind resistance in that gear? You might find if it is a big jump from 4th you dont get to use 5th as much as you'd like to. Check out the 3L ratios and see what jump 4th to 5th is in them. They are lighter, better aero, more torque and have a turbo power band.

Yeah, i was thinking the same. Did over 300 miles yesterday on the m network (85 mpg!) and it dawned on me that the SDI is tuned as stock to be the most economical at exactly 100kph or 64ish mph. Too slow for me. I've gas flowed the inlet path so it definitely 'feels' more torquey than before. A lot. At about 100clicks you can really feel the torque band peak. And hear it now.

But. the idea is that you don't even need to pull the gearbox out to change the 5th gear set. Just take the end cover off, remove the sleeves and clips, swap and reassemble. An hour's work I'd guess. And if no good, easy to put back again...

Both the regular TDI and 3L have the same gear sets? I might try and get that x reg tdi in bristol for £250 and break it for bits. I have a feeling some mk2 golfs and breadvan polos also used the exact same gears.

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Taller tyres would be an easier swap, they only need to go on the front as well (unless you have abs maybe). 

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Yeah. Would need to use my gps phone as a speedo...

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I have some 195/65/14 on e30 bottle tops they looked hilarious but were touching the footwell, I doubt they would clear at standard ride height either, 175/65/14 are very similar diameter as 185/55/15 which i had on my TDI for a year, they are about the biggest you can fit without mods and a few mph over what the speedo says.

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Running 185/55/14 = circumference of (185 x 0.55 x 2 + 14 x 25.4) x pi = 1756.5mm

so if i swap to a spare set of 14s off a mk2 golf, 175/65/14 I'd get 1991.8mm per rev

Gives a ratio of 1991.8 / 1756.5 = 1:1.134 (13%)

80mph compared to 64mph is a change of 1:1.25 or 25%. Wow that much?!

13% slower- Yeah that'd move the max torque to 72.3mph. Speedo 13% error! Getting there. Just realised that the 5th gear from an FLE box still wouldn't be enough as it's only a change of 10% i think. 0.74 to 0.64....

Or have I messed up my maths somewhere? 

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Yeah, messed up. 0.74 is 100% (original). So 0.64 is actually 15.6% slower. Mmm. I need 25%

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I run 185/60x14s and the speedo is spot on.

You have a 085 box, the TDi uses the 02J. Totally different. The TDi box has the highest first gear and diff of any VW. 3.3 and 3.158. Total ratio 10.42:1 which is abnormally high. Most cars have a 12.5:1 first gear. If it's not too hard to swap to the 02J, and the block drilling and starter position are probably different, that would be the simplest option. I've just removed my EXB to fit a hybrid DTA with a longer 5th. Including the diff, the ratios are 10.42, 6.14, 4.13, 2.89 and 2.08. 80 should 2,500 rpm.

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Sounds good. You've engineered it properly :)

I just want to try a different gear set for 5th and leave everything else. I can't find cross over part numbers to early polos and mk2 golfs, but I kniw for sure they share the internals with 085 boxes.

I don't think 02J has the same gear internals as the 085. Interesting that the 1st gear is 10:1. I bet the clutch wears out faster than most with the TDI...

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eqx and fff 1.9 diesel have longer 5th gear, but not by the amount you want.

https://workshop-manuals.com/volkswagen/polo-mk3/power_transmission/5-speed_manual_gearbox_085/technical_data/gearbox_identification/code_letters_gearbox_allocation_ratios_capacities_2/

185/60/14 is indeed the sweet spot for 14 tyres.

Edited by Sausage

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Completely different designs.

realoem.com is an online EKTA. I spent many hours researching a 085 box for my mk1 Golf. The standard ratios are very compromised if you want performance. The shaft centres are too close to allow decent ratios. One choice you may have is the 02K which is designed to go on the same mounting pattern as the 085 in the petrol engined cars but is the same internally as the 02A, which evolved into the 02J.

You should look at what other VW's use the SDI engine. The Caddy uses a different gearbox on the 1.9 SDI. That may give you some off the shelf alternatives. I believe the 02J in the TDi sits in the same position relative to the chassis as it would if there was a 4 cylinder engine so the TDi shafts, mounts, gearchange etc should work. The starter is at the front of the box near the battery but that's only 1 wire and thick cable.

