S3 master cylinder

[seniorchristo]

My brakes lock up occasionally for what seems like no reason. I will be driving along. come to a stop and the brakes will not release until a bleed screw is opened and the pedal depressed. I've decided to rebuild the master cylinder but the rebuild kit for the S3 Super Safety is unique in that the dual master cylinder is .750" vs. the .700" of the S4. RD enterprises doesn't list a kit for this MC. The part number for the kit is 036J6060. Does anyone know a source for this kit or have an alternate solution?
Thanks
Chris

[StressCraxx]

There have been other posts/threads about this. It may be the push rod from the pedal assembly is too long. The piston does not come all the way back allowing the pressure within the master to relieve itself back to the reservoir.

There should be some free take-up at the pedal before the push rod pushes the piston down the bore.

[seniorchristo]

Moss Motors has a kit for Austin Healey Sprite, dual cylinder, .75' bore. I will look into seeing if that will work.
Chris

[Elan45]

Christo,

A couple of points about your delima.

Elans use Girling brakes, Sprites use Lockheed, brakes. Even though the diameter may be the same, the master cyls are much different. You could not use a Lockheed kit in a Girling cylinder. On my Super Safety, which is still in Florida, I used a Girling kit SP2610, which is what was called out in my Girling catalog #213 and catalog 220/2. In both catalogs, this is also the kit called for the S4 and Sprint as well as late S3. This is also the kit I used back in the mid 1980s when I rebuilt the whole car on a new galvo chassis. After nearly 25 years, I rebuilt the whole hydraulic system and used a new SP2610 kit. I don't know about .70 vs .75 bore diameters, as I'm not sure if I ever measured the cylinder. I just used the same kit I used in 1984.

You may still have problems if the push-rod is too long.

Roger

[seniorchristo]

Hi Roger
Thanks for the response. I won't know for sure what the diameter of the cylinder actually is until I take it apart. It may have been changed at one time to an S4 type. I've already got the .700" repair kit on order. It is part # 036J6062. This is a Lotus part number and is different than the Girling number. If the only difference is the two cylinder seals, I may be able to use this kit along with .750" seals from the Girling single brake master cylinder kits. Your help with the Super Safety models as always appreciated.
Regards,
Chris

[Elan45]

Christo,

I don't think theou copies of Lotus pages 2 seals in the tandam cylinder are the same, so I don't think you'll be able to do as you'd like. I believe the front seal is a quad ring. It has to provide pressure for the front circuit and seal the front from the back circuit.You should be able to buy the SP2610 kit from your local BAP-Geon dealer. I'll send you copies of the Lotus pages if you want to send me a PM.Also, I'll be through the Carolinas in the next few weeks, taking another car ( Falcon bodied Sprite) down to Florida.

Roger

[seniorchristo]

I think I resolved the issue of locked up brakes. After sizing up the possibilities, I decided to try spacing out the master cylinder. It only worked for about 10 miles. Then brake pedal was all the way back and brakes locked solid. I opened a bleed screw to relieve pressure and limped home. With help from Glen (Certified Lotus) I was able to replace the master cylinder with an extra one he had on hand and so far so good. Brakes are good but pedal seems closer to the floor then previously. I plan to dissect the old MC to see if I can detect the actual cause. Thanks for everyone's help!
Chris

[Certified Lotus]

Chris, Glad to help a fellow ?lan owner! You've got a great car. Let's plan on a back roads drive in the fall.