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Bleeding Wheel Cylinders after Improper Assembly

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Loyer Avatar
Loyer Dennis Loyer
Chatham, ON, Canada   CAN
When I first bought my 1951 TD I had all six wheel cylinders and master cylinder replaced. My brakes were still very poor after this.

I learned later that the mechanic who installed the cylinders did not pre-fill each wheel cylinder with brake fluid before re-assembling.

I have read in this web site that the wheel cylinders have a design issue were an air bubble remains in the cylinder if not pre-filled . I believe this may be the problem with my brakes (ie: will not lock wheels under any circumstance and peddle travels a lot).

Question: Do all 6 wheel cylinders need to be removed and bleed properly or is the issue only on the cylinders that are currently mounted with the travel piston in the down position ?

Any help would be greatly appreciated.

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GB3 George B
Winter Haven, USA   USA
What was improperly assembled? I have worked on several T-series cars over the years and never had to pre-fill the cylinders. One car in particular was difficult to bleed. Are you using silicone DOT5 fluid by chance? It is difficult to bleed well. Remember you have to adjust the shoe adjusters a few times after applying hydraulic pressure, as that centers and moves the shoes. Were shoes replaced? George

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J Stone John R
Aptos, CA, USA   USA
You can pressure bleed them. Avoid "pumping" them up with the brake pedal.

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Loyer Avatar
Loyer Dennis Loyer
Chatham, ON, Canada   CAN
In reply to # 3900110 by GB3 What was improperly assembled? I have worked on several T-series cars over the years and never had to pre-fill the cylinders. One car in particular was difficult to bleed. Are you using silicone DOT5 fluid by chance? It is difficult to bleed well. Remember you have to adjust the shoe adjusters a few times after applying hydraulic pressure, as that centers and moves the shoes. Were shoes replaced? George

My mechanic did the work for me and not sure what DOT he used. The shoes were not replaced. Are you able to lock up your wheels ? Why is DOT5 a bad idea ?

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Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
Dot5 is great, but can be a little more difficult to bleed.
Dave H

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Ian Williams Avatar
Ian Williams Ian W
Chipping Longjourney, Toofarupnorth, UK   GBR
Is it just the TD that needs the cylinders filling, or all MG'S ?

In reply to # 3900085 by Loyer When I first bought my 1951 TD I had all six wheel cylinders and master cylinder replaced. My brakes were still very poor after this.

I learned later that the mechanic who installed the cylinders did not pre-fill each wheel cylinder with brake fluid before re-assembling.

I have read in this web site that the wheel cylinders have a design issue were an air bubble remains in the cylinder if not pre-filled . I believe this may be the problem with my brakes (ie: will not lock wheels under any circumstance and peddle travels a lot).

Question: Do all 6 wheel cylinders need to be removed and bleed properly or is the issue only on the cylinders that are currently mounted with the travel piston in the down position ?

Any help would be greatly appreciated.

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GB3 George B
Winter Haven, USA   USA
Suggest looking at the topic on the MG cars.org TD-TF board. Go to archives and search bleeding brakes. There are many threads about it. DOT 5 is silicone fluid which does not absorb moisture, search for threads about that too, some controversy there but that is all I have used for many years. A TD should lock up and make 4 even skid marks on dry concrete. It is also easy to install the front cylinders backwards , but that wouldn't explain soft pedal. The shoes should have been put in the exact position they were removed from as well or that can cause issues.

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Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
I've never felt the need on my TF, but some people like to do it - we all have our preferences. I fitted automatic bleed valves, others like to use a vacuum.
Dave H

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AZTD Avatar
AZTD Silver Member Mike Grogan
Glendale, AZ, USA   USA
1953 MG TD
If he did not tell which DOT fluid he installed, I get back there and make him do it all over again with you watching.
If he had taken the front backing plates off to clean, they should be installed correctly. BUT they can be installed backwards.
This I have done and the brakes would not work right. I had to check it out and found my mistake.
if new shoes, then it takes a bit for them to wear and form to the drum.



