505 GTI diff change
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Thread: 505 GTI diff change

  1. #1
    Fellow Frogger!
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    Default 505 GTI diff change

    Gearing in the GTI always seemed a bit low but I've been too lazy to do anything about it. Not sure what motivated me on Saturday, but I put in a 504 diff that I've had lying around for longer than I've had this 505 (25 years).

    I'll bypass the joys of diff oil running down my arms -- the old syringe is now on the scrapheap -- and get to the point. I'm kicking myself that I didn't do this when I first bought the car. On paper, a change from 4.11 to 3.89 doesn't seem much, just a 5% lift in gearing. Tyre tread depth alone is about 2%. But suddenly, first is a useful gear, and fourth is pretty nice around town. Perhaps I shouldn't be surprised, but going through the gears now feels much more like the old 504. And it's good mental exercise adding 1/20th to the speedo reading all the time too.

    With the Megasquirt my 505 has a bit more torque than standard and I think the ideal ratio would be the 3.70 diff (code 'M'). I believe this was in some 604s. If anyone has one of these knocking around, I'd be interested in giving it a good home. But if not, I'm still enjoying the longer legs the 504 ratio has given my GTI. Recommend it to others.

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    Have fun,

    Rob.
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  2. #2
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    Now go to Jaycar and buy a GPS speedo

  3. #3
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by ianrobbo View Post
    Now go to Jaycar and buy a GPS speedo
    https://www.jaycar.com.au/lcd-gps-speedometer/p/LA9025
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  4. #4
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    Good idea. If I get the 3.7 diff I can add 10% in my head, but I have to close my eyes to add 5% and that might be dangerous.

    Have fun,

    Rob.

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    I have a 3.7 diff , happy to swap for a 4.11.
    Peugeot 504 Rally car V6
    Peugeot 504 LTI
    Peugeot 504 Ti
    Citroen SM
    Citroen Light 15
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    Toyota Land Criuser V8 Super charged ( to tow the rally car )
    Rally with www.AMSAG.com.au

  6. #6
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    Many thanks Rally; pm sent.

    I took a lie down under my 604 last night, just to see what ratio it had. The table that has been posted here in the past wasn't much help. Checking the 604 manual, the last letter on the side of the diff housing indicates the ratio. On my 604 it's 'R' which stands for 3.58. Other possible endings are 'B', 3.78 and 'C', 3.70. These codes are nothing like the table that has been posted here in the past. Weird that Peugeot did such a good job standardising the diff itself, but couldn't fix on an identification scheme.

    Was toying with the idea of trying out the 3.58 but am very happy that Rally's offer will spare me a double diffectomy.

    Have fun,

    Rob.

  7. #7
    Fellow Frogger! Rally's Avatar
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    Quote Originally Posted by robs View Post
    Many thanks Rally; pm sent.

    I took a lie down under my 604 last night, just to see what ratio it had. The table that has been posted here in the past wasn't much help. Checking the 604 manual, the last letter on the side of the diff housing indicates the ratio. On my 604 it's 'R' which stands for 3.58. Other possible endings are 'B', 3.78 and 'C', 3.70. These codes are nothing like the table that has been posted here in the past. Weird that Peugeot did such a good job standardising the diff itself, but couldn't fix on an identification scheme.

    Was toying with the idea of trying out the 3.58 but am very happy that Rally's offer will spare me a double diffectomy.

    Have fun,

    Rob.
    i have a 3.6 from a 604 and a 3.7 from a 504 Ti and a 3.89 from a 504 carby And a few diesel diffs that I am not sure of the ratios , if you have a preference.
    Peugeot 504 Rally car V6
    Peugeot 504 LTI
    Peugeot 504 Ti
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    Citroen Light 15
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  8. #8
    1000+ Posts BIGRR's Avatar
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    My Ti had 3.58 in it for years. Pulled it really well. Until I started towing a 680kg trailer and car (Lots of clutch required off the line).
    Present fleet:-
    Peugeot 93' 205 Gti 16v
    Peugeot 73' 504 Ti from new
    Peugeot 08' 407 Hdi Coupe from new

    Previous fleet:-
    Peugeot 95' 605 Sv
    Peugeot 92' 205 Gti
    Renault 72' 16TS from new
    Renault 69' 10
    Renault 71' 10s
    Renault 68' 10 from new

    "Be reasonable do it my way!"


  9. #9
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    Interesting. I'd have thought the 3.58 would be much too tall. While I don't tow a trailer, I am afflicted with a steep driveway, and the 505 has a slightly taller 1st ratio than the 504 too. Still musing about what would be ideal.

