TB42 Turbo - Clutch Pedal Rock Hard Under Boost - Help Needed!

[TiHightop]

Hey All,
Would Love some help if possible please. Recently Installed Crane Ignition and Upped the boost on my TB42 Maverick. Its a 91 model with the Clutch Booster Setup. Now with the increased boost (10-12psi) when trying to change gears its very hard as the pedal is so firm. Previously running 7-8psi it was still firm but manageable.

So my question is, what can i do to keep the boost pressure out of the clutch booster? Any help from those who have experienced the same issue would be great.
I can see the brake booster line has a one way valve in it but not the clutch booster. I can take a photo of the setup if need be but im sure most of you know what the standard arrangement is.

Cheers,
Shaune

[BigRAWesty]

You should have no boost pressure in the assisters.. they run on vacume not boost.
do you have a cannister in the line somewhere to "store" the vacume like the td engines do?

[TiHightop]

Thanks for the reply mate. Care to elaborate? Not too sure what you mean there.
I get that the brake/clutch booster run on vacuum from intake manifold.
What issues are you referring to? So no turbo boost pressure should be making its way to the clutch booster?

[TiHightop]

Not sure if it makes a difference but im running gas research with all petrol related components removed.

[BigRAWesty]

A vacume leak is quite common especially with the desiel engines. We run a small vacume pump behind our alternater..

How do the brakes go under boost? Soft to press or hard like the clutch??

[TiHightop]

Brakes are fine under boost, no issues with pedal. From what i can see no canister in the line to store vacuum. I will investigate the td vacuum pump behind the alternator.

Cheers

[BigRAWesty]

This is the reply from my brother who knows his stuff..

" He'll need a decent sized vac tank like on the td42 & a one way check valve in the hose from the manifold."

So it sounds like they have sorta done it. Maybe try move the one way valve to the line off the manifold first so it works for both clutch and brakes. A vac cannister will only make it better again.

[mudski]

The TB's get their vacuum via the intake manifold dont they? Its been a while since i have looked at a petrol motor....So im assuming because its turbo'd its increased manifold pressure hence less vacuum? If this is correct you need to find a way to increase the vacuum.

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[tuckertrucker]

The TB's get their vacuum via the intake manifold dont they? Its been a while since i have looked at a petrol motor....So im assuming because its turbo'd its increased manifold pressure hence less vacuum? If this is correct you need to find a way to increase the vacuum.

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He does need to increase the vacuum somehow - but if theres any boost at all there will be NO vacuum in the manifold - its under boost. So if his hoses are coming from there and hes trying to use his brakes and clutch under boost, he'll be pushing against 12psi in the boosters.

I'd check that the vacuum hose doesn't come from the manifold. If it does that could be why its solid now, and was firm before the boost increase.

[jff45]

If brakes are fine under boost, it sounds like you might have a defective one way valve in your clutch vacuum system.

[BigRAWesty]

He's mentioned there is no one way in the clutch but there is on the brakes.

[the evil twin]

This is the reply from my brother who knows his stuff..

" He'll need a decent sized vac tank like on the td42 & a one way check valve in the hose from the manifold."

So it sounds like they have sorta done it. Maybe try move the one way valve to the line off the manifold first so it works for both clutch and brakes. A vac cannister will only make it better again.


He's mentioned there is no one way in the clutch but there is on the brakes.

Agree with ^^^^
In a N/A or low boost Turbo... almost immediately you lift the noise pedal the manifold is at max vac so clutch works OK as factory
High boost means the pressure lags and it will affect Clutch.
Braking is OK because it has a check valve and accumulator so brakes can still be applied even after loss of Manifold Vac.

If the Clutch operation is normal when coasting down hill say... a check valve may fix it but a check valve and accumulator for the Clutch will definitely solve the problem

[jff45]

He's mentioned there is no one way in the clutch but there is on the brakes.

Ah, well he needs to fit one then and isolate his clutch vacuum system

[TiHightop]

Thanks for the responses everyone. Had a bit of a better look and viewed the nissan epc and worked out the funny looking t piece is in fact a check valve on the clutch booster path.
So as mentioned that could be faulty. I have another bone stock tb42 Maverick here so i might try and swap the valve from that to see if it makes a difference.
If not, any ideas how i could rig in an vacuum tank or accumulator setup?

Cheers

[BigRAWesty]

A small vacume cannister would be simple as.. any small metal canister with a vacume line into it.. you can have an out line but not necessary..
Then add the one way between the manifold and canister.. the stock td canister will give you 2 good pumps of the pedal in back up.
But the td canisters use a 12mm hose. Pretty sure your only using small stuff ey..