Front calipers on the rear

Discussion in 'Workshop Forum' started by carl, Dec 5, 2018.

  1. carl

    carl True Classic

    Location:
    Virginia
    Just got done doing this conversion. The mechanics of it are quite simple, the rear thread in flex hose works fine on a front caliper, same thread as the banjo bolt for front installation and the front and rear caliper mounting brackets are the same. Obviously no more hand brake.

    First drive around the neighborhood was inconclusive, pedal travel seemed too far and pedal feel was very mushy as if I had air in the system but I don't. The more I drove it the more the mushiness was going away. I really need to get it out for a long drive to get the brakes to settle in. The pads are brand new but not the same brand as the fronts....MWB performance pads on the front and Ferodo street pads on the back. I think braking is better, as it should be but I need more seat time. Also can easily compare to my other X that has stock brakes.

    If anyone else has done this, for street or track, I'd like to hear your views.
    I'll give further feedback as I get more miles on it but hard to motivate yourself when it's 39 degrees out, even if sunny.
     
  2. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    I'd imagine things will feel a bit different once the new pads bed in. And you might want to do a quick bleed again after that. A longer peddle with different feel would be expected due to the larger caliper piston bore (with the same master cylinder bore). Some prefer that as opposed to an abrupt "on-off" feel. It will be interesting to hear what you think. Thanks for sharing and please keep us posted.
     
  3. MikeHynes

    MikeHynes True Classic

    Location:
    Goodfield, IL.
    I've got the front calipers on the rear of a racecar. But, I've also got a way to adjust brake bias and other mods. I can't really give you very good feedback but I will caution you to be careful in the rain. I take rear bias out of mine in the rain.
     
  4. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    I agree, an adjustable bias valve would be a good idea. But I'm confused by part of your comment Mike; what's this "rain" you speak of?
     
  5. MikeHynes

    MikeHynes True Classic

    Location:
    Goodfield, IL.
    It's a natural thing. As far as I can tell it's God's way of bringing you back to reality. You know, just in case you're having too much fun racing on a dry track.
     
  6. carl

    carl True Classic

    Location:
    Virginia
    it's a street car and not meant to be driven in the rain if avoidable....initially the car didn't even have wipers, now it has one. Half the guys in the local club have spun their Xs in the rain and that's with stock brakes.

    Once I have the brake setup performing at max I will decide if I want a bias adjustor (which would seem to defeat the whole purpose of what I'm doing).
    On the 128s I put rear discs on I had to use a bias adjustor as the rears would lock up way to easily.
     
  7. Eugene Harvey

    Eugene Harvey True Classic

    Location:
    Auckland, NZ
    Found out the hard way you don't need rain, just be a cheap arse and skimp on the quality of the tyres. With my first X in my early 20's there was a specific section of tight twisty road I used to enjoy racing through as hard as I could when it was clear, the way you could chuck the little X around and it would hang on for dear life. Then after a rather long trip driving with the same vigor, wrecked the rear pirellis (tore the belt from the rubber), and being young and poor, and Pirellis being expensive, opted for some cheaper rears.
    Needless to say, the next time through my twisty little road in the dry the rear let go and in a cloud of smoke I was drifting sideways towards the curb!
     
  8. carl

    carl True Classic

    Location:
    Virginia
    Car currently has a set of Federals which seem just fine but admittedly I don't do stupid anymore...at least for driving. The 77X has 12 year old tires and I'm not happy about that but am getting a set of hardly used Federals from a friend for that car.
     
  9. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Glad you clarified that. :D
     
  10. Ulix

    Ulix True Classic

    Location:
    Stuttgart, Germany
    Carl,
    I have kept quiet so far because I have no real world experience on the matter, but how can the front caliper possibly work in the rear without a valve?
    I other threads we are discussing if changing from a 36mm to a 38mm rear caliper might induce too much rear bias.
    And you want to change to a 48mm caliper?
    I am looking forward to your experiences.

    Same goes for the pedal travel. That was also discussed as possibly being an issue with the 38mm calipers. (It is not, I run those on my car).
     
