TR4/4A TR4 brake problem

[steve_sims]

Howdy All, About 2 months ago we rebuilt both front calipers, master cylinder and replaced both rear wheel cylinders. Brakes worked great until last friday when during a nice twisty turny mountain ride, the brake pedal started to get spongy. By time i got home there was almost no pedal and no brakes. There are no leaks showing anywhere. Car is up on blocks with all wheels off and i have looked everywhere.Fluid was about 3/4 of an inch from top of master cylinder. Started bleeding the brakes today and got no air at the rear but the front are full of air. I went thru almost a pint of fluid and the wife pumped brakes till her leg got sore. There is still lots of air coming out and you can actually hear air bubbles when she hits the pedal with the bleeder closed. How can air get in without fluid leaking out? Any ideas? Up untill this problem , i have been driving almost everyday without any problems since i got her back on the road. Thanks Steve

 

[DougF]

Where did you buy your rebuild kits and what type of fluid are you using?

 

[steve_sims]

Hi, Kits came from the Roadster factory and i'm using DOT 3 fluid.

 

[TR4]

Do you have air on both sides of the front?

 

[steve_sims]

Yes , Both sides have air , seems like more on left front.

 

[TR4]

I suggest you close up the system and really stand on the brakes to see if you can detect a leak looking along the front lines first. If air is getting in while bleeding, I would expect fluid to flow out when the system is closed.

 

[KVH]

Three thoughts:

a) be sure you didn't reverse the direction of the rubber bushing/washer on the master cylinder piston--or any other piston;

b) check the bleed screws to be sure they are the right ones;

c) check the "splitter" that sends the fluid in two directions to the front wheels and make sure it's not leaking

If none of those, I wonder if you need a new master cylinder.

I'd like to hear the fix. Good luck.

 

[steve_sims]

Hi guys, I pumped and pumped and still can't get all of the air out and still can't find any leaks. Brakes worked fine for the last month. How can air get in without fluid going out? Could master cylinder suck air without loosing fluid? Bleed screws on calipers are the ones that came on the car, rear ones came with new wheel cyliders. No fluid leaks at splitter. I am getting air at rear wheels too now. more air on left rear than right. 2 pints of new fluid thru the system so far. Any advice is greatly appreciated. Steve

 

[Andrew Mace]

I'm beginning to think that your master cylinder is bad, either from a bad seal (or backwards seal) or possible damage to the bore. Can you pump the pedal and get solid brakes? If so, what happens when you then hold the pedal firmly for 15-20 seconds? That could indicate a master cylinder that's "leaking" internally, but with the amount of air you seem to have in the system, it might not be a valid test....

 

[steve_sims]

I haven't been able to get the brakes to pump up to a sloid pedal yet. I guess that i'll pull the master cylinder out and apart tomorrow. Steve

 

[TR3driver]

I'm with Andy, only explanation I can think of is the MC sucking air around the piston seal. The seal is supposed to cup inward, so pressure forces it tighter against the bore ... which could potentially cause it to leak only during bleeding, on the return stroke when the pressure in the system actually goes negative.

A faint possibility is that the link between the piston and the 'foot' valve inside the MC has come loose, so the valve isn't pulled open by the return spring.

What happens if you try to bleed right at the MC ?

 

[LarryK]

DOT 3 fluid not compatible with Triumph systems. bleed out and use DOT 4 Castrol LMA or Prestone DOT 4. You probably heated fluid and maybe crimped the rubber hydralic lines. If the DOT 3 deteriorated cups in master cylinder will need to renew. Going on assumption curvy roads and spirited driving. While bleeding calipers tap with a small hammer or rubber hammer to jolt air out. Also, you must bleed Master at bench before installing. Any residual air left in M/C can multiply at calipers.

 

[steve_sims]

Howdy All, After going thru my records, i found that i bought rebuilt master cylinder on ebay instead of rebuilding myself.{brain [censored]} I am taking off cylinder and draining all fluid from system. I have a rebuild kit and will rebuild master cylinder and replace all fluid. I have 2 quarts of Valvoline SynPower Synthetic fluid. Is this OK to use? Thanks Steve

 

[steve_sims]

HALLELUJAH !!!!!!It was the "rebuilt" master cylider. Cleaned everything up and reassembled with new kit. Bench bled, installed and flushed and bled system and i have GREAT BRAKES. Time for a nice twisty/ turny mountain road test. Thanks everyone!!!!! Steve

 

[LarryK]

Just remember to bleed synthetic a couple of times after use to make sure all old fluid is out. Also, recommend bleed once a year as synthetic will not absorb water and will push it to cylinders. Good choice as DOT 5 compatible with most everything and will not hurt paint. Just a little more maintenance, especially for show cars.

 

[TR3driver]

Just to be clear, Valvoline Synpower "synthetic" brake fluid is NOT DOT 5 nor silicone.
https://www.valvoline.com/pages/products/product_detail.asp?product=51