MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Flushing Brake Lines

Been through the archive & my query wasn't addressed. It's been suggested that metho is a good first flush for lines that have been standing for a while, prior to using the fluid, (Dot 4 in my case), however there are conflicting opinions on this. The pros recommend flushing with the brake fluid but others on the Net suggest that metho will remove more of the gunk that may have accumulated as well as absorbing the moisture that will have accumulated in the system. The system was completely rebuilt about 5 years ago & the car has not been driven since. Brakes were pumped every couple of months just to keep the pistons moving. So metho or brake fluid? Cheers
Peter TD 5801
P Hehir

On a car that has brakes only five years old, I would flush with DOT 4. If you were converting to DOT 5, or you had reason to suspect a problem with the lines, I like Acetone followed by a thorough air spray. Seems to dry everything out, and then it evaporates nicely.

Warmly,
dave
Dave Braun

Brake cleaner sprayed through followed by a blast of high pressure air.
Gene Gillam

There is no reason why there should be "gunk" in the system. And the lines aren't going to absorb much moisture, if any, just sitting unused. Flush with brake fluid and you are good to go. If in the unlikely event there is a corrosion problem, the worst that will happen is the wheel cylinders may weep a bit and flushing with solvent won't prevent that anyway.
Steve Simmons

Ok I'll go with the Dot 4. Been such a long time since I've topped them up is there a filler level on the master cylinder? Cheers
Peter TD 5801
P Hehir

I don't want to hijack your thread Peter but why are you using DOT4 VS DOT5? I was going to use 5 in mine so I wouldn't have potential paint damage should the system start to leak since my system is entirely new and nothing to contaminate with mismatched fluids. I was told by the owner of the race shop next door that DOT5 will eat the rubber which I find highly unlikely or they wouldn't be on the market very long and DOT5 has been around for years. I use it exclusively in my motorcycles to protect the finish and have never had a failure of the rubber parts associated with it.

Any one care to chime in?

TIA

Bill Chasser jr
TD4834
W. A. Chasser Jr

The Dot 4 does have its limitations Bill but so does the Silicone. I don't want to have to rebuild the wheel cylinders & the master cylinder, which I'd have to do if I were to change over, is the short answer. Dot 5 is ideal for racing & copes with the higher brake temperatures way better than Dot 4, but I don't plan to go that fast. Also there is some issue with Dot 5 & servos I believe? Not that I have one though. Cheers
Peter TD 5801
P Hehir

DOT5 does not eat rubber. He may have been referring to changing from DOT4 to 5. The two fluids have different swelling agents so rubber seals may expand or contract, causing leaks after the changeover. Therefore it is always recommended to change all rubber components in the system when switching between silicon and glycol fluids. Additionally, dirty DOT4 mixed with DOT5 will create a gelatinous goo that can clog brake system components. Even the trace amounts in the rubber can cause it, so again it's best to change all lines and seals, and thoroughly clean any metal parts.

I run DOT5 in my cars with master cylinders above the firewall for paint protection, and DOT4 in those below where there is no danger of it leaking onto a painted surface. Only the frame and backplates could get fluid on them and since I coat those with POR15, they are impervious to its ability to remove paint.

Peter, I believe the issue you are thinking of is with DOT5 and anti-lock braking systems. Never combine the two!
Steve Simmons

Dot 5 does not deal with heat well...that is why they restrict the use here in the states to cars without anti skid disc brakes. Regards, Tom
tm peterson

Thank you gentlemen for the clarification. I will use my DOT5 with confidence

Cheers

Bill Chasser Jr
TD4834
W. A. Chasser Jr

I use DOT 5 in both my MGTD and my MGB. In both cars, I rebuild the entire brake system and flushed the pipes with alcohol, then used air to dry the lines prior to adding the DOT 5.

My two issues with DOT 5 are.

1. It is harder to get a good solid pedal. You have to bleed it a number of times to get all the air bubbles out.

2. You will have silicon on your paint and if you need to do any painting, you have to remember to really clean the area to be painted very very well or you will get fisheye.

The positives? No paint issues when there is a spill or a leak. No moisture issues. Used to have to take the brakes apart once a year when I brought the cars out of winter storage. After changing to DOT 5, I have not had to do this once. TD has had silicon for over 25 years and the B for 9. Have not had to do a single thing to the brakes on either car
Bruce TD4139 Cunha

Some further info on Dot 4 versus Dot 5. Dot 5 does have a higher boiling point than Dot 4. The dry/wet boiling point comparisons are as follows:

Dot 4: 230 C Dry & 155 C Wet
Dot 5: 260 C Dry & 180 C Wet

This seems to suggest Dot 5 handles heat better than Dot 4 which I guess is why it is used within the racing fraternity. At some point Bruce I'll definitely make the change as your information suggests the positives far outweigh the negatives. Cheers
Peter TD 5801
P Hehir

Agree with Bruce - a bit harder to get the initial "hard" pedal feeling but after that smooth sailing. Using it in both my TCs for years.
Gene Gillam

DOT5 should deal with heat better than DOT4. Higher boiling point. I agree with the rest, although if you get it on the paint then at least there will still be paint left. DOT 3/4 eats paint faster than some paint thinners.
Steve Simmons

DOT 5 aerates more readily, and the antilock systems can pulsate enough to aerate the fluid. The aeration is partially to blame for the difficulty in bleeding DOT 5. Take it slow with partial pedal strokes.

DOT 5 is not used for racing, because although it has a significantly high temperature range, the compressibility factor changes with temperature leading to a loss of pedal feel and more travel under hard use.

Most of the moisture that enters a braking system comes through the rubber brake hoses (amazingly enough!) not the 'lid'. Since the DOT 5 is lining the rubber and lacks an affinity to moisture (as opposed to DOT 3 or 4 which attract moisture) the amount of moisture you get in a DOT 5 system is much less than what you can get in a DOT3 or 4 system.

DOT 5 is what I use in my British Cars.

Under normal use, and properly bled, I don't think you can detect the slight compressibility difference. I've not have had any cylinder or master problems related to DOT 5 use in brakes or clutches.

Warmly,
dave
Dave Braun

This thread was discussed between 09/04/2015 and 10/04/2015

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.