1953 MG TD TD23816

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Loyer Avatar
Loyer Dennis Loyer
Chatham, ON, Canada   CAN
In reply to # 3900231 by AZTD If he did not tell which DOT fluid he installed, I get back there and make him do it all over again with you watching.
If he had taken the front backing plates off to clean, they should be installed correctly. BUT they can be installed backwards.
This I have done and the brakes would not work right. I had to check it out and found my mistake.
if new shoes, then it takes a bit for them to wear and form to the drum.

Backing plate ?

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AZTD Avatar
AZTD Silver Member Mike Grogan
Glendale, AZ, USA   USA
1953 MG TD
What the shoes and cylinder's mount to.
That small hole belongs toward the front.
and a LEFT and RIGHT.
it does matter !



1953 MG TD TD23816



Edited 1 time(s). Last edit at 2019-02-28 04:51 PM by AZTD.


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LaVerne Avatar
LaVerne LaVerne Downey
Fruita, CO, USA   USA
1954 MG TF "Green Hornet"
1969 MG MGB
1979 Triumph TR8 "Wedgie"
Filling the wheel cylinders with fluid before bleeding the brake system doesn't really help with the inherent design flaw of the brake line routing. Trapped air will rise to the highest point in the fluid line. At the rear of the system the lines make a loop over the top of the axle before connecting to the wheel cylinders. At the front, the line connecting the two wheel cylinders goes up and over the axle also. The bleed valves being much lower that the lines contribute to air being trapped at the high point of the line. Silicone fluids ( DOT 5) magnify the issue as they frequently trap microscopic air bubbles that would escape other brake fluids. The trapped air will compress and any air in the system will cause poor braking. The TD/TF braking may require repeated bleeding to obtain satisfactory braking and that is where I would start. There may be other issues as well but certainly a proper bleeding may prove all that is needed. Even though DOT 5 make bleeding the system more difficult, I find the benefits of preventing the corrosion that would otherwise occur with the use of conventional fluids inside the wheel cylinder make it highly worth while.

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Paul J Avatar
Locust Grove, OK, USA   USA
The way I usually fill a dry system is by using a pressure bleeder and pumping fluid in through the bleeders with a special fitting I made for the job. Once fluid goes into the master cylinder I put the bleeder back in wheel cylinder and move to the next one, doing all cylinders that way. You have to watch the MC to make sure it doesn't run over and suck the extra fluid out until all is done, a vented cap with a hose attached to a container works a treat, then check the MC. It's a pain, but it seems to fill all the voids. With silicon, you have to work slow as mentioned before to eliminate air, DOT 3, not too much of a worry. PJ

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Loyer Avatar
Loyer Dennis Loyer
Chatham, ON, Canada   CAN
In reply to # 3900295 by AZTD What the shoes and cylinder's mount to.
That small hole belongs toward the front.
and a LEFT and RIGHT.
it does matter !

The car is in storage until April but I wanted to get my facts straight when I take it to the mechanic. My front brakes are very poor and I need to verify they have not been installed incorrectly:
1) wheel cylinders are oriented correctly (ie: front cylinder with adjust in down position; other cylinder reversed)
2) Brake shoes oriented correctly ( lining gap on shoe to the adjuster of the brake cylinder)
3) rebleed all again
4) back plate oriented correctly. I do not understand this situation though do not doubt your advice. Can you explain why the back plate orientation matters?

With your help I hope to change a car with crappy brakes into a decently stopping auto.

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GB3 George B
Winter Haven, USA   USA
IMHO, The only issue wit backplates on wrong side is that the banjo front banjo bolt fouls the steering arm, which has nothing to do with stopping ablility. You can still mount the cylinders correctly, just nearly impossible to tighten the bolt. All of the shoes are the same, front and rear. They only fit one way on the front, with the concavity in the one end fitting into the adjuster. You can pull a wheel and use a flashlight to see if the cylinders are correct or not. George

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