    I took a run up to Bathurst on Thursday. It is interesting what a difference this 5% ratio change has made. Yeah, it cruises 150rpm lower, but the most striking thing is how much wider the apparent gear spacing has become. With the low diff I typically short-shifted my way to 5th, and it was good from about 50kph upwards. With the taller diff, short-shifting is not rewarded; you need to hold each gear for a bit longer so the next gear will be somewhere useful on the torque curve. So the widened gear ratios more or less force you to drive in a more spirited way. 5th feels much more like a cruising speed gear rather than an all-day gear.

    It's definitely an improvement; I just have to unlearn the habits of the last couple of decades and drive it more like the 504.

    Have fun,

    Rob.
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  10. #10
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    A quick update on this.

    Took up Rally's kind offer. My old 4.11 is now in pastures green and his 3.70 is back into full time service.

    I installed it on Saturday morning but have only had it for short runs so far. It has further lengthened the car's legs and means 5th is definitely for cruising. 4th is the gear for suburban roads and I'm glad to say that 1st manages my driveway well enough -- it wouldn't want to be much taller. Time spent in each gear away from the lights has been lengthened.

    Very happy with the change. I did get a GPS speedo, but I'm not sure I'll get to like it. Mounting is so-so and power cord isn't pretty. Will see. The mental arithmetic isn't too bad.

    Anyhow, many thanks to Rally for the diff swap. Hope my old diff serves him just as well.

    Have fun,

    Rob.
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  11. #11
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    Another quick update.

    I've put several tanks through with the new diff. Economy is markedly improved with each fill being in the 7's. Last night's fill was 7.7L/100km (715km, 55L). This has been with the more spirited driving the higher ratio encourages too -- I haven't been sparing the horses. The Megasquirt is responsible for most of the fuel economy, but the taller diff has definitely boosted the range.

    It's quieter in the cabin when cruising, though wind noise means it's still much noisier than modern cars.

    A very worthwhile upgrade. Many thanks to Rally for the swap.

    Have fun,

    Rob.

  12. #12
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    Good to hear you're enjoying.
    I never understood how Peugeot chose the gearbox/diff combo
    and why there are so many variations.
    Chadi

    1982 504 SR white manual sedan with A/C (257 000 Km)
    2012 308 1.6 VTi Vapor Grey manual H/B (35000 Km)
    1994 405 1.6 white manual sedan (208 000 Km)
    1992 605 SV24 (91 000 Km)
    2005 406 2.0L automatic (Replaced with a 2013 C5)
    1983 505 GR white manual sedan with A/C (170000 Km)

    All since new


  13. #13
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    At one stage I investigated the possibility of transplanting a tacho mechanism into a speedo dial face and cobbling the driver electronics.

    That idea was scrapped when I found the Jaycar GPS speedo.

    Could a good project for you with arduino, and the speedo would look the same.
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  14. #14
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    That's an interesting thought. A couple of points where your advice would be welcome:

    • How to sense the speed? Were you planning to watch the cable at the dash end? What sort of sensor? Or was there some speedo pickup that might fit in the standard speedo drive at the gearbox? Or perhaps you were thinking of some sort of pickup (e.g. bicycle speedo) at an axle..
    • Dismantling these things without damaging them. Looks like two fine flat head screws to separate the face from the mechanism. How does the needle come off?

    Thinking about it, if I can get the needle off, it wouldn't be too hard to make up a blank face (already did it for the tacho side). It'd then be a matter of making a suitable transfer with the numbers at the right locations. Can't say it's as interesting as the electronic approach, but it seems pretty simple.

    BTW, I updated my mini-dashboard firmware recently. The double-height digits are really easy to read. I've also had a go at designing a proper circuit board for it and there are a handful of takers for it over at the Megasquirt/Extra forum. Fun getting to grips with this electronics stuff. So much to learn!

    Have fun,

    Rob.

  15. #15
    1000+ Posts robmac's Avatar
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    As to speed sensing.

    I'd probably go for a magnet on the rear driveshaft, near the diff on the ds cover and a hall effect sensor out of an old dissy.(not necessarily pug)

    Failing that, some manufacturer must have a speedo drive to hall effect or prox adaptor. I'd trawl the diy wreckers.

    It just depends if the mechanical conversion is feasible.