 

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Yeah, completely agree. And good ideas chaps. Thanks. 👍🏻

I don't think the 02J box would fit between the chassis rails on a little lupo SDI? As it is there's only about 10mm clear between the 5th gear cover and the chassis leg. The caddy is wider. I was trying to see if I could get tools in there to get everything off without pulling the box. Tight but do-able! Would still need to lower that end during the work process though.

The big question though, to which I can't find the answer without having two gearboxes in front of me is if i get the cogs and synchromesh cone from a 02A or J, would they fit the shafts from a 085. My guess is yes, but I don't want to spend £££ on a box for parts which I'd end up not using. Hmm.

Hey, I just thought- maybe that's why they all fail- the bearings are tiny because they had no choice. The shaft centres are too close...

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Finding  a cheap / scrap box with the right codes to pillage 5th gear would take some luck and time.

I fixed 5th on my 1.4s under the arch, hardest bit is making a 2 legged puller and shaping the legs to fit the gear, luckily it wasnt on there tight so the thing i ended up with worked a treat.

 

Dscn5100.jpg

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I've heard that some people warm up the cog to pull it off with finger force. But with that plastic needle race in there, I don't like it. Yeah, I'll have to mod one of my spare 3 legged pullers. Apparently the trick is to pull from behind without leaving so much as a nick or burr on the cog. 

Edited by mk2

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The little legs are from a 3 legged puller and there was no way 3 legs will get in there as there are bits of gearbox case in the way of one of them under the gear, so I put those little legs on a larger 2 leg puller. There is only one viable position even with two legs, that is why i had to shave one right down to get it in there.

100c on the heating if i remember right, I suppose the plastic can take that or else they just expect you to renew them. I just gave it some juice on the burner until it was too hot to touch while the puller had some pressure on it. Didnt bother with heat when refitting though.

Edited by Sausage

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I've spent years designing interference fits on shafts. You don't need a lot of temperature differential to assembly or disassemble. Clearance will probably start at around 50deg.C difference. 80 deg.C cog in 20 deg.C ambient. You can achieve this with a hot air gun. Most engineering plastics can take 120 deg.C for a while but the air gun will be kicking out 250+. Just shield the plastic from the direct air.

Get Kukko style puller. Much better. Here's a chinese copy:

https://www.ebay.co.uk/itm/Bearing-gear-hub-puller-internal-external-2-leg-splitter-removal-tool-100x98mm/273371704481?hash=item3fa6392ca1:g:7E0AAOSwDMZbV3HT

Cheap enough that you can grind the legs to suit and won't feel too bad when they break. I've had a few.

The 6K caddy is a 6N Polo chassis just like the Lupo/Arosa and these came with the 1.7SDI too. The Caddy is fitted with a big block gearbox. Not sure what it's derived from but that maybe where you should be looking.

 

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Finally got mine working. Typical VW, the boxes used on the 1.4TDI have unique castings and the lugs are missing for the lower mount. Now does 33-34mph per 1k rpm. Can't do 30 in 5th anymore. Now needs more power to make the most of the spread.

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Just digging in the parts catalogue for fun. The 1.9SDI engines in other VAG group models were fitted with 02x derived gearboxes. I have some VW TDi engine drawings with the gearbox mounting positions dimensioned. Could you get access to a spare box or even the spacer plate to measure?

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Have a read of this thread, the seller fitted a 1.9 tdi engine and box to an Arosa, he said the gearbox was visually identical to the 1.4 tdi box he removed

 

I might still have his phone number too

Edited by weslangdon

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Yeah, i have an SDI 1.7 (1.9) engine on a crate somewhere. Can measure it. Which bits do you need to know. Pic would be easiest....

 Either I have it completely wrong or the part numbering system doesn't work! Ok, so the lupo sdi is the exact same lump as the 1.9, and comes as standard with the 085 FFV box variant (in the lupo). The engine is slightly angled backwards by I'd guess maybe 10 degrees. The 1.4 tdi uses an 02 something (as I understand which is to fit engines mounted at a different angle -I think). 1.9 TDI engines have bigger boxes for the increased torque, which I don't think fit the lupo without messing with cv joints and halfshafts and other stuff I'd imagine. I don't know what internals cross over. So where am I at? Have I got it all wrong?

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You can see the case webbing that gets in the way of the puller legs there, although it is other shaft in pic.

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