  11. carl

    carl True Classic

    Location:
    Virginia
    Good questions Ulix, in the future don't hold back! I have had to deal with too many old wives tales about mods on Fiats, the first being that dual IDFs would never work on a stock spider motor which total BS.

    With a heavy rear weight bias I am hoping the conversion will work sensibly without a valve but I'm not adverse to adding one later if needed. I work on a painfully cheap budget and I had these calipers whereas 38 rear calipers are not readily available and certainly not cheap. The whole purpose of this car is to try strange stuff within my budget. I did expect longer pedal travel but my concern at the moment is a somewhat mushy pedal. If I can't get rid of that then the project is dead. I was hoping to hear from others who have done this so I know what to expect.
     
  12. Rupunzell

    Rupunzell Bernice Loui

    Location:
    California
    Well.... using front brake calipers on the rear works. The LeMons racer has been set up this way for many years and retains the front brake calipers on the rear to this day. Those who have taken their exxe to a road course and run the exxe for any extended amount of time and have used the brakes to the limit of their ability will know or discover how the front brakes will cook past well-done. The front caliper in the rear cures this and aids significantly in moving the brake bias to the rear while tuning down the cooking heat at the front brakes.

    This alteration will increase the brake pedal travel due to the increase in brake fluid to the larger (46mm-vs-34mm) brake caliper pistons for a given amount of piston travel.

    It is also curious to discover rear brake pads from Gen-1 Mazda RX-7 are a direct fit to Fiat brake brackets. This is relevant as Hawk F-carbon pads can be had for the Gen-1 RX-7. We used these at the front with semi-metallic pads in the rear. This produced GOOD brake balance for a road course endurance racer. The thinner Gen-1 RX-7 pads in the front held up for the most of a leMons race. They are thinner than stock and needed replacement due to wear under endurance race conditions. The rears.. were long wearing due to the thicker front pads and semi metallic compound. Knowing this, using different pad materials is another way to alter brake bias front -vs- rear, rear -vs- front.

    Brake bias valves often work by limiting brake line pressure, this is NOT the same effect as a brake bias bar. The brake bias bar is mechanical and linear from the beginning of brake pedal travel, the brake pressure limiting vale is not and not all brake pressure limiting valves function in the same way with their pressure limiting curve.

    It should be noted really GOOD drivers will use the brakes to aid in changing the car's direction aka turn in or similar. For drivers at this level of skill, give then a proper mechanic or similar brake bias adjust to allow them to set brake bias to their needs. It will aid in their ability to control the car and adjust for changes in the cars dynamic personality due to tire wear, fuel load, track conditions and more. Much the same applies to an adjustable stability bar.

    Bernice
     
  13. carl

    carl True Classic

    Location:
    Virginia
    Thanks for the input Bernice. My car will be strictly for street driving in a spirited but not stupid manner and won't be driven in the rain. I'm hardly a really GOOD driver and my track day experiences pretty much proved that.
     
  14. Ulix

    Ulix True Classic

    Location:
    Stuttgart, Germany
    Bernice,
    So you used the front calipers on the rear without any other mod to limit rear bias other than different pads front/rear?
    Did you try it with same pads front/rear?
     
  15. Rupunzell

    Rupunzell Bernice Loui

    Location:
    California
    Only other alteration when the front calipers were put at the rear was the previous change from stock stock steel braid reinforced EPDM hose to PTFE with outer stainless steel braid hose.

    Yes, we did try same pads front and rear, the drivers did not like it. We mixed and pads front -vs- rear_rear -vs- front until the brake balance was acceptable for the drivers. This can be a bit tricky as it requires an assortment of brake pads and track time and willing drivers to test how the brakes work for their driving needs.

    Not sure if this is a good thing on a street car as there will be no parking brake and IMO, a bit too much rear brake for all the various weather, environmental, and road conditions that can happen in real world driving.

    Think the best trade off for street-road is Fiat Uno Turbo front brakes (vented rotors and might not fit 13" wheels) with Feredo street pads and Fiat 38mm rear calipers with essentially stock rear brake pads. Do have a Wilwood pressure limiter valve on the front brakes, but have never needed it, so it is set full on. This brake set up has been on the 74' for a while now and it works really well overall in real world street-road-weather conditions.


    Bernice

     

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