    I was hoping the speedo mechanism and tacho mechanism had the same mounting centres.
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  16. #16
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    Thanks robmac. Driving off the axle sounds good to me. Means I can play musical chairs with diff ratios and not worry about the speedo again.

    Have fun,

    Rob.

  17. #17
    1000+ Posts robmac's Avatar
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    If you have fabrication facilities, the sensor below may be option, driven off the speedo cable.

    http://au.element14.com/zf-cherry/gs...a-92315478965&

    And at $30 odd won't break the bank.

    However if change the diff ratio, a software change is necessary.

    I think I would probably use this sensor.

    EDIT:
    After a bit of thought a custom PLL chip, configured as a pulse scaler may be easier than a Arduino.
    Last edited by robmac; 23rd November 2017 at 11:04 AM.
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  18. #18
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    Thanks for the suggestion. Agree, decent price. Be nice if they provided it with a pigtail. Element14 don't seem to carry that connector, but it's at RS Components for $3.36 (and they don't carry the sensor!). I think I have all the tools to get it fitted (don't remember though -- is the speedo worm gear splined to the output shaft?). It'd keep me off the streets for a while.

    I thought a microcontroller was a bit of overkill for just converting one pulse rate to another. Playing with a PLL chip would be a bit of fun.

    Will procrastinate for now while I think about it.

    Have fun,

    Rob.

  19. #19
    1000+ Posts robmac's Avatar
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    But Arduino is cheap, they range from $7 -$20, AND the development is mostly by software rather than a soldering iron.

    I shudder to think how out of date I am, when I gravitate towards (Russian)valves for my proposed 400w linear amplifier for my rig.

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    "I shudder to think how out of date I am, when I gravitate towards (Russian)valves for my proposed 400w linear amplifier for my rig.

    Surplus Parts & Equipment"

    Russian valves! You're lucky! We had to live with Chinese 807 valves (Nanking brand) in the 60's, as part of a trade deal with China.
    We used to watch their parameters deteriorate by the minute when checked in the old AVO valve testers. Lucky to get 10% pass rate.
    (Sorry to hijack the thread)
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  21. #21
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    No worries, it's not a hijack.

    There are heaps of people using war surplus Russian valves and RF parts. Because they are cheap and of consistent quality.

    In fact a friend with a Circa 1943 Bc 375 aircraft transmitter , replaced the aging Western Electric 813 triodes , with some Russian 813s.

    He didn't even have to adjust the neutralization.

    They just plugged in and worked and the output went from 80w to 120 w.
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  22. #22
    Fellow Frogger! neural revolt's Avatar
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    Quote Originally Posted by robmac View Post
    No worries, it's not a hijack.

    There are heaps of people using war surplus Russian valves and RF parts. Because they are cheap and of consistent quality.

    In fact a friend with a Circa 1943 Bc 375 aircraft transmitter , replaced the aging Western Electric 813 triodes , with some Russian 813s.

    He didn't even have to adjust the neutralization.

    They just plugged in and worked and the output went from 80w to 120 w.
    Not familiar with the BC 375.
    Had a bit of experience with the BC 624/625 Rx/Tx combo, ex aircraft VHF. They were used extensively in the 50's and 60's at regional airports in Oz for air/ground/air comms.
    Past Frogs:
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  23. #23
    1000+ Posts robmac's Avatar
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    HF transmitter/ receiver pair. The tx band switching is done by several plug in "tuning units". AM via screen/cathode modulation. Good for a couple of hundred watts.

    Used in aircraft comms, early- mid 1940s . Powered by motor-generator from aircraft DC supply.

    Only a serious collector/ fanatic would use one on air today.

    https://www.youtube.com/watch?v=k-fmiD_vSDI
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  24. #24
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    Quote Originally Posted by robmac View Post
    HF transmitter/ receiver pair. The tx band switching is done by several plug in "tuning units". AM via screen/cathode modulation. Good for a couple of hundred watts.

    Used in aircraft comms, early- mid 1940s . Powered by motor-generator from aircraft DC supply.

    Only a serious collector/ fanatic would use one on air today.

    https://www.youtube.com/watch?v=k-fmiD_vSDI
    Yes, I think I have seen one ; used as a standby H.F Tx at Dubbo airport in the 1960's.
    Fond memories of the Bird thruline wattmeter in the video
    Past Frogs:
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    Alpine White 1972 R16TS
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  25. #25
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    Quote Originally Posted by robmac View Post
    No worries, it's not a hijack.
    Was a nice joyflight, but how did we end up in Cuba?

    Have fun,

    Rob.

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